Colorimetric and Electrochemical Dual-Mode Detection of Thioredoxin 1 Based on the Efficient Peroxidase-Mimicking and Electrocatalytic Property of Prussian Blue Nanoparticles.

As a potent detection method for cancer biomarkers in physiological fluid, a colorimetric and electrochemical dual-mode sensing platform for breast cancer biomarker thioredoxin 1 (TRX1) was developed based on the excellent peroxidase-mimicking and electrocatalytic property of Prussian blue nanoparticles (PBNPs). PBNPs were hydrothermally synthesized using K3[Fe(CN)6] as a precursor and polyvinylpyrrolidone (PVP) as a capping agent. The synthesized spherical PBNPs showed a significant peroxidase-like activity, having approximately 20 and 60% lower Km values for 3,3',5,5'-tetramethylbenzidine (TMB) and H2O2, respectively, compared to those of horseradish peroxidase (HRP). The PBNPs also enhanced the electron transfer on the electrode surface. Based on the beneficial features, PBNPs were used to detect target TRX1 via sandwich-type immunoassay procedures. Using the strategies, TRX1 was selectively and sensitively detected, yielding limit of detection (LOD) values as low as 9.0 and 6.5 ng mL-1 via colorimetric and electrochemical approaches, respectively, with a linear range of 10-50 ng mL-1 in both strategies. The PBNP-based TRX1 immunoassays also exhibited a high degree of precision when applied to real human serum samples, demonstrating significant potentials to replace conventional HRP-based immunoassay systems into rapid, robust, reliable, and convenient dual-mode assay systems which can be widely utilized for the identification of important target molecules including cancer biomarkers.

Anti-aggregation colorimetric sensing of cysteine using silver nanoparticles in the presence of Pb2.

Using silver nitrate as the silver source and sodium borohydride as the reducing agent, we synthesized negatively charged silver nanoparticles (AgNPs). Subsequently, the AgNPs solution was mixed with positively charged lead ions, resulting in AgNPs aggregation via electrostatic interactions. This led to a color change in the solution from yellow to purple and eventually to blue-green. Our study focused on a colorimetric method that exhibited high selectivity and sensitivity in detecting cysteine using AgNPs-Pb2+ as a sensing probe. Upon the introduction of cysteine to the AgNPs-Pb2+ system, the absorbance of AgNPs increased at 396 nm and decreased at 520 nm. The formation of a complex between cysteine and lead ions prevented the aggregation of silver nanoparticles, enabling the colorimetric detection of cysteine. The relationship between the concentration of ΔA396/A520 and cysteine showed linearity within the range of 0.01 to 0.1 µM; the regression equation of the calibration curve is ΔA396/A520 = 9.0005c - 0.0557 (c: µM), with an R2 value of 0.9997. The detection limit was found to be 3.8 nM (S/N = 3). This method demonstrated exceptional selectivity and sensitivity for cysteine and was effectively used for the determination of cysteine in urine. Our findings offer a new perspective for the future advancement of anti-aggregation silver nanocolorimetry.

Colorimetric and SERS dual-mode detection of GSH in human serum based on AuNPs@Cu-porphyrin MOF nanozyme.

BACKGROUND: Rapid and accurate detection of glutathione content in human blood plays an important role in real-time tracking of related diseases. Currently, surface-enhanced Raman scattering/spectroscopy (SERS) combined with nanozyme material has been proven to have excellent properties in the detection applications compared to many other methods because of it combines the advantages of trace detection capability of SERS and efficient catalytic activity of nanozymes. However, there are still existing problems in real sample detection, and to achieve quantitative detection is still challenging. RESULTS: In this study, gold nanoparticles (AuNPs) were synthesized in situ on the surface of two-dimensional Cu-porphyrin metal-organic framework (MOF) nanosheets to produce the AuNPs@Cu-porphyrin MOF nanozyme, which exhibited both oxidase-like activity and SERS detection ability. On one hand, the intrinsic oxidase-like activity of the nanozyme could be inhibited due to the chelation of glutathione (GSH) and Cu, which thus led to the visual color change of the solution. On the other hand, the abundant Raman "hot spots" at the nanogap generated by Au NPs and the internal standard (IS) signal provided by Cu-meso-tetra (4-carboxyphenyl) porphine (Cu-TCPP) MOF improved the sensitivity and quantitative accuracy of detection. SIGNIFICANCE AND NOVELTY: A dual-mode signal output sensor based on the nanozyme was thus established, which could be used in the trace detection of GSH. Such a dual-mode sensor possesses excellent detection performance, with the advantage of both wide detection range from 1 to 300 µM in the colorimetric detection mode and high sensitivity with LOD of 5 nM in the SERS detection mode, and can be applied to GSH detection in actual serum samples with reliable results.

