Nanozyme-Enabled Analytical Chemistry

Portable colorimetric probe based on high-entropy alloy nanozyme for rapid detection of fruit freshness

Freshness, crucial for quality, especially in nutrient-rich fruits and vegetables, declines with nutrient degradation during storage. Measuring antioxidant content effectively indicates freshness, but traditional methods like HPLC and MS are expensive and non-portable. Nanozyme-based colorimetric sensors offer a faster, cost-effective, and portable alternative. Here, five-element high-entropy (HE)-alloys were synthesized via a simple co-precipitation method, and their peroxidase-like catalytic properties were studied. Alloys containing Zn, Ni, and Fe showed notable activity, with CuZnCoNiFe performing best, followed by CuMgZnNiFe and CuZnMnNiFe. Activity was attributed to the high proportion of Cu2+ and the electrostatic effects, as indicated by zeta potential, ICP-MS, and XPS analyses. Then, CuZnCoNiFe was used to create a portable, smartphone-assisted colorimetric paper sensor, capable of rapid detecting antioxidant levels and distinguishing naturally or artificially ripened fruits, providing a practical tool for assessing food freshness.

A trifunctional surface ligand-directed general synthesis of 2D MOF hybrid nanozymes for customizable applications

Two-dimensional metal-organic frameworks (2DMOFs)-based hybrid nanozymes integrate the excellent catalytic activity of 2DMOFs with intriguing properties of other functional nanomaterials, offering great opportunities in biosensing and catalysis applications. However, the versatile synthesis of 2DMOF-based hybrid nanozymes remains challenging due to the difficulty in precisely controlling interactions between 2DMOFs and other functional nanocomponents. In this work, a trifunctional surface ligand-mediated strategy was developed to rationalize these interactions and promote the general synthesis of 2DMOF hybrid nanozymes. The surface ligand not only prevents the nanocomponents from self-aggregation and keeps 2DMOF monodispersed to form ultrathin nanosheets, but also drives the assembly of 2DMOF and nanocomponent to form composite nanostructures. Using this strategy, a series of customizable hybrid nanozymes exhibiting synergistically catalytic activity, recyclability, cascade catalysis, and photo-enhanced catalysis were fabricated, respectively. Moreover, these hybrid nanozymes displayed excellent performance in H2O2 detection, glucose sensing, and pollutant degradation. The successful demonstration of a general and facile strategy for synthesizing two-dimensional metal-organic framework (2D MOF) hybrid nanozymes paves the way for the development of 2D MOF-based nanomaterials and nanozymes with customizable functions. These materials hold significant potential in various applications, including catalysis, biosensing, disease diagnosis, and energy conversion.

Catalytic preference-enabled exclusive bimodal detection of methyl-paraoxon in complex food matrices using double site-synergized organophosphorus hydrolase-mimetic fluorescent nanozymes

Pesticide sensing crucially safeguards food safety and public health against environmental and health hazards. While oxidoreductase-type nanozymes (peroxidase and oxidase) have been widely used in optical pesticide detection, their susceptibility to redox interference as well as poor target specificity limits practical applications. To overcome the deficiencies, here we developed Ca2+-chelated 2-aminoterephthalic acid on nanosized ceria (Ca-ATPA@CeO2) as an organophosphorus hydrolase mimic. This design integrates stable fluorescence and dual-site catalytic activity to specifically detect methyl-paraoxon (MP) in complex food matrices. The synergy between Ca2+ (hard Lewis acid) and CeO2 creates dual active sites to catalyze MP hydrolysis into yellow p-nitrophenol (pNP), and the latter quenches nanozyme fluorescence via inner filter effect. The system enables cross-validated quantification of MP in complex samples, eliminating redox interference through target-specific catalysis. The bimodal "on" colorimetric (pNP color signal) and "off" fluorescence (nanozyme fluorescence intensity) detection achieved linear ranges within 1-200 μM, providing detection limits of 1.43 μM and 0.087 μM, respectively. Our work proposes a reliable strategy for selective MP detection that can avoid redox interference, also providing a simple yet efficient design of high-activity fluorescent hydrolase mimics with broadened applications in food safety analysis and beyond.

Breaking the conventional: Ligand-triggered Zn-MOF nanozyme with unusual oxidase activity for dual-channel sensing of benfuracarb

The activity of MOF-based nanozyme mainly relies on the metal sites, the development of organic ligands with intrinsic enzymatic-activity is of great significance for nanozyme-mediated sensors but it remains a huge challenge. Herein, the oxidase-like activity of an azo ligand, 4,4'-azodipyridine (AZPY), was first discovered by rational screening. A new Zn-MOF (JLU-MOF221) was successfully constructed based on the pillar-layered strategy to achieve well-isolated AZPY ligand and robust framework. JLU-MOF221 exhibited excellent affinity for 3,3',5,5'-tetramethylbenzidine (TMB) (Km: 0.180 mM; Kcat: 5.72 s-1), as well as a rapid response time (60 s) and high storage stability (87 % activity over 8 months). The study revealed the unique four-electron O2-to-H2O reaction pathway without relying on active oxygen species. Moreover, combining the hydrolysis behavior of benfuracarb and nanozyme inhibition strategy, a colorimetry and fluorescent dual-channel sensor was firstly developed towards benfuracarb, reaching a low limit of detection of 130 ng/mL and 76 ng/mL, respectively. The breakthrough in enzyme activity of organic ligands not only provides an efficient alternative for the traditional assay to detect benfuracarb, but also greatly promotes nanozyme-mediated sensors to a new stage.

Iron/cobalt co-doped boron quantum dots as nanozymes with peroxidase-like activities and the nanozyme-involved cascade catalysis system for ratiometric fluorescence and dual-mode visual detection of glutamate

To further explore the boron-involved nanomaterials toward efficient applications in chemo/bio sensing and detection fields, this work reports facile preparation of the emerging iron/cobalt co-doped boron quantum dots (Fe/Co@BQDs) that were explored as new artificial nanozymes for ratiometric fluorescence (FL) and visual detection of glutamate (Glu). In the presence of glutamate oxidase (GLOD), Glu was oxidized to produce H2O2, and then the H2O2 was catalyzed by Fe/Co@ BQDs nanozymes to produce hydroxyl radical (•OH). Afterwards, the •OH induced FL quenching responses of rhodamine B (RhB) and Fe/Co@BQDs. Therefore, a new nanozyme-assisted cascade catalysis platform was explored, consisting of Fe/Co@BQDs, GLOD, and RhB. The platform was successfully used for ratiometric FL sensing of Glu and liquid/solid dual-channel FL visual semi-quantitative detection of Glu. The platform exhibits a board linear detection range of 1-500 µM, a low limit of detection of 0.3 µM, highly selective ratiometric FL responses on Glu over potential interferents, and high-performance practical detection of Glu in biological samples. Experimental results verify high peroxidase-like activities of Fe/Co@BQDs that enable efficient applications for unique enzymatic reactions and nanozyme-involved cascade catalysis reactions. The platform can facilitate further development of other types of metal-doped nanomaterials with natural biological enzyme-like activities and their promising applications, especially chemo/bio sensing, bioimaging and therapeutics at the levels of living cells and small animals.

