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The concept of photonanozyme, which refers to enzyme-mimicking nanomaterials with a light-harvesting capacity, has recently gained significant attention. It offers a promising opportunity to use light as a "trigger" to initiate or enhance nanozymatic activity. In this study, a nanocomposite (PdNPs@GOF) based on a graphene oxide framework (GOF) containing ultra-fine palladium nanoparticles (particle size ∼4 nm) in its gallery space was established as a photonanozyme due to its narrow semiconductor-like bandgap. This nanocomposite exhibits excellent peroxidase-mimic and oxidase-mimic activity toward the oxidation of the chromogenic 3,3′,5,5′-tetramethylbenzidine (TMB) substrate under visible light irradiation. PdNPs@GOF was employed to develop a colorimetric assay for the quantitative detection of the important biomarker dopamine (DA) within a wide linear range of 0.05–20 μM based on its dual photonanozymetic activity with a limit of detection (LOD) as low as 0.18 μM. The developed colorimetric assay manifests excellent selectivity toward DA detection when compared against several other antioxidant biothiols, biomolecules, and salts. The colorimetric assay was successfully used to quantitatively detect different concentrations of DA in spiked fetal bovine serum and qualitatively detect DA in mammalian muscle cell lysates. The PdNPs@GOF nanocomposite remains stable, maintaining nearly constant efficiency to detect DA for up to 4 months. This study shows that GOF-based nanocomposites can be used as bifunctional photonanozymes for colorimetric detection of the DA biomolecule with low LOD, good selectivity, and long-term stability. [ABSTRACT FROM AUTHOR]

Despite all the advancements in aqueous synthesis of gold nanoparticles, certain features like one-pot/one-step method with minimal reactants using greener solvents are still demanding. The challenge in the aqueous phase synthesis is to balance the nucleation and precise growth of nanoparticles avoiding aggregation. In this work, we report a unique versatile unexplored molecule aminosalicylate sodium (Na-4-ASA) which functions as a capping, reducing, stabilizing and more interestingly as an encapsulating agent for gold nanoparticles. This multi-faceted molecule showed excellent control in synthesizing monodisperse tunable encapsulated nanoparticles of sizes (60 nm, 53 nm and 12 nm) exhibiting absorbance bands at 560 nm, 540 nm and 520 nm respectively. X-ray diffraction and Fourier Transmission Infra-Red validated crystalline structure and binding of Na-4-ASA onto gold nanoparticles surface respectively. Furthermore, the AuNPs were investigated for their ability to detect metal ions through colorimetric change where purification via centrifugation turned out to be a key parameter in enabling the detection. Selectivity towards Al3+ was observed with the 12 nm sized nanoparticles at 0.5 ppm metal ion concentration. The AuNPs of sizes 60 nm and 53 nm detected Al3+/Cr3+/Fe3+ and Al3+/Fe3+ respectively indicating the impact of size in heavy metal ions detection. The greater the size of AuNPs, lower is the selectivity where detection of three metal ions were observed and vice versa i.e. smaller-sized AuNPs showed high selectivity by detecting single metal ion. Also, the time duration for detection increased with decreasing size of the AuNPs. Finally, LOD for the heavy metal ions Al3+, Cr3+, and Fe3+ were calculated as 67 ppb, 78 ppb, 76 ppb respectively. [ABSTRACT FROM AUTHOR]

Until now, there have been many reports on the regulation of inorganic metal ions on the catalytic activity of nanozymes, but few reports on the regulation of anions (such as NO2−) on enzyme activity. In this work, a copper-molybdenum doped carbon dots (Cu, Mo-CDs) with peroxidase-like (POD) activity was synthesized by simple one-step microwave digestion method. The Cu, Mo-CDs + NO2− system can promote 3,3′,5,5′-tetramethylbenzidine (TMB) oxidizing to blue oxidative product (oxTMB) due to the formation of ∙NO2 free radical. While Hg2+ was introduced into the system, the POD-like activity of Cu, Mo-CDs + NO2− system was inhibited due to the strong interaction and the electron transfer between Cu, Mo-CDs and Hg2+. The formation of ∙NO2 and the electron transfer capability of Cu, Mo-CDs + Hg2+ were confirmed through ESR spectra and FMN experiments. The bioenzyme-free colorimetric assay based on Cu, Mo-CDs nanozyme is used for detection of NO2− and Hg2+, showing lower detection limit (LOD) of 1.63 µg/L for NO2−, 0.13 µg/L for Hg2+, respectively and good recovery from 90.79 to 108.90%. The work paves a new way to design a nanozyme-based colorimetric protocol for traces NO2− and Hg2+ residues in food analysis. [ABSTRACT FROM AUTHOR]

