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Hexavalent chromium (Cr (VI)) is highly carcinogenic to humans. Ascorbic acid (AA) deficiency can be hazardous to health. And the dual-effect fluorescence detection of them is an important research topic. Carbon dots (CDs) based on cellulose are excellent candidates for the fluorescence probes due to their low cost and environmental friendliness. But most of them exhibit shortwave emission, small Stokes shift and poor fluorescence performance, all of which limit their use. Therefore, there is an urgent need for cellulose CDs with longer emission wavelengths and larger Stokes shifts in dual-effect fluorescence detection of Cr (VI) and AA. Under optimal conditions (180 °C, 12 h), we prepared cellulose-based nitrogen-doped carbon dots (N-CDs) by a simple one-step hydrothermal process, which display longer emission wavelengths (ex: 370 nm, em: 510 nm), larger Stokes shifts (140 nm) and high fluorescence quantum yield (QY: 19.27 %). The continuous "turn-off" and "turn-off-on" fluorescence detection platforms were constructed based on the internal filtering effect (IFE) between Cr6+ and N-CDs, and Cr6+ reduced to Cr3+ by AA at pH = 6. The platform has been successfully simultaneous detect Cr (VI) and AA with a wide range of 0.01–40 μM and 0.1–100 μM. And the lowest limits of detection (LOD) are 0.0303 μM and 0.072 μM, respectively. In the presence of some other metals, non-metal ions and water-soluble acids in the fruits, this fluorescent platform can demonstrate a high level of interference immunity. This represents the first yellow-green cellulose-based N-CDs with large Stokes shift for dual-effect detection of Cr (VI) and AA in real water samples and fresh fruits. The fluorescence detection platform has the advantage of low volume detection. Less than 2 mL of sample is required for testing and results are available in <5 min. This method is rare and supply a novel idea for the quantitative monitoring of Cr (VI) and AA. [Display omitted] • The continuous fluorescence platforms for Cr(VI) and AA were constructed based on N-CDs and Cr(VI). • The platform of N-CDs@Cr (VI) emitts yellow-green fluorescence with a big Stokes shift of 140 nm. • LOD of N-CDs and for N-CDs@Cr (VI) Cr6+ and AA have the lowest values of 0.0303 μM and 0.072 μM, respectively. • The detection platforms have been successfully applied in real samples. • The detection mechanism was verified based on IFE and AA reducing Cr (VI) to Cr (III) to restore the fluorescence. [ABSTRACT FROM AUTHOR]

Due to their excellent stability, low toxicity, flexible modification and adjustable functionality, carbon dots (CDs) have a promising application prospect in the field of chromatographic stationary phases. Hydrogels are new functional polymer materials with three-dimensional network structure that have excellent hydrophilicity, high porosity and unique mechanical properties, which are also good candidate materials for liquid chromatography. Nevertheless, a review of the literature reveals that CDs based nanocomposite hydrogels have not yet been reported as HPLC stationary phases. In this work, amphiphilic CDs with multiple functional groups and polyacrylic acid hydrogel were grafted to the surface of silica gel by an in-situ polymerization method, and a CDs/polyacrylic acid nanocomposite hydrogel stationary phase (CDs/hydrogel@SiO 2) was prepared. CDs act as the macroscopic cross-linking agents to form a cross-linked network with polyacrylic acid chains through physical cross-linking by hydrogen bonding and chemical cross-linking by amidation and esterification reactions, which not only improve the swelling property of the hydrogel but also increase its stability. Additionally, the introduction of CDs with multifunctional groups modulates the hydrophilic-hydrophobic balance of the hydrogel that also imparts good hydrophobicity to the composite hydrogel. Through the study of retention mechanism and influencing factors, it is certificate that the CDs/hydrogel@SiO 2 has mixed-mode chromatographic performance. Furthermore, the CDs/hydrogel@SiO 2 column shows great potential for the determination of organic contaminants in environmental water samples. This work confirms the potential application of CDs/hydrogel composite for the separation of various samples and provides the possibility of developing CDs based nanocomposite hydrogel in the field of liquid chromatography. Introducing CDs into hydrogel can open up a new way for nanocomposite hydrogels to be used in HPLC, which expands the advance of hydrogel and CDs in separation field. A novel amphiphilic carbon dots-based nanocomposite hydrogel modified silica stationary phase (CDs/hydrogel@SiO 2) was proposed for mixed mode liquid chromatography. [Display omitted] • An amphiphilic carbon dots (CDs) based nanocomposite hydrogel was proposed for HPLC. • CDs act as the macroscopic cross-linking agents to produce a nanocomposite hydrogel. • Introduction of CDs adjusts the hydrophilic-hydrophobic balance of composite hydrogel. • Potential application of CDs/hydrogel for efficient HPLC separation was confirmed. • A new way for CDs-based nanocomposite hydrogels to be used in HPLC was opened up. [ABSTRACT FROM AUTHOR]

Tetracycline (TC), a cost-effective broad-spectrum antibacterial drug, has been excessively utilized in the livestock and poultry industry, leading to a serious overabundance of TC in livestock wastewater. However, conventional analytical methods such as liquid chromatography and gas chromatography face challenges in achieving sensitive detection of trace amounts of TC in complex substrates. Therefore, it is imperative to develop a highly sensitive and anti-interference analytical method for the detection of tetracycline in livestock wastewater. A porphyrin-based MOF (PCN-224)-confined carbon dots (CDs) material (CDs@PCN-224) was synthesized by a "bottle-around-ship" strategy. The reduced carrier migration distance is conducive to the separation of electron-hole pairs and enhanced the photocurrent signal due to the tight coupling of CDs and PCN-224. Further, molecularly imprinted polymer (MIP) was synthesized by rapid in-situ UV-polymerization and employed as a recognition element. The specific recognition of the target by imprinted cavities blocks electron transfer, resulting in a "turn off" response signal, thus realizing the selective detection of TC. Under optimal conditions, the constructed MIP-PEC cathodic sensor detected 1.00 × 10−12 M to 1.00 × 10−7 M of TC sensitively, with a limit of detection of 3.72 × 10−13 M. In addition, the proposed MIP-PEC sensor demonstrated good TC detection performance in actual livestock wastewater. The strategy based on MOF pore-confined quantum dots can effectively enhance the photocurrent response of the photosensitive substrate. Simultaneously, the MIP constructed by in-situ rapid UV-polymerization showed excellent anti-interference and reusable properties. This work provides a promising MIP-PEC cathodic sensing method for the rapid and sensitive detection of antibiotics in complex-matrix environmental samples. [Display omitted] • The cathodic photocurrent is amplified by encapsulating CDs into the pores of PCN-224. • Molecularly imprinted polymer was in-situ introduced rapidly by UV-polymerization. • The MIP-PEC sensor exhibited a wide range and low LOD for the detection of tetracycline. [ABSTRACT FROM AUTHOR]

A new strategy for the fluorescent and colorimetric sensing of hydrogen peroxide (H 2 O 2) and glucose based on the metal oxide – carbon-dot hybrid structure was investigated. The sensing system is related to the catalytic oxidation reaction of glucose-by-glucose oxidase (GOx) to H 2 O 2. In this study, a metal oxide hybrid with nitrogen-doped carbon dots (MFNCDs) that showed intrinsic peroxidase-like activity was synthesized and used as a catalyst instead of GOx to oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) to blue-emitting oxidized TMB (oxTMB) in the presence of hydrogen peroxide (H 2 O 2). The fluorescence of MFNCDs/TMB at 405 nm was quenched in the presence of H 2 O 2 through the inner filter effect (IFE) and electron transfer within MFNCDs, oxTMB, and glucose system. Therefore, the fluorescence and absorbance intensity can be applied to the quantitative determination of the concentration of H 2 O 2 and glucose with a wide linear range. The detection limit for H 2 O 2 and glucose based on the colorimetric method were as low as 84 nM and 0.41 μM, respectively. In contrast, the detection limit for H 2 O 2 and glucose based on the fluorescent method were as low as 97 nM and 0.85 μM, respectively. Furthermore, the colorimetric readout on the paper device based on the changing color of the solution could also be integrated with a smartphone platform to conduct the on-site analysis of glucose without the use of the spectrometer. In addition, this dual sensor can be applied to detect glucose in real serum with highly accurate results, making it a good candidate for biosensor applications. Image 1 • Metal oxide hybrid with N-doped carbon dots (MFNCDs) as a peroxidase-like catalyst was fabricated by a hydrothermal method. • A colorimetric and fluorescent sensor for H 2 O 2 and glucose was developed. • The MFNCDs exhibited excellent selectivity towards glucose. • MFNCDs showed low cytotoxicity and excellent biocompatibility. [ABSTRACT FROM AUTHOR]

In this work, a facile ratiometric fluorescence sensor for GSH measurement was designed based on MnO 2 nanosheet (NS), carbon dots (CDs), as well as a simple substrate o-phenylenediamine (OPD). Herein, MnO 2 NS played triple essential roles in the sensing system. First, it could be reduced by GSH through a special reaction, and therefore served as GSH recognizer. Second, it played as a fluorescence nanoquencher to strongly quench the fluorescence of CDs. Third, it could directly oxidize OPD to yield a luminescent product 2, 3-diaminophenazine (DAP) via the intrinsic oxidase-like activity. It revealed that MnO 2 NS could be reduced to Mn2+ in the presence of GSH. Thus its oxidase-like activity and fluorescence quenching abilities were inhibited, which then restricted the generation of DAP and recovered the fluorescence of CDs. Based on this phenomenon, a novel ratiometric fluorescence sensor for GSH determination was fabricated by measuring the ratio of fluorescent intensity of DAP to that of CDs. Besides, the constructed ratiometric fluorescent sensor, which could be facilely operated with single-wavelength excitation, exhibited high sensitivity and selectivity with a wider linear range and a lower detection limit. Image 1 • A facile single-wavelength excitation ratiometric fluorescence sensor was constructed for GSH. • MnO 2 nanosheets can not only effectively quench the fluorescence of CDs but also oxidize OPD into luminescent DAP due to its intrinsic oxidase-like activity. • DAP could also quench the fluorescence of CDs through the inner filter effect. [ABSTRACT FROM AUTHOR]

