Fabrication of natural enzyme-covered / amino-modified Pd-Pt bimetallic-doped zeolitic imidazolate framework for ultrasensitive detection of metabolites.

The present article introduced an natural enzyme-covered/amino-modified Pd-Pt bimetallic-doped zeolitic imidazolate framework (NAPPZ) for ultrasensitive and specific detection of glucose. The dodecahedral nanomaterial zeolitic imidazolate framework (ZIF-8)-loaded Pd-Pt bimetallic nanoparticles endowed the composite with peroxidase-like activity. The modification with glucose oxidase (GOx) facilitated the rapid access of H2O2 produced through glucose oxidation to the Pd-Pt nanoparticles vicinity reducing diffusion. GOx specifically catalyzes the transformation of glucose into H2O2, which then H2O2 rapidly migrates to the Pd-Pt nanoparticles, catalyzing the oxidation of colorless o-phenylenediamine into the orange-yellow product 2,3-diaminophenazine. Based on the aforementioned cascade reaction, the NAPPZ and NAPPZ based on ChOx were utilized for detecting glucose in human urine samples and cholesterol in milk, respectively. The NAPPZ strategy presented a broad detection range (20-1100 µmol L-1) and a low detection limit (15.9 µmol L-1) for glucose, and the NAPPZ based on ChOx strategy approach offered a broad detection range (10-500 µmol L-1) and low detection limit (6.4 µmol L-1) for cholesterol. Therefore, this novel method holds significant potential in the areas of clinical diagnostics and food safety.

Hyperspectral Imaging Database of Human Facial Skin.

The perceived color of human skin is the result of the interaction of environmental lighting with the skin. Only by resorting to human skin spectral reflectance, it is possible to obtain physical outcomes of this interaction. The purpose of this work was to provide a cured and validated database of hyperspectral images of human faces, useful for several applications, such as psychophysics-based research, object recognition, and material modeling. The hyperspectral imaging data from 29 human faces with different skin tones and sexes, under constant lighting and controlled movements, were described and characterized. Each hyperspectral image, which comprised spectral reflectance of the whole face from 400 to 720 nm in 10 nm steps at each pixel, was analyzed between and within nine facial positions located at different areas of the face. Simultaneously, spectral measurements at the same nine facial positions using conventional local point and/or contact devices were used to ascertain the data. It was found that the spectral reflectance profile changed between skin tones, subjects, and facial locations. Important local variations of the spectral reflectance profile showed that extra care is needed when considering average values from conventional devices at the same area of measurement.

Biocompatible sensors for ammonia gas detection.

In this work, three different dyes have been tested for the determination of gaseous ammonia. This gas is one of the products of microbial degradation and therefore its presence is an indicator of deterioration and could be used as a food freshness indicator. Three different sensors have been prepared and tested, two of them using the natural pigments curcumin and anthocyanin and the other one using bromothymol blue. All of them are biocompatible and therefore allowed to use in contact with food. Different compositions, materials for deposition, stability and reversibility for ammonia gas detection have been studied under high humidity conditions simulating real packaged food conditions. Colorimetry is the technique used to obtain the analytical parameter, the H coordinate of the HSV colour space, simply using a camera, avoiding the use of complex instrumentation. Sensibility, toxicity grade and stability found show that the sensor could be implemented in packaged food and form the basis of a freshness indicator for the food industry.

The Effect of Cigarettes Smoke on the Color and Properties of a Silicone for Maxillofacial Prostheses.

Although deterioration of silicone maxillofacial prostheses is severely accentuated in smoking patients, the phenomenon has not been systematically studied. To address a gap in the literature concerning the stability of maxillofacial prostheses during service, in this contribution, the effect of cigarette smoke on the aspect and physical properties of M511 silicone elastomer was evaluated. The aspect, surface, and overall properties of the silicone material, pigmented or not, were followed by AFM, color measurements, FTIR, water contact angle measurements, TGA-DTG and DSC, hardness and compression stress-strain measurements. The types of the contaminants adsorbed were assessed by XRF, ESI-MS, MALDI-MS, and NMR spectral analyses. Important modifications in color, contact angle, surface roughness, local mechanical properties, and thermal properties were found in the silicone material for maxillofacial prostheses after exposure to cigarettes smoke. The presence of lead, nicotine, and several other organic compounds adsorbed into the silicone material was emphasized. Slight decrease in hardness and increase in Young's modulus was found. The combined data show important impact of cigarette smoke on the silicone physical properties and could indicate chemical transformations by secondary cross-linking. To our knowledge, this is the first study making use of complementary physical methods to assess the effect of cigarette smoke on the aspect and integrity of silicone materials for maxillofacial prostheses.