Utilizing the Thermostability of Nanozymes for Joule Heating to Remove Background Peroxidase Activities in Lateral Flow Assays

Lateral flow assays (LFAs) are essential for point-of-care testing. The use of peroxidase-mimicking nanozymes as catalytic labels is an actively developing direction in LFA, primarily focused on enhancing sensitivity. However, endogenous peroxidases, naturally present in various samples, can interfere with nanozyme signal amplification, leading to a high background signal and making visual detection more challenging. The issue of endogenous peroxidases is particularly significant for LFAs as wash-free biosensors. In this study, we showcase the remarkable thermostability of nanozymes in contrast to enzymes, applied to the analytically relevant use of lateral flow assays for the detection of aflatoxin B1. By employing Joule heating in a portable battery-powered device, the test strips were rapidly heated to 75-80 °C after completing the conventional LFA process. This heating caused thermal denaturation of endogenous peroxidases without affecting the Au@Pt nanozymes. As a result, substrate oxidation on the test strip was carried out solely by the Au@Pt nanozymes, which reduced background noise and improved the limit of detection by a factor of 3.5 compared to the assay without heating.

High-visual-resolution colorimetric immunoassay with attomolar sensitivity using kinetically controlled growth of Ag in AuAg nanocages and poly-enzyme-boosted tyramide signal amplification

Colorimetric enzyme-linked immunosorbent assays (CELISAs) have long been used for protein biomarker detection in diagnostics. Unfortunately, as confined by the monochromatic nature of detection signals and the limited catalytic activity of enzymes, CELISAs suffer from poor visual resolution and low sensitivity, hindering their effectiveness for early diagnostics in resource-limited settings. Herein, we report an ultrasensitive, high-visual-resolution CELISA (named PE-TSA-AuAg Cage-CELISA) that combines kinetically controlled growth of Ag in AuAg nanocages with poly-enzyme-boosted tyramide signal amplification (PE-TSA), enabling visual semiquantitative detection of protein biomarkers at attomolar levels with the naked eye. Specifically, the assay begins with the formation of sandwich-type immunocomplexes on a microplate in the presence of targets, and the labeled poly-horseradish peroxidases (poly-HRPs) initiate TSA, resulting in attaching numerous alkaline phosphatases (ALPs) on the microplate. The ALPs further catalyze ascorbic acid 2-phosphate to produce ascorbic acid, triggering the kinetically controlled growth of Ag inside AuAg nanocages. This process induces vivid multicolor variations spanning the visible spectrum range of 691∼477 nm, allowing for visual semiquantitation of protein biomarkers at ultralow levels without requiring specialized equipment. Using interleukin-12 as a model protein biomarker, we demonstrate that the PE-TSA-AuAg Cage-CELISA achieves a visual semiquantitative limit of detection (LOD) of 5 fg mL-1 (67 aM) and an instrumental quantitative LOD of 0.71 fg mL-1 (9.5 aM), representing an 853-fold improvement compared to the conventional HRP-based CELISA. Our findings suggest that the PE-TSA-AuAg Cage-CELISA has the potential to serve as an affordable and effective biosensing platform for early diagnostics in resource-limited settings.

Mimicking phosphatase function using Ce4+-modified metal-organic frameworks as heterogeneous catalysts for the discrimination of phosphorylated peptides

In this study, a general approach to prepare metal-organic framework (MOF)-based heterogeneous catalysts is proposed. The Ce4+-modified MOFs were obtained by the co-precipitation of catalytic active Ce4+ ions and catalytic inactive MOFs (ZIF-67, MOF-5, and ZIF-8). The Ce4+-modified MOFs retained the phosphatase-like activity of Ce4+ ions and were used for the fluorescent detection of phosphorylated amino acids by using o-phospho-L-tyrosine (p-Tyr) as a model target. Using Ce4+-modified ZIF-67 particles as the heterogeneous catalysts, the linear range for p-Tyr detection is 1-10 µM with a detection limit of 0.26 µM. Compared with homogeneous Ce4+ ion catalysts, a significant improvement in the sensitivity was achieved by using Ce4+-modified ZIF-67 particles as heterogeneous catalysts (from 11.21 to 0.26 µM). As the proposed method holds great promise in the fluorescent detection of phosphorylated amino acids, the Ce4+-modified ZIF-67-based catalytic system was further used for the discrimination of normal peptides and phosphorylated peptides with excellent resolution.

Prospects for the use of nanozyme-based electrochemical and colorimetric sensors for antibiotic detection

Rapid and accurate monitoring of residual antibiotic concentrations is of great importance in environmental monitoring. Therefore, research is active to develop new methods for analyzing antibiotics. Biosensors, including those based on nanozymes, are very successful for antibiotic analysis. Nanozymes (nanomaterials with enzymelike activity) have emerged as a promising solution offering improved stability, cost-effectiveness, and versatility, as compared with natural enzymes. The use of nanozyme-based electrochemical and colorimetric sensors for detecting antibiotics remains underexplored. This review presents the main prospects for the use of electrochemical and colorimetric nanozyme sensor systems to detect antibiotics. It identifies major shortcomings of these platforms and ways to deal with them. Finally, it highlights the advantages of these sensors over other systems and explains the main mechanisms of signal generation for antibiotic detection.