Fe3O4 nanoparticles entrapped in the inner surfaces of N-doped carbon microtubes with enhanced biomimetic activity.

Tubular structured composites have attracted great interest in catalysis research owing to their void-confinement effects. In this work, we synthesized a pair of hollow N-doped carbon microtubes (NCMTs) with Fe3O4 nanoparticles (NPs) encapsulated inside NCMTs (Fe3O4@NCMTs) and supported outside NCMTs (NCMTs@Fe3O4) while keeping other structural features the same. The impact of structural effects on the catalytic activities was investigated by comparing a pair of hollow-structured nanocomposites. It was found that the Fe3O4@NCMTs possessed a higher peroxidase-like activity when compared with NCMTs@Fe3O4, demonstrating structural superiority of Fe3O4@NCMTs. Based on the excellent peroxidase-like catalytic activity and stability of Fe3O4@NCMTs, an ultra-sensitive colorimetric method was developed for the detection of H2O2 and GSH with detection limits of 0.15 µM and 0.49 µM, respectively, which has potential application value in biological sciences and biotechnology.

Construction of a dual-signal readout platform for effective glutathione S-transferase sensing based on polyethyleneimine-capped silver nanoclusters and cobalt-manganese oxide nanosheets with oxidase-mimicking activity.

A novel dual-mode fluorometric and colorimetric sensing platform is reported for determining glutathione S-transferase (GST) by utilizing polyethyleneimine-capped silver nanoclusters (PEI-AgNCs) and cobalt-manganese oxide nanosheets (CoMn-ONSs) with oxidase-like activity. Abundant active oxygen species (O2•-) can be produced through the CoMn-ONSs interacting with dissolved oxygen. Afterward, the pink oxDPD was generated through the oxidation of colorless N,N-diethyl-p-phenylenediamine (DPD) by O2•-, and two absorption peaks at 510 and 551 nm could be observed. Simultaneously, oxDPD could quench the fluorescence of PEI-AgNCs at 504 nm via the inner filter effect (IFE). However, in the presence of glutathione (GSH), GSH prevents the oxidation of DPD due to the reducibility of GSH, leading to the absorbance decrease at 510 and 551 nm. Furthermore, the fluorescence at 504 nm was restored due to the quenching effect of oxDPD on decreased PEI-AgNCs. Under the catalysis of GST, GSH and1-chloro-2,4-dinitrobenzo (CDNB) conjugate to generate an adduct, initiating the occurrence of the oxidation of the chromogenic substrate DPD, thereby inducing a distinct colorimetric response again and the significant quenching of PEI-AgNCs. The detection limits for GST determination were 0.04 and 0.21 U/L for fluorometric and colorimetric modes, respectively. The sensing platform illustrated reliable applicability in detecting GST in real samples.

Bridging biological and food monitoring: A colorimetric and fluorescent dual-mode sensor based on N-doped carbon dots for detection of pH and histamine.

Rapid and sensitive monitoring of pH and histamine is crucial for bridging biological and food systems and identifying corresponding abnormal situations. Herein, N-doped carbon dots (CDs) are fabricated by a hydrothermal method employing dipicolinic acid and o-phenylenediamine as precursors. The CDs exhibit colorimetric and fluorescent dual-mode responses to track pH and histamine variations in living cells and food freshness, respectively. The aggregation-induced emission enhancement and intramolecular charge transfer result in a decrease in absorbance and an increase in fluorescence, which become readily apparent as the pH changes from acidic to neutral. This property enables precise differentiation between normal and cancerous cells. Furthermore, given the intrinsic basicity of histamine, pH-responsive CDs are advantageous for additional colorimetric and fluorescent monitoring of histamine in food freshness, achieving linearities of 25-1000 µM and 30-1000 µM, respectively, which are broader than those of alternative nanoprobes. Interestingly, the smartphone-integrated sensing platform can portably and visually evaluate pH and histamine changes due to sensitive color changes. Therefore, the sensor not only establishes a dynamic connection between pH and histamine for the purposes of biological and food monitoring, but also presents a novel approach for developing a multifunctional biosensor that can accomplish environmental monitoring and biosensing simultaneously.