Herein, novel intrinsic dual-emitting carbon dots (CDs) are prepared through a one-step hydrothermal treatment of glucose and 3-nitroaniline in sulfuric acid solution and utilized for ratiometric determination of Cu2+ and aspartic acid (Asp). The CDs exhibited an interesting pH-switchable emission behavior displaying an intrinsic dual-emitting peak with emission maxima at 400 and 610 nm at pH 4.0–5.0. The presence of Cu2+ intensively quenched the first emission peak at 400 nm, but it had a negligible effect on the second emission peak. The ratiometric signal displayed a high selectively for Cu2+ over other metal ions and provided a linear response over the concentration range of 0.01–1.00 μM with a detection limit of 7.0 nM. Moreover, at pH 4.0, Asp was able to restore the quenched fluorescence of the CDs-Cu2+ system with a much more successful performance than other amino acids. This on-off-on fluorescence behavior provided a selective ratiometric fluorescence method for the determination of Asp in the concentration range of 0.2–15 μM. The acceptable detection results for Cu2+ in a river water sample (compared to Inductively Coupled Plasma (ICP) method) and for Asp in human serum samples confirmed the potential application of this ratiometric nanoprobe for sensing in real samples. Image 1 • Novel carbon dots with intrinsic dual-emitting optical properties are reported. • Carbon dots were used for ratiometric determination of Cu2+ and aspartic acid. • This report provide the first ratiometric nanoprobe for the determination of aspartic acid. • The acceptable detection results for Cu2+ and Asp in real samples were obtained. [ABSTRACT FROM AUTHOR]

A novel dual-emission ratiometric fluorescent sensor (CDs@Eu-MOFs) has been synthesized successfully by encapsulating water-soluble fluorescent CDs into the chambers of Eu-MOFs via a simple one-pot hydrothermal method, which can be used for the detection of Hg2+ in environmental water samples. The synthesized CDs@Eu-MOFs inherited simultaneously the excellent luminescence performance of Eu3+ and CDs and exhibited good structural and fluorescence stability in aqueous solution. The presence of Hg2+ changed the fluorescence intensity of CDs, while the fluorescence intensity of Eu-MOFs hardly changed, which could be used as the recognition part and the reference part respectively to construct the ratiometric fluorescence sensor. The obtained Hg2+ fluorescent probe showed a wide linear range (0–300 μM) and a low detection limit (0.12 nM). The developed method can be used as a multi-functional fluorescent sensor with high sensitivity and good selectivity for the determination of Hg2+ in actual water samples. Image 1 • CDs@Eu-MOFs composite was prepared using in-situ synthesis method. • A green, simple, eco-friendly strategy for synthesizing CDs was established. • The ratiometric fluorescence sensor can recognize Hg2+ highly sensitively. [ABSTRACT FROM AUTHOR]

The fluorescence-based assay of iodide ion (I−) has been extensively studied by the use of different sensing probes and techniques, but it remains a tricky task to eliminate the interference of chloride ion (Cl−) for the analysis of low-level I− in complex genuine samples. Herein, we develop a redox pretreatment strategy for specific separating I− from human urine. Simultaneously, a novel ratiometric fluorescent probe is constructed by a simple mixing of dimer DNA silver nanoclusters (dDNA-AgNCs) and carbon dots (CDs) with the ratio of 5:1 in fluorescent intensity, and used for visual assay of I−. After addition of I−, the fluorescence of orange dDNA-AgNCs can be quenched by I− as the result of I−-induced oxidative etching and aggregation of dDNA-AgNCs, while blue CDs as the stable internal standard are unresponsive to I−. With the increase of I−, the fluorescence intensity ratio (I 577 /I 446) of binary-color probe gradually decreased, which leads to color variation from salmon pink to lighter salmon pink to lilac to light steel blue to final deep sky blue (under a UV lamp) with a sensitive detection limit of 19.8 nM. The assay for I− can also be convenient to implement for visual monitoring of I− by observing color change of test paper printed with the ratiometric probe, responding to 50 nM that is about 1 order of magnitude lower than the median urinary I− concentration defined by the World Health Organization (WHO) for school-age children. The sensitive test paper can provide an advanced platform for colorimetric and visual monitoring of I− in human urine. Image 1 • Uric sample is pretreated by redox reaction to completely eliminate the interference of Cl−. • A binary probe with 5:1 ratio of orange to blue in fluorescent intensity is used for I−assay. • Fluorescence quenching mechanism for I− assay is I−-induced oxidative etching and aggregation of dDNA-AgNCs. • A portable test paper with wide color evolution is prepared by printing binary probe on paper for uric I− monitoring. • The test paper offers a colorimetric and convenient diagnosis whether we fall in hyperthyroidism or hypothyroidism. [ABSTRACT FROM AUTHOR]

In this study, we reported a highly sensitive method for detecting carcinoembryonic antigen (CEA) based on an azide cofunctionalized graphene oxide (GO-N 3) and carbon dot (CDs) biosensor system. Carbon dots-labeled DNA (CDs-DNA) combined with GO-N 3 using copper-free click chemistry (CFCC), which quenched the fluorescence of the CDs via fluorescence resonance energy transfer (FRET). Upon the addition of CEA, fluorescence was recovered due to the combination of CEA and aptamer. Under optimal conditions, the relative fluorescence intensity was linear with CEA concentration in the range of 0.01–1 ng/mL (R2 = 0.9788), and the limit of detection (LOD) was 7.32 pg/mL (S/N = 3). This biosensor had a high sensitivity and good selectivity for CEA detection in serum samples, indicating that the novel sensor platform holds a great potential for CEA and other biomarkers in practical applications. A highly sensitive method for detecting carcinoembryonic antigen (CEA) based on an azide cofunctionalized graphene oxide (GO-N 3) and carbon dot (CDs) system was reported. Image 1 • A fluorescence biosensor based on carbon dots (CDs) was developed. • Azide cofunctionalized graphene oxide quenched the fluorescence with copper-free click chemistry. • The method has high sensitivity and good selectivity. [ABSTRACT FROM AUTHOR]

For decades, researches have been involving in improving and optimizing solid-phase microextraction (SPME) technique to fit the growing environmental analysis demand. But it is more significant now to introduce meaningful information into the analysis line instead of improving every step in SPME. Herein, we design a carbon dots (CDs) based SPME platform and report its unique application in selective early screening and sensitive detection of 2-nitroaniline. The fluorescence quenching state of the CDs fiber after extraction could be used to prejudge whether an environmental sample contains 2-nitroaniline exceeding the maximum permitted level (30 μg L−1) regulated by the Chinese Ministry of Environmental Protection or not. Photo-induced electron transfer (PET) is believed to be the primary quenching route that leads to electron transfer from the electron-rich CDs to the electron-deficient analyte. A preliminary in vivo study on Daphnia magna and a 2-nitroaniline assay in environmental water and biofluid samples suggested the safety and the excellent qualitative ability of the proposed platform. As a result, the innovative incorporation of fluorescence sensing and SPME not only achieves the information imbedding of environmental analysis system, but also combines the advantages of two techniques including early visual-screening, reusability (≥50 times), high specificity and excellent quantitative ability (detection limit: 0.011 μg L−1). We believe this study can open new avenues in the field of environmental toxicant monitoring. Image 1 • A carbon dots (CDs) based solid-phase microextraction (SPME) platform was designed. • Nitroaniline's concentration level could be prejudged by the device's fluorescence. • The quenching point of the CDs fiber could be tuned as needed. • 2-Nitroaniline in urine/environmental samples was visual-screened and quantified by GC-MS. [ABSTRACT FROM AUTHOR]

In this work, a novel bright yellow fluorescent carbon dots (CDs) was synthesized from N-methyl-1,2-phenylenediamine hydrochloride in ethanol solvent through the solvothermal method. The obtained carbon dots had no fluorescence in water, but could specifically light up in the cell which makes the staining process without washing. Interestingly, the imaging process can be performed by simply shaking the culture with the cells for only 1 min, indicating ultrafast and easy to operate fluorescence imaging. Moreover, the carbon dots with abundant amino functional groups had good lysosome targeting properties (the Pearson's correlation coefficient is 0.92) and could achieve the ultrafast lysosome imaging in cell and zebrafish and monitoring cell apoptosis status. This is the first lysosome targeting carbon dots that allows the combination of a short incubation at the second-level with wash-free process providing great potential for continuous observation lysosome in vivo. The obtained carbon dots can not only accumulate in lysosome rapidly by the clathrin-mediated endocytosis and were used for wash-free in lysosome and zebrafish imaging, but also monitor the dynamic change of lysosomal apoptosis. Image 1 • The method has intrinsic lysosome targeting without further modification. • The carbon dots can accumulate in lysosomes within 1 min by the clathrin-mediated endocytosis. • The obtained carbon dots were used for wash-free lysosome imaging in living and fixed cells. • The carbon dots can monitor the dynamic change of lysosomal apoptosis. • The obtained carbon dots were also used for ultrafast and wash-free imaging in zebrafish. [ABSTRACT FROM AUTHOR]

