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A smartphone-assisted electrochemiluminescence (ECL) strategy based on Ru(bpy)2(L)4+ as chromophores confined with metal − organic frameworks (Ru(bpy)2(L)4+@MOF-5) for the signal-amplified detection of miRNA-21 was developed. We synthesized a derivative of tris(2,2'-bipyridyl)ruthenium(II) complex (Ru(bpy)2(L)4+) with high charges, which can be loaded into the MOF-5 by strong electrostatic interaction to prevent from leakage. In addition, nucleic acid cycle amplification was used to quench the signal of Ru(bpy)2(L)4+@MOF-5 by ferrocene. This method was applied to detect the concentration of miRNA-21 ranging from 1.0 × 10−14-1.0 × 10−9 M with a low LOD of 7.2 fM. This work demonstrated the construction of a signal quenching strategy ECL biosensor for miRNA using Ru(bpy)2(L)4+@MOF-5 systems and its application in smartphone-assisted ECL detection. [ABSTRACT FROM AUTHOR]

Salicylic acid (SA) is widely used in food storage, preservatives, additives, healthcare, and the pharmaceutical industry. However, various poisoning symptoms are frequently reported upon ingestion of a large amount of SA. Therefore, discovering new tools for sensing SA with fast, simple, and portable performance is imperative. Herein, five rhodamine-based fluorescent sensors were constructed, and investigated their SA detection profiles. Probe 1 was excellent selective with a rapid response, highly sensitive (LOD = 2.5 μM), good interference resistance, and unaided eye recognition. The spray experiment and paper-based test strips indicating that probe 1 enables to the on-site and quantitatively detect SA on actual food surfaces by using a smartphone identifying the RGB values. The sensing performance was validated in soil samples, water, and various agricultural food samples. Overall, the constructed SA sensor can function as a promising, convenient, and affordable tool for point-of-care detection of SA in diversiform environmental samples.

Nanozyme-assisted alkaline phosphatase (ALP) assay is a commonly used detection technique. However, this type of sensor faces several challenges, including a "signal-off" detection model, dependence on oxidase mimics, and the need for spectrometers. In this study, by optimizing stabilizers, we obtain chitosan-coated platinum–ruthenium nanoparticles (CS-Pt/Ru NPs) for the first time, which have superior peroxidase (POD) mimic activity. CS-Pt/Ru nanozymes can catalyze phenol oxidation in the presence of 4-aminoantipyrine and hydrogen peroxide to produce an enhanced red color, while phenol can be obtained by ALP-mediated hydrolysis. Thus, ALP activity is quantified by absorbance in a "signal-on" model. This approach demonstrates a remarkably low limit of detection (0.01 U·L–1) and a wide linear range (0.03–10 U·L–1). In addition, we combine CS-Pt/Ru nanozymes with a hydrogel to form a CS-Pt/Ru@Gel sensor, which enables a visual ALP assay using a smartphone. It can detect ALP activity as low as 0.1 U·L–1, with a linear range of 0.15–10 U·L–1. Finally, both Pt/Ru NPs and Pt/Ru@Gel are successfully employed to detect ALP activity in clinical blood samples. Our study develops an excellent hydrogel-supported POD nanozyme system and paves the way for an ALP assay using a "signal-on" and visual model. [ABSTRACT FROM AUTHOR]