Determination of ammonium and nitrate in soils by digital colorimetry.

A method of digital colorimetric determination of ammonium and nitrate in soils is proposed. The method is based on corresponding photometric procedures of ammonium and nitrate determination after potassium chloride extraction from soil samples. Ammonium is determined as an indophenol dye, and nitrate is determined as an azo dye. The original procedures were modified to overcome the lower sensitivity of the digital colorimetric method. For ammonium determination, the time required for the reaction to proceed completely was studied. Along with the use of a 96-well microplate protected from ambient light by a special frame, mathematical correction of scattered radiation using black ink and taking the images by a scanner in transmission mode without any post-processing, the resulting colorimetric methods proved to provide accuracy and sensitivity close to those of the spectrophotometric method, and the overall analysis speed for tens of samples was even higher. Limits of detection and quantitation for NO3- were 0.42 and 1.4 mg/kg, and for NH4+, they were 1.1 and 3.7 mg/kg, which is lower than for standard methods. The methods' validity was proven by the analysis of standard samples and by the analysis of soil samples collected in several districts of the Moscow region.

Fill, Fold, Photo: Preconcentration and Multiplex Detection of Trace Level Heavy Metals in Water.

Heavy metal contamination is an increasing global threat to human and environmental health, particularly in resource-limited areas. Traditional platforms for heavy metal detection are labor intensive and expensive and require lab facilities. While paper-based colorimetric sensors offer a simpler approach, their sensitivity limitations prevent them from meeting legislative requirements for many metals. Existing preconcentration systems, on the other hand, can achieve lower detection limits but typically focus on analyzing only one metal, making comprehensive monitoring difficult. We address these limitations by introducing a low-cost preconcentration system coupled with colorimetric analysis for the simultaneous detection of seven metal ions at low ppb levels without the need for external equipment outside a smartphone. The system achieved detection limits of 15 ppb (Ni(II)), 7 ppb (Cu(II)), 2 ppb (Fe(III)), 20 ppb (Cr(VI)), 13 ppb (Pb(II)), 26 ppb (Hg(II)), and 15 ppb (Mn(II)) with six out of seven limits of detection values falling well below EPA regulatory guidelines for drinking water. The user-friendly Fill, Fold, Photo approach eliminates complex pretreatment steps. Smartphone-based detection offers portable quantification within seconds. Employing masking strategies ensured higher selectivity for each assay on the card, while our packaging protocols enable system stability for over 4 weeks of study, facilitating mass production and deployment within a realistic time frame. To validate the sensor's performance in real-world scenarios, the sensor was tested with environmental water samples. The sensor demonstrated good recovery, ranging from 77% to 94% compared to the standard ICP-MS method. Furthermore, spike recovery analysis confirmed the sensor's accuracy, with a relative standard deviation (RSD) of less than 15%. This technology holds significant promise for future development as a convenient, portable solution for field-based monitoring of a broad spectrum of water contaminants, including pesticides, PFAS, fertilizers, and beyond.

Highly active Ti3C2Tx MXene nanoribbons@AuPt bimetallic nanozyme constructed in a "two birds with one stone" manner for colorimetric sensing of dipterex.