Ultrasensitive colorimetric detection of deoxynivalenol in infant milk powder based on the inhibitory effect of silver ions on the peroxidase-like activity of Ni@Pt nanoparticles

Deoxynivalenol, a hazardous mycotoxin, poses significant health risks to humans and animals, necessitating highly sensitive detection methods due to its low abundance in food. Herein, we present a colorimetric sensing strategy for deoxynivalenol detection based on the inhibitory effect of silver ions on the peroxidase-like activity of Ni@Pt nanoparticles. Silver ions adsorb onto the surface of Ni@Pt nanoparticles, blocking the active site and consequently impeding their catalytic activity. By integrating antigen-antibody interactions with the biotin-streptavidin system, a specific aptamer can be introduced to chelate silver ions, thereby modulating the activity of Ni@Pt nanoparticles for signal readout through the 3,3',5,5'-tetramethylbenzidine/hydrogen peroxide system. This method achieves a detection limit of 47.4 pg/mL, surpassing traditional enzyme-linked immunosorbent assays and rivaling the sensitivity of precision instrumental analysis. Furthermore, this colorimetric method demonstrates robust recovery and has been successfully challenged deoxynivalenol detection in infant milk powder samples, highlighting its potential for practical applications.

MOF-engineered Cu2O nanozymes with boosted peroxidase-like activity for colorimetric-fluorescent dual-mode detection of deoxynivalenol

The development of a high sensitivity biosensor for the detection of highly toxic deoxynivalenol (DON) is vital for human health and food security. In this work, by integrating metal-organic frameworks (MOF) with cubic Cu2O nanoparticles (Cu2O@MOF), the nanocomposite achieved a 4.8-fold increase in specific surface area compared to pristine Cu2O, which synergistically enhanced its peroxidase-like (POD) activity through optimized substrate affinity and accelerated charge transfer. Consequently, based on the marriage properties of POD activity and fluorescence signal from Cu2O@MOF nanoparticles and carbon dots (CDs), a colorimentric-fluorescent dual-mode biosensor was constructed for DON detection. Concurrently, the competitive binding of DON with immobilized antigens on Cu2O@MOF-CDs results in antibody displacement, leading to progressive reduction of captured probes with increasing DON concentrations, thereby inducing proportional attenuation in both colorimetric and fluorescence signal intensities. Under the optimum conditions, the established biosensor achieved a detection limit of 0.0018 ng/mL for DON. Furthermore, the prepared dual-mode biosensor was successfully applied to detect DON in tap water, wheat and corn, demonstrating its practical utility for real-world applications. Overall, this work not only advances nanozyme design through MOF-mediated interface engineering but also provides a rapid, accurate, and field-deployable strategy for monitoring mycotoxins in complex matrices.

Atomic Pt-Layer-Coated Au Peroxidase Nanozymes with Enhanced Activity for Ultrasensitive Colorimetric Immunoassay of Interleukin-12

Interleukin-12 (IL-12), a crucial biomarker for immune and inflammatory responses, plays a pivotal role in diagnosing and managing diverse pathological conditions. Although colorimetric enzyme-linked immunosorbent assays (CELISAs) have been extensively employed to detect IL-12 in biological samples, their sensitivity is inherently limited by the catalytic efficiency of enzyme labels, presenting substantial challenges in achieving ultrasensitive detection and enabling pre-symptomatic diagnosis of diseases. In this study, we address this limitation by developing a novel peroxidase nanozyme, featuring ultrathin Pt skins consisting of only ~4 atomic layers, coated on Au nanoparticles (denoted as Au@Pt4LNPs). These Au@Pt4LNPs exhibit remarkable catalytic performance, achieving a ~1063-fold enhancement in peroxidase-like activity compared to horseradish peroxidase (HRP), while minimizing Pt consumption, thereby improving Pt utilization efficiency and reducing costs. This advancement facilitates the construction of an ultrasensitive CELISA capable of detecting IL-12 at femtomolar concentrations. Using Au@Pt4LNPs as the signal labels, the developed CELISA demonstrates a quantitative detection range from 0.1 to 100 pg mL-1, with a limit of detection (LOD) as low as 0.084 pg mL-1 (1.1 fM), offering ~10 times greater sensitivity than the HRP-based CELISA. This study highlights the potential of Au@Pt4LNP nanozymes as advanced signal labels, opening new avenues for next-generation ultrasensitive bioassays.

Amino-Acid-Engineered Bionanozyme Selectivity for Colorimetric Detection of Human Serum Albumin

Nanozymes are emerging nanomaterials owing to their superior stability and enzyme-mimicking catalytic functions. However, unlike natural enzymes with inherent amino-acid-based recognition motifs for target interactions, manipulating nanozyme selectivity toward specific targets remains a major challenge. In this study, we introduce the de novo strategy using the supramolecular assembly of l-tryptophan (l-Trp) as the recognition amino acid with copper (Cu) ions for creating a human serum albumin (HSA)-responsive bionanozyme. This amino-acid-engineered bionanozyme enables selective colorimetric detection of HSA, a critical urinary biomarker for kidney diseases, overcoming the challenge that HSA is neither a typical substrate nor an inhibitor for most nanozymes. Kinetic studies and competitive tests reveal that HSA subdomain IIIA binding to l-Trp sites limits the electron-transfer-induced structural changes of l-Trp-Cu chelate rings, resulting in noncompetitive inhibition. This inhibition effect is significantly stronger than that observed for canonical amino acids, common proteins, and urinary interference species. Colorimetric monitoring of bionanozyme activity enables sensitive HSA detection with a detection limit of 1.3 nM and a quantification range of 2 nM to 10 μM. This approach is exceptionally more sensitive and offers a broader detection range compared to conventional colorimetric and fluorescent methods, suitable for diagnostics across various clinical stages of disease. This innovative rational strategy to designing and manipulating selective nanozyme-target interactions not only addresses the limitations of nanozymes but also expands their precise applications in complex biological systems.