A novel portable smartphone-assisted colorimetric method was reported for the determination of Hg2+ with good analytical performance. A Zr(IV)-based metal–organic framework functionalized with amino groups (NH2-UiO-66) has been adopted as a supporting platform to anchor gold nanoparticles (AuNPs), avoiding the migration and aggregation of AuNPs. With the addition of Hg2+, the formation of gold amalgam proved possible to enhance peroxidase-like activity of the composite (AuNPs/NH2-UiO-66), accelerating the oxidization of zymolyte 3,3′,5,5′-tetramethylbenzidine (TMB). In the meantime, the color of the reaction solution turned a vivid blue, and the red, green, and blue (RGB) values of the solution color changed accordingly. On account of this strategy, the quantitative detection of Hg2+ could be achieved. After the optimization of the experiment conditions, the average color intensity (Ic) resulting from RGB values was linear related to the concentration of Hg2+ from 10 to 100 nM, accompanied with a detection limit (LOD) down to 5.4 nM calculated by 3σ/S. The successful application of the designed method has been promoted to detect Hg2+ in some water samples, displaying a great potential in practical application. Furthermore, the use of a smartphone made our proposed method simple and accurate, and thus puts forward a possible way for in situ and real-time monitoring. A portable smartphone-assisted RGB colorimetric method for Hg2+ detection based on Hg2+-enhanced peroxidase-like activity of AuNPs modified on NH2-UiO-66. [ABSTRACT FROM AUTHOR]

A multi-signal aptasensor for thrombin determination is proposed based on catalytically active gold nanoparticles (AuNPs) and fluorescent silicon quantum dots (SiQDs). Yellow 4-Nitrophenol (4-NP) could be converted to colorless 4-Aminophenol (4-AP) by catalytically active aptamer-modified AuNPs (S1-AuNPs). The SiQDs emitted strong blue fluorescence at 455 nm at the excitation wavelength of 367 nm. When thrombin was absent, S1-AuNPs could catalytically reduce yellow 4-NP to colorless 4-AP. When thrombin was added, the aptamer could be transformed into a G-quadruplex structure, which masked the surface-active catalytic sites of AuNPs and restrained the reduction of 4-NP. Thus, the fluorescence of SiQDs was greatly quenched by 4-NP through the inner filter effect (IFE), and the solution color remained yellow. As the concentration of thrombin increased, the catalytic activity of S1-AuNPs decreased. The concentration of 4-NP that was converted to 4-AP declined and the unconverted 4-NP increased. In this process, the absorption peak of 4-NP at 400 nm increased while the fluorescence emission of SiQDs at 455 nm decreased. The linear ranges of the fluorometric and colorimetric aptasensor were 0.5–30 nM and 0.3–30 nM, respectively. The limits of detection (LOD) for the two modes were 0.15 nM and 0.13 nM. Furthermore, a portable sensing platform was constructed by combining the smartphone-based device with the software ImageJ for the determination of thrombin. With the advantages of cost-effectiveness, simplicity of operation and broad applicability, this aptasensor provided a new perspective for on-site determination of thrombin in the clinical field. [ABSTRACT FROM AUTHOR]

The long-term and excessive use of glyphosate (GLY) in diverse matrices has caused serious hazard to the human and environment. However, the ultrasensitive detection of GLY still remains challenging. In this study, the smartphone-assisted dual-signal mode ratiometric fluorescent and paper sensors based on the red-emissive gold nanoclusters (R-AuNCs) and blue-emissive carbon dots (B-CDs) were ingeniously designed accurate and sensitive detection of GLY. Upon the presence of GLY, it would quench the fluorescence of B-CDs through dynamic quenching effect, and strengthen the fluorescence response of R-AuNCs due to aggregation-induced enhancement effect. Through calculating the GLY-induced fluorescence intensity ratio of B-CDs to R-AuNCs by using a fluorescence spectrophotometer, low to 0.218 μg/mL of GLY could be detected in lab in a wide concentration range of 0.3–12 μg/mL with high recovery of 94.7–103.1% in the spiked malt samples. The smartphone-assisted ratiometric fluorescent sensor achieved in the 96-well plate could monitor 0–11 μg/mL of GLY with satisfactory recovery of 94.1–107.0% in real edible malt matrices for high-throughput analysis. In addition, a portable smartphone-assisted ratiometric paper sensor established through directly depositing the combined B-CDs/R-AuNCs probes on the test strip could realize on-site measurement of 2–8 μg/mL of GLY with good linear relationship. This study provides new insights into developing the dual-signal ratiometric sensing platforms for the in-lab sensitive detection, high-throughput analysis, and on-site portable measurement of more trace contaminants in foods, clinical and environmental samples. [Display omitted] • A two swords combination sensing strategy was proposed for the first time for glyphosate detection. • Smartphone-assisted dual-signal mode ratiometric fluorescent and paper sensors were constructed. • Blue-CDs and red-AuNCs were mixed to fabricate the dual-signal ratiometric fluorescent probes. • Smartphone-assisted ratiometric fluorescent sensor in the 96-well plate could achieve high-throughput analysis. • Smartphone-assisted ratiometric paper sensor could realize on-site measurement 2–8 μg/mL of glyphosate. [ABSTRACT FROM AUTHOR]