The bimetallic nanoparticles have received significant attention in the field of colorimetric sensing, while the majority of the previous methods for synthesizing such nanoparticles typically require the use of reducers and involve highly harsh synthesis conditions. In this work, the AuPt bimetallic nanoparticles (AuPtNPs) decorated Ti3C2TxNR nanohybrid (Ti3C2TxNR@AuPt) was firstly synthesized in a "two birds with one stone" manner. Innovatively, during the synthesis process, Ti3C2TxNR served as both reducing agent and supporting agent to prevent aggregation of bimetallic nanoparticles. Due to the good synergistic effect of AuPtNPs and the strong metal-support interaction between AuPtNPs and Ti3C2TxNR, the as-prepared Ti3C2TxNR@AuPt exhibited boosted peroxidase (POD)-like activity. In advantage of the exceptional POD-like activity, a cost-effective and sensitive colorimetric sensing platform was fabricated for dipterex detection with a broad linearity of 1.0 ng mL-1-1.0 µg mL-1 and a low detection limit (0.479 ng mL-1). The detection of dipterex in insecticide samples also yielded favorable recoveries. Moreover, this approach provided a convenient and effective strategy to design and develop novel nanozymes via a "two birds with one stone" strategy.

Colorimetric pH-sensing of artificial gastric fluid using naphthalimide-based CH acids.

In this study, we introduce novel colorimetric pH-sensing probes based on naphthalimide malonate derivatives. These probes were synthesized by reacting 4-bromo-1,8-naphthalimide with various malonates, including malononitrile, ethyl cyanoacetate, and diethyl malonate. Each derivative exhibited distinct pH-sensing characteristics due to their differing CH acidities. The malononitrile-based probe, NPI-N2, demonstrated pronounced chromogenic pH-signaling behavior, transitioning from colorless to red-violet, accompanied by a decrease in fluorescence intensity. Notably, NPI-N2 retained its pH-sensing capability in the presence of common metal ions, anions, and pepsin, a key component of gastric fluid. The pKa of NPI-N2 was determined to be 3.08 through pH-dependent absorbance curve fitting. To modulate the pH-sensing range, ester-nitrile (NPI-EN) and diethyl ester (NPI-E2) subunits were incorporated into the naphthalimide framework, resulting in increased pKa values of 6.73 and 10.76, respectively. The pH-signaling mechanism of NPI-N2 was elucidated by 1H and 13C NMR spectroscopy, revealing deprotonation of the malononitrile moiety and subsequent resonance extension through the naphthalimide structure. To facilitate practical pH determination, NPI-N2 was integrated into a paper-based test strip, enabling convenient and reliable pH measurement of artificial gastric fluid.

Coomassie Brilliant Blue G for Smart Colorimetric Determination of the Ionic Surfactants in Triton X-100 Solutions.

The conditions for the smart colorimetric determination of cetylpyridinium chloride and sodium dodecyl sulfate by reaction with Coomassie brilliant blue G (CBBG) have been proposed. The nature of the absorption and fluorescence spectra of aqueous solutions of CBBG as a function of acidity has been investigated. A variety of reagent forms and associations with ionic surfactants have been demonstrated. The composition of the associates formed in the CBBG-cationic surfactant system has been established. The increase in the analytical signal of the cationic surfactant and the stabilization of the colloid-chemical state of the system during reactions in the organized medium of the nonionic surfactant Triton X-100 has been demonstrated. These effects are realized through association in premicellar solutions and as a result of the solubilization of components in Triton X-100 micellar solutions. The addition of long-chain cationic surfactants to the reagent occurs with the replacement of the heteroatom proton. The absorption of CBBG-cationic surfactant associates solutions increases with the length of the cationic surfactant hydrocarbon chain. Ethanol additives decrease the aggregation of CBBG. The technique of cationic surfactant determination has been tested in the analysis of the pharmaceutical. The results show that the simplicity of analytical signal registration with satisfactory correctness and acceptably high sensitivity of determination is an advantage of the developed technique.

Laccase-mimicking activity of octahedral Mn3O4 nanoparticles and fluorescence of carbon dots as dual-mode signals for the specific detection of arsenic(V) in environmental water samples.