Signal "Off-On Model'' for Colorimetric Sensing Proanthocyanidin B2 Achieved by the Organic Solvent-Processed Amorphous BiVO4 Nanozyme

Here, we report a "off-on model"-based colorimetric sensor without the assistance of H2O2, achieved by organic solvent-processed amorphous BiVO4 nanoparticles favorable for large-scale manufacturing. The amorphous material beyond traditional crystalline nanozymes has both vanadium vacancy (Vv) and oxygen vacancy (Ov), as well as single oxidase-like activity with both hydroxyl radical (•OH) and superoxide anion (O2•-) as electron acceptors. Despite the high enzymatic performance, the dual-defect-rich amorphous BiVO4 preserves good long-term activity in either buffer solution or the solid state. The specially designed BiVO4 is capable of accelerating TMB oxidation in the presence of polyphenols, thus leading to an interesting signal-intensified colorimetric response. This is probably due to the coordination of the ortho dihydroxyl group in polyphenols with the catalyst by replacing the surface-adsorbed NO3-, which results in faster charge transfer between BiVO4 and substrate and, thus, more rapid depletion of radicals for TMB oxidation. Based on these findings, a sensor platform for proanthocyanidin (PAC) B2 is established with a limit of detection (LOD) as low as 65 nM and good specificity. The sensor shows higher sensitivity than the standard Porter method (LOD: 0.29 μM) and comparable accuracy when analyzing PAC B2 in commercially available grape seed capsules, with quantitative recoveries varying from 104.0 to 108.3% and relative standard deviations ranging from 1.7 to 5.7%. To date, this is the only nanozyme-based chemical sensor that is active for the signal "off-on model" for the detection of reducing polyphenols. Also, this method seems quite general, and it can be used for sensing of a series of specific polyphenols in addition to PAC B2.

Multiple recognition-powered abiotic bimetallic oxide nanozyme-based colorimetric platform for the selective detection of allergen β-lactoglobulin

β-lactoglobulin (β-lg) is the major allergen in dairy products, and poses a significant threat to special people including infants and young children. Therefore, a convenient, cost-efficient, and aptamer-free colorimetric sensing platform is developed for β-lg assay based on a germanium/zinc bimetallic oxide nanozyme (GeO2/ZnO). The CTAB-assisted intercalation growth of ZnO nanoparticles between GeO2 layers endows GeO2/ZnO with enhanced peroxidase-mimicking activity and β-lg affinity. By virtue of multiple recognition-meditated specific protein corona formation, the catalytic activity of GeO2/ZnO is greatly deteriorated in the presence of β-lg. The selective discrimination and accurate detection of β-lg in dairy samples is achieved with a detection limit of 14.1 nM, and a portable kit is further established for point-of-care testing and visual colorimetric analysis. This study not only provides a promising strategy for allergen assay, but paves an avenue for engineering the abiotic protein affinity sensors for food safety analysis.

Intelligent hydrogel and smartphone-assisted colorimetric sensor based on Bi-metallic organic frameworks for effective detection of kanamycin and oxytetracycline

A smartphone-integrated colorimetric sensor is introduced for the rapid and simultaneous detection of kanamycin (KAN) and oxytetracycline (OTC). This sensor relies on the peroxidase-mimicking activity of Fe/Zr Bi-metallic organic frameworks (UIO-66(Fe/Zr)-NH2). This Bi-metallic MOF can facilitate the oxidation of a colorless substrate, 3,3',5,5'-tetramethylbenzidine (TMB), by reactive oxygen species (ROS) derived from hydrogen peroxide (H2O2), resulting in the formation of blue-colored oxidized TMB (ox-TMB). Consequently, Fe/Zr MOF was utilized for the detection of KAN and OTC under optimized conditions. In the presence of KAN and OTC, the interaction between TMB and H2O2 is inhibited, resulting in varying colorimetric responses. The approach accurately measured KAN and OTC, with detection limits as low as 0.44 and 6.86 nM, respectively. To achieve real-time and portable analysis even in harsh conditions, the proposed sensor was integrated with hydrogel-assisted smartphone technology thereby eliminating the need for expensive and cumbersome laboratory-based testing apparatus. Furthermore, the sensor was successfully used for real water sample analysis, with good recovery results. The proposed sensor provides a quick, visual, and highly sensitive approach for the simultaneous and accurate determination of KAN and OTC residues in polluted water, even at trace quantities. This study advances the application of MOF-based nanozymes in environmental monitoring, while also offering extensive opportunities for use in other fields.

Progress in the Computer-Aided Analysis in Multiple Aspects of Nanocatalysis Research

Making the utmost of the differences and advantages of multiple disciplines, interdisciplinary integration breaks the science boundaries and accelerates the progress in mutual quests. As an organic connection of material science, enzymology, and biomedicine, nanozyme-related research is further supported by computer technology, which injects in new vitality, and contributes to in-depth understanding, unprecedented insights, and broadened application possibilities. Utilizing computer-aided first-principles method, high-speed and high-throughput mathematic, physic, and chemic models are introduced to perform atomic-level kinetic analysis for nanocatalytic reaction process, and theoretically illustrate the underlying nanozymetic mechanism and structure-function relationship. On this basis, nanozymes with desirable properties can be designed and demand-oriented synthesized without repeated trial-and-error experiments. Besides that, computational analysis and device also play an indispensable role in nanozyme-based detecting methods to realize automatic readouts with improved accuracy and reproducibility. Here, this work focuses on the crossing of nanocatalysis research and computational technology, to inspire the research in computer-aided analysis in nanozyme field to a greater extent.

Nanozyme-Enabled Biomedical Diagnosis: Advances, Trends, and Challenges

As nanoscale materials with the function of catalyzing substrates through enzymatic kinetics, nanozymes are regarded as potential alternatives to natural enzymes. Compared to protein-based enzymes, nanozymes exhibit attractive characteristics of low preparation cost, robust activity, flexible performance adjustment, and versatile functionalization. These advantages endow them with wide use from biochemical sensing and environmental remediation to medical theranostics. Especially in biomedical diagnosis, the feature of catalytic signal amplification provided by nanozymes makes them function as emerging labels for the detection of biomarkers and diseases, with rapid developments observed in recent years. To provide a comprehensive overview of recent progress made in this dynamic field, here an overview of biomedical diagnosis enabled by nanozymes is provided. This review first summarizes the synthesis of nanozyme materials and then discusses the main strategies applied to enhance their catalytic activity and specificity. Subsequently, representative utilization of nanozymes combined with biological elements in disease diagnosis is reviewed, including the detection of biomarkers related to metabolic, cardiovascular, nervous, and digestive diseases as well as cancers. Finally, some development trends in nanozyme-enabled biomedical diagnosis are highlighted, and corresponding challenges are also pointed out, aiming to inspire future efforts to further advance this promising field.