Many studies relating to the preparation of magnetic composites from various raw materials have been reported. However, for the first time, the magnetic Fe‐decorated carbon nanosheets (FeCNs) were prepared using waste facemasks with iron‐containing nose strip as both carbon source and iron source. The uniform decoration of Fe3O4 nanoparticles not only endows carbon matrix with magnetic separation property but also enriches the lamellar structure to furnish more catalytically active sites. The as‐prepared FeCNs nanozymes behave optimal peroxidase‐like activity under pH of 4 and temperature of 50°C, excellent reusability, and substrate affinity. Based on FeCNs, a convenient colorimetric strategy was successfully constructed for flavonoid detection in simulated and real samples. Experimental and theoretical results show that hydroxyl radicals (•OH) and superoxide radical (•O2−) are the major active species in the reactions that are catalyzed by FeCNs in the presence of H2O2. And the generation of these radicals can be attributed to the electron transfer between Fe2+/Fe3+ pairs and H2O2 molecules. This work provides a new way for preparing magnetic carbon‐based nanozymes and realizes the resource utilization of waste facemasks. [ABSTRACT FROM AUTHOR]

Efficient activation of hydrogen peroxide (H2O2) through biomimetic catalysis still faces a major challenge. In this work, inspired by the catalytic pocket of natural peroxidase, Cu single atom (CuSA) and AuCu nanoparticles (AuCuNPs) anchored on nitrogen‐doped carbon skeleton (CuSA‐AuCuNPs/NC) serve as dual active sites that significantly accelerate the charge transfer process and thus achieve efficient H2O2 activation. Meanwhile, the experimental and theoretical calculations show that the well‐established electronic communication effect between CuSA and AuCuNPs results in moderate electronic modifications to CuSA, which promotes the heterolysis of H2O2 and the timely desorption of H2O. As a proof of concept, CuSA‐AuCuNPs/NC show remarkable performance in detecting uranyl ions in seawater. This work provides new insights into the H2O2 activation for colorimetric sensing. [ABSTRACT FROM AUTHOR]

By preparing Cu@CuO aerogel as a nanozyme which exhibits prominent peroxidase-like (POD) activity, an innovative homogeneous electrochemistry (HEC) coupled with the colorimetry dual-model sensing strategy is proposed to detect perfluorooctane sulfonate (PFOS) for the first time. Cu@CuO aerogel accelerates the oxidation process of colorless o-phenylenediamine to form yellow 2,3-diaminophenazinc (DAP), and meanwhile, DAP as an electroactive substance creates a reduction peak current upon the electrochemical measurements. Interestingly, in the presence of PFOS, the POD activity of Cu@CuO aerogel is inhibited since the specific coordination between PFOS and Cu(II) can cover the active sites, resulting in the color of the sensing system becoming light and the peak current of DAP decreasing. This innovative dual-mode detection method showed excellent electrochemical detection of PFOS in the concentration range 10.0 ~ 1125.0 nM with a limit of detection (LOD) as low as 3.3 nM and a LOD of 20.8 nM in the colorimetric detection in the range 62.3 ~ 875 nM. Furthermore, the sensor was successfully used for the analysis of real samples with an RSD value ≤ 6.5%. The successful application of this two-mode sensing method for the determination of PFOS holds promise for the detection of other contaminants in the future. [ABSTRACT FROM AUTHOR]

The extensive usage of organophosphate pesticides (OPs) has posed severe harm to human health and environmental system, but achieving highly effective and on-site detection is still a great challenge. In this work, a novel nanozyme Nb2CTx MXene/bimetallic PdPt (Nb2CTx@PdPt) was synthesized firstly through a simple self-reduction method, and the results show that the as-prepared Nb2CTx@PdPt nanozyme exhibits outstanding peroxidase-like activity. Interestingly, the nanozyme activity of Nb2CTx@PdPt is restrained remarkably in the presence of acetylcholine chloride and acetylcholinesterase while it can be restored through the addition of OPs (selecting glyphosate as a model). Based on this phenomenon, a sensitive colorimetric assay coupled with hydrogel and smartphone for OPs was then constructed. After optimizing various conditions, the designed sensing platform can achieve stable, rapid, and sensitive on-site detection for OPs, showing superior sensing performances: a wide linearity of 1.0 ng mL−1–1.0 µg mL−1 and low detection limit of 0.419 ng mL−1. [ABSTRACT FROM AUTHOR]

The detrimental effects of nitrite (NO2−) on environment as well as living organisms have attracted immense interest to sensitively detect it in the drinking water system. So, for this purpose, we have developed a highly sensible and portable colorimetric NO2− sensor based on the CZ-2 nanocomposite (NC). The three dimensional (3D) with large hierarchical structure CZ-2 NC sensor was formed by the coupling of g-C3N4 nanosheets (NSs) and ZIF-67 nanoparticles (NPs) by a simple hydrothermal process. The prepared sensor was successfully employed to detect NO2−, which manifests higher sensing characteristics like extensive sensitivity with large detection linear range of (1 × 10−3–7.20 × 10−1 μM) having a R2 of 0.999 and a lowest limit of detection (LOD) value of 0.16 ± 0.05 nM. Further, it also manifests excellent reversibility, better stability and durability, optimal reproducibility and superior repeatability. In addition, the sensor also depicts large selectivity towards NO2− and improved practicability in real water sampling. These commendable sensing properties were mainly ascribed to the large conductive structure and highest surface area of the CZ-2 NC structure. Thus, as a result, we analyzed that our fabricated colorimetric sensor was highly potent, its applications in the sensing fields can be explored for future perspective. [ABSTRACT FROM AUTHOR]

