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The rational design of nanozymes with superior activities is essential for improving bioassay performances. Herein, nitrogen and boron co-doped graphene nanoribbons (NB-GNRs) are prepared by a hydrothermal method using urea as the nitrogen source and boric acid as the boron source, respectively. The introduction of co-doped and edge structures provides high defects and active sites. The resultant NB-GNRs nanozymes show superior peroxidase-like activities to nitrogen-doped and boron-doped counterparts due to the synergistic effects. By taking advantage of their peroxidase-like activities, NB-GNRs are used for the first time to develop enzyme-linked immunosorbent assay for the detection of interleukin-6. The biosensors exhibit a high performance with a linear range from 0.001 ng/mL to 1000 ng/mL and a detection limit of 0.3 pg/mL. Due to their low cost and high stability, the proposed nanomaterials show great promise in biocatalysis, immunoassay development and environmental monitoring.

In this work, a very simple dual-readout lateral flow test strip (LFTS) platform was developed for sensitive detection of alkaline phosphatase (ALP) based on a portable device. In this assay, quantum dots (QDs) conjugated with bovine serum albumin (QDs-BSA) were chosen as fluorescence signal labels. In the absence of ALP, MnO2 nanosheets aggregate on the test line and exhibit an obvious brown color, which can be observed by naked eyes to realize semi-qualitative analysis. Meanwhile, fluorescence intensity of QDs-BSA can also be effectively quenched by MnO2 nanosheets due to inner-filter effect. Correspondingly, in the presence of ALP, ALP can catalyze the hydrolysis of ascorbic acid 2-phosphate (AAP) to generate L-ascorbic acid (AA), which can reduce MnO2 into Mn2+, accompanying with the obvious fluorescence recovery of the QDs. By simply monitoring the change of colorimetric and fluorescent signal on the test line, trace amount of ALP can be quantitatively detected. Under the optimal conditions, measurable evaluation of ALP was reached in a linear range from 1 U/L to 20 U/L with a detection limit of 0.7 U/L based on fluorescence signal. Furthermore, this colorimetric/fluorescent dual-readout assay was successfully applied to monitor ALP in human serum samples, showing its great potential as a point of care biosensor for clinical diagnosis.

Accurate detection of hydrogen sulfide (H2S) is of great significance for environmental monitoring and protection. We propose a colorimetric method for the detection of H2S by the use of mixed-node Cu-Fe metal organic frameworks (Cu-Fe MOFs) as highly efficient mimic enzymes for target-induced deactivation. The Cu-Fe MOFs were synthesized by a simple solvothermal method and could catalyze the H2O2 mediated oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to oxTMB with a blue color. The presence of dissolved H2S would deactivate the mimic enzymes, and then the blue color disappeared. The mechanism of the sensor was discussed by steady-state kinetic analysis. The designed assay was highly sensitive for H2S detection with a linear range of 0−80 μmol/L and a detection limit of 1.6 μmol/L. Moreover, some potential substances in the water samples had no interference. This method with the advantages of low cost, high sensitivity, selectivity, and visual readout with the naked eye was successfully applied to the determination of H2S in industrial wastewater samples.

Piezoresistive sensors based on three-dimensional graphene foams (GFs) can be used in health monitoring, electronic skin and wearable smart devices. It is still challenging to obtain sensors with high sensitivity and a wide linear range through a simple and an efficient method. In this paper, a graphene foam pressure sensor based on a fractal electrode (GFPSFE) is proposed. The GFPSFE contains a wave-structured GF (WSGF), a fractal electrode (FE), and a normal electrode. The FE regulates the contact resistance of the WSGF, improving the sensitivity and the linear range of the GFPSFE. We compared three GFPSFEs with different FEs, and investigated the influence of FEs on the sensitivity and the linear range of GFPSFEs. The GFPSFE with zigzag FE (Z-GFPSFE) has high sensitivity (134.75 kPa−1), wide linear range (0–35 kPa), fast response/recovery (83 ms and 166 ms), and excellent stability (2000 cycles). In addition, the sensor was attached to the human body to measure motions and pulse, demonstrating the potential application in the fields of health monitoring and human-machine interfaces.

This research explores the possibilities and limitations of WD-XRF, applied as a method for quantification of 20 elements in plant material, using spiked cellulose standards for calibration. Three different analytical methods were investigated: 1) standards created from pure spiked cellulose; 2) spiked cellulose mixed with 20% of binder and 3) spiked cellulose applied as a thin layer on an inert carrier. Sensitivity, linearity, limit of detection, limit of quantification, repeatability, intralaboratory reproducibility, and accuracy were determined and compared. The accuracy of the investigated methods was tested by analysis of standard reference materials and comparison with other routinely used analytical techniques (ICP-OES and ICP-MS). The comparison included real plant samples which were collected from the environment characterized by different pollution levels. The accuracy of the semiquantitative standardless method was also considered and compared with other investigated methods. Tested methods can be very precise, with good intralaboratory reproducibility over wide linear range. Supplementary material: [https://cherry.chem.bg.ac.rs/handle/123456789/4615] This is the peer-reviewed version of the article: Orlić, J., Gržetić, I., Goessler, W., Braeuer, S., Čáslavský, J., Pořízka, J.,& Ilijević, K.. (2021). Artificial cellulose standards as calibration standards for wavelength-dispersive X-ray fluorescence analysis of elements in plant samples. in Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms Elsevier., 502, 106-117. [https://doi.org/10.1016/j.nimb.2021.06.012]

In the present work, Chlorella vulgaris, a well-known microalga was used as a carbonic precursor, to synthesis the water-soluble carbon dots (CDs) via hydrothermal method. To improve the properties, acidic carbon dots (ACDs) were also synthesized via ultrasoncation of microalgal biomass after acidic hydrolysis (using diluted acidic solution). The aqueous solution of ACDs was used as a sensor for glucose determination based on glucose oxidase enzyme (GOx) reaction and fluorescence quenching of ACDs in the presence of Fe3+ ions under the optimized conditions. The linear range of glucose in the blood serum was measured from a range of 5 µM to 500 µM with a limit of detection (LOD) 2.84 µM. Additionally, the hydrogen peroxide, as the conventional reactive oxygen species (ROS) was determined based on the Fenton reaction. The linear range of H2O2 was obtained from 10 µM to 200 µM with LOD of 975 nM. In all of these applications, fluorescence quenching of ACDs was followed according to photo-induced electron transfer (PET) mechanism in the presence of generated Fe3+ ions by Fenton reaction.

In this paper, a composite based on chitosan and cobalt phthalocyanine immobilized onto a glassy carbon electrode is presented for the sensitive determination of sulfanilamide in pharmaceutical and urine samples. The modification performed on the electrode surface, by the deposition of this composite, exhibits an irreversible anodic peak at 0.97 V vs. Ag/AgCl, KClsat in phosphate buffer at pH 7.00 for sulfanilamide. Results show that peak potential is influenced linearly by the pH of the supporting electrolyte, exhibiting a slope of 0.054 V/pH. Using differential pulse voltammetry, detection of sulfanilamide was possible in a linear range from 1.00 to 53.00 μmol dm−3 with a detection limit and quantification limit of 0.27 and 0.91 μmol dm−3, respectively. Importantly, the sensor showed practical applications as an analytical tool for the quantification of sulfanilamide in pharmaceutical formulations and urine samples. The electrochemical approach detailed here has been validated to drug samples using a spectrophotometric method. The method proposed presents good linearity, low quantification and detection limits being of excellent applicability in pharmaceutical and urine samples.