Realizing Ultrasensitive and Accurate Point-of-Care Profiling for ATP with a Triple-Mode Strategy Based on the ATP-Induced Reassembly of a Copper Coordination Polymer Nanoflower.

New strategies for accurate and reliable detection of adenosine triphosphate (ATP) with portable devices are significant for biochemical analysis, while most recently reported approaches cannot satisfy the detection accuracy and independent of large instruments simultaneously, which are unsuitable for fast, simple, and on-site ATP monitoring. Herein, a unique, convenient, and label-free point-of-care sensing strategy based on novel copper coordination polymer nanoflowers (CuCPNFs) was fabricated for multimode (UV-vis, photothermal, and RGB values) onsite ATP determination with high selectivity, sensitivity, and accuracy. The resulting CuCPNFs with a 3D hierarchical structure exhibit the ATP-triggered decomposition behavior because the competitive coordination between ATP and the copper ions of CuCPNFs can result in the formation of ATP-Cu, which reveals preeminent peroxidase mimics activity and can accelerate the oxidation of 3, 3', 5, 5'-tetramethylbenzidine (TMB) to form oxTMB. During this process, the detection system displayed not only color changes but also a strong NIR laser-driven photothermal effect. Thus, the photothermal and color signal variations are easily monitored by a portable thermometer and a smartphone. This multimode point-of-care platform can meet the requirements of onsite, without bulky equipment, accuracy, and reliability all at once, greatly enhancing its application in practice and paving a new way in ATP analysis.

Magnetically Controlled Photothermal, Colorimetric, and Fluorescence Trimode Assay for Gastric Cancer Exosomes Based on Acid-Induced Decomposition of CP/Mn-PBA DSNBs.

The accurate quantification of cancer-derived exosomes, which are emerging as promising noninvasive biomarkers for liquid biopsies in the early diagnosis of cancer, is becoming increasingly imperative. In our work, we developed a magnetically controlled photothermal, colorimetric, and fluorescence trimode aptasensor for human gastric cancer cell (SGC-7901)-derived exosomes. This sensor relied on CP/Mn-PBA DSNBs nanocomposites, created by decorating copper peroxide (CP) nanodots on polyethyleneimine-modified manganese-containing Prussian blue analogues double-shelled nanoboxes (PEI-Mn-PBA DSNBs). Through self-assembly, we attached CD63 aptamer-labeled CP/Mn-PBA DSNBs (Apt-CP/Mn-PBA DSNBs) to complementary DNA-labeled magnetic beads (cDNA-MB). During exosome incubation, these aptamers preferentially formed complexes with exosomes, and we efficiently removed the released CP/Mn-PBA DSNBs by using magnetic separation. The CP/Mn-PBA DSNBs exhibited high photoreactivity and photothermal conversion efficiency under near-infrared (NIR) light, leading to temperature variations under 808 nm irradiation, correlating with different exosome concentrations. Additionally, colorimetric detection was achieved by monitoring the color change in a 3,3',5,5'-tetramethylbenzidine (TMB) system, facilitated by PEI modification, NIR-enhanced peroxidase-like activity of CP/Mn-PBA DSNBs and their capacity to generate Cu2+ and H2O2 under acidic conditions. Moreover, in the presence of Cu2+ and ascorbic acid (AA), DNA sequences could form dsDNA-templated copper nanoparticles (CuNPs), which emitted strong fluorescence at around 575 nm. Increasing exosome concentrations correlated with decreases in temperature, absorbance, and fluorescence intensity. This trimode biosensor demonstrated satisfactory ability in differentiating gastric cancer patients from healthy individuals using human serum samples.

A novel fluorescent probe with a large Stokes shift for colorimetric and selective detection of cysteine in water, milk, cucumber, pear and tomato.