The detrimental growth of water pollutants such as heavy metals has become a life-threatening problem in the modern era. Challenges remain in the development of rapid and accurate methods for detecting pentavalent arsenic [As(V)] in environmental water. The octahedral Mn3O4 nanoparticles (NPs) did not display excellent laccase-mimicking catalytic activity, whereas the adsorbed As(V) on the surface significantly enhanced the catalytic activity. Meanwhile, the quinone imine generated from the substrates 2,4-dichlorophenol (2,4-DP) and 4-aminoantipyrine (4-AAP) catalyzed by octahedral Mn3O4 NPs further quenched the carbon dots fluorescence. Thus, it is possible to establish a fast and accurate dual-mode sensor for detecting As(V). The developed dual-mode method of As(V) detection has good sensitivity and selectivity. The limit of detection for As(V) in colorimetric mode is 6.96 µg·L-1, whereas in the fluorescent mode, it is as low as 2.56 µg·L-1. Moreover, the detection data obtained by the dual-mode method can be validated by each other, thereby ensuring the dependability of the sensing system. The constructed dual-mode method with merits of sensitivity, speed and accuracy can offer a powerful tool for As(V) detection in environmental water. Furthermore, the application of laccase-mimicking activity in dual-mode detection provides new strategies for other environmental hazard detection.

Thermal measurement of erythema across skin tones: Implications for clinical identification of early pressure injury.

AIM: To assess the effectiveness of thermography, colorimetry, and oximetry at detecting temperature changes after erythema induction across diverse skin tones in healthy adults. MATERIALS AND METHODS: Erythema was induced at the forearm and ulnar head (UH) using a cupping device. Temperature via thermal image, erythema value via colorimeter, and oxygen saturation via oximeter were collected immediately and 5-10 min (delayed) after cupping at both sites. RESULTS: At the forearm, the delayed timepoint was significantly warmer than baseline. At the UH, the immediate timepoint was significantly colder than baseline. Erythema increased at both timepoints and both locations. The correlation between temperature change and erythema change was weak. Change in temperature did not differ between skin tone groups. The Intermediate Low Eumelanin skin tone group had more change in erythema compared to the Intermediate Mid (i.e., darkest) skin tone group immediately after cupping at the UH and at the delayed timepoint at the forearm. CONCLUSIONS: This study observed differences in the change of erythema across skin tones but did not observe differences in temperature across skin tones. Given high variability in results, it is premature to conclude thermal imaging works equally well across all skin tones. Further research is necessary to validate the effectiveness of thermal imaging in diverse populations. Results suggest visual erythema may be a problematic indicator as less erythema was consistently noted in participants with dark skin tones. The potential of technology to increase our ability to detect erythema warrants further investigation.

Phosphatase-mimicking Zr@PDA nanozyme with excellent dispersion stability for the detection of fructose 1,6-diphosphate.

Zr4+-doped polydopamine (Zr@PDA) nanozyme with phosphatase-like activity was synthesized by a one-pot hydrothermal method for the first time. Compared with previous representative phosphatase-mimicking nanozymes (i.e., CeO2 NPs, ZrO2 NPs and UiO-66), Zr@PDA not only exhibited higher dispersion stability in water, but also higher catalytical efficiency. Kcat/Km of Zr@PDA is 35 and 12 times that of UiO-66 and ZrO2 NPs, respectively, which would endow the Zr@PDA-based analytical methods with high sensitivity. As a demonstration, a novel colorimetric method based on Zr@PDA nanozyme was developed for sensitive detection of the drug fructose 1,6-diphosphate. The linear range is 1-15 µM with a detection limit as low as 0.38 µM.

Low-cost, immediate, general-purpose, and high-throughput (LIGHt) smartphone colorimetric screening assay for water-soluble protein.

An efficient and rapid method for the detection of total soluble protein in tobacco leaves, utilizing a smartphone-based colorimetric approach has been developed. The proposed low-cost, immediate, general-purpose, and high-throughput (LIGHt) smartphone colorimetric screening assay integrates commercially available microplates, enabling on-site, high-throughput screening of tobacco leaf quality. The study involves preparing protein standard solutions and constructing standard curves using both spectrophotometric and smartphone-based methods. The LIGHt smartphone colorimetry yielded an average relative standard deviation of 10.6 %, a limit of detection of 2 µg/mL, and an average recovery of 93 %. The results demonstrated a comparable performance between intensities from the blue channel and the absorbance values in reflecting protein concentrations, validating the feasibility of utilizing smartphone colorimetry for protein concentration determination. Our approach demonstrates the potential for practical implementation in the field, providing a cost-effective and user-friendly solution for rapid quality assessment in the tobacco industry. The LIGHt smartphone colorimetry enhances quality control practices in the tobacco sector and offers a promising tool for on-site production quality testing in various industries, such as fruits and vegetables.