Nowadays, given the booming demand of blood sugar control from the soaring number of diabetes patients and the insufficient stability of costly enzyme-based glucose sensors in clinic, the development of enzyme-free sensors has been drawing tremendous attraction. Herein, we fabricated a unique structure of Ni/NiO hybrid nanoparticles with mixed-valence states encapsulated in and cross-linked by nitrogen-doped graphene via a facile Ni-MOF-annealing approach and developed its notable feature in efficiently non-enzymatic glucose sensing. The microstructure and valence states, proved vital to the electrochemical activity and sensing performance, were simultaneously regulated by the annealing temperature. The optimized sample obtained at 400 °C displays the superior activation behavior and best glucose sensing performance, offering a high sensitivity of 3.2518 mA mM−1 cm−2, a wide linear range (0.001–3.568 mM), a low detection limit (0.032 μM, S/N = 3) as well as excellent selectivity, good reproducibility, long-term stability, and satisfactory applicability in real sample. By further investigation of the electrochemical kinetics mechanism, the synergistic effect of multivalent system and well-organized microstructure was proved beneficial for charge transfer, activation of reaction sites, and elimination of electrode polarization as well, thus providing a promising strategy in designing non-enzymatic biosensor platform for glucose detection in actual diagnosis.

In this work, a dual-labeled multiple aptasensor that can simultaneously detect multiple antibiotics was constructed, with kanamycin (KAN) and tobramycin (TOB) used as the model analytes. The aptasensor reported here featured three key elements, namely the RNA-based aptamer strands, semiconductor quantum dots (QDs), and gold nanoshells (AuNSs). Due to the high-affinity pairing between streptavidin (SA) and biotin (Bio), the two biotinylated aptamers (kanamycin aptamer, KAP; tobramycin aptamer, TAP) responsible for the specific recognition of KAN and TOB were conjugated to SA-coated cadmium sulfide (CdS) and lead sulfide (PbS) QDs, respectively for the syntheses of KAP-Bio-SA-CdS and TAP-Bio-SA-PdS composites. Moreover, the AuNSs had a very high loading efficiency for the as-prepared two composites on the gold electrode surface due to their outstanding surface-area-to-volume ratio. In the presence of target antibiotics, CdS and PbS QDs were released from AuNSs followed by dissolution into their respective metal ions for stripping analysis by differential pulse voltammetry (DPV). As a result, intensified signals from DPV peaks were obtained due to the large amount of the metal ion labels dissolved in the solution. The devised aptasensor exhibited wider detection linear range (KAN, 1–4 × 102 nM; TOB, 1–1 × 104 nM) and lower detection limits (KAN, 0.12 nM; TOB, 0.49 nM) compared to the previously reported sensors. Furthermore, the detection of KAN and TOB spiked in milk samples was successfully demonstrated. Therefore, the proposed aptasensor provides a novel sensitive platform for multi-antibiotics detection.

A visible-light-driven self-powered photoelectrochemical (PEC) aptasensor was developed for ampicillin (AMP) detecting based on carbon dots (CDs) hybrid MIL-68(In)-derived In2O3 In2S3 hollow tubular heterojunction (CDs/In2O3 In2S3). In2S3 nanosheets uniformly grew in-situ on the surface of In2O3 hollow tubes, forming a close contact heterogeneous interface, which significantly promoted the transfer and separation of photo-generated carriers, and provided a large specific surface area and rich active sites for the PEC aptasensing platform. Furthermore, the CDs/In2O3 In2S3/ITO electrode, which was obtained by dipping assembly, showed remarkable and stable photoelectric signals at zero-bias under visible light irradiation. The amino-functionalized AMP aptamer was fixed on the working electrode as a biological recognition element, and the concentration of AMP was determined by observing the change in photocurrent intensity caused by the specific capture of AMP molecules in solution. Under optimized conditions, the developed PEC aptasensor displayed a relatively wide linear range from 0.001 ng mL−1 to 300 ng mL−1, as well as a low detection limit (LOD) of 0.06 pg mL−1. Besides, the novel self-powered PEC AMP-aptasensor exhibited excellent reproducibility, good stability and selectivity, which open a potential avenue for antibiotic residues detection in environmental media.

Sensitive detection of redox active analytes utilising its fluorescent nature requires a direct non-complicated approach to amplify its emission intensity. In this regard, we investigated nanoscale cerium oxide for its unique nanosized structure, surface reactivity and redox activity coupled with surface complexation. Variations in either oxidation state or the surface-terminated oxygen of the cerium oxide nanoparticales provide gaps for the adsorption of redox functionalities. It enables ceria particles to concentrate the analyte molecules on their surface promoting fluorescence signal amplification. As a proof of concept, we integrated surface complexation feature of nanoceria towards improved fluorescent response and successively implemented them for ultra-sensitive identification of a redox active Ochratoxin A (OTA) at specific wavelength range. Results obtained indicate that higher amplification efficacy of nanoparticles is due to its higher electron mobility along with good absorbability. Different identification techniques including XRD SEM, UV–Vis, EDX, FTIR, photoluminescence, RAMAN spectroscopy and finally fluorescence assays were performed to examine morphology and nano-surface chemistry along with signal amplified strategy of the developed nano-probe. Various experimental factors including incubation time, pH and concentrations of OTA and ceria particles were also optimised. Under optimised environment, the limit of detection was as smaller as 0.1 ng mL−1 with 0.5–100 ng mL−1of linear range. Thus, we proposed a highly sensitive and selective fluorescent nanoprobe for analytical applications based on surface complexation affinity and fluorescence signal amplification ability of nanoceria.

Tetracycline (TC) represents a broad-spectrum antibiotic to treat bacterial infections. In this study, a ratiometric fluorescence (FL) probe was developed for the detection of TC in water samples by using waste printing paper extract as a FL indicator. In this ratiometric probe, the emission of printing paper extract at 436 nm gradually decreased and the emission of mixed solution at 538 nm significantly increased with the sequential addition of TC upon being excited at 390 nm, coupled with a remarkable FL color change from bright blue to faint yellow. Thus, a ratiometric F538 /F436 FL probe was created for TC detection by simply mixing the printing paper extraction and TC. Under the optimized conditions, the linear range from 1-100 μM and a detection limit of 0.48 μM (S/N = 3) for TC were obtained. Importantly, the FL probe can be easily prepared with rapid response, high sensitivity, and good selectivity. The application of the waste printing paper extract for the detection of TC in environmental water samples was demonstrated.