Nowadays, modulating and tuning the lattice strain of nanozymes has emerged as a powerful tool to boost the enzymatic performance of the material for sensitive bioassays. Here, a two-step lattice strain tuning method was adopted to synthesize highly curved, porous, and thin palladium nanosheet assemblies (Pd–H NSAs), serving as oxidase mimics. These nanostructures showed excellent oxidase-like activity due to hydrogen intercalation, enabling rapid electron transfer and substrate accumulation. Utilizing Pd–H NSAs, we designed a sensitive colorimetric platform for detecting acid phosphatase and alkaline phosphatase activity with a limit of detection (LOD) of 0.0032 and 0.0057 U/L, respectively. We also created a simple colorimetric assay for malathion detection, achieving a linear range of 0.1–10 μM and an LOD of 0.014 μM. Moreover, we applied a paper-based smartphone sensing platform for real fruit sample analysis, highlighting the potential of our biosensor assay for environmental pesticide detection. [ABSTRACT FROM AUTHOR]

Uric acid serves as a vital diagnostic marker for diseases like arthritis, gout, etc. Accurate quantification of UA is crucial for diagnosis. The hydroxyapatite (HAp), being catalytic in nature, was used as a template for copper nanoparticles (CuNPs) synthesis and for providing surface area for chemical reactions needed for sensing uric acid. HAp was synthesized from waste chicken bones, followed by doping with copper metal salt through calcination. The synthesis of copper hydroxyapatite (Cu‐HAp) nanocomposite was confirmed using different techniques. SEM displayed the nanoporous morphology of the material. The hexagonal crystal structure of HAp was revealed by X‐ray diffraction analysis, and energy dispersive X‐ray analysis showed the successful doping of Cu on HAp. The Cu‐HAp nanocomposite and 3,3′,5,5′‐tetramethylbenzidine (TMB) dye were employed as a new colorimetric sensing platform for uric acid sensing. The fabricated sensing platform detected uric acid with excellent sensitivity (LOD, 0.24 μM) and a wide linear range (1–270 μM). Optimization experiments demonstrated that the proposed sensor performs best at 4 mg of Cu‐HAp nanocomposite, pH 6, with a response time of 100 s. Furthermore, TMB and H2O2 concentrations of 12 and 8 mM were used, respectively. The proposed sensor successfully detected uric acid in physiological samples. [ABSTRACT FROM AUTHOR]

Serotonin (5-HT), an essential neurotransmitter, regulates numerous physiological processes in the human body. Imbalances in 5-HT levels contribute to various health conditions, including neurodegenerative diseases, depression, diabetes mellitus, and serotonin syndrome. 5-HT also functions as a growth factor for tumor cells, influencing various stages of tumor development. Measuring 5-HT concentrations in biological fluids such as blood and serum could facilitate early diagnosis of these conditions. Traditional label-free colorimetric aptasensors often struggle to detect small molecules due to false positives from nonspecific interactions with gold nanoparticles (AuNPs). To address this issue, we propose a novel colorimetric sensing method for specific serotonin detection by eliminating nonspecific AuNP interactions. By incorporating a complementary aptamer hybridization step, our label-free aptamer-based method can selectively detect serotonin while avoiding nonspecific AuNP interactions. We optimized detection conditions and established a calibration curve for 5-HT detection, achieving a limit of detection (LOD) of 2.2 nM. Our method shows high selectivity and sensitivity, even for structurally similar compounds such as dopamine and tryptophan. It successfully quantifies 5-HT directly in complex biological samples with minimal preparation, achieving average recoveries between 92 and 108% (RSD: 9.5–12.9%; n = 5). This label-free aptamer-based approach shows promise for the reliable detection of 5-HT and other small molecules in real biological samples. [ABSTRACT FROM AUTHOR]

Nanozymes have demonstrated superior properties compared to natural enzymes and traditional artificial enzymes in a variety of fields. Although significant progress has been achieved, it remains challenging to develop nanozymes with an adequate catalytic activity. Herein, we, for the first time, bring cerium oxysulfate cluster (Ce-clusters) materials into nanozyme research by a saturated fatty acid regulation strategy due to their potential catalytic activity. It is found that the saturated fatty acids can control the growth, assembly, and size of Ce-clusters in the coprecipitation process, which can enhance the oxidase-like activity of Ce-clusters. With the increase of the alkyl chain length, the catalytic activity gradually decreases because of the strengthened intermolecular interactions between fatty acids and clusters. Notably, the Ce-clusters synthesized with lauric acid present the highest oxidase-like activity among these Ce-clusters. The catalytic activity of nanozyme follows typical Michaelis–Menten kinetics, and the ·O2– and h+ are the main reactive species produced during the catalytic process. Benefiting from the excellent oxidase-like activity, the resultant nanozyme is successfully applied for reductive molecule colorimetric sensing applications. This study not only introduces Ce-clusters into nanozyme research and enriches the oxidase-mimicking nanozyme family but also provides an extremely simple strategy to enhance the catalytic activity of nanozymes, holding great promise in a wide variety of nanozyme applications. [ABSTRACT FROM AUTHOR]