Cysteine is an important amino acid that is related to human health and food safety. How to effectively detect Cys in food has received widespread attention. Compared with other methods, fluorescent probes have the advantages of simple operation, high sensitivity, and good selectivity. Therefore, a selective fluorescence probe 2 for Cys in food was designed and synthesized. Probe 2 employed the acrylate group as a thiol-recognition site for Cys, which endowed probe 2 with better selectivity for Cys over Hcy and GSH. The recognition pathway underwent Michael addition, intramolecular cyclization, and concomitant release of the piperideine-based fluorophore, along with a chromogenic change from yellow to orange. This pathway was supported by 1H NMR analysis and DFT calculations. In addition, probe 2 displays a linear response to Cys concentrations (0-30 µM), low detection limit (0.89 µM), and large Stokes shift (125 nm). Overall, probe 2 showed great application potential for the quantitative determination of Cys in water, milk, cucumber, pear and tomato.

Silver-palladium bimetallic nanoparticles stabilized by elm pod polysaccharide with peroxidase-like properties for glutathione detection and photothermal anti-tumor ability.

Noble metal nanoparticles show good application prospects in biosensors and anti-tumor drug research. Herein, the near-spherical silver­palladium bimetallic nanoparticles supported by elm pod polysaccharide (EPP-AgPd1.5 NPs) were prepared by using the elm pod polysaccharide (EPP). EPP acts as a stabilizer and reducing agent due to its water solubility and weak reducing ability. The particle size of EPP-AgPd1.5 NPs was 33.6 ± 5.5 nm. In addition, EPP-AgPd1.5 NPs had peroxidase-like activity to catalyze 3,3',5,5'-tetramethylbenzidine (TMB) to oxidized TMB by catalyzing H2O2 to OH. Based on the peroxidase-like activity of EPP-AgPd1.5 NPs, a method for detecting glutathione was established, and the detection limit and linear range of glutathione concentration were 0.279 µM and 0-400 µM, respectively. More importantly, the photothermal conversion efficiency of EPP-AgPd1.5 NPs reached 39.7 %, and their inhibition rate in HeLa cells reached 69.9 %. Silver­palladium bimetallic nanoparticles stabilized by EPP had good performance in glutathione detection and anti-tumor drugs.

A colorimetry-enhanced tri-functional film with high stability by polyphenol-anthocyanin co-pigmentation/conjugate: New prospect for active intelligent food packaging.

A highly stable "tannin-anthocyanin conjugated" trifunctional active intelligent film was developed by incorporating bilberry anthocyanins (BA) as an indicator and tannin acids (TA) as a co-pigment into a sodium alginate-carrageenan polysaccharide matrix (SC-BA/TA). The doping of TA conferred outstanding antioxidant (DPPH scavenging rate > 90%) and antibacterial properties to the film, particularly effective against S. aureus. The SC-BA/TA films effectively blocked UV rays (close to 0%, effectively impeding most UVA, as well as nearly all UVC and UVB) within the range of 200-320 nm. The TA-BA co-pigment effect significantly improved the anthocyanins' storage and color stability (retention rate > 70% under UV and natural light conditions). TA forms conjugate with anthocyanins by π-π stacking and hydrogen bonding interactions with co-pigmentation rate increases of 10.5% and 11.0% for pH 2 and pH 3, respectively. The film exhibited good responsiveness to volatile amines within 4 min, and offered real-time monitoring of beef freshness, as indicated by visualizing color changes (from red to dark yellow color). Furthermore, the integration of the film's RGB value with beef quality via a smartphone App effectively reduces the variability in visual recognition among individuals. To sum up, composite films based on the "tannin-anthocyanin conjugate" approach hold great potential in the field of food freshness monitoring, opening new possibilities for the development of highly stable active smart packaging films.

Ag-carbon dots with peroxidase-like activity for colorimetric and SERS dual mode detection of glucose and glutathione.