Accurate and low-cost onsite assay of residual antibiotics in food and agriculture-related matrixes (e.g., milk) is of significant importance for evaluating and controlling food pollution risk. Herein, we employed hybrid Cu-doped-g-C3N4 nanozyme to engineer smartphone-assisted onsite visual sensor for reliable and precise reporting the levels of tetracycline (TC) residues in milk through π-π stacking-triggered blocking effect. Benefiting from the synergetic effects of Cu2+ and g-C3N4 nanosheet, Cu-doped-g-C3N4 nanocomposite exhibited an improved peroxidase-like activity, which could effectively catalyze H2O2 to oxidate colorless TMB into steel-blue product oxTMB. Interestingly, owing to the blocking effect caused by the π-π stacking interaction between TC tetraphenyl skeleton and Cu-doped-g-C3N4 nanozyme, the affinity of Cu-doped-g-C3N4 nanocomposite toward the catalytic substrates was remarkably blocked, resulting in a TC concentration-dependent fading of solution color. Using smartphone-assisted detection a simple, low-cost, reliable, and sensitive portable colorimetric sensor-based nanozyme for onsite visual monitoring the residual TC in milk was successfully developed with a detection limit of 86.27 nM. Of particular mention is that this detection limit is comparable to most other reported colorimetric methods and below most official allowable residue thresholds in milk matrixes. This work gave a novel insight to integrate two-dimensional (2D) artificial nanozymes-based π-π stacking-triggered blocking effect with smartphone-assisted detection for developing efficient and low-cost colorimetric point-of-care testing of the risk factors in food and agriculture-related matrixes. [ABSTRACT FROM AUTHOR]

Heavy metal pollutants, such as Pb2+ ions, pose a substantial hazard to human health and ecosystems, and it was of great significance to develop cost-effective and portable techniques for online and visual detection of Pb2+. Herein, we fabricated a novel chromogenic and fluorogenic dual-channel sensor NQA through a Schiff base reaction involving a dicyanoisophorone derivative and isoniazid, enabling effective detection of Pb2+ ions. Upon complexation with Pb2+ ions at a 1:1 M ratio, the fluorescence intensity of NQA exhibited a remarkable enhancement. The naked-eye colorimetric detection utilizing NQA demonstrated a distinct color change to specific Pb2+ ions concentration from yellow to light pink. Based on this principle, a smartphone-assisted sensing platform was developed for visual and high-quality identification of Pb2+ in real samples. The UV binding constant for Pb2+ ions was determined to be 1.84 × 105 M−1, with a detection limit of 0.38 μM. Furthermore, the versatility of NQA extended to applications in naked-eye test paper experiments, the detection of Pb2+ ions in real water samples and living cells, showcasing its potential for environmental and biological monitoring. A novel chromogenic and fluorogenic dual-channel sensor NQA has been rationally desired for specific and visual detection of Pb2+. The smartphone-assisted NQA could serve as a high-performance detector for quick, on-site and portable detection of Pb2+ in real environmental and biological samples. [Display omitted] • A novel colorimetric/fluorometric dual-channel probe NQA has been developed for visual detection of Pb2+. • Limit of detection (LOD) of NQA for Pb2+ was as low as 51 nM. • NQA could serve as a high-performance detector for onsite detection of Pb2+ in the environment. • The smartphone-assisted NQA provided a portable and low-cost method for Pb2+ ions detection. • NQA was successfully applied to bioimaging of PK-15 cells. [ABSTRACT FROM AUTHOR]