We have developed a simple and convenient route to prepare fluorescent carbon dots with dual emission peaks respectively at 470 and 570 nm. The prepared dual-emission carbon dots can be used for ratiometric detection of Fe3+ ions in the range from 0 to 50 μmol·L-1 with 0.8 μmol·L-1 detection limit based on the fluorescence quenching at 570 nm. The quenched fluorescence induced by Fe3+ ions could be recovered by pyrophosphate. We further used the carbon dots-Fe3+ ions-pyrophosphate mixed system for ratiometric detection of acid phosphatase in the range from 0.08 to 6.75 μg·mL-1 with 0.01 μg·mL-1 detection limit. Image 1 • The carbon dots were directly prepared by carbonizing gallic acid and o-phenylenediamine in aqueous solutions. • The carbon dots exhibited dual emission peaks at 470 nm and 570 nm with excitation of 360 nm. • An obvious fluorescence quenching around 570 nm was observed with the addition of Fe3+ in acidic environments. • The GN-CDs can be used as a ratiometric probe for detection of Fe3+ ions and acid phosphatase. [ABSTRACT FROM AUTHOR]

The expression level of miRNA-21 is closely related to the occurrence and development of cancer, especially in gastrointestinal cancer. Monitoring miRNA-21 has clinical application in the diagnosis and evaluation of gastrointestinal cancer. A turn-on ratiometric fluorescence bioassay based on the T7 exonuclease-mediated cyclic enzymatic amplification method was developed for miRNA-21 determination by using carbon dots (CDs) and FAM-labeled ssDNA as the signal source. CDs demonstrated the triple functions of built-in internal fluorescence, probe carrier, and quencher in this strategy. In the absence of miRNA-21, FAM-labeled ssDNA would be adsorbed and quenched by CDs. The addition of miRNA-21 induced cycle hydrolysis from the 5′ end by the T7 exonuclease and then released the short-cleaved FAM-labeled oligonucleotides. Then, the increased FAM signal (F FAM) and the stable CD signal (F CDs) would be tested through a ratiometric routine for the quantification of miRNA-21. The F FAM /F CDs value showed a good linear relationship with the concentration of miRNA-21 in the range of 0.05–10 nM, and the detection limit for miRNA-21 was 1 pM with excellent selectivity and reproducibility. Furthermore, this sensor successfully evaluated the expression level of miRNA-21 in clinical blood samples from healthy individuals and gastrointestinal cancer patients, and the results were highly consistent with those of qRT-PCR, suggesting the great clinical application value in the diagnosis of cancer associated with miRNA-21 expression levels. Image 1 • A turn-on ratiometric fluorescence bioassay based on the T7 exonuclease and carbon dots (CDs) was developed for miRNA-21. • CDs demonstrated the triple functions of built-in internal fluorescence, probe carrier, and quencher in this strategy. • The assay showed a good linear relationship with low detection limit, excellent selectivity and reproducibility for miRNA-21. • The expression level of miRNA-21 is closely related to the occurrence and development of gastrointestinal cancer. • This method successfully evaluated miRNA-21 in clinical blood samples in accord with the results from qRT-PCR. [ABSTRACT FROM AUTHOR]

Carbon dots (CDs) were synthesized from p -aminophenol and ethylenediamine via one-step under mild condition and used as a sensitive fluorescent nanoprobe for the activity determination of N -acetyl-β- d -glucosaminidase (NAG). In this assay, p -nitrophenol was in situ produced from p -nitrophenyl-β-D- N -acetyl-glucosaminide, which was exclusively hydrolyzed by NAG. The UV absorption peak of p -nitrophenol (maximum at 400 nm) overlapped the excitation peak of CDs with maximum wavelength at 415 nm, which caused the fluorescence decline of CDs based on inner filter effect. The activity of NAG was determined by the fluorescence changes. The assay is highly sensitive to NAG with a low detection limit of 0.75 U L−1 (K = 3) and showed a good linear relationship in the range from 1 to 45 U L−1. This CDs nanoprobe was successfully applied for the determination of NAG activity in human serum and urine samples. Image 1 • Carbon dots were used as a fluorescent nanoprobe for the activity detection of N -acetyl-β- d -glucosaminidase. • Carbon dots were synthesized by heating p -aminophenol and ethylenediamine at 50 °C. • The detecting mechanism was based on inner filter effect. • The assay provided high sensitivity and selectivity. • The assay was successfully applied in human serum and urine samples. [ABSTRACT FROM AUTHOR]

Herein, gold nanoparticles (Au NPs) in solution protected by various concentration of DNA at different aggregation states were found to have different quenching effect to the fluorescence of carbon dots (CDs). Au NPs wrapped up in more amount of DNA were able to quench the fluorescence of CDs more effectively, and vice versa. Based on this phenomenon, a facile and novel fluorescence sensing platform without labeling was constructed by designing the sequence of DNA as the aptamer of the detection target. With the addition of specific molecule, taking acetamiprid as representative, DNA was prior to bind with target and the Au NPs became less protected, leading to the fluorescence recovery of the CDs. Experimental results showed that the fluorescence of CDs was linearly recovered by acetamiprid in the concentration range of 7.8 × 10−9–1.4 × 10−6 mol/L, with the detection limit of 1.5 × 10−9 mol/L. This promising sensor might provide a new aspect for exploring the versatile application of CDs in various fields. Image 1 • Au NPs in different aggregation state are discussed as the quencher of CDs with clear mechanism. • Taking DNA protected Au NPs as quencher renders ease of finding the specific molecule for recovery of CDs fluorescence. • Acetamiprid, by designing the DNA sequence as its aptamer, has been sensitively and selectively detected via this method. • More targets may be involved in CDs fluorescence sensing platform. [ABSTRACT FROM AUTHOR]

Carbon dots (CDs) were prepared by a solvent-involved molecular fusion strategy using o-phenylenediamine (OPD) as the carbon source and formamide as the reaction solvent. The CDs possessed not only the functional groups inherited from the carbon source and the reaction solvent, but also numerous C=N groups in the structure, resulting from the Schiff base reaction between –NH 2 of OPD and C=O of formamide. These functional groups endowed the final CDs with a favorable soft-base property, leading to the high tolerance level toward hard-acid type metal ions and prominent detection selectivity toward Ag+. Moreover, the obtained CDs displayed outstanding biocompatibility and low cytotoxicity, and demonstrated potential as an effective photoluminescence probe for intercellular Ag+ and Cys imaging, preventing the interference of autofluorescence from living tissues. This study focused on the solvent-involved molecular fusion strategy could provide new insights into the design of novel carbon-based nanostructures and optimization of the structure-property relationship of CDs. CDs prepared via a solvent-involved molecular fusion strategy using formamide as reaction solvent exhibits prominent detection selectivity toward Ag+. Image 1 • A solvent-involved molecular fusion strategy is adopted for the CDs preparation. • The CDs exhibits prominent detection selectivity toward Ag+. • The obtained CDs can be used as an effective photoluminescence probe for intercellular Ag+ and Cys imaging. [ABSTRACT FROM AUTHOR]

In recent years, the escalating water pollution has resulted in serious harm to human health and ecological environment due to the excessive discharge of toxic metal ions such as Al3+ and Hg2+. Therefore, it is crucial to develop a simple, efficient, and rapid detection method for monitoring the levels of the metal ions in water environment to ensure public health and ecological safety. In this study, carbon dots (CDs) containing heteroatom Si were successfully synthesized by the solvothermal method. Subsequently, a novel dual-functional fluorescent sensor (CDs@ZIF-90) was constructed by integrating CDs with zeolitic imidazolate framework-90 (ZIF-90). The fluorescent composite CDs@ZIF-90 showed outstanding optical properties and excellent structural and luminescence stability in aqueous medium. Particularly, its fluorescence at 453 nm can be remarkably enhanced by Al3+ and quenched upon exposure to Hg2+. As a result, the CDs@ZIF-90 was applied in sensitive and selective determination of Al3+ and Hg2+ ions with wide linear ranges (1–200 μM and 0.05–240 μM) and low detection limits (0.81 μM and 19.6 nM). Moreover, a convenient and rapid fluorescence test strip was also successfully prepared for visual detection of Al3+ and Hg2+ ions. This work is the first try to use the CDs@ZIF-90 fluorescence sensing material for highly sensitive and selective determination of Al3+ and Hg2+ based on "turn-on" and "turn-off" dual modes, respectively and it provides a new idea for monitoring quality of drinking water and environmental water. It is of great significance for human health and environmental protection. [Display omitted] • A di-functional fluorescent probe CDs@ZIF-90 is prepared for Al3+ and Hg2+ detection. • A facile fluorescence test strip is prepared for visual detection of Al3+ and Hg2+. • This method applies to detection of Al3+ and Hg2+ in environmental water samples with low LODs. [ABSTRACT FROM AUTHOR]