Currently, nanozymes have made important research progress in the fields of catalysis, biosensing and tumor therapy, but most of nanozymes sensing systems are single-mode detection, which are easily affected by environment and operation, so it is crucial to construct nanozymes sensing system with dual-signal detection to obtain a more stable and reliable performance. In this paper, Ag-carbon dots (Ag-CDs) bifunctional nanomaterials were synthesized using carbon dots as reducing agent and protective agent by a facile and green one-step method. A simple and sensitive colorimetric-SERS dual-mode sensing platform was constructed for the detection of glucose and glutathione(GSH) in body fluids by taking advantage of good peroxidase-like and SERS activities of Ag-CDs. Ag-CDs catalyzes H2O2 to hydroxyl radicals(•OH), which oxidized TMB to form ox-TMB blue solution with characteristic absorption peak at 652 nm and Raman characteristic peak at 1607 cm-1. Ag-CDs sensing method exhibited high performance for glucose and GSH with detection limits for colorimetric and SERS as low as 11.30 µM and 3.54 µM, 0.38 µM and 0.24 µM respectively (S/N = 3). In addition, Ag-CDs have good stability and uniformity, ensuring long-term applicability of catalytic system. This colorimetric-SERS dual-mode sensing platform can be used for the determination of glucose and GSH in saliva and urine, and has the advantages of simple, low cost, rapid, and high accuracy, which has a potential application prospect in biosensor and medical research.

Prolidase activity assays. A survey of the reported literature methodologies.

Prolidase (EC.3.4.13.9) is a dipeptidase known nowadays to play a pivotal role in several physiological and pathological processes. More in particular, this enzyme is involved in the cleavage of proline- and hydroxyproline-containing dipeptides (imidodipeptides), thus finely regulating the homeostasis of free proline and hydroxyproline. Abnormally high or low levels of prolidase have been found in numerous acute and chronic syndromes affecting humans (chronic liver fibrosis, viral and acute hepatitis, cancer, neurological disorders, inflammation, skin diseases, intellectual disability, respiratory infection, and others) for which the content of proline is well recognized as a clinical marker. As a consequence, the accurate analytical determination of prolidase activity is of greatly significant importance in clinical diagnosis and therapy. Apart from the Chinard's assay, some other more sensitive and well validated methodologies have been published. These include colorimetric and spectrophotometric determinations of free proline produced by enzymatic reactions, capillary electrophoresis, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, electrochemoluminescence, thin layer chromatography, and HPLC. The aim of this comprehensive review is to make a detailed survey of the in so far reported analytical techniques, highlighting their general features, as well as their advantages and possible drawbacks, providing in the meantime suggestions to stimulate further research in this intriguing field.

Nanozyme sensor array based on Fe, Se co-doped carbon material for the discrimination of Sulfur-containing compounds.

Developing methods for the accurate identification and analysis of sulfur-containing compounds (SCCs) is of great significance because of their essential roles in living organisms and the diagnosis of diseases. Herein, Se-doping improved oxidase-like activity of iron-based carbon material (Fe-Se/NC) was prepared and applied to construct a four-channel colorimetric sensor array for the detection and identification of SCCs (including biothiols and sulfur-containing metal salts). Fe-Se/NC can realize the chromogenic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by activating O2 without relying on H2O2, which can be inhibited by different SCCs to diverse degrees to produce different colorimetric response changes as "fingerprints" on the sensor array. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) revealed that nine kinds of SCCs could be well discriminated. The sensor array was also applied for the detection of SCCs with a linear range of 1-50 µM and a limit of detection of 0.07-0.2 µM. Moreover, colorimetric sensor array inspired by the different levels of SCCs in real samples were used to discriminate cancer cells and food samples, demonstrating its potential application in the field of disease diagnosis and food monitoring. ENVIRONMENTAL IMPLICATIONS: In this work, a four-channel colorimetric sensor array for accurate SCCs identification and detection was successfully constructed. The colorimetric sensor array inspired by the different levels of SCCs in real samples were also used to discriminate cancer cells and food samples. Therefore, this Fe-Se/NC based sensor array is expected to be applied in the field of environmental monitoring and environment related disease diagnosis.

Linker-Preserved Iron Metal-Organic Framework-Based Lateral Flow Assay for Sensitive Transglutaminase 2 Detection in Urine Through Machine Learning-Assisted Colorimetric Analysis.