Azodicarbonamide (ADA), as a dough conditioner food additive in flour, can be turned into toxic biurea and semicarbazide after high temperature processing. Hence, the using of ADA in food material should be strictly controlled, and the detection of ADA is very important for consumers’ safety and health. Herein, a simple and fast colorimetric strategy has been developed for ADA detection based on the MnO2 nanosheets-3,3′,5,5′-tetramethylbenzidine (TMB)-glutathione (GSH) as oxidative sensing system (MnO2-TMB-GSH). Since the ADA can selectively react with GSH via oxidizing the sulfydryl (-SH) group of GSH to disulfide bond (S-S), which makes GSH unable to reduce MnO2 nanosheets and restore its oxidase-like activity. The absorbance changes of the TMB solution depended on ADA content. The MnO2-TMB-GSH colorimetric platform can detect the ADA with a linear range of 10 μmol L−1 (11.6 ppm) to 400 μmol L−1 (464 ppm), and the limit of detection (LOD) is 3.3 μmol L−1 (3.51 ppm). Some potential interferences in real sample were tested and did not affect the MnO2-TMB-GSH colorimetric platform for ADA detection. Furthermore, the sensing platform was applied for detecting ADA in real flour sample with a recovery of 96%–105% (RSD

Purpose Based on DNase I and reduced graphene oxide (rGO)-magnetic silicon microspheres (MNPS), a highly sensitive and selective fluorescent probe for the detection of PD-L1 was developed. Design/methodology/approach Here °C we present a feasibility of biosensor to detection of PD-L1 in lung tumors plasma. In the absence of PD-L1°C the PD-L1 aptamer is absorbed on the surface of graphene oxide modified magnetic nanoparticles °8rGO-MNPS°9 and leading to effective fluorescence quenching. Upon adding PD-L1°C the aptamer sequences could be specifically recognized by PD-L1 and the aptamer/PD-L1 complex is formed°C resulting in the recovery of quenched fluorescence. Findings This sensor can detect PD-L1 with a linear range from 100 pg mL−1 to 100 ng mL−1, and a detection limit of 10 pg•m−1 was achieved. Originality/value This method provides an easy and sensitive method for the detection of PD-L1 and will be beneficial to the early diagnosis and prognosis of tumors.

In this study, we demonstrate a facile approach for the synthesis of strontium tungstate (G-SrWO4) using Pomelo leaf extract via the sonochemical method. The electrocatalytic performance of G-SrWO4 solubilized Nafion (Nf) (G-SrWO4/Nf) modified GC electrode was evaluated for uric acid (UA) detection. The characteristic properties of the prepared G-SrWO4 nanocomposite were analyzed by techniques like XRD, FT-IR, FESEM, EDX, HR-TEM, SEAD, XPS, and TGA analysis. The G-SrWO4/Nf modified GC electrode displayed excellent electrocatalytic performance in UA sensing. The amperometric studies revealed that the G-SrWO4/Nf modified GC electrode performed admirably by attaining a wide linear range response of UA 0.001 μM to 0.5 μM with a limit of detection 33ppm and sensitivity of 486 μAμM−1cm−2. Meanwhile, the G-SrWO4/Nf modified GC electrode exhibited good selectivity, rapid and stable response towards UA. The practical applicability of the sensor was successfully tested by performing UA detection in the urine and serum samples with acceptable recovery results.

An improved ssDNA library immobilized systematic evolution of ligands by enrichment (SELEX) was applied to select aptamers against carbaryl. After nine selection rounds, a highly enriched ssDNA pool was obtained. The Apta3 was demonstrated as the optimal aptamer. In order to facilitate the modification of aptamer, the Apta3 was further truncated with the dissociation constant (Kd) of 0.364 ± 0.055 μmol/L and a fluorescent aptasensor was developed. The linear range for carbaryl was from 100 nmol/L to 1500 nmol/L, with the limit of detection was as low as 15.23 nmol/L. Besides, the biosensor was validated for the carbaryl spiked real samples, and the recoveries were between 97.7% and 107.3%.

The leaf-shaped copper oxide (CuO) was first fabricated by a direct precipitation method. Then, the flake-shaped Co-Ni layered double hydroxides (CoNi-LDHs) were grown on the leaf-shaped CuO by using an electrodeposition method to form a unique nanostructured electrocatalyst. Due to the unique structural and compositional advantages, CoNi-LDHs wrapped around the leaf-shaped CuO exhibited good electrocatalytic characteristics. The optimized CuO/CoNi-LDHs exhibited improved non-enzymatic electrochemical sensing performance for glucose, with a reliable linear range (0.1 μM–0.384 mM) and a low limit of detection (0.065 µM, S/N = 3). The utilization of the CuO/CoNi-LDHs sensor for glucose detection in human serum was also corroborated, implying promising potential for glucose monitoring. Results demonstrated that the developed sensor provides new horizons for facile and sensitive glucose detection.

Integration of novel bio-/nanostructures as effective sensing platforms is still of great significance for robust and rapid analysis. Herein, a novel metal-organic framework-derived NiCo2O4 was synthesized via a feasible templating method. Significantly, redox couples of both Ni3+/Ni2+ and Co3+/Co2+ provided richer oxidation-reduction reactions, thereby leading to an enhanced catalytic activity. Furthermore, NiCo2O4 as an enzyme mimic with peroxidase-like activity and oxidase-like activity could oxidize colorless thylbenzidine (TMB) to blue oxTMB in the absence of H2O2. Thus, a sensitive chromogenic sensing platform for detecting Fe2+, thiourea, cysteine (Cys), and epigallocatechin-3-gallate (EGCG) was proposed. The colorimetric detection methods exhibited great features of low limit of detection (LOD) and broad linear range. Owing to the complexation reaction, the chromogenic sensing system of TMB + NiCo2O4 + Cys achieved effective detection of Cu2+ and Mn2+ with the LODs of 0.0022 and 0.0181 mM, respectively. Developed detection methods with wide linear ranges of 0.008-0.1 mM for Cu2+ and 0.08-1 mM for Mn2+ had excellent practical potential. Similarly, the reaction system of TMB + NiCo2O4 + EGCG could achieve the colorimetric detection of Cu2+ and Fe3+. The great chromogenic sensing performance for detecting Cu2+ and Fe3+ with a broad linear range and a low LOD could be also realized.

A novel electrochemical DNA sensor was designed to detect Helicobacter pylori based on accordion-like Ti3C2Tx. Here the multilayer Ti3C2Tx obtained by DMSO delamination was used to modify the glass carbon electrode, with a large specific surface area and excellent conductivity. Au nanoparticles were supported on the modified electrode and worked as an effective carrier to fix the capture probe (cpDNA) with sulfhydryl group through the firm binding of Au-S bond. Such an accordion-like Ti3C2Tx structure provides an ultrahigh electroactive surface area and ample binding sites for accommodating Au nanoparticles, which is advantageous for the signal amplification during the detection. And further, the sandwich structure formed by hybridizing cpDNA with target DNA sequence (tDNA) and rpDNA (rpDNA is a strand of DNA that can be base-paired with the tested tDNA) increases greatly the current signal and enhances the sensitivity of the electrochemical DNA sensor. Under optimal conditions, the developed electrochemical DNA sensor showed a wide linear range from 10−11 to 10−14 M and a low detection limit of 1.6 × 10−16 M and exhibited good sensitivity, reproducibility, and stability.

Here, a BSA/anti-CEA/Pd@Pt/MoS2-Gr/GCE electrochemical immunosensor was constructed to quantitatively detect CEA. By using graphene as a growth framework, the introduction of molybdenum disulfide (MoS2) effectively solves the problem of easy accumulation of graphene during hydrothermal reduction and self-assembly. Also, it increases the specific surface area and electrochemical performance. The core-shell Pd@Pt composite metal nanoparticles with obvious concavity on the outer surface can provide larger specific surface area, higher conductivity, more catalytic active sites, better biocompatibility, and other advantages. MoS2-Gr also solves the problem of low direct loading of precious metal nanoparticles. Applying the modification materials Pd@Pt/MoS2-Gr to the electrode, the prepared elctrochemical immunosensor has a detection limit of 0.005 pg/mL for CEA and a linear range of 0.00001–100 ng/mL; meanwhile, it shows good selectivity, reproducibility, and stability that achieve effective and accurate detection of CEA.