A sensitive method for the detection of β-glucuronidase was established using functionalized carbon dots (β-CD-SiCDs) as fluorescent probes. The β-CD-SiCDs were found to be obtained through in situ autopolymerization by mixing the solutions of methyldopa, mono-6-ethylenediamine-β-cyclodextrin and N -(β-aminoethyl)-γ-aminopropyltrimethoxysilane at room temperature. The method has the characteristics of low energy consumption, simple and rapid. β-CD-SiCDs exhibited green fluorescence at 515 nm emission with a quantum yield of 7.9 %. 4-nitrophenyl-β-D-glucuronide was introduced as a substrate for β-glucuronidase to generate p -nitrophenol. Subsequently, p -nitrophenol self-assembled with β-CD-SiCDs through host-guest recognition to form a stable inclusion complex, resulting in the fluorescence quenching of β-CD-SiCDs. The linear range of β-CD-SiCDs for detecting β-glucuronidase activity was 0.5–60 U L−1 with a detection limit of 0.14 U L−1. For on-site detection, gel reagents were prepared by a simple method and the images were visualized and quantified by taking advantage of smartphones, avoiding the use of large instrumentation. The constructed fluorescence sensing platform has the benefits of easy operation and time saving, and has been successfully used for the detection of β-glucuronidase activity in serum and cell imaging. [Display omitted] • Amination induced in situ self-polymerization formation of β-CD-SiCDs without external energy. • β-CD-SiCDs can selectively recognize p -nitrophenol through host-guest recognition. • Smartphone-integrated hydrogel sensing platform was used to detect β-glucuronidase on site. • The approach is suitable for detecting β-glucuronidase in serum and bioimaging in cells. [ABSTRACT FROM AUTHOR]

Carbon nanoparticles (CDs) have recently drawn a great attention in (bio)chemical analysis, sensing and bioimaging owing to their photostability, water stability, minimal toxicity, biocompatibility and ease of surface functionalization. While the vast majority of CDs applications rely on exploiting their fluorescent properties, doping such nanomaterials with various elements has recently received increasing attention as an effective approach to modify their optoelectronic characteristics, introducing novel improved optical features such as phosphorescence, upconversion luminescence or multimodal imaging capabilities. This review article focuses in the recent advances on the synthesis of heteroatom-doped CDs, exhibiting distinctive features of high value for sensing and imaging, as well as various functionalization schemes developed for guided analyte labeling. Relevant applications in chemical sensing, bioimaging and disease therapy are here presented. A final section intends to provide an overview towards future developments of such emerging light-emitting nanomaterials in the design of future devices and strategies for (bio)analytical chemistry. [Display omitted] • Different strategies for tuning the optical properties of doped-CDs are revised. • Doped-CDs with phosphorescence, upconverting or multimodal capabilities. • Functionalization approaches with target-recognition molecules are summarised. • Challenges of doped-CDs for chemical and biomedical applications are discussed. • Drawbacks, challenges, and future perspectives of doped CDs are discussed. [ABSTRACT FROM AUTHOR]

Abstract The traditional synthesis methods of carbon dots (CDs) have some disadvantages of complicated operation and a large amount of energy consumption. To address these limitations, we synthesized yellow-green luminescent CDs at room temperature according to the principle of amine-aldehyde condensation in this work. This reaction is simple, economical, energy saving and is extremely consistent with the concept of green synthesis and sustainable development. In addition, studies have found that tetracycline hydrochloride (TC) can quench the fluorescence of the as-prepared CDs through Inner filter effect (IFE). The changes of the fluorescence intensity also have a good linear relationship with the concentration of TC in the range of 10.0–400.0 μM, and the detection limit is 6.0 μM. This method has been successfully used to determine the tetracycline content of tetracycline tablets. Finally, the interaction mechanism between TC and CDs was analyzed and discussed. Graphical abstract Carbon dots (CDs) was synthesized at room temperature with a spherical structure. Tetracycline hydrochloride (TC) can quench the fluorescence of the as-prepared CDs through Inner filter effect (IFE) because the ultraviolet absorption band of TC overlaps with the excitation band of CDs. Image 1 Highlights • A simple, green and time-saving method to synthesize CDs at the room temperature was developed. • A selective carbon dots (CDs) fluorescent probe for TC sensing was developed with the advantages of simple and fast. • This method has been successfully used to determine the tetracycline content of tetracycline tablets. [ABSTRACT FROM AUTHOR]

Abstract Ratiometric sensing suffers from less interference and can obtain more accurate results than single-signal assay. Here, a new ratiometric optical sensing strategy for H 2 O 2 detection is developed by etching silver nanoparticles (AgNPs) to deactivate fluorescence resonance energy transfer (FRET) and reduce Rayleigh scattering based on a hyphenated technique of fluorescence and second-order Rayleigh scattering (SRS). The ratiometric detection of H 2 O 2 is achieved through exploiting a hybrid system fabricated by fluorescent carbon dots and silver nanoparticles (CDs/AgNPs). In the CDs/AgNPs system, the fluorescence of CDs is quenched because of FRET, and the scattering is strong due to the intrinsic high light-scattering power of AgNPs. With the introduction of H 2 O 2 , the AgNPs are etched and the CDs are released from the AgNP surface, resulting in the fluorescence enhancement and scattering decline. As a result, ratiometric sensing of H 2 O 2 can be achieved based on the CDs/AgNPs system by simultaneous collection of fluorescence and SRS signals. The sensing system is further used for H 2 O 2 -generation bioanalysis, and as a proof-of-concept, ratiometric assay of glucose and evaluation of glucose oxidase activity are performed successfully. This work provides a new perspective for sensing applications of plasmonic nanoparticles. Graphical abstract Image 1 Highlights • A ratiometric sensor of H 2 O 2 was fabricated by Ag nanoparticles (AgNPs) and carbon dots (CDs). • The sensor was developed by combining fluorescence and second-order Rayleigh scattering. • The CDs/AgNPs system was endowed with weak fluorescence and strong scattering. • Fluorescence increased and scattering declined after AgNPs were etched by H 2 O 2. • The sensor was extended to ratiometric assay of glucose and glucose oxidase activity. [ABSTRACT FROM AUTHOR]

Abstract Isomers discrimination plays a vital role in modern chemistry, and development of efficient and rapid method to achieve this aim has attracted a great deal of interest. In this work, a novel carbon dot-decorated chiral porous organic cage hybrid nanocomposite (CD@RCC3) was prepared and used to fabricate fluorescent sensor. The resultant CD@RCC3 was characterized by using a range of techniques, finding that CD@RCC3 possesses strong and stable fluorescent property in common organic solvents, especially it exhibits chiral property. The potential application of CD@RCC3 in fluorescence sensing was demonstrated by isomers discrimination. The designed sensor was successfully used to rapid discriminate nitrophenol isomers. Meanwhile, it exhibited differentiation ability towards phenylalaninol and phenylethanol enantiomers. Our work enriches the type of synthetic materials for fluorescence sensing, and provides a simple method for distinguishing structural isomers and chiral isomers. Graphical abstract Image 1 Highlights • A novel carbon dot-decorated chiral porous organic cage hybrid nanocomposite prepared. • CD@RCC3 shows excellent fluorescent property and exhibits chiral property. • Fluorescent sensor was developed based on CD@RCC3. • The sensor was used to rapid discriminate nitrophenol isomers. • The sensor exhibited differentiation ability to phenylalaninol and phenylethanol enantiomers. [ABSTRACT FROM AUTHOR]

Abstract High-efficient orange fluorescence nitrogen-doped carbon dots (N-CDs) were facilely prepared from P-phenylenediamine as a precursor via hydrothermal method. The as-prepared N-CDs with an average diameter of 3.65 nm displayed excitation-independent emission at 590 nm. The N-CDs demonstrated a remarkable fluorescence enhancement behavior with the increase of pH. A sigmoidal curve was well fitted using BiDoseResp equation with pK a1 3.57 and pK a2 6.01, which can be ascribed to the unique surface properties of N-CDs. Two-segment linear ranges of 2.6–4.6 and 5.0–6.8 broaden the response range to pH of the orange-emission N-CDs to some extent. The confocal fluorescent microscopic images of SMMC7721 cells were performed successfully, which demonstrating that N-CDs possess exceptional cell membrane permeability and can implement as biosensing platform to monitor pH fluctuations in living cells. Graphical abstract Image 1 Highlights • The long-wavelength fluorescent N-CDs were prepared by one-step hydrothermal method and using water as the reaction solvent. • The N-CDs displayed excitation-independent emission at 590 nm, which can better applied in biosensor and bioimaging. • The N-CDs shown a remarkable fluorescence enhancement behavior with the increase of pH corresponding to double pK a. • The N-CDs possessed favorable biocompatibility, high photostability, ultra-low toxicity and cellular labeling capability. [ABSTRACT FROM AUTHOR]

Abstract Hepatocellular carcinoma (HCC) is among the leading causes of mortality in the world. The detection of HCC in its early stage is the key for early treatment and thus the improvement of the chances of survival. Among the various methods of HCC screening, assays based on the detection of biomarker that is specific to HCC such as alpha- l -fucosidase (AFU) have been regarded as the most prominent methods. In this regards, a new assay for the detection of AFU to screen HCC was developed. This assay was based on the energy transfer between carbon dots (C-dots) and gold nanoparticles (AuNPs), the concentration of AFU could be monitored by the degree of C-dots fluorescence quenching due to the energy transfer. With this assay, a limit of detection of 3.4 nM (well below the diagnostic cutoff point of 80 nM), and a broad linear range of detection from 11.3 to 200 nM were achieved. We also demonstrate the determination of the concentration of AFU in human blood serum. Graphical abstract Image 1 Highlights • Energy transfer between carbon dots and AuNPs was used to design assay for the detection of alpha- l -fucosidase. • A sandwich assay was designed by combining polyclonal antibody coated AuNPs with monoclonal antibody attached to carbon dots. • A limit of detection of 3.4 nM and linear range from 11.3 to 200 nM were achieved. [ABSTRACT FROM AUTHOR]