Formaldehyde (FA) is a reactive toxic volatile organic compound (VOC), produced both exogenously from the environment and endogenously within most organisms, and poses significant health risks to humans at elevated concentrations. Consequently, the development of reliable and sensitive FA sensing technologies is crucial for environmental monitoring, industrial safety, and public health protection. This review will provide a concise overview of FA sensing methodologies, highlighting key principles, sensing mechanisms, and recent advancements. The main aim of this review article is to comprehensively discuss recent advancements in FA sensors utilizing small molecules, nanoparticles, organic materials, and polymers, along with their successful applications across various fields, with particular emphasis on in situ FA sensing using polymeric probes due to their advantages over small molecular probes. Additionally, it will discuss prospects for future design and research in this area. We anticipate that this article will aid in the development of next-generation polymeric FA sensing probed with improved physicochemical properties.

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Neurotransmitters are essential chemical messengers required for proper brain function, and any changes in their concentrations can lead to neuronal diseases. Therefore, sensitive and selective detection is crucial. This study presents a fast and simple colorimetric method for dopamine detection using three reagent solutions: AgNP and MPA, Ag/Au nanocomposite, and mercaptophenylacetic acid. TEM images showed a narrow distribution of Ag and Au nanoparticles with average sizes of 20 nm and 13 nm, respectively, with gold nanoparticles bound to the edges of silver nanoparticles. A paper-based biosensor was created using manual wax printing for the colorimetric detection of dopamine. Visual detection onsite showed color changes with both the silver nanoparticles and mercaptophenylacetic acid mixture and the silver–gold nanoparticle composite. Electrochemical detection using a glassy carbon electrode modified with 8 mM mercaptophenylacetic acid demonstrated high selectivity and sensitivity towards dopamine, with a peak in the range of 0.7–0.9 V. Interferences were minimized, ensuring high sensitivity and selective detection of dopamine. [ABSTRACT FROM AUTHOR]

Arsenic, existing in various chemical forms such as arsenate (As(V)) and arsenite (As(III)), demands serious attention in water and environmental contexts due to its significant health risks. It is classified as "carcinogenic to humans" by the International Agency for Research on Cancer (IARC) and is listed by the World Health Organization (WHO) as one of the top 10 chemicals posing major public health concerns. This widespread contamination results in millions of people globally being exposed to dangerous levels of arsenic, making it a top priority for the WHO. Chronic arsenic toxicity, known as arsenicosis, presents with specific skin lesions like pigmentation and keratosis, along with systemic manifestations including chronic lung diseases, liver issues, vascular problems, hypertension, diabetes mellitus, and cancer, often leading to fatal outcomes. Therefore, it is crucial to explore novel, cost-effective, and reliable methods with rapid response and improved sensitivities (detection limits). Most of the traditional detection techniques often face limitations in terms of complexity, cost, and the need for sophisticated equipment requiring skilled analysts and procedures, which thereby impedes their practical use, particularly in resource-constrained settings. Colorimetric methods leverage colour changes which are observable and quantifiable using simple instrumentation or even visual inspection. This review explores the colorimetric techniques designed to detect arsenite and arsenate in water. It covers recent developments in colorimetric techniques, and advancements in the role of nanomaterials in colorimetric arsenic detection, followed by discussion on current challenges and future prospects. The review emphasizes efforts to improve sensitivity, selectivity, cost, and portability, as well as the role of advanced materials/nanomaterials to boost the performance of colorimetric assays/sensors towards combatting this pervasive global health concern. [ABSTRACT FROM AUTHOR]

Metal nanoparticles (MNPs) have gained significant attention due to their multifunctional properties and broad applications in various fields. In this study, we present a novel and sustainable approach for the synthesis of silver nanoparticles (AgNPs) using waste materials, dried banana pith extract (BPE) and rice water. The synthesised AgNPs exhibit a size of 43 nm and zeta potential of −24.1 mV. A maximum temperature rise of 4°C with an efficiency of 41% is achieved within a short time by the photothermal activity. The qualitative colorimetric detection of Fe3+ and its quantitative spectroscopic detection are achieved in a linear detection range of 20–80 μM and with a limit of detection of 8.5 μM. The sensing mechanism is explained in terms of cooperative binding of Fe3+ ions to BPE-AgNPs. A homogeneous, flexible and stable AgNP-rice starch gel is formed. The work offers environmentally conscious nanomaterials for diverse applications. [ABSTRACT FROM AUTHOR]