The detection of glucose plays an important role in monitoring and controlling diabetes as well as its complications caused by high blood glucose levels. There have been a lot of research on glucose sensors and integrated flexible sensing platforms; however, the detection in oxygen-restrictive environments is few reported. Herein, we described the use of a novel system made up of TiO2 and ceria-cerium phosphate (CeO2-CePO4) composite nanostructures synthesized by a simple procedure to address the oxygen dependence problem confronted in the first-generation amperometric glucose biosensors. The enzymatic activity of sensors was tested in both oxygen-rich and restrictive environments. Our results showed that the resulting composites present good electro-catalytic activity towards glucose oxidation. The electrodes decorated by TiO2/CeO2-CePO4 showed a wide linear range from 0.1 to 1.7 mM with a low detection limit of 17.1 μM while the CeO2-CePO4 showed the linear range of 0.1–2.5 mM with limit of detection of 58.0 μM in oxygen-rich environment. Two types of decorated electrodes both responded to glucose well under the oxygen-restrictive environment but former showed better response performance. The as-fabricated electrodes also owned the good anti-interference, stability, and reproducibility. This strategy promises for increasing the sensitivity of glucose biosensors and provides more opportunities for operation in oxygen-restrictive conditions.

New three-enzyme lactose amperometric biosensor based on platinum disc electrode modified by nanosized semipermeable poly (meta-phenylenediamine) film was developed in this work. It was studied the influence of different conditions of meta-phenylenediamine electropolymerization on the parameters (sensitivity and selectivity) of the amperometric transducers. The most optimal parameters were achieved after performing the electropolymerization of 5 mM meta-phenylenediamine applying 10–13 cyclic voltammograms. The bioselective element of lactose biosensor consisted of three enzymes (β-galactosidase, mutarotase, glucose oxidase) that were immobilized on the surface of modified working electrode. The analytical characteristics of the developed biosensor were studied. The linear range of lactose determination extended from 0.01 mM to 1.25 mM. The response time of the biosensor was 30 s. The biosensor showed high signal reproducibility (RSD = 1.16%), high sensitivity (LOD = 0.005 mM) and high selectivity. The proposed biosensor was tested for measurement of lactose concentration in milk samples. The high correlation between results obtained with lactose biosensor and HPLC was shown (R = 0.96%). Thus, the developed biosensor is suited for rapid, inexpensive, sensitive, selective and simple determination of lactose in milk samples.

Anderson-type polyoxometalate containing Fe3+ and Mo6+, (NH4)3[H6Fe(III)Mo6O24] (FeMo6), was found to work as an oxidase-mimicking nanoenzyme for the first time, exhibiting the ability of catalytic oxidation of o-phenylenediamine (OPD), 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTs), and 3,3′,5,5′-tetramethylbenzidine (TMB), which features easy synthesis, low cost, simple operation, and low consumption. Attributed to the nature of FeMo6 and Fenton-like effect, a novel sensor based on two consecutive “turn on” fluorescence was developed for detecting dopamine (DA) by employing the FeMo6-OPD system, and the linear range was from 1 to 100 μM with the detection limit 0.0227 μM (3σ/s). Moreover, to increase oxidase-mimic activity of FeMo6, reduced graphene oxide (rGO) loading FeMo6 composites (FeMo6@rGO (n), n = 5%, 10%, 15%) was fabricated, and results show that oxidase-like activities of FeMo6@rGO (n) are dependent on the mass ratio of FeMo6/rGO, and FeMo6@rGO (10%) exhibits the highest oxidase-mimic activity and the fastest respond time (4 min) among all reported oxidase mimic of DA to date.

In this work, a new generation of hydrophobic deep eutectic solvents (DESs) was prepared using eugenol (as hydrogen bond donor) and benzyltriethylammonium bromide, benzyltributylammonium bromide, benzyltriethylammonium chloride and benzyltributylammonium chloride (as hydrogen bond acceptor) in different molar ratios. These DESs were applied to vortex-assisted dispersive liquid-liquid microextraction of Sudan dyes from food samples, followed by high-performance liquid chromatographic determination. The influencing parameters, including the type of DES, amount of DES, extraction time, solution pH and salt addition, were investigated and optimized. Under the optimized conditions, a linear range of 2–1000 ng mL−1 with determination coefficients of

Hydrogen peroxide (H2O2) has been reported to mediate a variety of physiological and pathological processes in living systems. In this work, a biosensor for determination of H2O2 was prepared by using an HRP/Ti3C2/Nafion film-modified glassy carbon electrode (GCE). Ti3C2 nanosheets with remarkable conductivity and high specific surface area were chosen as carriers for HRP. Moreover, this biosensor modified with HRP has a specific catalytic effect on H2O2. The difference in peak current could reflect the quantitative change of H2O2. The linear range of the biosensor is 5-8000 μM, and the detection limit is 1 μM (S/N = 3). This biosensor was used to detect H2O2 in clinical serum samples of normal controls and patients with acute myocardial infarction (AMI) before and after percutaneous coronary intervention (PCI). The results showed that the difference between normal controls and patients is significant (P < 0.05), as well as the difference for patients before and after PCI (P < 0.01), but no significant difference existed between postoperative patients and normal controls. This biosensor has the advantages of simple preparation, high sensitivity, and quick detection, showing potential application in clinical diagnosis.

We report a novel strategy to offer a high-performance biosensor platform by fabricating an electrically conductive and adhesive electrode composed of polypyrrole (PPy)/polydopamine (PDA) with enzymes (i.e., glucose oxidase (GOx) or lactate oxidase (LOx)) by one-step electrochemical coating. We focused on electrochemical glucose sensing using PDA/PPy and GOx as a model biosensor. PDA/PPy/GOx biosensor was highly sensitive (28 times higher) compared to the PPy/GOx, which appeared to result from enhanced GOx immobilization and efficient signal transduction by PDA/PPy. A selective layer of polyphenol (PPh) on the PDA/PPy/GOx successfully eliminated possible interference. Finally, the GOx biosensor displayed a good sensitivity of 22.15 μ A mM−1 cm-2, a short response time of 5−6 s, a linear range up to 5.0 mM, and a detection limit of 138 μM glucose (R2 = 0.995). Human blood serum tests accurately measured glucose concentration. PPh-layered PDA/PPy/GOx biosensor maintained exceptional stability over 90 days (93.9%). Furthermore, we fabricated a lactate biosensor (PDA/PPy/LOx) by electrochemical PDA/PPy deposition with LOx and demonstrated the significant improvement of a lactate sensing ability compared to PPy/LOx. This facile fabrication strategy involving PDA/PPy and enzymes will serve as an attractive platform for highly sensitive and stable biosensors, such as urate and bilirubin detection.

In this work, Bi2XO6 (X = W, Mo) are synthesized at different temperatures. The results of tests find the optimal temperatures of Bi2WO6 and Bi2MoO6 are 180 and 160°C (BW-180, BM-160). Then, BW-180 and BM-160 are further compounded with different contents of CuS. The results of photoelectrochemical (PEC) tests show that CuS can improve the PEC performance of semiconductor materials, and it has better performance when CuS mass fraction is 5%. These maybe the photoelectron potentials generated by CuS/Bi2XO6 (X = Mo, W) heterojunction reduce the combination of photogenerated electrons and holes. When the PEC sensor based on 5%-CuS/BW-180 detects Cr(VI), it has a linear range of 1–80 μmol/L with detection limit of 0.95 μmol/L, while the PEC sensor based on 5%-CuS/BM-160 detects Cr(VI) has a linear range of 0.5–230 μmol/L and a detection limit of 0.12 μmol/L. Thus, 5%-CuS/Bi2XO6 has potential application in hexavalent chromium detection.