Metal-Organic Framework (MOF) based nanozymes with clear structure are beneficial for exploration of structural-performance and exhibit broad prospects in improving activity. In this study, the prepared bimetallic Fe 3 Ni-MOF nanozyme was superior to single metal MOF in the peroxidase-like activity. Subsequently, a derivative nanozyme (Fe 3 Ni-MOF-Ar) was prepared by pyrolysis using Fe 3 Ni-MOF as the precursor in argon atomoshere with controlled temperature. The investigated of Fe 3 Ni-MOF-Ar revealed that the irregular macroporous state and the presence of heterovalent FeIII/FeII sites of Fe 3 Ni-MOF-Ar enable the retention, exposure, and electronic structure regulation of active sites, promoting the dual mechanism (the generation of •OH and electron transfer mechanism) and significantly increasing the peroxidase-like activity. Fe 3 Ni-MOF-Ar exhibited a strong affinity for substrate H 2 O 2 , which is higher than horseradish peroxidase. Ascorbic acid and cysteine are typical substances of antioxidants. Fe 3 Ni-MOF-Ar was used for sensitive colorimetric detection of ascorbic acid and cysteine, and the detection limit was as low as 150 and 60 nM. In addition, the smartphone devices was used to detection of antioxidant equivalent ascorbic acid, with a detection range of 0.5–120 μM. Fe 3 Ni-MOF-Ar nanozyme is feasible for sensitive detection of saliva total antioxidant capacity. [Display omitted] • The derivative Fe 3 Ni-MOF-Ar has higher POD-like activity compared to Fe 3 Ni-MOF. • Fe 3 Ni-MOF-Ar has the irregular macroporous state and heterovalent FeIII/FeII sites. • Fe 3 Ni-MOF-Ar achieves the retention, exposure, and electronic structure regulation of active sites. • This study established a method of on-the-spot smartphone-assisted detection of saliva TAC. [ABSTRACT FROM AUTHOR]

A smartphone-assisted fluorescence color sensing system for rapid, convenient, and on-site detection of copper ions was developed. The ratiometric fluorescence sensor was fabricated by using silica-coated blue-light-emitting carbon dots and surface-grafted red-light-emitting cadmium-telluride quantum dots. After exposure to Cu2+ in 20 s, the red fluorescence was quenched obviously, while the blue fluorescence remained unchanged, and the sensor color changes continuously from red to blue under the ultraviolet lamp. The concentration (50–1200 nM) of copper ions could be measured by the fluorescence spectrum (excitation at 360 nm, dual-emission at 441 and 640 nm) with a detection limit of 7.7 nM. The fluorescence colors were converted to digital RGB values to calculate the concentration of copper ions by a smartphone with a detection limit of 9.6 nM. The method was applied to detecting copper ions spiked in real samples with recovery from 97.9 to 108.0% and RSD from 3.8 to 8.9%. Thus, this convenient and practical fluorescence color sensing system presents a new strategy for rapid, sensitive, and on-site determination of copper ions in environmental or biological samples. [ABSTRACT FROM AUTHOR]