The emergence of "superbugs" due to antibiotics overuse poses a significant threat to human health and security. The development of sensitive and effective antibiotics detection is undoubtedly a prerequisite for addressing antibiotics overuse-associated issues. However, current techniques for monitoring antibiotics typically require costly equipment and well-trained professionals. Hence, we developed herein a rapid, instrument-free, and on-site detection method for antibiotic residues such as norfloxacin (NOR) based on a ratiometric sensing platform utilizing "on–off–on" response properties of polychromatic fluorescence for direct visual quantitative NOR analysis. Specifically, this platform integrated iron ions (Fe3+)-chelated blue carbon dots (BCDs) for signal sensing and red carbon dots (RCDs) as an internal reference. The sensor mechanism is selective quenching of BCDs' blue fluorescence by Fe3+ via an inner filter effect with unaffected RCDs' red fluorescence. Further NOR addition led to competitive binding with BCDs due to Fe3+ shedding from the BCDs' surface for a recovered blue fluorescence signal. Notably, the ratiometric fluorescence sensor demonstrated rapid and highly sensitive NOR detection in a concentration range of 1–70 μM with an impressive detection limit of 6.84 nM. The ratiometric fluorescence sensing platform was constructed by integrating smartphone and paper-based strategies, which exhibited exceptional sensitivity, selectivity, and rapid response for portable, instrument-free, visual quantification of NOR in real samples. [Display omitted] • A polychromatic ratiometric nanosensor via "on–off–on" response is explored. • The fluorescence detection signal is selectively quenched by Fe3+ through IFE. • The smartphone sensing platform allows on-site and real-time detection of NOR. • The reliability of the method is confirmed by real samples without treatment. [ABSTRACT FROM AUTHOR]

Chlorpyrifos (CPF) is a commonly used insecticide found in many water sources and is related to several health and environmental effects. Biosensors based on aptamers (single-stranded nucleic acid oligonucleotides) are promising alternatives to achieve the detection of CPF and other pesticides in natural waters. However, several challenges need to be addressed to promote the real application of functional aptasensing devices. In this work, an ssDNA aptamer (S1) is combined with carbon quantum dots (CD) and graphene oxide (GO) to produce a stable fluorescent aptasensor characterized through spectrophotometric and electrophoretic techniques. For a deeper understanding of the system, the mechanism of molecular interaction was studied through docking modeling using free bioinformatic tools like HDOCK, showing that the stem-loops and the higher guanine (G) content are crucial for better interaction. The model also suggests the possibility of generating a truncated aptamer to improve the binding affinity. The biosensor was evaluated for CPF detection, showing a low LOD of 0.01 μg L−1 and good specificity in tap water, even compared to other organophosphates pesticides (OPs) like profenofos. Finally, the recovery of the proposed aptasensor was evaluated in some natural water using spiked samples and compared with UPLC MS-MS chromatography as the gold standard, showing a good recovery above 2.85 nM and evidencing the need of protecting ssDNA aptamers from an erratic interaction with the aromatic groups of dissolved organic matter (humic substances). This work paves the way for a better aptasensors design and the on-site implementation of novel devices for environmental monitoring. [Display omitted] • A biosensor based on ssDNA aptamer and Carbon Dots was developed for CPF detection. • The mechanism of interaction for the aptamer and CPF was proposed through docking modeling. • The biosensor shows low LOD for CPF and good specificity. • The biosensor showed good detection of CPF in superficial waters. [ABSTRACT FROM AUTHOR]

Facing the difficulties in chromatographic separation of polar compounds, this investigation devotes to developing novel stationary phase. Molecularly imprinted polymers (MIPs) have aroused wide attention, owing to their outstanding selectivity, high stability, and low cost. In this work, a novel stationary phase based on carbon dots (CDs), MIP layer, and silica beads was synthesized to exploit high selectivity of MIPs, excellent physicochemical property of CDs, and outstanding chromatographic performances of silica microspheres simultaneously. The MIP doped CDs coated silica (MIP-CDs/SiO 2) stationary phase was systematically characterized by scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area measurement, and carbon elemental analysis. Furthermore, the chromatographic performance of the MIP-CDs/SiO 2 column was thoroughly assessed by using a wide variety of compounds (including nucleosides, sulfonamides, benzoic acids, and some other antibiotics). Meanwhile, the separation efficiency of the MIP-CDs/SiO 2 stationary phase was superior to other kinds of stationary phases (e.g. nonimprinted NIP-CDs/SiO 2 , MIP/SiO 2 , and C18–SiO 2). The results demonstrated that MIP-CDs/SiO 2 column exhibited best performance in terms of chromatographic separation. For all tested compounds, the resolution value was not less than 1.60, and the column efficiency of MIP-CDs/SiO 2 for thymidine was 22,740 plates/m. The results further indicate that the MIP-CDs/SiO 2 column can combine the good properties of MIP, CDs, with those of silica microbeads. Therefore, the developed MIP-CDs/SiO 2 stationary phase can be applied in the separation science and chromatography-based techniques. MIP-CDs/SiO 2 stationary phase was synthesized by the combination of MIPs, CDs, and silica microspheres. The MIP-CDs/SiO 2 column exhibited excellent chromatographic performance towards nucleosides, sulfonamides, benzoic acids, and some other antibiotics. [Display omitted] • The good physicochemical property of MIP, CDs, and silica microbeads were combined. • MIP-CDs/SiO 2 column was prepared via slurry method. • Nucleosides, sulfonamides, and benzoic acids were used as analytes. • MIP-CDs/SiO 2 column possesses outstanding chromatographic performances. [ABSTRACT FROM AUTHOR]

Acid phosphatase (ACP) as a clinical diagnostic biomarker for several pathophysiological diseases has aroused widespread interest. Compared to commonly developed single-mode ACP detection technology, the multi-mode detection method with self-validation can provide more reliable results. Herein, we proposed a triple-mode phosphorescence, fluorescence, and colorimetric method for ACP detection in combination with CDs@SiO 2. HAuCl 4 with oxidase-like activity can catalyze the oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to the blue oxide TMB (TMBox), offering absorption signals and quenching the phosphorescence and fluorescence of CDs@SiO 2 based on the internal filtration effect (IFE). ACP can hydrolyze ascorbic acid 2-phosphate (AAP) to yield ascorbic acid (AA), thereby reducing TMBox to TMB, triggering solution fading and restoring phosphorescence and fluorescence signals. When the ACP inhibitor malathion is present, the reduction of TMBox is hindered, which successively led to the suppression of CDs@SiO 2 phosphorescence and fluorescence signal recovery. According to these principles, triple-mode ACP (LOD = 0.0026 mU mL−1) and malathion detections (LOD = 0.039 μg mL−1) with favorable accuracy and sensitivity are realized. With simplicity, robustness, and versatility, the triple-mode sensor can be extended to the detection of the AAP hydrolase family and the screening of corresponding inhibitors. [Display omitted] • Phosphorescence, fluorescence, and absorption signals are integrated into one sensor. • A triple-mode sensor is constructed for the detection of ACP and its inhibitors. • Accuracy and reliability are improved by comparing triple results. • The sensor can be extended to other AAP hydrolases and their inhibitors detection. [ABSTRACT FROM AUTHOR]

Highly sensitive and selective detection of microRNA-21 (miRNA-21) in biological samples is critical for the disease diagnosis and cancer treatment. In this study, a nitrogen-doped carbon dots (N-CDs)-based ratio fluorescence sensing strategy was constructed for miRNA-21 detection with high sensitivity and excellent specificity. Bright-blue N-CDs (λ ex / λ em = 378 nm/460 nm) were synthesized by facile one-step microwave-assisted pyrolysis method by using uric acid as the single precursor, and the absolute fluorescence quantum yield and fluorescence lifetime of N-CDs were 35.8% and 5.54 ns separately. The padlock probe hybridized with miRNA-21 firstly and then was cyclized by T4 RNA ligase 2 to form a circular template. At the present of dNTPs and phi29 DNA polymerase, the oligonucleotide sequence in miRNA-21 was prolonged to hybridize with the surplus oligonucleotide sequences in circular template, generating long and reduplicated oligonucleotide sequences containing abundant guanine nucleotides. Separate G-quadruplex sequences were generated after the addition of Nt.BbvCI nicking endonuclease, and then hemin bound with G-quadruplex sequence to construct the G-quadruplex DNAzyme. Such G-quadruplex DNAzyme catalyzed the redox reaction of o -phenylenediamine (OPD) with H 2 O 2 , finally producing the yellowish-brown 2,3-diaminophenazine (DAP) (λ em = 562 nm). Due to the inner filter effect between N-CDs and DAP, the ratio fluorescence signal of DAP with N-CDs was utilized for sensitive detection of miRNA-21 with detection limit of 0.87 pM. Such approach has practical feasibility and excellent specificity for miRNA-21 analysis during highly homological miRNA family in HeLa cell lysates and human serum samples. [Display omitted] • N-CDs with fluorescent QY of 35.8% were synthesized through one-step hydrothermal method. • Ratio fluorescence sensing strategy for miRNA-21 was established based on N-CDs and DAP via IFE. • Nuclease-assisted rolling circle amplification strategy was used to enhance the detection sensitivity significantly. • Ratio fluorescence probe was used to detect as low as 0.87 pM of miRNA-21 in solution. • This method excellent specificity for miRNA-21 during its highly homological family in living HeLa cells. [ABSTRACT FROM AUTHOR]