Trace level detection of drugs and hazardous analytes is more critical in electrochemical sensor. In this work, a simple sonochemical-assisted synthesis of Bismuth-EDTA complex/GO flakes was achieved and was developed to analyze mesalazine (MSA) sensing. The 3D hollow bricks were obtained for the Bi-EDTA complex without PVP. Surprisingly, PVP influenced the formation of broken glass-like structured for PVP with Bi-EDTA complex. Bi-EDTA complex modified GCE was developed to determine the role of PVP and its activity in electrochemical sensors. The results obtained by modifying the electrode Bi-EDTA complex with PVP showed good electrochemical performance compared to bare and other controls like GO and Bi-EDTA complex without PVP. The synergetic effect and high electroactive sites of Bi-EDTA complex/GO modified sensor implied low LOD (0.55 nM) and wide linear range from 0.005–585 µM. Furthermore, Bi-EDTA complex/GO showed an excellent selectivity in sensing MSA. Moreover, the Bi-EDTA complex exhibits advantages such as good stability, reproducibility, and repeatability. The modified Bi-EDTA complex/GCE sensor has been practically done to determine trace levels of MSA in human urine samples containing mesalamine tablets with satisfactory results.

Monitoring glucose levels in physiological fluids can help prevent severe complications associated with hypo- and hyper-glycemic events. Current glucose-monitoring systems require a three-electrode setup and a power source to function, which can hamper the system miniaturization to the patient discomfort. Enzymatic fuel cells (EFCs) offer the opportunity to develop self-powered and minimally invasive glucose sensors by eliminating the need for an external power source. Nevertheless, practical applications demand for cost-effective and mass-manufacturable EFCs compatible with integration strategies. In this study, we explore for the first time the use of gold electrodes on a printed circuit board (PCB) for the development of an EFC and demonstrate its application in saliva. To increase the specific surface area, the PCB gold-plated electrodes were modified with porous gold films. At the anode, glucose oxidase is immobilized with an osmium redox polymer that serves as an electron-transfer mediator. At the cathode, bilirubin oxidase is adsorbed onto the porous gold surface with a blocking agent that prevents parasitic reactions while maintaining the enzyme catalytic activity. The resulting EFC showed a linear response to glucose in phosphate buffer within the range 50 μM to 1 mM, with a sensitivity of 14.13 μA cm-2 mM-1. The sensor was further characterized in saliva, showing the linear range of detection of 0.75 to 2 mM, which is within the physiological range, and sensitivity of 21.5 μA cm-2 mM-1. Overall, this work demonstrates that PCBs are suitable platforms for EFCs, paving the way for the development of fully integrated systems in a seamless and miniaturized device.

In this work, the batch injection analysis system with amperometric detection using reduced graphene oxide as a modifier of glassy carbon electrode (GCE) was investigated for the simple, fast, and sensitive monitoring of levofloxacin (LEVO) and ciprofloxacin (CIPRO) in samples of pharmaceutical formulations, synthetic urine, and milk (low- and high-fat content). LEVO and CIPRO were quantified in seven samples using amperometric measurements at +1.10 V vs Ag/AgCl, KCl(sat). The developed methods showed excellent analytical performance with limits of detection of 0.30 and 0.16 μmol L−1, linear range from 3.0 to 50 μmol L−1 and 1.0 to 50 μmol L−1, relative standard deviation below 9.7 and 3.1%, and recovery ranges ranging from 80 to 107% and from 78 to 109% for LEVO and CIPRO, respectively. In addition, the minimum sample preparation (simple dilution) combined with a high analytical frequency (130 to 180 analyses per hour) can be highlighted. Thus, the methods are promising for implementation in routine analysis and quality control to different samples.

Ochratoxin A (OTA), a group of highly toxic fungal secondary metabolites, is one of the most common mycotoxins that contaminate a wide range of agricultural products. Herein, we designed a label-free and selective surface plasmon resonance (SPR) based sensor for detection of OTA contamination in dried fig. The molecularly imprinted polymer film (MIP) was fabricated onto the SPR sensor chip by using light-initiated polymerization of N-methacryloyl-(L)-phenylalanine and 2-Hydroxyethyl methacrylate in the presence of OTA as a template. SPR chips were characterized by using contact angle, atomic force microscopy, and ellipsometry. OTA imprinted sensor was displayed a broad linear range, between 0.1 ng/mL and 20 ng/mL. The limit of detection was calculated as 0.028 ng/mL. The selectivity studies of the OTA imprinted SPR sensor was performed in the presence of aflatoxin M1, aflatoxin B1, and citrinin. The imprinting factor was found to be 2.85. The adsorption behavior of the OTA imprinted sensor was found as suitable for the Langmuir model. Results displayed that the OTA imprinted SPR sensor was successfully applied to determine OTA in dried fig samples.

In the current study, a molecularly imprinted polymer (MIP)-based potentiometric sensor was fabricated for a label-free determination of recombinant human erythropoietin (rhEPO). The MIP sensor was operated under zero current conditions using tetra-butyl ammonium bromide as a marker ion. A highly ordered rhEPO surface imprinted layer was prepared using 3-aminopropyl triethoxysilane and tetraethoxysilane as a monomer and cross-linker, respectively, under mild reaction conditions. A two-fold increase in the signal output was obtained by polymeric surface minimization (0.5 mm) that allowed more pronounced molecular recognition (imprinting factor = 20.1). The proportion of cross-reactivity was examined using different interfering biomolecules. Results confirmed sensor specificity for both structurally related and unrelated proteins. An ~40% decrease in the response was obtained for rhEPO-β compared to rhEPO-α. The imprinted polymeric surface was evaluated using scanning electron microscopy and Fourier transform infrared spectroscopy. Under the optimal measurement conditions, a linear range of 10.00–1000.00 ng mL−1 (10−10 − 10−8 M) was obtained. The sensor was employed for the determination of rhEPO in different biopharmaceutical formulations. Results were validated against standard immunoassay. Spiked human serum samples were analyzed and the assay was validated. The presence of non-specific proteins did not significantly affect (~8%) the results of our assay. A concentration-dependent linear response was produced in an identical range with detection limit as low as 6.50 ng mL−1 (2.14 × 10−10 M). The facile fabricated MIP sensor offers a cost-effective, portable, and easy to use alternative for biosimilarity assessment and clinical application.

A fundamental challenge, particularly, in surface-enhanced Raman scattering (SERS) analysis is the detection of analytes that are distant from the sensing surface. To tackle this challenge, we herein report a long-range SERS (LR-SERS) substrate supporting an extension of electric field afforded by long-range surface plasmon resonance (LRSPR) excited in symmetrical dielectric environments. The LR-SERS substrate has a sandwich configuration with a triangle-shaped gold nanohole array embedded between two dielectrics with similar refractive indices (i.e., MgF2 and water). The finite-difference time-domain simulation was applied to guide the design of the LR-SERS substrate, which was engineered to have a wavelength-matched LRSPR with 785 nm excitation. The simulations predict that the LR-SERS substrate exhibits great SERS enhancement at distances of more than 10 nm beyond its top surface, and the enhancement factor (EF) has been improved by three orders of magnitude on LR-SERS substrates compared to that on conventional substrates. The experimental results show good agreement with the simulations, an EF of 4.1 × 105 remains available at 22 nm above the LR-SERS substrate surface. The LR-SERS substrate was further applied as a sensing platform to detect microRNA (miRNA) let-7a coupled with a hybridization chain reaction (HCR) strategy. The developed sensor displays a wide linear range from 10 aM to 1 nM and an ultralow detection limit of 8.5 aM, making it the most sensitive among the current detection strategies for miRNAs based on the SERS-HCR combination to the best of our knowledge.