The convenient detection of ethyl carbamate (EC) still faces some challenges due to certain interfering substances in liquor. Herein, the peroxidase-mimic activity of V 6 O 13 nanobelts was inhibited by EC1–34 aptamer, and a novel rapid method for EC detection was established using EC1–34 aptamer as a specific recognition molecule. The composite probe consisting of V 6 O 13 nanobelts and EC1–34 aptamer was immobilized on the paper to construct a colorimetric nanozyme sheet. The presence of EC1–34 aptamer would effectively inhibit the peroxidase-mimic activity of V 6 O 13 nanobelts, making the colorimetric nanozyme sheet exhibit light blue or even colorless. Once the EC was added to nanozyme sheet, the EC1–34 preferentially bound to EC molecules, restoring the peroxidase-like activity of V 6 O 13 nanobelts. The degree of the blue-gray change of the constructed colorimetric nanozyme sheets was positively correlated with the EC concentration. Moreover, a smartphone was used to assist in obtaining the image data and then drawing a standard curve. The visual limit of detection of the rapid colorimetric nanozyme sheets was 20 μg·L−1, and the limit of detection (LOD) was calculated as 14.17 μg·L−1. The novel rapid detection nanozyme sheets constructed in this study can be generally applied in detecting EC in liquor. [Display omitted] • The peroxidase-like activity inhibited by EC1–34 aptamer was revealed. • The V 6 O 13 -aptamer recognition probe was first immobilized on nanozyme sheets. • The colorimetric nanozyme sheets was first applied for ethyl carbamate detection. • Smartphone-assisted analysis of ethyl carbamate by nanozyme sheet was obtained. • The colorimetric nanozyme sheet was well applied in liquor samples. [ABSTRACT FROM AUTHOR]

• Smartphone-assisted self-powered sensor is developed for Ultra-sensitive detection of microRNA. • Binary 3D DNA Walkers combined with CRISPR/Cas12a system greatly enhances the sensitivity of biosensor. • Integrated capacitors amplify detection signal, enhancing sensitivity by 20.7-fold. • The dual-mode detection strategy significantly enhances the accuracy of the method. Malignant tumors are significant diseases that pose a threat to human life and health. The advancement of highly sensitive and specific methods is of excellent significance. This study proposes a novel detection platform that employs a smartphone-assisted self-powered sensing system with binary 3D DNA Walkers mediated CRISPR/Cas12a system and ultra-thin 2D graphdiyne for ultrasensitive dual-mode detection of breast cancer biomarker microRNA-let-7a. The binary 3D DNA Walkers possess high efficiency in movement and multifunctional characteristics. When combined with the CRISPR/Cas12a system, they can retain the advantages of 3D DNA Walker while releasing a large of trigger strands complementary to CRISPR RNA, thereby greatly enhancing the sensitivity of the sensor. In addition, capacitors are also integrated into the sensing system to further amplify the detection signal, resulting in a 20.7-fold increase in sensitivity of the method. Additionally, the adoption of an electrochemical/colorimetric dual-mode detection strategy significantly enhances the accuracy of the new approach. The newly developed detection method exhibits a linear range of 0.0001–10000 pM with a detection limit of 8.11 aM (S/N = 3). This work offers a reliable portable sensor for sensitive and accurate detection of tumor biomarkers, enabling remote disease sensing and on-site monitoring applications. [ABSTRACT FROM AUTHOR]

We have proposed a signal dual-amplification electrochemiluminescence (ECL) strategy based on tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy) 3 2+) as chromophores confined with three-dimensional (3D) zinc oxalate metal−organic frameworks (Ru(bpy) 3 2+@MOFs) for the detection of miRNA-21. The three-dimensional chromophore connectivity in zinc oxalate MOFs provided a network among Ru(bpy) 3 2+ units, shielding the chromophores from solvent molecules and resulting in high Ru(II) complex emission efficiency. Additionally, we discovered that magnetic beads (MBs) used as carrier for enriched signals contribute to enhanced ECL intensity of the chromophore. To evaluate its clinical application, we applied this method to determine the concentration of miRNA-21 solutions ranging from 1.56 to 100 nM, obtaining a calibration curve of ECL intensity versus logarithm of concentration (logC) of miRNA-21 with a high correlation coefficient. This work demonstrates the construction of a signal amplification strategy ECL biosensor for miRNA using Ru(bpy) 3 2+@MOF systems and its application in ECL detection for analyte methodology. [Display omitted] • A smartphone-based ECL device for point-of-need quantitation of the breast cancer tumor marker miRNA-21 was designed. • A signal dual-amplification ECL strategy based on Ru(bpy) 3 2+@MOFs for the sensitive detection of miRNA-21 was developed. • Magnetic beads used as carrier for enriched signals contribute to enhanced ECL intensity of the chromophore. • The sensor was used to detection of miRNA in normal human serum samples. [ABSTRACT FROM AUTHOR]