Carbon dots (CDs) are promising nanomaterials for biosensing, bioimaging, and drug delivery due to their large surface area, excellent optical properties, and thermal and chemical stability. However, biosafety of CDs is still understudied, and there is not a generally accepted standard to evaluate the toxicity of CDs. We present a gradient network generator microfluidic device for dose-dependent testing of toxicity of CDs to a unicellular eukaryotic model organism, yeast Pichia pastoris . We fully characterized the microfluidic model and compare its performance with a conventional method. The gradient generator increased the contact area between the mixing species and enabled a high-throughput testing of CDs in a wide range of concentrations in cell chambers. Real time monitoring of yeast cell proliferation in the presence of CDs showed dose-dependent growth inhibition and various budding cell shape profiles. Comparing the result of microfluidic platform and conventional method revealed statistically significant differences in the proliferation rate of the cells between the two platforms. To understand the toxicity mechanism, we studied binding of CDs to P. pastoris and found increasing interactions of CDs with the cell surface at CDs larger concentrations. This study demonstrated the utility of the gradient generator microfluidic device as a convenient tool for toxicity assessment of nanomaterials at a cellular level. [ABSTRACT FROM AUTHOR]

The distance-dependent based sensing mechanism, such as fluorescence resonance energy transfer (FRET) and surface plasmon resonance (SPR) absorption of gold nanoparticles, has been used widely in visual detection. In this work, we report another distance-dependent detection method for nucleoside triphosphates (NTPs) based on carbon dots (CDs) ( 1 O 2 donor) and 9, 10-diphenylanthracene-2-boronic acid (DABA, 1 O 2 acceptor). The CDs can generate singlet oxygen ( 1 O 2 ) which allows diffusion within 200 nm. Thus, the distance between CDs and DABA decreased through binding of NTPs (<200 nm), leading to absorption changes of DABA under light irradiation due to 1 O 2 trapping. This sensing system (CDs@DABA) has high selectivity for the detection of NTPs due to the double molecular recognition and a linear response in the 0–80 μM concentration range was accomplished with the detection limit as low as 4.35 μM. [ABSTRACT FROM AUTHOR]

Cyclobutane pyrimidine dimmers (CPDs) and 6–4-[pyrimidine-2′-one] pyrimidine (6-4 PP) are major UV induced DNA damage lesions formed from solar radiation and other sources. CPD lesions are presumably mutagenic and carcinogenic that inhibit polymerases and interfere in DNA replication. An easy and cost effective way for visual detection of these lesions by using fluorescence based method is shown here. Artificial UVA and UVB lights were used for the generation of CPD and 6-4 PPs in selected DNA samples. Binding of Hg 2+ ions with DNA before and after induction of CPD and 6-4 PP lesions was evaluated in the presence of highly fluorescent blue emitting carbon dots (CDs). Induction of CPD and 6-4 PPs in DNA causes distortion of DNA structure which hinders the binding of Hg 2+ ions to DNA nucleobases. Quenching of fluorescence intensity of CDs by unbound Hg 2+ ions was found to be proportional to the amount of CPD and 6-4 PP lesions induced by UV irradiation of DNA samples that offer a biosensing platform for the sensitive detection of CPD lesions in DNA. The fluorescent quenching was visually detectable using hand held UV light without the intervention of any equipment. [ABSTRACT FROM AUTHOR]

A novel and general strategy of split-type immunoassay is developed based on redox chemical reaction modulated photoelectrochemistry of carbon dots (CDs). Specifically, the photocurrent of the CDs sensitized titanium dioxide nanoparticles (TiO 2 NPs) modified fluorine doped indium tin oxide (FTO) (that is the FTO/TiO 2 /CDs) electrode was inhibited obviously by KMnO 4 due to the oxidation of surface hydroxyl groups of CDs to electron accepting carbonyls. While the inhibited photocurrent of the KMnO 4 treated FTO/TiO 2 /CDs electrode can be restored by ascorbic acid (AA) because of the regeneration of electron donating hydroxyls to promote electron-hole separation. Take carcinoembryonic antigen (CEA) as a model analyte and alkaline phosphate (ALP) as a catalytic label tracer to hydrolyze ascorbic acid 2-phosphate (AAP) for producing AA, which greatly stimulated the photocurrent of the transducer of KMnO 4 treated FTO/TiO 2 /CDs photoelectrode for signal output. This redox chemical reaction modulated PEC strategy enabled the separation of the immunoreaction from the photoelectrode (that is, a split-type PEC detection), eliminating potential damage of biomolecules during the PEC detection processes and leading to enhanced throughput detection as compared to conventional PEC configurations. A low detection limit of 7.0 fg/mL was achieved for CEA. This convenient, split-type PEC immunoassay with high throughput may be easily extended to other bioaffinity assays for versatile targets. [ABSTRACT FROM AUTHOR]

The various synthetic routes of carbon dots (C-dots) feature a considerable step toward their potential use in chemical sensors and biotechnology. Herein, by coupling phosphorus and nitrogen element introduction, the adenosine-derived N/P co-doped C-dots with fluorescence enhancement were achieved. By separately employing adenosine, adenosine monophosphate, adenosine diphosphate, and adenosine-5′-triphosphate as precursors, the effect of N/P co-doping on the fluorescence emission is discussed in detail. The formed C-dots with adenosine monophosphate exhibited strong blue fluorescence with a high quantum yield of 33.81%. Then the C-dots were employed as a fluorescent probe and utilized to develop a fast, sensitive, and selective picric acid sensor. The fluorescence of C-dots can be quenched by picric acid immediately, giving rise to a picric acid determination down to 30 nM. The possible mechanism of fluorescence quenching was discussed, which was proved to be inner filter effect and static quenching. Moreover, this method has the potential to detect picric acid in environmental water samples. [ABSTRACT FROM AUTHOR]

Photoluminescent-carbon nanoparticles (PL-CNPs) are a new class of materials that received immense interest among researchers due to their distinct characteristics, including photoluminescence, high surface-to-volume ratio, low cost, ease of synthesis, high quantum yield, and biocompatibility. By exploiting these outstanding properties, many studies have been reported on its utility as sensors, photocatalysts, probes for bio-imaging, and optoelectronics applications. From clinical applications to point-of-care test devices, drug loading to tracking of drug delivery, and other research innovations demonstrated PL-CNPs as an emerging material that could substitute conventional approaches. However, some of the PL-CNPs have poor PL properties and selectivity due to the presence of impurities (e.g., molecular fluorophores) and unfavourable surface charges by the passivation molecules, which impede their applications in many fields. To address these issues, many researchers have been paying great attention to developing new PL-CNPs with different composite combinations to achieve high PL properties and selectivity. Herein, we thoroughly discussed the recent development of various synthetic strategies employed to prepare PL-CNPs, doping effects, photostability, biocompatibility, and applications in sensing, bioimaging, and drug delivery fields. Moreover, the review discussed the limitations, future direction, and perspectives of PL-CNPs in possible potential applications. [Display omitted] • This review offers extensive knowledge on the recent applications of PL-CNPs. • Synthesis and optical and surface morphological properties of PL-CNPs were presented. • PL-CNPs for sensing, bioimaging and drug delivery applications were summarized. • Photostability and biocompatibility of PL-CNPs were discussed. • Drawbacks, challenges, and future perspectives of PL-CNPs were thoroughly briefed. [ABSTRACT FROM AUTHOR]

Nitrite (NO 2 −) is extensively found in the daily dietary environment. However, consuming too much NO 2 − can pose serious health risks. Thus, we designed a NO 2 −-activated ratiometric upconversion luminescence (UCL) nanosensor which could realize NO 2 − detection via the inner filter effect (IFE) between NO 2 −-sensitive carbon dots (CDs) and upconversion nanoparticles (UCNPs). Due to the exceptional optical properties of UCNPs and the remarkable selectivity of CDs, the UCL nanosensor exhibited a good response to NO 2 −. By taking advantage of NIR excitation and ratiometric detection signal, the UCL nanosensor could eliminate the autofluorescence thereby increasing the detection accuracy effectively. Additionally, the UCL nanosensor proved successful in detecting NO 2 − quantitatively in actual samples. The UCL nanosensor provides a simple as well as sensitive sensing strategy for NO 2 − detection and analysis, which is anticipated to extend the utilization of upconversion detection in food safety. [Display omitted] • A ratiometric upconversion-carbon dots nanosensor was designed for NO 2 − detection. • UCNPs acting as donor could effectively eliminate the background interference from actual samples. • This nanosensor possessed high stability, sensitivity, and specificity. • Application of this nanosensor to detect NO 2 − in actual samples was confirmed with satisfactory results. [ABSTRACT FROM AUTHOR]