Chromium contamination of soil and water is a serious environmental and public health concern as the hexavalent form of chromium [Cr(VI)] is readily soluble in water and is a confirmed carcinogen. There is an imminent need for a robust, low-cost, and simple analytical technique to facilitate in situ monitoring of Cr(VI) in water. Current quantitative methods of Cr(VI) detection are largely laboratory-based, time-consuming, expensive, and require training for implementation. In this contribution, a portable, easy-to-use, and compact measuring tool is presented that provides Cr(VI) concentration within 10 min of water sampling over a linear range of 0–3 mg L−1. This tool utilizes a relatively inexpensive camera-enabled smartphone with a custom-made test chamber attachment to seamlessly perform Cr(VI) measurements on water samples in the field. For analysis, an android-based software application was developed that directs the user to perform a simple series of steps following the diphenylcarbazide-based colorimetric method prescribed by the American Public Health Association. The tool was validated against a standard UV-visible spectrophotometer for a variety of synthetic and naturally contaminated water samples, with correlation factors greater than 0.993 (p

A needle electrochemical sensor was developed based on a nitrogen-doped graphene (NDG) microelectrode for the analysis of salicylic acid (SA) in plants. Self-supporting NDG microelectrodes were synthesized by electron-assisted hot filament chemical vapor deposition using ethanol and nitrogen as the C and N sources, respectively. The formation mechanism of the NDG microelectrodes is discussed by analyzing the ethanol decomposition and nitrogen-doping processes. The microelectrodes were composed of few-layered NDG nanosheets, and the N content of the nanosheets varied in the 0.96–12.5 at% range. Furthermore, a novel needle sensor was constructed based on a cylindrical three-electrode system consisting of a Pt wire, optimized NDG microelectrode, and Ti tube with diameters of approximately 0.3, 0.9, and 1.5 mm, respectively, arranged concentrically. The needle sensors were also assembled into a parallel array consisting of four sensors. At a pH range of 4.5–7.5, the NDG-microelectrode-based needle sensor array exhibited a low detection limit (0.32–0.14 μA μM−1, S/N = 3), wide linear range (1–500 μM), and excellent reproducibility, selectivity, and stability for the detection of SA. The NDG-based needle sensors and sensor arrays are reliable electrochemical platforms for the detection of SA in plant tissue both in vivo and in vitro.

Currently, the quantitative analysis methods for uranium that are widely used in laboratories, such as the volumetric method and inductively coupled plasma mass spectrometry (ICP-MS) cannot achieve low cost, simple operation, and little influence by other elements. The inductively coupled plasma optical emission spectrometer (ICP-OES) has a wide linear range, and high stability, and can be used to identify multiple elements simultaneously. However, when ICP-OES is used for quantitative analysis of uranium, the settings for the RF power, nebulizer flow, and pump rate can affect the analysis results. In this work, these parameters were carefully optimized for identifying uranium. Based on experiments, we selected two spectrum peaks 409.014 nm and 424.167 nm for quantitative analysis with the lowest interference. The optimal parameters obtained are atomizer flow rate of 0.75 L/min, a sample pumping rate of 1.6 mL/min, and a high-frequency power of 1400 W. Then we compared the accuracy of the volumetric method, ICP-MS method and ICP-OES method with the optimized parameter for analysis of experimental samples and references. The results showed that the ICP-OES with the optimized parameters proposed in this paper can be used to perform a convenient, quick, and efficient quantitative analysis of uranium in minerals.

A simple and selective photoelectrochemical (PEC) biosensor was constructed for Hg2+ detection based on zinc phthalocyanine (ZnPc) dye-sensitized CdS using alginate not only as a carrier but also as a binder. First, CdS as a photoactive material was in situ modified on the electrode surface using a rapid and simple electrodeposition to obtain an initial photocurrent signal. Second, ZnPc was loaded in the amphiphilic alginate micelle and then was coated onto the CdS film surface via alginate as the binder. The photocurrent was subsequently enhanced due to the favorable dye sensitization effect of ZnPc to CdS. Finally, the thymine-rich probe DNA was immobilized on the modified ITO surface via coupling reaction between the carbonyl groups of the amphiphilic polymer and the amino groups of the probe DNA. In the presence of Hg2+, the thymine-Hg2+-thymine (T-Hg2+-T) structure was formed due to the specific bond of Hg2+ with thymine, resulting in the decrease of photocurrent due to the increase of steric hindrance on the modified electrode surface. The proposed PEC biosensor for Hg2+ detection possessed a wide linear range from 10 pM to 1.0 μM with a detection limit of 5.7 pM. This biosensor provides a promising platform for detecting other biomolecules of interest.

This work highlights the protocol employed for the simultaneous electroanalysis of tryptamine, serotonin and dopamine using a conducting poly-murexide-based electrode. To date, this is the first-of-its-kind report of simultaneous electrochemical determination of these three targets. Features of the developed electrode were identified by employing FE-SEM analysis. Under optimized conditions, the analytes underwent an irreversible electro-oxidation at the modified electrode surface, with a linear range of 0.5–40 μΜ, 0.4–40.4 μΜ and 0.5–40 μΜ for dopamine, serotonin and tryptamine, respectively. The electrolytic medium employed for the sensing was a phosphate-buffered solution with pH 7. The specificity of the developed electrode was also satisfactory in the presence of other biomolecules including L-phenylalanine, L-serine, glucose and ascorbic acid. Thus, the developed murexide-derived conducting-polymer-based electrode was used for the simultaneous sensing of the neurochemicals dopamine, serotonin and tryptamine. Electroanalysis was also demonstrated for these targets in human serum.

As one of the most important parameters to characterize the organic pollution of water, biochemical oxygen demand (BOD) determined through a rapid, in situ and on line method is very attractive. In this paper, a new BOD biosensor has been developed, which are composed of the ecofriendly precursor of Saccharomyces cerevisiae (S. cerevisiae) embedded in bacterial cellulose (BC) matrix and the Ketjen Black (KB) modified glassy-carbon electrode. Furthermore, a doublemediator system is constructed using potassium ferricyanide and menadione in reaction cell to transfer electron from the microbe to electrode. The responses of glucose glutamic acid (GGA) standard solutions are amperomertrically measured with an applied potential of 0.25 V versus Hg/Hg2Cl2 in a three-electrode system. Under the optimum conditions, the (BC/S. cerevisiae-menadione)/KB modified electrode shows a high operational stability with relative standard deviation (RSD) of 4.16% (fourteen assays), a good repeatability (RSD=3.10%), a fast response time (in 20 minutes) and a wide linear range (from 10–220 mg O2l−1). The BOD values measured by this method have been highly correlated with the standard BOD 5-day method for wastewater samples (R2=0.9859, n=3), indicating that it can meet the requirement of BOD rapid measurement.

A simple analytical method was developed to quantify indoxyl sulfate (InS) in plasma using a salting-out assisted liquid–liquid extraction and spectrofluorimetry. Plasma samples were deproteinized by acetonitrile. Then, sodium chloride solution was added to separate acetonitrile and aqueous phase. The fluorescence intensity of InS which extracted to acetonitrile phase was determined by spectrofluorimetry. The method of presentation has a linear range between 2.5 and 40 µg/ml with a coefficient of determination (R2) of 0.995. Accuracy (% error) and precision (relative standard deviation) were 15% at nominal concentration and less than 15% at all levels, respectively. This established analytical method, which is sensitive and reproducible, could be applied for the quantification of InS in real plasma samples.