Colorimetric detection of furin based on enhanced catalytic activity of G-quadruplex/hemin DNAzyme.

BACKGROUND: Rapid and sensitive colorimetric detection methods are crucial for diseases diagnosis, particularly those involving proteases like furin, which are implicated in various conditions, including cancer. Traditional detection methods for furin suffer from limitations in sensitivity and practicality for on-site detection, motivating the development of novel detection strategies. Therefore, developing a simple, enzyme-free, and rapid colorimetric analysis method with high sensitivity for furin detection is imperative. RESULTS: Herein, we have proposed a colorimetric method in this work for the first time to detect furin, leveraging the assembly of G-quadruplex/hemin DNAzyme with enhanced catalytic activity. Specifically, a peptide-DNA conjugate (PDC) comprising a furin-recognition peptide and flanking DNA sequences for signal amplification is designed to facilitate the DNAzyme assembly. Upon furin treatment, PDC cleavage triggers a cyclic catalytic hairpin assembly reaction to form the complementary double-stranded structures by hairpin 1 (HP1) and hairpin 2 (HP2), bringing the G-quadruplex sequence in HP1 closer to hemin on HP2. Moreover, the resulting G-quadruplex/hemin DNAzymes exhibit robust peroxidase-like activity, enabling the catalysis of the colorimetric reaction of ABTS2- for furin detection. Our method demonstrates high sensitivity, rapid response, and compatibility with complex sample matrices, achieving a detection limit as low as 1.1 pM. SIGNIFICANCE: The DNAzyme reported in this work exhibits robust catalytic activity, enabling high sensitivity and good efficiency for the detection. By eliminating the requirement for exogenous enzymes, our approach enables visual furin detection without expensive instrumentation and reagents, promising significant utility in biomedical and clinical diagnostic applications. Given the various design of peptide sequence and the programmability of DNA, it can be readily applied to analyzing other useful tumor biomarkers.

"Shock kidney-like Appearance": Objective evaluation of renal color changes in hemorrhagic shock deaths.

Severe bleeding due to various traumatic injuries can cause hemorrhagic shock, which is difficult to diagnose using forensic medicine. Therefore, we defined the difference in color between the renal cortex and medulla observed in hemorrhagic shock deaths as "shock kidney-like appearance (SKLA)" and digitally analyzed the color difference with a digital camera and color analysis software. The aim of this study was to develop and evaluate a method for objectively determining SKLA and improve the accuracy of forensic diagnosis. We examined the kidneys of 122 cases (83 males and 39 females; average age, 64.8 years) autopsied at our facility. Using Image J, we analyzed the color of the cortex and medulla from photographs of bisected kidneys. We defined the color difference between the cortex and medulla in the L*a*b* color space as cortical-medullary color difference and performed a comparative analysis between the hemorrhage and control groups. Significant differences were observed in ΔL* and Δa* values between the two groups (p < 0.05 and p < 0.001, respectively). Analysis of Δa* values showed that the cortex was less reddish than the medulla in the hemorrhage group. The cutoff value for determining SKLA was set at Δa* = -1.33 (sensitivity, 0.79; specificity, 0.81; AUC, 0.859). Traditional evaluations of color rely on subjective assessments, which raise issues of reliability and reproducibility. This study successfully overcame the limitations of subjective evaluation by objectively assessing cortical-medullary color difference in the kidneys. Our results represent an important step towards improving the objectivity of color evaluations.

Colorimetric sensors constructed with one dimensional PtNi nanowire and Pt nanowire nanozymes for Hg2+ detection.