Recently, α-glucosidase inhibitor has been widely used in clinic for diabetic therapy. In the present study, a facile and sensitive fluorescent assay based on enzyme activated inner filter effect (IFE) on nitrogen-doped carbon dots (CDs) was first developed for the detection of α-glucosidase. The N-doped CDs with green emission were prepared by a one-step hydrothermal synthesis and gave the fluorescence quantum yield of 30%, which were used as the signal output. Through α-glucosidase catalysis, 4-nitrophenol was released from 4-nitrophenyl-α- d -glucopyranoside (NGP). Interestingly, the absorption of 4-nitrophenol and the excitation of CDs were completely overlapping. Due to its great molar absorptivity, 4-nitrophenol was capable of acting as a powerful absorber to affect the fluorescent signal of CDs (i.e. IFE). By converting the absorption signals into fluorescence signals, the facile fluorescence assay strategy could be realized for α-glucosidase activity sensing, which effectively avoided the complex modification of the surface of CDs or construction of the nanoprobes. The established IFE-based sensing platform offered a low detection limit of 0.01 U/mL (S/N = 3). This proposed sensing approach has also been expanded to the inhibitor screening and showed excellent applicability. As a typical α-glucosidase inhibitor, acarbose was investigated with a low detection limit of 10 −8 M. This developed method enjoyed many merits including simplicity, lost cost, high sensitivity, good reproducibility and excellent selectivity, which also provided a new insight on the application of CDs to develop the facile and sensitive biosensor. [ABSTRACT FROM AUTHOR]

Microwave synthetized sulfur and nitrogen co-doped carbon dots responded selectively to nitric oxide (NO) at pH 7. Citric acid, urea and sodium thiosulfate in the proportion of 1:1:3 were used respectively as carbon, nitrogen and sulfur sources in the carbon dots microwave synthesis. For this synthesis, the three compounds were diluted in 15 mL of water and exposed for 5 min to a microwave radiation of 700 W. It is observed that the main factor contributing to the increased sensitivity and selectivity response to NO at pH 7 is the sodium thiosulfate used as sulfur source. A linear response range from 1 to 25 μM with a sensitivity of 16 μM −1 and a detection limit of 0.3 μM were obtained. The NO quantification capability was assessed in standard and in fortified serum solutions. [ABSTRACT FROM AUTHOR]

The widespread presence of tetracyclines in the environment has raised concerns about the potential risks to ecosystems and human health. The ratiometric fluorescence sensor for detecting tetracyclines was developed using europium-doped carbon dots (Eu-CDs) as probes under alkaline conditions. The sensing mechanism of sensor for tetracyclines was considered as inner filter effect (IFE), antenna effect (AE), and self-quenching effect (SQE). The sensor had a wide linear detection range than the reported europium ions-based tetracyclines sensors. The linear detection ranges of oxytetracycline (OTC), tetracycline (TC), doxycycline (DC) and chlorotetracycline (CTC) were respectively 0.00–603.75 μM, 0.00–623.82 μM, 0.00–594.61 μM and 0.00–601.54 μM, and the corresponding detection limits were respectively 9.50 nM, 15.80 nM, 10.40 nM and 90.30 nM. The smartphone with RGB Color Picker was further employed to analyze the concentration of tetracyclines, which provided a new method for visual tetracyclines detection. The application of Eu-CDs test paper was also explored, and the results showed that the Eu-CDs test paper has great potential application in the visual detection of tetracyclines. In addition, the accuracy of the established tetracyclines sensor was compared with that of the China national standard method by high-performance liquid chromatography (HPLC), and the results showed that the established method in this work has similar accuracy to the China national standard method. The sensor has been employed to detect tetracyclines in the actual samples with satisfactory results, which indicated that this method has promising applications in the real-time monitoring tetracyclines of food and environment. A dual-signal fluorescent colorimetric tetracyclines sensor was developed based on multicolor carbon dots as probes with smartphone-assisted visual assay. [Display omitted] • The tetracyclines could be detected by fluorometric and colorimetric methods. • The sensor hasa wide linear detection range. • The sensor has good sensitivity, selectivity, and anti-interference ability. • Eu-CDs integrated with a smartphone allowed visual detection of tetracyclines. • The proposed method has similar accuracy to the China national standard method. [ABSTRACT FROM AUTHOR]

The dynamic interplay of nanotechnology and immunoassay has unlocked an arena for developing next-generation techniques to contribute to detecting disease biomarkers. Herein, the work establishes the strategic fabrication of an immunosensor by sandwich technique based on the fluorescence phenomenon of carbon dots for the detection of the disease biomarker VEGF (Vascular Endothelial Growth Factor). VEGF, a biomarker for angiogenesis, is considered cancerous if found in elevated levels in the blood, and so is paramount for early detection of disease. Carbon dots derived from a biogenic source were synthesized employing a green microwave-assisted method followed by conjugating with a detection antibody, human immunoglobulin G (IgG), via EDC-NHS amidation reaction. On the other hand, the VEGF biomarker was immobilized onto the capture antibody. The detection antibody tagged with the fluorescent probe is employed as a bridge to connect with the VEGF biomarkers bound to the capture antibody. The response to different concentrations of VEGF biomarkers was recorded in terms of the fluorescence intensity of the carbon dots. The fluorescence immunosensor could exhibit a wide linear range of 0.1 fg/mL to 10 pg/mL with a low detection limit of 5.65 pg/mL towards VEGF. The potentiality of this designed immunosensor was qualitatively assessed with human blood plasma samples, showing promising results, thereby upholding the applicability of carbon dots as fluorescent labels in immunoassay techniques. [Display omitted] • Carbon dots derived from a biogenic source were synthesized (OCD). • Carbon dot conjugating with a detection antibody(IgG) via amidation reaction IgG-OCD. • A IgG^VEGF^(IgG-OCD) sandwich immunocomplex is formed in presence of VEGF. • The immunosensor could exhibit a wide linear range of 0.1 fg/mL to10 pg/mL. • The immunosensor could exhibit low detection limit of 0.1 fg/mL towards VEGF. [ABSTRACT FROM AUTHOR]

In this work, pH-sensitive blue fluorescent carbon dots (CDs) with high fluorescence quantum yield (17.24%) were synthesized by hydrothermal method using Toona sinensis leaves and ethylenediamine (EDA) as raw materials. The CDs can detect urea with a limit of detection (LOD) of 6.700 mmol L−1. For more sensitive detection of urea, we constructed a ratiometric fluorescent probe (CDs@5-FAM) using CDs and 5-carboxyfluorescein (5-FAM). The CDs@5-FAM probe can rapidly and sensitively detect urea according to the changes of I 514 /I 405 , with LOD as low as 0.014 mmol L−1. Furthermore, with the help of a smartphone and RGB analysis software, urea's visual intelligent detection was realized using a CDs@5-FAM probe. The method proposed in this paper is consistent with the standard method, which indicates that the pH-sensitive ratiometric fluorescent probe CDs@5-FAM is accurate and reliable for practical application. It provides a new way for rapid and visual detection of urea. [Display omitted] • CDs with high quantum yield were first prepared using toona sinensis leaf as carbon source. • The pH-sensitive CDs@5-FAM fluorescent probe is far more sensitive to detect urea than CDs alone. • CDs@5-FAM can detect urea rapidly, sensitively, selectively, and without interference. • Smartphones enable the visualization and intelligence of the detection of urea by CDs@5-FAM. [ABSTRACT FROM AUTHOR]

Composited carbon nanomaterials have attracted wide attention and are used for high-sensitivity biological assays due to their low toxicity, good biocompatibility, and excellent electrical conductivity. To further promote electron transfer and enhance electrocatalytic activity to detect dopamine (DA), this study proposed carbon dots (CDs) based on glycerol synthesized by liquid dielectric barrier discharge (DBD) microplasma. Combined with the multi-walled carbon nanotubes (MWCNTs) with excellent electrical conductivity, a composited carbon nanomaterial electrode of CDs/MWCNTs was constructed. As a DA biosensor, the interaction and electron exchange between MWCNTs, CDs, and DA can be enhanced thanks to the π-π stacking force, thereby facilitating the sensitive electrochemical detection of DA. The sensor exhibits good sensing performance toward DA detection with a linear range of 2.0–100 μM, a limit of detection (LOD) of 11.08 nM (S/N = 3), and a sensitivity of 29020 μA cm−2 mM−1. The proposed electrode successfully detected DA levels in human serum samples with satisfactory selectivity and recovery rate. The microplasma-enabled synthesized method provides a promising path for preparing and applying carbon-based nanomaterials. [Display omitted] • Carbon dots were synthesized by liquid dielectric barrier discharge microplasma using glycerol as the sole carbon source. • The π−π interaction between CDs, MWCNTs, and the aromatic rings of DA facilitates the sensitive detection of DA. • It provides a promising path for preparing of other carbon-based nanomaterials. [ABSTRACT FROM AUTHOR]

In this work, a La3+ assisted glutathione-capped gold nanoclusters and carbon dots (GSH-Au NCs/CDs) nanoplatform for sensitive detection of fenthion (FEN) is fabricated. The fluorescence response of GSH-Au NCs significantly increases due to aggregation-induced emission enhancement (AIEE) effect induced by La3+, which is further enhanced with adding FEN due to the coordination between La3+ and FEN. Taking the fluorescence intensity of CDs as the signal background, the ratiometric fluorescence of GSH-Au NCs and CDs has a good linear relationship with the FEN concentration from 0.01 to 1.10 μg mL−1, and detecting FEN exhibits a good sensitivity at a low detection limit of 6.74 ng g−1. The La3+ assisted GSH-Au NCs/CDs nanoplatform demonstrates desirable selectivity and applicability for monitoring trace level of FEN in fruit and vegetable samples. The non-enzymatic strategy by taking advantage of successive AIEE of GSH-Au NCs has a great potential for facile screening organophosphate pesticides in agro-products. [Display omitted] • A non-enzymatic ratiometric fluorescence probe for FEN is facilely fabricated. • Sensitive detection of FEN is realized by La3+ induced successive AIEE of Au NCs. • The La3+-CDs/Au NCs system is applicable for FEN residue analysis in agro-products. [ABSTRACT FROM AUTHOR]