In this study, a porous coordination network zirconium‐porphyrin‐based nanoparticle with oxygen vacancies (OVs) was prepared using acetic acid and benzoic acid as modulators via a simple hydrothermal method. The presence of OVs was confirmed by various characterization methods and was found to enhance oxygen uptake and activation. This resulted in the generation of more reactive peroxyl radicals (•O2−) and led to an improved oxidase (OXD) mimetic activity. Additionally, it promoted 2,2′‐azino‐bis(3‐ethylbenzthiazoline‐6‐sulfonic acid) (ABTS) oxidation, with a low Km value of 0.07 mM and a high Vmax of 1.47 × 10−7 M·s−1. As aflatoxin B1 (AFB1) inhibits the Pt@PCN‐222‐ABTS nanozyme system, a colorimetric probe for AFB1 detection was constructed. The limit of detection (LOD) was 0.074 µg·L−1. This research presents a novel approach for designing a nanozymatic‐based colorimetric method to analyze trace AFB1 residues in food. [ABSTRACT FROM AUTHOR]

A new salicylamide ethyl rhodamine derivatives RB-SA for multiple signal sensing of Fe3+ was designed and synthesized, and its structure was characterized by H NMR and 13C NMR.RB-SA shows colorimetric and fluorescent dual signal response toward Fe3+ over other tested metal ions in aqueous solution. With the addition of Fe3+, a new absorption peak appears at 560 nm with the color of the solution changing from colorless to red, which can be attributed to the spirolactam ring of probe RB-SA changing to the open form. Simultaneously, a new emission peak at 587 nm was observed with the fluorescent color changing from dark to red emission. Probe RB-SA shows a high sensitivity toward Fe3+ with the low detection limited (LOD) of 10.3 nmol L-1, and the binding constant of 1.03×104 (mol.L-1)-1. [ABSTRACT FROM AUTHOR]

Colorimetric biosensor-based nanozymes have received considerable attention in various fields thanks to the advantages of the simple preparation, good stability, and regulable catalytic activity of nanozymes. In this study, a bimetallic nanozyme Fe3O4@Co3O4/CN was prepared via the high-temperature calcination of Fe3O4-PVP@ZIF-67. The material retained its skeletal structure before calcination, which prevented the aggregation of nanoparticles and exposed more active sites of the nanozyme, substantially enhancing the intrinsic dual enzyme-mimetic activities, including peroxidase- and oxidase-like activities. In particular, Fe3O4@Co3O4/CN with oxidase-like activity catalyzed the colorless tetramethylbenzidine (TMB) to become blue oxTMB with oxygen. Reducing glutathione (GSH) could inhibit the above oxidation reaction. In contrast, with respect to the existence of mercury(II), GSH bound to mercury(II) due to the strong affinity between mercury(II) and -SH, thus eliminating the inhibition and restoring the oxTMB signal. A simple and effective colorimetric sensor was fabricated to detect mercury(II) based on the above principles. The proposed measurement had a linear range of 0.1–15 μM and a limit of detection (LOD) of 0.017 μM. It was shown that the established colorimetric sensing system could be successfully applied to detect mercury(II) in water samples, and the Fe3O4@Co3O4/CN nanozyme proved to be a promising candidate for biosensing application. [ABSTRACT FROM AUTHOR]

We report a silver nanoparticle (AgNP) sensor array to detect SARS-CoV-2 viral particles utilizing five peptide receptors to produce a colorimetric response. We show that the interaction of the virus particles with the peptides interferes with the shift in plasmonic absorbance and hinders the formation of snowflake-like fractal assemblies between the AgNPs and the bridging peptides. The limit of detection in water of the sensor array was 500,000 viral copies/mL. We demonstrate the capabilities of the sensor array to distinguish between SARS-CoV-2 (Beta, Delta, and Omicron variants) from the influenza virus at the 99% confidence level through linear discriminant analysis. The sensor array was also able to discriminate three out of five negative exhaled breath condensate samples from five positive SARS-CoV-2 EBC samples. [ABSTRACT FROM AUTHOR]

The rapid, simple, and selective colorimetric sensing method of cortisol has been successfully developed using AuNPs modified with 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (AuNPs-AHMT). The principle of this method is based on the color change from wine red to purple (redshift) when AuNPs-AHMT interacts with cortisol. The hydrogen bonding between the hydroxyl group from cortisol and the amine group from AHMT induces the aggregation of AuNPs. The modification of the AuNPs surface with AHMT aims to increase its stability. The properties of AuNPs and AuNPs-AHMT were characterized by UV-vis spectrophotometer. The interaction between AuNPs-AHMT and cortisol was studied by UV-vis and FTIR spectroscopies. The proposed method was optimized and validated. Au(III) was reduced to AuNPs at an optimum NaBH4 concentration of 1.0 mM. Validation of the proposed method showed good analytical performance with linearity from 1.0–50.0 nM, accuracy 91.07–102.77%, intra-day precision