Smartphones as a platform for molecular analysis: concepts, methods, devices and future potential

Over the past 15 years, smartphones have had a transformative effect on everyday life. These devices also have the potential to transform molecular analysis over the next 15 years. The cameras of a smartphone, and its many additional onboard features, support optical detection and other aspects of engineering an analytical device. This article reviews the development of smartphones as platforms for portable chemical and biological analysis. It is equal parts conceptual overview, technical tutorial, critical summary of the state of the art, and outlook on how to advance smartphones as a tool for analysis. It further discusses the motivations for adopting smartphones as a portable platform, summarizes their enabling features and relevant optical detection methods, then highlights complementary technologies and materials such as 3D printing, microfluidics, optoelectronics, microelectronics, and nanoparticles. The broad scope of research and key advances from the past 7 years are reviewed as a prelude to a perspective on the challenges and opportunities for translating smartphone-based lab-on-a-chip devices from prototypes to authentic applications in health, food and water safety, environmental monitoring, and beyond. The convergence of smartphones with smart assays and smart apps powered by machine learning and artificial intelligence holds immense promise for realizing a future for molecular analysis that is powerful, versatile, democratized, and no longer just the stuff of science fiction.

Single-Probe Sensing Array Based on Au Nanozyme for Simple, Rapid, and Low-Cost Colorimetric Identification of Antioxidants

Identification of biological antioxidants is of vital importance because of the essential role of antioxidants in keeping the balance of various diseases. Here, we designed a simple, rapid, and low-cost nanozyme sensing array for colorimetric identification of multiple antioxidants based on Au nanoparticles (Au NPs) synthesized via a facile and green aqueous phase method. In the presence of H2O2, Au NPs possessed peroxidase-like catalytic activity and could effectively catalyze the color-less 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized product with comparable enzyme kinetics parameters. The function of the colorimetric sensing array was based on the inhibitory effect of diverse antioxidants on the chromogenic system to varying degrees under different pH conditions, resulting in various "turn-off" colorimetric signal responses. Based on the developed sensing array, four kinds of antioxidants with various concentrations and different proportions of the mixtures were successfully discriminated from each other with the aid of principal component analysis. Moreover, the sensing array showed good performance in differentiating antioxidants in human serum samples, which broaden the analytical application of Au NPs. Compared with the existing sensing array, the single Au NP-based sensing array significantly simplified the sensing element and detection process, opening a new avenue for biological molecule identification in real complex samples.

Rapid Colorimetric Detection of Sulfite in Red Wine Using Alginate-Copper Laccase Nanozyme with Smartphone as an Optical Readout

Compared with the conventional analytical methods, nanozyme-based colorimetric sensors offer simpler and more accessible solutions for point-of-need food safety monitoring. Herein, Alginate-Cu (AlgCu) is reported as a robust laccase mimetic nanozyme for the colorimetric detection of sulfite in red wine, a common preservative in winemaking. AlgCu represents a rational design of nanozymes where the multifunctional group alginate is used as a coordination environment for the Cu catalytic center, mimicking the amino acids microenvironment in the natural laccase. The laccase activity of the AlgCu is evaluated using 2,4-dichlorophenol as a model substrate, where its oxidized product reacts with 4-aminoantipyrine, forming a reddish-pink compound with an absorption peak at 510 nm. The result showed that the AlgCu exhibited 32.81% higher laccase activity than pristine copper NPs, highlighting the role of a coordination environment in improving catalytic activity. The addition of sulfite decreased the intensity of the catalytic chromogenic product, confirming that sulfite inhibited the laccase mimetic activity of AlgCu. The observed inhibition is linearly related to the sulfite concentration from 2 to 100 μM (R 2 = 0.996), enabling the detection of sulfite down to 0.78 μM. Furthermore, a sulfite concentration down to 4.9 μM could be detected by integrating the colorimetric assay with smartphone color readouts. Analysis of sulfite-spiked red wine samples gave recoveries between 96 and 106%. Overall, the obtained analytical figures of merits signify AlgCu as a robust nanozyme-based colorimetric chemosensor suitable for a point-of-need application in wine quality control and food safety monitoring in general.

One-step construction of bioinspired multi-enzyme mimicking nanozyme as a universal platform for multi-mode sensing and catalytic degradation

Nanozymes, a category of nanomaterials with exceptional enzyme-like activity, exhibit the significant promise to overcome the inherent limitations of natural enzymes. Inspired by the active site structure of natural laccase, a biomimetic MA-Cu nanozyme with three-dimensional network structure was constructed in water system through one-step complexation based on the specific coordination between nitrogen-rich triazine heterocyclic melamine and Cu2+, in a facile, green and economical manner. Compared to natural laccase, MA-Cu possesses superior multi-enzyme mimicking activity, stability and cost-effectiveness. Through comprehensive characterizations, activity tests and theoretical calculations, the catalytic mechanism and the ligand-tunability of enzyme-like activity have been thoroughly investigated. Based on its multi-enzyme-like activities, a multifunctional monitoring platform for sulfide in food, epinephrine in preparations and glutathione in cells was successfully constructed, respectively. Notably, a green degradation and discrimination platform based on MA-Cu for various pollutants was developed, exhibiting distinguished substrate universality and detoxication capacity. As a stable, easily scalable and commercially applicable nanozyme, MA-Cu is expected to become a compelling candidate for replacing natural enzyme, showing excellent prospects in environmental remediation and biosensing.

Smartphone-assisted fluorescence/colorimetric dual-mode sensing strategy for uranium ion detection using cerium-sulfonyl calix[4]arene

A novel fluorescence/colorimetric dual-mode detection strategy for uranium ions (UO22+) is presented based on a cerium-sulfonyl calix[4]arene (SC4A) platform. The exo- and endo-rim sites of SC4A can coordinate with Ce3+ and Ce4+ ions, respectively, quenching Ce3+ fluorescence and influencing the oxidase-like activity of Ce4+. In the absence of UO22+, the solution of 3,3,5,5-tetramethylbenzidine (TMB) remains blue, but upon UO22+ binding, Ce3+ dissociates from SC4A, restoring fluorescence, while UO22+ interacts with oxTMB, turning the solution from blue to colorless. This dual-mode system provides a linear fluorescence detection range of 30-800 nM with a detection limit of 20.20 nM, and a colorimetric range of 30-800 nM with a detection limit of 27.78 nM. By combining high-sensitivity fluorescence with visual colorimetric analysis, the proposed method possesses high sensitivity, accuracy, and reliability. Notably, smartphone-based color capture facilitates rapid and convenient sample analysis, enabling straightforward quantification at varying UO22+ concentrations. The method has been successfully applied to real water and urine samples, demonstrating its practical utility in environmental and biological monitoring of UO22+.