A groundbreaking demonstration of the utilization of the metal-organic framework MIL-101(Fe) as an exceptionally perceptive visual label in colorimetric lateral flow assays (LFA) is described. This pioneering approach enables the precise identification of transglutaminase 2 (TGM2), a recognized biomarker for chronic kidney disease (CKD), in urine specimens, which offers a remarkably sensitive naked-eye detection mechanism. The surface of MIL-101(Fe) was modified with oxalyl chloride, adipoyl chloride, and poly(acrylic) acid (PAA); these not only improved the labeling material stability in a complex matrix but also achieved a systematic control in the detection limit of the TGM2 concentration using our LFA platform. The advanced LFA with the MIL-101(Fe)-PAA label can detect TGM2 concentrations down to 0.012, 0.009, and 0.010 nM in Tris-HCl buffer, urine, and desalted urine, respectively, which are approximately 55-fold lower than those for a conventional AuNP-based LFAs. Aside from rapid TGM2 detection (i.e., within 20 min), the performance of the MIL-101(Fe)-PAA-based LFA on reproducibility [coefficients of variation (CV) < 2.9%] and recovery (95.9-103.2%) along with storage stability within 25 days of observation (CV < 6.0%) shows an acceptable parameter range for quantitative analysis. A sophisticated sensing method grounded in machine learning principles was also developed, specifically aimed at precisely deducing the TGM2 concentration by analyzing immunoreaction sites. More importantly, our developed LFA offers potential for clinical measurement of TGM2 concentration in normal human urine and CKD patients' samples.

Development of a point-of-care colorimetric metabolomic sensor platform.

Metabolomics is the large-scale study of small molecule metabolites within a biological system. It has applications in measuring dietary intake, predicting heart disease risk, and diagnosing cancer. Metabolites are often measured using high-end analytical tools such as mass spectrometers or large spectrophotometers. However, due to their size, cost, and need for skilled operators, using such equipment at the bedside is not practical. To address this issue, we have developed a low-cost, portable, optical color sensor platform for metabolite detection. This platform includes LEDs, sensors, microcontrollers, a power source, and a Bluetooth chip enclosed within a 3D-printed light-tight case. We evaluated the color sensor's performance using both a range of dyed water samples as well as well-established colorimetric reactions for specific metabolite detection. The sensor accurately measured creatinine, L-carnitine, ascorbate, and succinate well within normal human urine levels with accuracy and sensitivity equal to or better than a standard laboratory spectrophotometer. Our color sensor offers a cost-effective, portable alternative for measuring metabolites via colorimetric assays, thereby enabling low-cost, point-of-care metabolite testing.

A skin-interfaced, miniaturized platform for triggered induction, capture and colorimetric multicomponent analysis of microliter volumes of sweat.

Eccrine sweat can serve as a source of biomarkers for assessing physiological health and nutritional balance, for tracking loss of essential species from the body and for evaluating exposure to hazardous substances. The growing interest in this relatively underexplored class of biofluid arises in part from its non-invasive ability for capture and analysis. The simplest devices, and the only ones that are commercially available, exploit soft microfluidic constructs and colorimetric assays with purely passive modes of operation. The most sophisticated platforms exploit batteries, electronic components and radio hardware for inducing sweat, for electrochemical evaluation of its content and for wireless transmission of this information. The work reported here introduces a technology that combines the advantages of these two different approaches, in the form of a cost-effective, easy-to-use device that supports on-demand evaluation of multiple biomarkers in sweat. This flexible, skin-interfaced, miniaturized system incorporates a hydrogel that contains an approved drug to activate eccrine sweat glands, electrodes and a simple circuit and battery to delivery this drug by iontophoresis through the surface of the skin, microfluidic channels and microreservoirs to capture the induced sweat, and multiple colorimetric assays to evaluate the concentrations of chloride, zinc, and iron. As demonstrated in healthy human participants monitored before and after a meal, such devices yield results that match those of traditional laboratory analysis techniques. Clinical studies that involve cystic fibrosis pediatric patients illustrate the use of this technology as a simple, painless, and reliable alternative to traditional hospital systems for measurements of sweat chloride.

Cascade reaction triggered colorimetric array for identification of organophosphorus pesticides congeners.