In this study, preparation of novel pH-sensitive N-doped carbon dots (NCDs) using glucose and urea is reported. The prepared NCDs present strong excitation-dependent fluorescence changes towards the pH that is a new behavior from these nanomaterials. By taking advantage of this unique behavior, two separated ratiometric pH sensors using emission spectra of the NCDs for both acidic (pH 2.0 to 8.0) and basic (pH 7.0 to 14.0) ranges of pH are constructed. Additionally, by considering the entire Excitation–Emission Matrix (EEM) of NCDs as analytical signal and using a suitable multivariate calibration method, a broad range of pH from 2.0 to 14.0 was well calibrated. The multivariate calibration method was independent from the concentration of NCDs and resulted in a very low average prediction error of 0.067 pH units. No changes in the predicted pH under UV irradiation (for 3 h) and at high ionic strength (up to 2 M NaCl) indicated the high stability of this pH nanosensor. The practicality of this pH nanosensor for pH determination in real water samples was validated with good accuracy and repeatability. [ABSTRACT FROM AUTHOR]

Supramolecular host molecules are used as tools in the design of multifunctional nanoparticles for sensors, catalysts, biometric elements, etc. Combining with carbon dots (CDs) has excellent host-guest recognition properties and fluorescence characteristics, which can precisely capture and identify target analytes. Consequently, supramolecular host molecules-based CDs can significantly improve the detection performance of ions and molecules with different structures or intrinsic chemical properties. This currently responds to a wide range of analytes including metal cations, anions, organic compounds and other biomolecules, yielding fascinating achievements in the field of chemistry. Therefore, the present review summarizes outstanding supramolecular host molecules-based CDs reported in the past ten years. The focus is on elucidating the mechanisms, methodologies, advantages and disadvantages of modifying or preparing CDs with supramolecular host molecules. Current challenges encountered and outlooks are also be discussed. Modification or preparation of carbon dots with supramolecular host molecules. [Display omitted] • Strategies for modification or preparation of CDs with supramolecular host molecules. • Roles of supramolecular host molecules-based CDs in fluorescence signal modulation and enhanced selective recognition. • Potential applications, current challenges and prospects of supramolecular host molecules-based CDs. [ABSTRACT FROM AUTHOR]

Enzyme-based electrochemical sensor possesses a significant advantage in the highly efficient detection of small molecules, however, the poor electron transport efficiency limits their wide application. In this study, taking advantage of the distinct biocatalytic activity of laccase and the excellent electroconductibility of carbon dots, a carbon dots-enhanced laccase-based electrochemical sensor for the detection of dopamine (DA) is established. Thereinto, laccase can specifically recognize DA and promote its electrocatalytic oxidation on the electrode, while, the carbon dots can be used as the immobilization substrate of laccase and enhance its electron transfer efficiency, thus achieving the highly sensitive detection of dopamine. The electrochemical performance of the modified electrode interface is studied by electrochemical impedance spectroscopy and differential pulse voltammetry. As demonstrated, the electrocatalytic activity of the proposed electrochemical sensor for DA is significantly improved and exhibits a low detection limit (0.08 μM) and a wide linear range (0.25 μM–76.81 μM). The excellent selectivity allows the sensor has the capacity for specific discrimination the DA from other interferents. Furthermore, by analyzing the DA in human serum verifies the practicability of this assay in real sample analysis. A laccase-based electrochemical sensor by using carbon dots as electron transport promoter for highly sensitive detection of dopamine. [Display omitted] • CDs can accelerate the electron transfer efficiency of laccase on the electrode. • Laccase with high specificity for dopamine can promote its electrocatalytic oxidation. • CDs enhanced Laccase-based electrochemical sensor with high sensitivity for dopamine. [ABSTRACT FROM AUTHOR]

Multifunctional sensing, a strategy to improve the efficiency of analysis and detection, has attracted much attention. In this study, a multifunction sensing platform was developed for temperature, pH, and proton pump inhibitors (PPI) with fluorescence carbon dots. Solvent-dependent carbon dots (PG-CDs) were synthesized through a one-step solvothermal method from phloroglucinol with the assistance of HCl. Base on the effect of functional groups on the surface, solvent-dependent behavior, temperature and pH responsive fluorescence can be observed. The PG-CDs display a reversible temperature-sensitive fluorescent behavior within 15–65 °C in N, N-dimethylacetamide. The fluorescence intensity of PG-CDs also responded to pH in a range of 3.0–7.0 with good reversibility and anti-interference. Therefore, the platform for temperature and pH sensing was proposed. In addition, since the synergistic effect of dynamic and static quenching, proton pump inhibitors (PPI) can be detected sensitively, including esomeprazole (EPZ), omeprazole (OPZ), and rabeprazole (RPZ). The linear range of detection for EPZ, OPZ, and RPZ is 2.0–80.0, 2.0–75.0, and 10.0–200.0 μM and the limits of detection is 0.29, 0.55, and 2.99 μM, separately. The recoveries for real samples were between 91.83 and 102.3%, which indicated that the platform for PPI sensing had good accuracy. [Display omitted] • Solvent-dependent carbon dots was prepared from phloroglucinol with the assistance of HCl. • A multifunction sensing platform was developed for temperature, pH, and proton pump inhibitors with fluorescence carbon dots. • Base on the effect of functional groups on the surface, solvent-dependent behavior, temperature and pH responsive fluorescence can be observed. • Since the synergistic effect of dynamic and static quenching, proton pump inhibitors can be detected sensitively. [ABSTRACT FROM AUTHOR]

Heteroatom doping has been proven as an efficient way to improve the fluorescent efficiency of carbon dots. Co-doping with heteroatoms may introduce more active sites to carbon dots, which would broaden applications of CDs in sensing. In this work, highly luminescent nitrogen and sulfur co-doped carbon dots (NSCDs) were synthesized through a facile one-step microwave assisted method by using citric acid and rubeanic acid as carbon, nitrogen, and sulfur sources. The well-isolated NSCDs not only exhibit an enhanced fluorescent efficiency with a relatively high quantum yield up to 17.6%, but also show potential use as a multi-sensing platform based on their fluorescence “on-off-on” and color changing behaviors. The NSCDs can be directly used for the selective determination of mercury cations without any functionalization. The detection limit is approximately calculated as 0.18 μM and linear range is 0–20 μM. The sensing mechanism is proposed as coordination reaction induced by oligomers upon the carbon core. Furthermore, in the presence of cyanide anions, the fluorescence shows linear recovery associated with the concentration of cyanide, indicating its potential usage for the detection of cyanide ion. The optimized pH range for such fluorescence “on-off-on” sensing system is investigated as pH 6–8, suggesting potential applications in bio-sensing and imaging area. In addition, by adding hydrosulfide anion to NSCDs@Hg 2+ complex, a notable color change could be clearly observed due to the formation of fuscous HgS. In application, a handy test paper for direct and rapid detection of Hg 2+ is manufactured for the evaluation of usage of NSCDs in the real circumstance. [ABSTRACT FROM AUTHOR]

A unique photoluminescence carbon dots (CDs) with larger size were prepared by microwave-assisted method. Complex functional groups on the surface of the CDs facilitate the nanoparticles to form affinity with some metal ions. Taking advantage of the effective fluorescence quenching effect of K + , a highly sensitive CD-based fluorescence analytical system for label-free detection of K + with limit of detection (LOD) 1.0 × 10 −12 M was established. The concentrations of potassium ion in biological samples such as human serum are usually found at millimolar levels or even higher. The proposed method begins with a substantial dilution of the sample to place the K + concentration in the dynamic range for quantification, which covers 3 orders of magnitude. This offers some advantages: the detection of K + only needs very small quantities of biological samples, and the dilution of samples such as serum may effectively eliminate the potential interferences that often originate from the background matrix. The determined potassium levels were satisfactory and closely comparable with the results given by the hospital, indicating that this fluorescent probe is applicable to detection of physiological potassium level with high accuracy. Compared with other relative biosensors requiring modified design, bio-molecular modification or/and sophisticated instruments, this CD-based sensor is very simple, cost-effective and easy detection, suggesting great potential applications for successively monitoring physiological potassium level and the change in biological system. [ABSTRACT FROM AUTHOR]

We report a low cost selective analytical method based on inner filter effect (IFE) for citrate-silver nanoparticle (cit-AgNP) detection, in which fluorescent amine-derivatized carbon dots ( a -CDs) act as the donor and aggregated cit-AgNPs as the energy receptor. Carbon dots (CDs) were chemically modified with ethylenediamine (EDA) moieties via amidic linkage displaying an emission band at 440 nm. The presence of cit-AgNPs produces a remarkably quenching of a -CD fluorescence via IFE, since the free amine groups at CD surface induce the aggregation of cit-AgNPs accompany by a red-shifting of their characteristic plasmon absorption wavelength, which resulted in “turn-on” of the IFE-decreased in CD fluorescence. The proposed method, which involves the use of chelating agents for removal of metal ions interferences, exhibits a good linear correlation for detection of cit-AgNPs from 1.23 × 10 −5 to 6.19 × 10 −5 mol L −1 , with limits of detection (LOD) and quantification (LOQ) of 5.17 × 10 −6 and 1.72 × 10 −5 mol L −1, respectively. This method demonstrates to be efficient and selective for the determination of cit-AgNPs in complex matrices such as cosmetic creams and reveals many advantages such as low cost, reusability, high sensitivity and non time-consuming compared with other traditional methods. [ABSTRACT FROM AUTHOR]