The anchoring of two-dimensional nanosheets (2D) with Prussian blue nanocubes has exhibited the advantage of high electron conductivity and better catalytic application. Herein, we reported the successful fabrication of molybdenum disulfide-supported Prussian blue nanocubes (MoS2@NiCo-PBANCs) and compared the bare MoS2 and NiCo-PBNCs for effective peroxidase, such as catalytic activity, which can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by the generation of H2O2, ensuring the appearance of blue colored solution. The MoS2@NiCo-PBANCs exhibited an excellent colorimetric sensing performance toward glucose in urine samples. Therefore, the present method demonstrates the high sensitivity, selectivity, simplicity, and fast colorimetric sensing ability for H2O2 and glucose detection. The synergistic effect of MoS2@NiCo-PBNCs reveals lower detection limits of 0.0075 µM and 0.01 µM for H2O2 and glucose, respectively. The exclusive structural morphology, excellent stability, large surface area, and high catalytic property have been utilized to achieve the closer interaction of glucose oxidase and TMB with MoS2@NiCo-PBANCs to oxidize glucose to gluconic acid. Overall, we utilized the MoS2@NiCo-PBNCs as a novel composite nanomaterial for the application of H2O2 and glucose peroxidase-like mimics in the urine sample. [ABSTRACT FROM AUTHOR]

This paper reviews the development of research on one-dimensional self-assembly of gold nano-particles. The experimental strategies to realize 1D self-assembly of gold nanoparticles are first introduced; the applications of gold self-assembled 1D nanomaterials in colorimetric sensing, Raman enhancement, electronic devices and biomedicine are then summarized; remarks on future directions of this research topic are presented. [ABSTRACT FROM AUTHOR]

Nitrite (NO2−) is an anionic species that holds paramount significance in cellular signalling pathways and have crucial physiological functions. Nevertheless, an excessive accumulation of nitrite ions can induce detrimental effects, including intrauterine growth restriction, birth abnormalities, and methemoglobinemia. Thus, quantitative detection of nitrite ions for in vivo and invitro studies is very important. This review presents a comprehensive overview of colorimetric techniques employed for the detection of nitrite ions. Various methodologies have been developed, encompassing diazo reaction‐based sensing, nitrosation reaction‐based sensing, redox reaction‐based sensing, non‐covalent interaction‐based sensing, and other approaches. Each method will be systematically discussed and critically evaluated in the context of this review. [ABSTRACT FROM AUTHOR]

The use of functionalized gold nanoparticles (GNPs) as a colorimetric sensor for heavy metal ions has been extensively studied due to their unique optical properties and ease of functionalization. Amino acid-functionalized GNPs have emerged as a promising platform for colorimetric sensing of various pollutants, including metal ions. However, the differential metal ion selectivity of the GNPs functionalized with different amino acids remains poorly understood. This study describes the synthesis and functionalization of Tween-20-stabilized citrated gold nanoparticles (Cit-T20-GNPs) using various amino acids and their interaction with metal ions. Tween-20 was found to be essential to provide stability to the nanoparticles for functionalization. The morphology, hydrodynamic diameter, and zeta potential of the GNPs were characterized using transmission electron microscopy and dynamic electrophoretic light scattering analysis. The GNPs were then functionalized with L-threonine, L-glutamine, L-alanine, L-tryptophan, L-cysteine, L-methionine, L-arginine, L-lysine, L-proline, and glycine. The metal-induced aggregation of the functionalized GNPs was studied using twelve different metal ions. At the experimental pH (5–6), the colloidal integrity of most amino acid-functionalized Cit-T20-GNPs remained intact upon treatment with the metal ions, except for Cit-T20-Arg-GNPs and Cit-T20-Lys-GNPs. These two GNPs showed interaction with most metal ions, which led to their aggregation. The study provides insights into the specific interaction and affinity of metal ions toward different amino acid ligands and highlights the potential of designing ion-specific colorimetric sensors. The possible mechanism behind these interactions has also been speculated. [ABSTRACT FROM AUTHOR]

This paper introduces a research-based comprehensive experiment involving the synthesis of quinoline derivatives and investigations on the effect of their structures on the colorimetric sensing performance of anions. During this experiment, students will learn and master the synthesis and characterization methods used for quinoline heterocyclic compounds and their derivatives. Based on the principle of organic small molecule sensing and recognition, students will learn to use ultraviolet-visible absorption spectroscopy instrumentation and study the anion sensing and recognition performance of quinoline compounds (P1, P2, and P3) as probes. Using the spectral data processed by Origin and visualized colorimetric images, students can better intuitively understand the anion sensing and recognition performance of different probes, along with the significance of the probe molecular structure in regulating sensing performance. [ABSTRACT FROM AUTHOR]