Kirkendall Effect-Mediated Transformation of ZIF-67 to NiCo-LDH Nanocages as Oxidase Mimics for Multicolor Point-of-Care Testing of β-Galactosidase Activity and Escherichia coli

Early and portable detection of pathogenic bacteria is crucial for ensuring food safety, monitoring product quality, and tracing the sources of bacterial infections. Moving beyond traditional plate-culture counting methods, the analysis of active bacterial components offers a rapid means of quantifying bacteria. Here, metal-organic framework (MOF)-derived NiCo-layered double hydroxide nanosheets (LDHs), synthesized via the Kirkendall effect, were employed as highly effective oxidase mimics to generate reactive oxygen species (ROS). These ROS quickly etched gold nanobipyramids (Au NBPs), producing a vivid multicolormetric response. Experimental results and theoretical calculations indicated that the exceptional oxidase-like activity of NiCo-LDHs stemmed from the presence of bimetallic active sites and oxygen vacancies modulating the local electronic structure of LDHs. Additionally, β-galactosidase (β-Gal), a biomarker of Escherichia coli, reacted with p-aminophenyl-β-d-galactopyranoside (PAPG) to form p-aminophenol (PAP), a reducing agent which consumes ROS, thereby inhibiting the etching of Au NBPs. Furthermore, a three-dimensional (3D)-printed point-of-care testing (POCT) shell was designed as a portable device to visually detect β-Gal and E. coli in conjugation with smartphones. This study not only provides a novel approach to the rational design of nanozymes but also establishes a vivid and portably visual biosensing platform for detecting β-Gal activity and pathogenic bacteria.

Frontiers in laccase nanozymes-enabled colorimetric sensing: A review

In recent years, nanozyme-based analytics have become popular. Among these, laccase nanozyme-based colorimetric sensors have emerged as simple and rapid colorimetric detection methods for various analytes, effectively addressing natural enzymes' stability and high-cost limitations. Laccase nanozymes are nanomaterials that exhibit inherent laccase enzyme-like activity. They can oxidize phenolic compounds to generate a coloured product, independently or with a chromogenic agent. This chromogenic reaction provides the basis for developing simple and robust colorimetric assays for various analytes, enabling rapid and point-of-need analytical decision-making in food safety, clinical diagnostics, and environmental monitoring. This review article provides a concise overview of laccase nanozymes, including their classification and catalytic mechanisms. The article mainly discusses colorimetric and dual-mode detection methods and outlines various strategies to enhance the colorimetric sensing performance of laccase nanozymes. Additionally, the article highlights future research directions that could further improve laccase nanozyme-enabled colorimetric sensing. We hope this work will enhance the field's understanding and help future researchers identify gaps in developing simple, low-cost colorimetric sensors.

Selective colorimetric detection of carbosulfan based on its hydrolysis behavior and Ti3C2/AuPt nanozyme

BACKGROUND

Carbosulfan (CBS) is a widely used carbamate pesticide in agricultural production, its easy decomposition into hypertoxic carbofuran poses serious threats to human health and food safety. Therefore, sensitive and accurate detection of CBS is of significant importance. Conventional chromatography-based techniques require expensive instruments and complicated sample pretreatment, limiting their application for fast detection. Current electrochemical and colorimetric methods for detection of pesticides based on the cascade catalytic reactions between acetylcholinesterase (AChE) and nanozymes, which exhibit inferior selectivity. Hence, selective, sensitive and fast detection of CBS is still challenging.

RESULTS

In this work, an AChE-free colorimetric method was proposed for selective detection of CBS based on its unique hydrolysis behavior and nanozyme. Ti3C2 nanosheets/AuPt nanoparticles (Ti3C2/AuPt NPs) with enhanced peroxidase-like activity were prepared via one-step self-reduction reaction. CBS can be hydrolyzed under acidic condition and produce -SH moieties, which could bond to Pt atoms of Ti3C2/AuPt NPs and shield the active sites of nanozyme, resulting in decreased catalytic activity. Based on the inhibitory effect on the peroxidase-like activity of Ti3C2/AuPt NPs, a colorimetric method was proposed for direct detection of CBS. Under optimal conditions, the method showed wide linear range (0.5 ng mL-1-5 μg mL-1), low limit of detection (0.342 nM), good selectivity and anti-interference ability. The feasibility of this method for practical use was confirmed by analysis of CBS in real lake water samples.

SIGNIFICANCE

This work proposed a simple colorimetric method for selective and fast detection of CBS, which avoided employing AChE and cascade catalytic reactions, significantly lowering the detection cost and improving detection efficiency. The method showed great potential for accurate detection of CBS in actual samples, and provided a new avenue for developing nanozyme-based colorimetric method for detection of other pesticide residues.

Multifunctional MOF: Cold/hot adapted sustainable oxidase-like MOF nanozyme with ratiometric and color tonality for nitrite ions detection

Integrating multiple functionalities into a single entity is highly important, especially when a broad spectrum of application is required. In the present work, we synthesized a novel manganese-based MOF (denoted as UoZ-6) that functions as a cold/hot-adapted and recyclable oxidase nanozyme (Km 0.085 mM) further developed for ratiometric-based colorimetric and color tonality visual-mode detection of nitrite in water and food. Nitrite ions promote the diazotization process of the oxTMB product, resulting in a decay in the absorbance signal at 652 nm and the emergence of a new signal at 461 nm. The dual-absorbance ratiometric platform for nitrite ion detection functions effectively across a wide temperature range (0 °C to 100 °C), offering a linear detection range of 5-45 μM with a detection limit of 0.15 μM using visual-mode. This approach is sensitive, reliable, and selective, making it effective for detecting nitrite ions in processed meat and water.

Mitochondria-targeting nanozyme for catalytical therapy and radiotherapy with activation of cGAS-STING

BACKGROUND

Overcoming radio-resistance and enhance radio-sensitivity to obtain desired therapeutic outcome plays an important role in treating cancer.

METHODS

Here we constructed a versatile enzyme-like nano-radiosensitizer MDP. MDP is composed of MnCO decorated and Ru-based nanozyme with triphenylphosphine (TPP) group coordinated on the surface.

RESULTS

Due to the mitochondria-targeting ability of TPP and enhanced permeability and retention effect (EPR) effect of MDP, MDP accumulated in the mitochondria of tumor cells. Therefore, quantities of reactive oxygen species were produced via multiple enzyme-like properties including peroxidase (POD) and catalase (CAT) in a tumor microenvironment mimicking status. In additional, more energy of radiation ionizing was deposed in tumor site via Compton effect and secondary electron scattering by Ru element. Impressively, it was disclosed that the nanozyme can act as a cGAS-STING agonist to provoke immune response of the system, which hereby further elevated this combined therapy.