BACKGROUND: In recent years, environmental pollution has attracted widespread global attention. Among them, environmental problems caused by heavy metal pollution pose a serious threat to human health and ecosystems. Mercury is a common heavy metal pollutant with high toxicity and wide distribution. Excessive intake of Hg2+ can cause permanent and severe damage to the nervous system, respiratory system, and kidneys in the human body. Therefore, developing both accurate and fast detection methods for Hg2+ is of great significance. RESULTS: A sensitive Hg2+ colorimetric sensor is designed based on PtNi nanowires (NWs) and Pt NWs with peroxidase-mimetic activity. PtNi NWs and Pt NWs catalyze the reaction of 3,3', 5,5'-tetramethylbenzidine (TMB) with hydrogen peroxide (H2O2) to produce blue oxidized TMB (oxTMB). The specific interaction of Pt-Hg significantly inhibits the peroxidase-mimetic activity of PtNi NW and Pt NW nanozymes, resulting in a lighter blue color. It is worth noting that compared with specific activity (SA) of Pt NWs (3.31 U/mg), PtNi NWs own superior SA (10.43 U/mg), which inevitably leads to a wider linear range of Hg2+ analysis (1 nM-200 µM) and a lower detection limit (0.6748 nM) for PtNi NWs-based colorimetric sensor, versus linear range (4 nM-5 µM) and LOD of 1.198 nM for Pt NWs-based colorimetric sensor, which are far below the Hg2+ threshold (10 nM) for drinking water set by the US Environmental Protection Agency. SIGNIFICANCE: The two nanozyme colorimetric sensors have been successfully used for the evaluation of Hg2+ in complex river water and tap water. Due to the advantages of simple operation, fast response, and high sensitivity, colorimetric sensors have broad application prospects in environmental monitoring.

A Versatile pH-Dependent Fluorometric, Colorimetric, and Electrochemical Sensor for H2S Monitoring in Water.

Hydrogen sulfide (H2S) is a colorless, foul smelling, toxic substance that can be found in water bodies and waste waters, especially in occupational susceptible environments, and can lead to harmful effects in humans at higher concentrations. An H2S monitoring probe NNAP is synthesized, which displays pH-dependent electrochemical, colorimetric, and fluorescence responses. NNAP functions as a fluorometric sensor at pH 7.4, with a limit of detection (LOD) of 0.70 mM, and as a colorimetric sensor at pH 12, where visible color changes are discernible to the naked eye, with an LOD of 4.28 mM. Additionally, it demonstrates utility in electrochemical sensing at pH 2, with a LOD of 2.5 mM. Furthermore, NNAP-coated paper strips have been successfully utilized for real-time H2S monitoring applications.

An ultrasensitive dual-mode stagey for 17ß-estradiol assay: Photoelectrochemical and colorimetric biosensor based on a WSe2/TiO2-modified electrode coupled with nucleic acid amplification.

BACKGROUND: The abuse of 17ß-estradiol(E2) has aroused wide concern in environmental and biomedical fields, which severely affects the endocrine function of human and animals. Therefore, an ultrasensitive and accurate assay of E2 is critically important. Traditional chromatography or immunoassay techniques exhibited good sensitivity and selectivity, but expensive instruments and antibodies may pose cost and stability issues, as well as difficulties in meeting on-site detection requirements. Ultrasensitive, reliable, and on-site detection of E2 at trace level remains a challenge. Hence, developing a simple, ultrasensitive assay to simultaneously achieve accurate detection and rapid visual analysis of E2 is extremely crucial. RESULTS: We developed a versatile dual-mode photoelectrochemical (PEC) and colorimetric biosensor based on isothermal nucleic acid amplification strategy for the ultrasensitive and accurate detection of E2. The method modified titanium dioxide (TiO2) with tungsten selenide (WSe2) nanoflowers to synthesize WSe2/TiO2 heterostructures as a substrate for signal amplification and nanoprobe modification. Isothermal nucleic acid amplification strategy has been proven to be a powerful tool for strong signal amplification. The presence of a target triggered the nucleic acid amplification reaction, and produced a large amount of tDNA that competed with G-quadruplex immobilized on the electrode surface. The remaining G-quadruplex/hemin catalyzed the 4-chloro-1-naphthol (4-CN) to form biocatalytic precipitation (BCP) and ABTS-H2O2 chromogenic reaction, thus, the dual-mode platform was capable of achieving PEC-colorimetric ultrasensitive detection based on the catalytic activity of G-quadruplex/hemin DNAzyme. Within optimal conditions, the dual-mode biosensor exhibited a remarkable detection limit as low as 0.026 pM. SIGNIFICANCE: Benefiting from the superior performance of WSe2/TiO2 and the power signal amplification of isothermal nucleic acid amplification strategy, this aptasensor achieved the ultrasensitive detection of E2. The independent transmission paths of photoelectrochemical and colorimetric provide mutual support and flexible switching, significantly enhancing the overall sensitivity and accuracy of the detection strategy, which can meet the needs for E2 precise quantification and rapid on-site detection.