N-doped carbon Co/CoOx with laccase-like activity was directionally designed by pyrolyzing Co-coordination polymer and applied to detect epinephrine, which revealed a new preparation strategy for laccase mimics. The formation mechanism of the N-doped carbon Co/CoOx nanozyme was reconnoitered by a thermogravimetric-mass spectrometry system (TG-MS). N-doped carbon Co/CoOx exhibited outstanding laccase-like activity, and the Michaelis–Menten constant and maximum initial velocity were calculated to be 0.087 mM and 0.0089 μM s–1, respectively. Based on this principle, a simple colorimetric sensing platform was developed for the quantitative detection of epinephrine, which can be used to diagnose pheochromocytoma. In addition, the visual platform for detecting epinephrine exhibited a linear range of 3 to 20 μg mL−1 and a calculated detection limit of 0.42 μg mL−1. Therefore, the proposed colorimetric sensing platform is a promising candidate to be applied in precise early pheochromocytoma diagnosis. [ABSTRACT FROM AUTHOR]

Optical sensors have drawn considerable attention these days due to their quick, easy and on-site detection of metal ions. In this research, a Schiff base "4-(Benzylideneamino)-1,5-dimethyl-2-phenyl-1,2-dihydropyrazol-3-one (V-AAP)" was studied for its naked eye chemosensing abilities to detect metallic ions, i.e., Fe2+, Fe3+, Mn2+, Co2+, Cu2+, Zn2+, Ag+, Hg2+, Pb2+ and AsO2−. This colorimetric probe exhibited selective color change from colorless to brownish yellow, pale yellow and greenish yellow for Fe2+, Fe3+ and AsO2− ions, with detection limits of 9.986 × 10–7 M (0.056 ppm), 1.285 × 10–6 M (0.072 ppm) and 2.465 × 10–5 M (2.64 ppm), respectively. Moreover, binding ratios of V-AAP and Fe2+, Fe3+ and AsO2− ions were calculated to be 1:1 with binding constants 1.22 × 102 M−1, 1.30 × 103 M−1 and 9.30 × 101 M−1, correspondingly. [ABSTRACT FROM AUTHOR]

Although significant advances have been witnessed in the application of nanozymes in recent years, exploring new strategies to enhance the enzyme-like activity of nanozymes is of urgent importance. Herein, we investigate the feasibility of accelerating the peroxidase-like reaction rate of CuO nanostructures through Fe doping. The coprecipitation method was used to synthesize Fe-doped CuO (Fe-CuO) nanozymes, and the results indicate that the diversified valence of Fe benefits the redox reaction driven by CuO-based nanozymes. With the improved peroxidase-like activity, the Fe-CuO nanozyme enables the significant chromogenic oxidation reaction of 3,3′,5,5′-tetramethylbenzidine (TMB), facilitating the construction of a visual sensing platform for the sensitive and selective determination of ascorbic acid. Under optimal conditions, the absorbance at 652 nm decreases linearly with the concentration of ascorbic acid in the range of 5–50 μM, with a limit of detection as low as 4.66 μM. This work exemplifies the activity enhancement for peroxidase-mimicking nanozymes with a metal-doping strategy and provides a broad prospect for the design of more high-performance nanozymes for biosensing applications.

Neurotransmitters are essential chemical messengers required for proper brain function, and any changes in their concentrations can lead to neuronal diseases. Therefore, sensitive and selective detection is crucial. This study presents a fast and simple colorimetric method for dopamine detection using three reagent solutions: AgNP and MPA, Ag/Au nanocomposite, and mercaptophenylacetic acid. TEM images showed a narrow distribution of Ag and Au nanoparticles with average sizes of 20 nm and 13 nm, respectively, with gold nanoparticles bound to the edges of silver nanoparticles. A paper-based biosensor was created using manual wax printing for the colorimetric detection of dopamine. Visual detection onsite showed color changes with both the silver nanoparticles and mercaptophenylacetic acid mixture and the silver–gold nanoparticle composite. Electrochemical detection using a glassy carbon electrode modified with 8 mM mercaptophenylacetic acid demonstrated high selectivity and sensitivity towards dopamine, with a peak in the range of 0.7–0.9 V. Interferences were minimized, ensuring high sensitivity and selective detection of dopamine.

Colorimetric biosensor-based nanozymes have received considerable attention in various fields thanks to the advantages of the simple preparation, good stability, and regulable catalytic activity of nanozymes. In this study, a bimetallic nanozyme Fe3O4@Co3O4/CN was prepared via the high-temperature calcination of Fe3O4-PVP@ZIF-67. The material retained its skeletal structure before calcination, which prevented the aggregation of nanoparticles and exposed more active sites of the nanozyme, substantially enhancing the intrinsic dual enzyme-mimetic activities, including peroxidase- and oxidase-like activities. In particular, Fe3O4@Co3O4/CN with oxidase-like activity catalyzed the colorless tetramethylbenzidine (TMB) to become blue oxTMB with oxygen. Reducing glutathione (GSH) could inhibit the above oxidation reaction. In contrast, with respect to the existence of mercury(II), GSH bound to mercury(II) due to the strong affinity between mercury(II) and -SH, thus eliminating the inhibition and restoring the oxTMB signal. A simple and effective colorimetric sensor was fabricated to detect mercury(II) based on the above principles. The proposed measurement had a linear range of 0.1–15 μM and a limit of detection (LOD) of 0.017 μM. It was shown that the established colorimetric sensing system could be successfully applied to detect mercury(II) in water samples, and the Fe3O4@Co3O4/CN nanozyme proved to be a promising candidate for biosensing application.