In analytical science, it is always of great scientific and practical significances to explore convenient, rapid, and reliable methods/devices to trace the H 2 O 2 level in various matrices. Herein, we fabricated a ready-to-use paper-based chemosensor by using mesoporous carbon-dispersed Pd nanoparticles (Pd NPs/meso-C) as a promising peroxidase mimic for the visual determination of H 2 O 2 . Thanks to the large exposed surface of the meso-C support and the highly dispersed active Pd NPs, the synthesized Pd NPs/meso-C exhibited favorable catalytic performance to trigger the chromogenic reaction of colorless TMB to blue TMBox mediated by H 2 O 2 , providing a K cat of 326.67 s −1 for H 2 O 2 and 0.55 s −1 for TMB, larger than the bare Pd NPs and even comparable to the activity of natural horse radish peroxidase. As demonstrated, this principle could be employed to colorimetrically detect H 2 O 2 in the linear scope of 5–300 μM. By simply immobilizing the Pd NPs/meso-C mimic and the TMB substrate onto a common filter paper, ready-to-use paper-based sensors were further prepared. By combining these test strips with a smartphone and an easy-to-access color-scanning APP together, the integrated platform could be used for the quantitative analysis of H 2 O 2 with advantages of simple operation, fast response, low cost, and good selectivity and repeatability. Furthermore, reliable sensing of the target in milk matrices suggested great promise of the integrated platform in practical applications. [ABSTRACT FROM AUTHOR]

• MnO 2 as a stabilizer for high internal phase emulsion-templated polymerization. • An enzyme-nanozyme integrated hierarchically porous hydrogel (AChE-MnO 2 @HPH). • Excellent catalytic activity and stability of AChE-MnO 2 @HPH for pesticide sensing. • A home-made smartphone-based device to read color information for detection. • High-performance, convenient and in-field analysis of pesticides. Due to their great threat to human health and the environment, it is always of significance to develop efficient tools to monitor pesticide residues. Although the enzyme inhibition-based strategy is considered as a potential method and has been intensively explored for pesticide analysis, both vulnerable enzymatic activity and tedious operation greatly hinder its practical applications. Developing robust, easy-to-use and efficient devices for pesticide sensing is still challenging. Herein, we recommend an enzyme-nanozyme integrated hierarchically porous hydrogel (AChE-MnO 2 @HPH) for the convenient detection of pesticides. MnO 2 microspheres were first employed as an emulsion stabilizer to fabricate MnO 2 @HPH by thermal polymerization, and AChE was then immobilized into the MnO 2 @HPH via a fast self-absorption process. With the unique porous structure and hydrophilic microenvironment, the constructed AChE-MnO 2 @HPH exhibited excellent enzymatic activity and stability as well as rapid response toward pesticides through inhibiting the activity of AChE. By applying a smartphone to read the color information originating from the chromogenic reaction of 3,3′,5,5′-tetramethylbenzidine (TMB) catalyzed by oxidase-mimicking MnO 2 , highly sensitive and convenient determination of fenthion, an organophosphorus pesticide model, was achieved with a detection limit down to 0.63 ng mL−1. Excellent performance robustness over 30 storage days and reliable detection of the target in real food samples were also demonstrated. With the advantages of easy operability, free of equipment, and good detection performance and long-term stability, the integrated AChE-MnO 2 @HPH will find promising use for pesticide residue in-field analysis. [ABSTRACT FROM AUTHOR]