CONCLUSIONS

Collectively, we fabricated a novel nanozyme with POD and CAT mimicking properties for the combination therapy of catalytical therapy, radiotherapy as well as immune therapy to eliminate cancer.

A Single-Cell RNA Sequencing Guided Multienzymatic Hydrogel Design for Self-Regenerative Repair in Diabetic Mandibular Defects

Conventional bone tissue engineering materials struggle to reinstate physiological bone remodeling in a diabetic context, primarily due to the compromised repolarization of proinflammatory macrophages to anti-inflammatory macrophages. Here, leveraging single-cell RNA sequencing (scRNA-seq) technology, the pivotal role of nitric oxide (NO) and reactive oxygen species (ROS) is unveiled in impeding macrophage repolarization during physiological bone remodeling amidst diabetes. Guided by scRNA-seq analysis, we engineer a multienzymatic bone tissue engineering hydrogel scaffold (MEBTHS) composed is engineered of methylpropenylated gelatin hydrogel integrated with ruthenium nanozymes, possessing both Ru0 and Ru4+ components. This design facilitates efficient NO elimination via Ru0 while simultaneously exhibiting ROS scavenging properties through Ru4+. Consequently, MEBTHS orchestrates macrophage reprogramming by neutralizing ROS and reversing NO-mediated mitochondrial metabolism, thereby rejuvenating bone marrow-derived mesenchymal stem cells and endothelial cells within diabetic mandibular defects, producing newly formed bone with quality comparable to that of normal bone. The scRNA-seq guided multienzymatic hydrogel design fosters the restoration of self-regenerative repair, marking a significant advancement in bone tissue engineering.

Iron oxide nanozymes as versatile analytical tools: an overview of their application as detection technique

Iron oxide nanozymes (IONzymes) have become fundamental components in various analyte detection methodologies such as colorimetric, electrochemistry, fluorescence and luminescence. Their tunability, stability and the possibility of modification, alongside their ability to mimic the catalytic properties of natural enzymes like peroxidase, render them invaluable in analytical chemistry. This review explores the diverse applications of IONzymes across analytical chemistry, with a particular highlighting on their roles in different detection techniques and their potential in biomedical and diagnostic applications. This information would be valuable for researchers and practitioners in the fields of analytical chemistry, biochemistry, biotechnology and materials science who are interested in applying IONzymes in their work. In essence, this review article on iron oxide nanozymes in analytical chemistry would serve as a valuable resource for researchers, educators and industry professionals, offering insights, guidance and inspiration for further study and application of this promising class of nanomaterials.

A fast visual onsite method for detection and quantitation of food additives using an engineered metal nanohybrid-based catalyst

Unsafe food additives pose a significant threat to global health, especially in developing countries. Many existing methods rely on clean laboratories, complicated optics equipment, trained personnel and lengthy detection time, which are not suitable for onsite food safety inspections in emergency situations, peculiarly in impoverished areas. In this paper, a fast and visual onsite method is designed for the detection and quantification of additives in food safety by engineering a nanohybrid (MoS2/SDBS/Cu-CuFe2O4)-based catalysis. Interestingly, the nanohybrid presents peroxidase-like mimetic activity toward the substrate containing 3,3',5,5'-tetramethylbenzidine (TMB) and hydrogen peroxide (H2O2), which are then integrated simply into a detection kit. The blue oxidated TMB in this kit can be converted completely to colorless by some bio-molecule additives in commercial food, such as glutathione (GSH), cysteine (Cys), and ascorbic acid (AA). Remarkably, this process takes just less than 2 min and the detection limits are 2.8 nM, 5.5 nM and 47 nM, respectively. These results show excellent repeatability with a statistical analysis with (*P < 0.05) over 30 tests. Next, the images of the color changes can be captured clearly using a smartphone by red-green-blue (RGB) channels, which provides an opportunity for the development of field-operation device. Additionally, our approach is applied to some targets-indicative foods, showing a recovery range between 95.8 % and 104.2 %, offering an attractive and promising pathway for future practical food safety inspection applications. More importantly, this method can easily be extended to the detection of reducing substances in other analytical fields.

Rational design of monodispersed Au@Pt core-shell nanostructures with excellent peroxidase-mimicking activity for colorimetric detection of Cr(VI)

Cr(VI) is one of the most typical heavy metal contaminants and rapid detection of Cr(VI) is highly important in food control and public health. Herein, a core-shell Au@Pt nanozyme-based colorimetric assay was developed for the rapid and sensitive detection of Cr(VI). The monodispersed Au@Pt core-shell nanoparticles exhibited high peroxidase-mimicking activity and can catalyze colorless TMB into blue-colored oxidized oxTMB. After the addition of Cr(VI), the oxTMB molecules can be reduced into colorless TMB. The ultrathin Pt shell can prevent the Pt component from aggregation, thus improving the catalytic activity of Au@Pt nanozyme. These Au@Pt nanozyme-based Cr(VI) assays exhibited high sensitivity and selectivity and displayed satisfactory recoveries in practical samples. Our work highlights opportunities for the development of core-shell nanozymes with extensive applications in food safety, biomedicine, and environmental monitoring.

Introducing molecular imprinting onto nanozymes: toward selective catalytic analysis

The discovery of enzyme-like catalytic characteristics in nanomaterials triggers the generation of nanozymes and their multifarious applications. As a class of artificial mimetic enzymes, nanozymes are widely recognized to have better stability and lower cost than natural bio-enzymes, but the lack of catalytic specificity hinders their wider use. To solve the problem, several potential strategies are explored, among which molecular imprinting attracts much attention because of its powerful capacity for creating specific binding cavities as biomimetic receptors. Attractively, introducing molecularly imprinted polymers (MIPs) onto nanozyme surfaces can make an impact on the latter's catalytic activity. As a result, in recent years, MIPs featuring universal fabrication, low cost, and good stability have been intensively integrated with nanozymes for biochemical detection. In this critical review, we first summarize the general fabrication of nanozyme@MIPs, followed by clarifying the potential effects of molecular imprinting on the catalytic performance of nanozymes in terms of selectivity and activity. Typical examples are emphatically discussed to highlight the latest progress of nanozyme@MIPs applied in catalytic analysis. In the end, personal viewpoints on the future directions of nanozyme@MIPs are presented, to provide a reference for studying the interactions between MIPs and nanozymes and attract more efforts to advance this promising area.