An ultrasensitive dual-mode aptasensor for patulin based on the upconversion particles and G-Quadruplex-hemin DNAzyme.

Patulin (PAT) is a mycotoxin-produced secondary metabolite that can contaminate foods, causing toxic effects on animal and human health. Therefore, for the first time, we have constructed a "turn-on" dual-mode aptamer sensor for PAT using oleic acid-coated upconversion nanomaterials (OA-UCNPs) and G-Quadruplex-hemin DNAzyme (G4-DNAzyme) as fluorescent and colorimetry probes. The sensor employs aptamers binding to PAT as recognition elements for specific molecule detection. Mxene-Au can be used as a biological inducer to assist OA-UCNPs in controlling fluorescence intensity. In addition, colorimetric signal amplification was performed using the trivalent G4-DNAzyme to increase detection sensitivity and reduce false positives. Under optimal conditions, the dual-mode aptasensor has a detection limit of 5.3 pg mL-1 in fluorescence and 2.4 pg mL-1 in colorimetric methods, respectively, with the wider linear range and limit of detection (LOD) of the colorimetric assay. The combination aptasensor can detect PAT with high sensitivity and high specificity and has broad application prospects in the field of food safety detection.

Engineering the nanozyme hydrogel beads by polyvinyl alcohol/chitosan encapsulation with recyclable and sustainable catalytic activity for visual analysis of hydrogen peroxide.

BACKGROUND: Hydrogen peroxide (H2O2) plays a vital role in human health and have been regarded as a crucial analyte in metabolic processes, redox transformations, foods research and medical fields. Especially, the long-time and excessive digestion of H2O2 may even cause severe diseases. Although conventional instrumental methods and nanozymes-based colorimetric methods have been developed to accomplish the quantitative analysis of H2O2, the drawbacks of instrument dependence, cost-effectiveness, short lifespan, non-portable and unsustainable detection efficacies will limit their applications in different detection scenarios. RESULTS: Herein, to address these challenges, we have proposed a novel strategy for nanozyme (RuO2) hydrogel preparation by the solid support from cross-linked polyvinyl alcohol (PVA) and chitosan (CS) to both inherit the dominant peroxidase-like (POD) activity and protect the RuO2 from losing efficacies. Taking advantages from the hydrogel, the encapsulated RuO2 were further prepared as the regularly spherical beads (PCRO) to exhibit the sustainable, recyclable, and robust catalysis. Moreover, the intrinsic color interferences which originated from RuO2 can be avoided by the encapsulation strategy to promote the detection accuracy. Meanwhile, the high mechanical strength of PCRO shows the high stability, reproducibility, and cyclic catalysis to achieve the recyclable detection performance and long lifetime storage (40 days), which enables the sensitively detection of H2O2 with the detection limit as lower to 15 µM and the wide detection linear range from 0.025 to 1.0 mM. SIGNIFICANCE: On the basis of the unique properties, PCRO has been further adopted to construct a smartphone detection platform to realize the instrument-free and visual analysis of H2O2 in multi-types of milk and real water samples through capturing, processing, and analyzing the RGB values from the colorimetric photographs. Therefore, PCRO with the advanced detection efficacies holds the great potential in achieving the portable and on-site analysis of targets-of-interest.