In this research, simultaneous quantification of cysteine (Cys) and histidine (His) using a paper-based sensor was investigated for the first time. A microfluidic paper-based sensor is a promising amino acid determination tool due to its low cost, low sample consumption, and fast analysis and is easy to make. We used SBA-15 as porous materials that are crystalline compounds formed with surfactants and TEOS as a silica source. The SBA-15 sample was characterized by X-ray diffraction, Fourier transform infrared, and scanning electron microscope techniques. The microfluidic paper-based sensors were fabricated using a wax pen, and the mesoporous SBA-15 modified filter paper. The fabricated sensors for Cys and His determination are operated based on an indicator-displacement assay. A comparative determination study of Cys and His on the sensors was carried out. The results illustrated that the addition of silica nanoporous material led to an immediate and uniform color change. The sensors were successfully exploited in the simultaneous determination of urinary Cys and His levels, thus providing the potential opportunity for clinical diagnosis. The linear range of 1.0 to 90.0 μM and 1.0 to 100 μM for His and Cys was obtained from the calibration data. The detection limits were also calculated (S/N = 3) for His and Cys of 0.5 μM and 1.5 μM, respectively. The proposed method showed a good agreement with the results achieved by a standard method.

Ciclopirox olamine is one of the basic antifungal agents used in medicine. The multiplicity of pharmaceutical and cosmetic preparations containing ciclopirox olamine causes the need for quick methods to assay it. In this work, the author proposes a method of assaying ciclopirox olamine using BDDE electrode modified with overoxidized polypyrrole (OPPy-BDDE). The work involved the analysis of optimum conditions of BDDE electrode modification. Ciclopirox olamine displayed a well-defined irreversible oxidation peak at the potential of +0.68 V (versus SCE electrode). The analysis of recorded currents depending on the scan rate showed their diffusion character. The pH values and the kinds of electrolyte were optimized using cyclic voltammetry. The optimization of characteristic parameters in the SWV method was conducted in Britton-Robinson buffer with pH 6.98. A linear range of ciclopirox olamine determination was obtained in the concentration range from 6.95 × 10−6 to 6.02 × 10−5 mol/L with the limit of detection of 2.02 × 10−6 mol/L and good repeatability (3.63%, n = 6 measurement, c = 2.34 × 10−5 mol/L). The influence of interferents was also tested. The proposed procedure was successfully used to assay the analyte in pharmaceutical preparations. The obtained results were compared with the values obtained with the comparative method. The error of the developed procedure in relation to the pharmacopoeial method did not exceed 2.5%.

Various concentrations (2.5, 5, 7.5, 10 wt%) of zirconium were doped onto MoS2 using hydrothermal method. X-ray diffraction affirmed existence of hexagonal phase and increased crystallite size upon doping. Synthesized nanosheets appeared agglomerated after doping. Raman analysis provided evidence about defect density, layered structure of S-Mo-S planes as well as electronic band configuration of Zr-doped MoS2. Furthermore, Zr-doped MoS2 nanosheets were applied on a glassy carbon electrode as a layer of sensor film using nafion adhesive to fabricate the working electrode of the proposed phenylhydrazine (PHyd) electrochemical sensor probe. A calibration curve based on concentration of PHyd versus current plot was recorded to be linear over the full concentration range of 0.1 nM to 1.0 mM. The concentration linear range (0.1 nM–0.1 mM) was denoted as the large dynamic range (LDR) for PHyd detection based on the measurement of calibration plot. The slope of LDR with active surface area (0.0316 cm2) of GCE was used to determine analytical parameters of the sensor such as sensitivity (13.4652 µA µM−1 cm−2), linearity, and detection limit (91.54 ± 4.58 pM). Besides these, the PHyd sensor performance was investigated in terms of reproducibility, long-term stability, response time, and validity with regard to its capability for effective analysis of real environmental samples in this field. All parameters exhibited satisfactory and acceptable results.

Pengchong Wang,1,2 Yan Yan,1,2 Ying Zhang,2 Tingting Gao,2 Hongrui Ji,2 Shiyan Guo,2 Ke Wang,2 Jianfeng Xing,2 Yalin Dong1 1Department of Pharmacy, The First Affiliated Hospital of Xi’an Jiaotong University, Xi’an, 710061, People’s Republic of China; 2School of Pharmacy, Xi’an Jiaotong University, Xi’an, 710061, People’s Republic of ChinaCorrespondence: Yalin Dong; Jianfeng Xing Email dongyalin@mail.xjtu.edu.cn; xajdxjf@mail.xjtu.edu.cnBackground: Carbon dots (CDs) emitting near-infrared fluorescence were recently synthesized from green leaves. However, the Hg2+ detection of CDs was limited because of the insufficient water solubility, low fluorescence and poor stability.Methods: Dual fluorescence emission water-soluble CD (Dual-CD) was prepared through a solvothermal method from holly leaves and low toxic PEI1.8k. PEG was further grafted onto the surface to improve the water solubility and stability.Results: The Dual-CD solution can emit 487 nm and 676 nm fluorescence under single excitation and exhibit high quantum yield of 16.8%. The fluorescence at 678 nm decreased remarkably while the emission at 470 nm was slightly affected by the addition of Hg2+. The ratiometric Hg2+ detection had a wide linear range of 0– 100 μM and low detection limit of 14.0 nM. In A549 cells, there was a good linear relation between F487/F676 and the concentration of Hg2+ in the range of 0– 60 μM; the detection limit was 477 nM. Furthermore, Dual-CD showed visual fluorescence change under Hg2+.Conclusion: Dual-CD has ratiometric responsiveness to Hg2+ and can be applied for quantitative Hg2+ detection in living cells.Keywords: chlorophyll, polyethyleneimine, polyethylene glycol, ratiometric Hg2+ detection, A549 cells

Herein, an induced self-enhanced electrochemiluminescence (ECL) sensor with superior ECL performances was simply fabricated by just dropping the ECL reagent (tris(4,4′-dicarboxylicacid-2,2′-bipyridyl) ruthenium (II) dichloride, Ru(dcbpy)3Cl2) and coreactant (nitrogen-doped carbon quantum dots, NCQDs) pair onto the surface of glassy carbon electrode. In this strategy, based on the carboxyl (–COOH) groups in Ru(dcbpy)32+ and oxygen, nitrogen-containing groups on NCQDs surface, an intermolecular hydrogen bonds-induced self-enhanced ECL composite was generated in the solid contact layer for the first time. Since Ru(dcbpy)32+ and NCQDs were co-existing in the same composite, the electron-transfer distance between them was shortened and the energy loss was decreased, thereby higher ECL efficiency was acquired. This working process greatly avoided the introduction of signal amplifier and simplified the experimental operation. On this basis, 17β-estradiol (E2) was selected as a target model to fabricate a self-enhanced ECL aptamer sensor for the investigation of its analytical performances. Resultantly, excellent detection properties of E2, including wider linear range of 1.0 × 10-14 − 1.0 × 10-6 mol L-1 and lower detection limit of 1.0 × 10-15 mol L-1 with superior selectivity, were successfully achieved. Finally, E2 spiked into milk powder was quantified to assess the practicability of this sensor. Prospectively, this strategy could be extensively applied for other analytes determination by adjusting the corresponding target aptamers.