A modern agriculture uses alternative pest control methods to boost productivity, leading to an accumulation of organophosphorus (OPPs) congeners. This necessitates an intuitive and quick way to identify OPPs congeners. A colorimetric sensor for detecting OPPs congeners using a double-enzyme cascade reaction has been successfully designed and constructed in this study. The OPPs regulate the color changes induced by manganese dioxide nanoflowers (MnO2 NFs) and specific alkaline phosphatases (ALP) during the etching of gold nanopyramids (Au NBPs). The ascorbic acid (AA) produced by ALP hydrolysis inhibits Au NBPs etching by MnO2 NFs oxidized 3, 3', 5, 5'-tetramethylbenzidine (TMB). By inhibiting ALP catalytic activity, OPPs prevent AA formation. In this process, Au NBPs will undergo further etching, resulting in various colors so they can be analyzed semi-quantitatively with the naked eye. It has been found that different types of OPPs inhibit enzymes differently and therefore result in varying degrees of etching of Au NBPs. Principal Component Analysis (PCA) is performed by smart devices that convert R, G, and B signals into digital signals. This colorimetric array tests various foods (tea, apple, and cabbage). Colorimetric visualization sensors combined with data analysis will be used in real-life product development.

CoO/Co-graphene quantum dots as an oxidative mimetic nanozyme for the colorimetric detection of L-cysteine.

The preparation of cobalt-based nanozymes with high oxidase-like activity still needs more efforts. In this paper, we report the synthesis of a CoO/Co-tryptophan-functional graphene quantum dot hybrid (CoO/Co-Try-GQD). Firstly, cobalt ions coordinate with the indole nitrogen on Try-GQD to form a complex, followed by thermal reduction and oxidation. The resulting hybrid presents a three-dimensional network structure, and CoO/Co nanoparticles are uniformly dispersed on the graphene sheet with an average size of 10 ± 0.24 nm. This unique structure improved the oxidase-like activity of the hybrid, enabling it to catalyze the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to rapidly produce deep blue ox-TMB with a strong absorbance at 652 nm (A652). A colorimetric method was developed for the highly sensitive determination of L-cysteine (L-cys) based on the inhibition of the hybrid's oxidase-like activity and low A652 caused by the binding of L-cys with Co atoms on CoO/Co via the Co-S bond. The A652 linearly decreased with increasing L-cys concentration in the range of 0.05-2 µM, and the detection limit was 0.032 µM. Further, the established method has been successfully applied to the determination of L-cys in milk.

ß-Glucuronidase-triggered reaction for fluorometric and colorimetric dual-mode assay based on the in situ formation of silicon nanoparticles.

BACKGROUND: ß-Glucuronidase (GUS) is considered as a promising biomarker for primary cancer. Thus, the reliable detection of GUS has great practical significance in the discovery and diagnosis of cancer. Compared with traditional organic probes, silicon nanoparticles (Si NPs) have emerged as robust optical nanomaterials due to their facile preparation, superior photobleaching resistance and excellent biocompatibility. However, most nanomaterials-based methods only output a single signal which is easily influenced by external factors in complex systems. Hence, developing nanomaterial-based multi-signal optical assays for highly sensitive GUS determination is still urgently desired. RESULTS: In this study, we developed a simple and efficient one-step method for the in situ preparation of yellow color and yellow-green fluorescent Si NPs. This was achieved by combining 3-[2-(2-aminoethylamino) ethylamino] propyl-trimethoxysilane with p-aminophenol (AP) in an aqueous solution. The obtained Si NPs showed yellow-green fluorescence at 535 nm when excited at 380 nm, while also exhibiting an absorption peak at a wavelength of 490 nm. Taking inspiration from the easy synthesis step regulated by AP, which is generated through the hydrolysis of 4-aminophenyl ß-D-glucuronide catalyzed by GUS, we constructed a direct fluorometric and colorimetric dual-mode method to measure GUS activity. The developed fluorometric and colorimetric sensing platform showed high sensitivity and accuracy with detection limits for GUS determination as low as 0.0093 and 0.081 U/L, respectively. SIGNIFICANCE: This study provides a facile dual-mode fluorometric and colorimetric approach for determination of GUS activity based on novel Si NPs for the first time. This designed sensing approach was successfully employed for the quantification of GUS in human serum samples and screening of GUS inhibitors, indicating the feasibility and potential applications in clinical cancer diagnosis and anti-cancer drug discovery.