It is valuable to develop simple and environmentally friendly methods for converting biowaste into functional nanomaterials with multiple applications. However, there are few reports on the facile preparation of multifunctional carbon–metal nanocomposites based on biowastes and their application from sensing to information technology. Herein, we used fish scale-derived carbon nanoparticles (FSCN) as reducing agents to directly and facilely prepare multifunctional carbon–gold nanocomposites (FSCN-AuNPs) in one step. Our prepared FSCN-AuNPs have multisignal response capabilities and can be used for colorimetric and fluorescence quantitative sensing of Pb2+ and Cu2+ with detection limits of 86.29 nM (for Pb2+) and 53.74 nM (for Cu2+), respectively. Additionally, FSCN-AuNPs can detect Pb2+ in milk and serum, as well as Cu2+ in water and serum. The multisignal selective responses of FSCN-AuNPs can be converted into binary strings by setting thresholds, which were further applied to encrypt and hide two types of information (like text and two-dimensional pattern information). Overall, this research not only promotes the preparation and comprehensive application of multifunctional carbon–metal nanocomposites but also accelerates the cross-integration of molecular science, such as the integration of molecular sensing and molecular information science. [ABSTRACT FROM AUTHOR]

Phenolic compounds are one of the main organic pollutants in the environment that can seriously affect ecosystems, even at very low concentrations. Due to the resistance of phenolic compounds to microorganisms, conventional biological treatment methods face challenges in effectively addressing this pollution problem. In this study, a novel laccase mimic (Tris-Cu nanozyme) is prepared using a simple and rapid synthesis strategy based on the coordination of copper ions and amino groups in Tris(hydroxymethyl)aminomethane (Tris). It is found that the Tris-Cu nanozyme exhibits good catalytic activity against a variety of phenolic compounds, the Km, Vmax and Kcat are determined to be 0.18 mM, 15.62 μM·min−1 and 1.57 × 107 min−1 using 2,4-dichlorophenol (2,4-DP) as the substrate, respectively. Then, based on the laccase-like activity of the Tris-Cu nanozyme, a novel colorimetric method for 2,4-DP (the limit of detection (LOD) = 2.4 μM, S/N = 3) detection in the range of 10–400 μM was established, and its accuracy was verified by analyzing tap and lake water samples. In addition, the Tris-Cu nanozyme shows excellent removal abilities for six phenolic compounds in experiments. The removal percentages for 2,4-DP, 2-chlorophenol (2-CP), phenol, resorcinol, 2,6-dimethoxyphenol (2,6-DOP), and bisphenol A (BPA) are 100%, 100%, 100%, 100%, 87%, and 81% at 1 h, respectively. In the simulated effluent, the Tris-Cu nanozyme maintains its efficient catalytic activity towards 2,4-DP, with a degradation percentage of 76.36% at 7 min and a reaction rate constant (k0) of 0.2304 min−1. Therefore, this metal–organic complex shows promise for applications in the monitoring and degrading of environmental pollutants. [ABSTRACT FROM AUTHOR]

The use of peroxidase mimics has great potential for various real applications due to their strong catalytic activity. Herein, a facile strategy was proposed to directly prepare CuO@g-C3N4 by Cu-MOF derivatization and demonstrated its efficacy in constructing a multiple enzymatic cascade system by loading protein enzymes onto it. The resulting CuO@g-C3N4 possessed high peroxidase-like activity, with a Michaelis constant (Km) of 0.25 and 0.16 mM for H2O2 and 3,3',5,5'-tetramethylbenzidine (TMB), respectively. Additionally, the high surface area of CuO@g-C3N4 facilitated the loading of protein enzymes and maintained their activity over an extended period, expanding the potential applications of CuO@g-C3N4. To test its feasibility, CuO@g-C3N4/protein oxidase complex was prepared and used to sense the ripeness and freshness of fruits and meat, respectively. The mechanism relied on the fact that the ripeness of fruits increased and freshness of food decreased with the release of marked targets, such as glucose and xanthine, which could produce H2O2 when digested by the corresponding oxidase. The peroxidase mimics of CuO@g-C3N4 could then sensitively colorimetric detect H2O2 in present of TMB. The obtained CuO@g-C3N4/oxidase complex exhibited an excellent linear response to glucose or xanthine in the range of 1.0–120 μmol/L or 8.0–350 μmol/L, respectively. Furthermore, accurate quantification of glucose and xanthine in real samples is achieved with spiked recoveries ranging from 80.2% to 120.0% and from 94.2% to 112.0%, respectively. Overall, this work demonstrates the potential of CuO@g-C3N4 in various practical applications, such as food freshness detection. [ABSTRACT FROM AUTHOR]