Simple, rapid, and sensitive ultraviolet-visible spectroscopy method was used to determine ultra-trace amounts of metformin (MET) in several samples such as drinking water, tablet, serum (blood), and urine without preconcentration step. Gold nanoparticles (AuNPs) were synthesized, and determination of MET was carried out based on the surface plasmon resonance property of AuNPs and the interaction between MET and AuNPs. Transmission electron microscopy (TEM) was utilized to characterize the structure of AuNPs before and after addition MET. Also, dynamic light scattering was used to investigate the size of nanoparticles distribution. The results showed that AuNPs were aggregated in the presence of the MET. Some parameters, including pH, AuNPs concentration, contact time, buffers, and ionic strength, were evaluated to select optimum conditions. Linear range obtained was 15–300 μg/L in the optimum conditions. Also, the correlation coefficient (R2), the limit of detection, and limit of quantification were equal to 0.9918, 0.99, and 1.12 μg/L, respectively. In addition, the effect of interfering species was investigated. Finally, the results of the analysis of different real samples indicated that the proposed method was suitable and accurate for determination of MET.

Dan Yu,1,2,* Qilong Yin,1,3,* Jiwei Wang,1,* Jian Yang,1 Zimeng Chen,1 Zihan Gao,1 Qingli Huang,1,4 Shibao Li1,3 1Medical Technology School of Xuzhou Medical University, Xuzhou, Jiangsu, 221000, People’s Republic of China; 2Jiangsu Key Laboratory of Medical Science and Laboratory Medicine, School of Medicine, Jiangsu University, Zhenjiang, Jiangsu, 212013, People’s Republic of China; 3Department of Laboratory Medicine, Affiliated Hospital of Xuzhou Medical University, Xuzhou, Jiangsu, 221000, People’s Republic of China; 4Public Experimental Research of Xuzhou Medical University, Xuzhou, Jiangsu, 221000, People’s Republic of China*These authors contributed equally to this workCorrespondence: Qingli HuangPublic Experimental Research of Xuzhou Medical University, Xuzhou, Jiangsu, 221000, People’s Republic of ChinaTel +86 15150043097Fax +86 516 83262091Email qlhuang@xzhmu.edu.cnShibao LiDepartment of Laboratory Medicine, Affiliated Hospital of Xuzhou Medical University, Xuzhou, Jiangsu, 221000, People’s Republic of ChinaTel +86 15895212960Fax +86 516 83353651Email sdjnshlb@xzhmu.edu.cnPurpose: Developing a sensitive SERS-based method to quantitatively detect serum biomarkers (Aβ 1-42 and P-Tau-181) for the early diagnosis of Alzheimer’s disease (AD).Methods: In this study, a novel SERS-based sandwich immunoassay, which consists of tannin-capped silver nanoparticles and magnetic graphene oxide (Fe3O4@GOs), was developed. We firstly applied this method for the detection of protein standards in buffer solution, obtaining the regression equation. Then, its potential value on real serum samples of AD was further explored.Results: The detection linear range of Aβ 1-42 and P-Tau-181 protein standards were observed to range from 100 pg mL− 1 to 10 fg mL− 1, 100 pg mL− 1 to 1 fg mL− 1 respectively. We finally explored clinical application of the proposed method in 63 serum samples. As a result, P-tau-181 differentiated AD from non-AD dementia patients (AUC = 0.770), with a more favored ROC than Aβ 1-42 (AUC =  0.383).Conclusion: The developed SERS-based immunoassay is successfully applied to the determination of Aβ 1-42 and P-Tau-181 in human serum specimens, which provides a promising tool for the early diagnosis of AD.Keywords: surface-enhanced Raman scattering, silver probe, Alzheimer’s disease, biomarker, diagnosis

A simple and sensitive bifunctional electrochemical aptasensor for detection of adenosine and thrombin has been developed using gold nanoparticles–electrochemically reduced graphene oxide (AuNPs-ERGO) composite film-modified electrode. Firstly, the reduced graphene oxide film and AuNPs were sequentially immobilized on glassy carbon electrode (GCE) surface. Secondly, thrombin aptamer was immobilized on the modified electrode. Finally, adenosine aptamer was hybridized with it to serve as a recognition element and methylene blue (MB) as electrochemical signal indicator. In the presence of adenosine or thrombin, the sensor recognized it and a conformational change was induced in aptamer, resulting in decrease of the peak current of MB. The linear relation between concentration of adenosine or thrombin and peak current of MB allowed quantification of them. Thanks to the special electronic characteristic of AuNPs-ERGO composite film, sensitivity of sensor was greatly improved. Under optimal conditions, the proposed aptasensor presented an excellent performance in a linear range of 25 nM to 750 nM for adenosine and 0.5 nM to 10 nM for thrombin. Detection limits were estimated to be 8.3 nM for adenosine and 0.17 nM for thrombin, respectively. Moreover, dual-analyte detection of adenosine and thrombin was achieved without potentially increasing the complexity and cost of the assay.

In this work, a new label free electrochemical immunosensor was designed to detect Newcastle disease virus (NDV). The immunosensor was constructed by modification of a glassy carbon electrode surface with multi wall carbon nanotubes, gold nanoparticles (AuNPs), 11-Mercapto Undecanoic acid (MUA) and 3-Mercapto Propionic acid. Then, it was stabilized by self-assembly and protein G (PrG) immobilized using 1-ethyl3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-Hydroxy Succinimide to oriented fixation of the antibody. The quantitative measurement of NDV was evaluated by square wave voltammetry method. The determination step was based on the formation of immunocomplex between the antigen and oriented antibody, which caused current decreased in [Fe(CN)6]/K4[Fe(CN)6] redox reaction. The response value was directly proportional to the concentrations of NDV. Scanning electron microscope, XRD, UV and FTIR methods were used to characterize the electrode surface. Also, the electrochemical electrode surface behavior at each step of modification was evaluated by cyclic voltammetry and electrochemical impedance spectroscopy methods. The parameters affecting the performance of the immunosensor such as amount of MWCNT, electrodeposition time of AuNPs, concentration and loading time of PrG, the antibody concentration and antigen incubation time were optimized. The biosensor showed detection limit of 1.6 EID50ml−1 and linear range of 10 to 105 EID50ml−1. The proposed immunosensor showed adequate reproducibility (RSD 6%) and stability (up to one month), which showed that it could be used as a sensitive device for agriculture applications.

A colorimetric paper-based enzyme-coupled antimony tin oxide nanoparticle (ATONP) nanobiosensor for selective detection of Cd2+ ions in clams and mussels is presented. Alkaline phosphatase (ALP) was immobilized on ATONPs via 16-phosphonohexadecanoic acid (16-PHA) to develop ATONP-ALP nanobiosensor. The biosensor was characterized using XPS, Raman spectroscopy, SEM, and EDX. ATONP-ALP nanobiosensor exhibited high selectivity towards detection of Cd2+ ion with a LOD 0.006 μg L−1 and linear range of detection 0.005–1 μg L−1. The developed biosensor was further integrated into a low-cost paper-based format. A visual color change was obtained for Cd2+ ion in the range 0.1–10 μg L−1. The developed biosensor was successfully demonstrated for the analysis of Cd2+ ions in clams with recoveries 101–104%. The ATONP-ALP nanobiosensor was validated using mussel tissue (BCR-668) and the conventional ICP-OES and ICP-MS techniques.