Polyoxometalate-based iron-organic complex nanozymes with peroxidase-like activities for colorimetric detection of hydrogen peroxide and ascorbic acid

As a new type of artificial enzyme, a nanozyme is an ideal substitute for natural enzymes and has been successfully applied in many fields. However, in the application of biomolecular detection, most nanozymes have the disadvantages of long reaction times or high detection limits, prompting researchers to search for new efficient nanozymes. In this work, the enzyme-like activities of three polyoxometalate-based iron-organic complexes ([Fe(bpp)2](Mo6O19), [Fe(bpp)2]2(Mo8O26)·2CH3OH, and [Fe(bpp)2]4H[Na(Mo8O26)]3), namely, FeMo6, Fe2Mo8, and Fe4Mo8Na, were analyzed. All three polyoxometalate-based iron-organic complexes were found to be capable of catalyzing hydrogen peroxide (H2O2) to oxidize 3,3',5,5'-tetramethylbenzidine and o-phenylenediamine, resulting in visible color changes, further exhibiting peroxidase-like activity. Results showed that Fe4Mo8Na had more active sites due to its long chain structure, endowing more prominent peroxidase-like activity compared with Fe2Mo8 and FeMo6. A colorimetric sensing platform for H2O2 and ascorbic acid detection based on Fe4Mo8Na was established. The linear response range for H2O2 detection was 0.5-100 μM, and the detection limit was 0.143 μM. The linear response for ascorbic acid detection ranges from 0 to 750 μM with a detection limit of 1.07 μM. This study provides a new perspective for developing new nanozymes and expanding the sensing and detection application of nanozymes.

Few-layered boron nitride nanosheet as a non-metallic phosphatase nanozyme and its application in human urine phosphorus detection

Human urine phosphorus (existing in the form of phosphate) is a biomarker for the diagnosis of several diseases such as kidney disease, hyperthyroidism, and rickets. Therefore, the selective detection of phosphate in urine samples is crucial in the field of clinical diagnosis. Herein, we reported the phosphatase-like catalytic activity of few-layered h-BNNS for the first time. As the phosphatase-like activity of few-layered h-BNNS could be effectively inhibited by phosphate, a selective fluorescent method for the detection of phosphate was proposed. The linear range for phosphate detection is 0.5-10 µM with a detection limit of 0.33 µM. The fluorescent method was then explored for the detection of human urine phosphorus in real samples. The results obtained by the proposed method were consistent with those of the traditional method, indicating that the present method has potential application for urine phosphorus detection in clinical disease diagnosis.

Gold Nanoparticles-Based Colorimetric Immunoassay of Carcinoembryonic Antigen with Metal-Organic Framework to Load Quinones for Catalytic Oxidation of Cysteine

This work reported gold nanoparticles (AuNPs)-based colorimetric immunoassay with the Cu-based metal-organic framework (MOF) to load pyrroloquinoline quinone (PQQ) for the catalytic oxidation of cysteine. In this method, both Cu2+ and PQQ in the MOF could promote the oxidation of inducer cysteine by redox cycling, thus limiting the cysteine-induced aggregation of AuNPs and achieving dual signal amplification. Specifically, the recombinant carcinoembryonic antigen (CEA) targets were anchored on the MOF through the metal coordination interactions between the hexahistidine (His6) tag in CEA and the unsaturated Cu2+ sites in MOF. The CEA/PQQ-loaded MOF could be captured by the antibody-coated ELISA plate to catalyze the oxidation of cysteine. However, once the target CEA in the samples bound to the antibody immobilized on the plate surface, the attachment of CEA/PQQ-loaded MOF would be limited. Cysteine remaining in the solution would trigger the aggregation of AuNPs and cause a color change from red to blue. The target concentration was positively related to the aggregation and color change of AuNPs. The signal-on competitive plasmonic immunoassay exhibited a low detection limit with a linear range of 0.01-1 ng/mL. Note that most of the proteins in commercial ELISA kits are recombinant with a His6 tag in the N- or C-terminal, so the work could provide a sensitive plasmonic platform for the detection of biomarkers.

Copper (II)-catalyzed polydopamine mediated photothermal sensors for visual quantitative point-of-care testing

BACKGROUND

Temperature sensing is commonly used in point-of-care (POC) detection technologies, yet the portability and convenience of use are frequently compromised by the complexity of thermosensitive processes and signal transduction. Especially, multi-step target recognition reactions and temperature measurement in the reaction vessel present challenges in terms of stability and integration of detection devices. To further combine photothermal reaction and signal readout in one assay, these two processes enable to be integrated into miniaturized microfluidic chips, thereby facilitating photothermal sensing and achieving a simple visual temperature sensing as POC detection.

RESULTS

A copper ion (Cu2+)-catalyzed photothermal sensing system integrated onto a microfluidic distance-based analytical device (μDAD), enabling the visual, portable, and sensitive quantitative detection of multiple targets, including ascorbic acid, glutathione, and alkaline phosphatase (ALP). The polydopamine nanoparticles (PDA NPs) were synthesized by the regulation of free Cu2+ through redox or coordination reactions, facilitating the transduction of distinct photothermal response signals and providing the versatile Cu2+-responsive sensing systems. Promoted by integration with a photothermal μDAD, the system combines PDA's photothermal responsiveness and thermosensitive gas production of ammonium bicarbonate for improved sensitivity of ALP detection, reaching the detection limit of 9.1 mU/L. The system has successfully achieved on-chip detection of ALP with superior anti-interference capability and recoveries ranging from 96.8 % to 104.7 %, alongside relative standard deviations below 8.0 %.

SIGNIFICANCE AND NOVELTY

The μDAD design accommodated both the photothermal reaction of PDA NPs and thermosensitive gas production reaction, achieving the rapid sensing of visual distance signals. The μDAD-based Cu2+-catalyzed photothermal sensing system holds substantial potential for applications in biochemical analysis and clinical diagnostics, underscored by the versatile Cu2+ regulation mechanism for a broad spectrum of biomarkers.

Visual and photoelectrochemical analysis of antibiotic resistance genes enabled by surface-engineered ZIF-8@Au cascade nanozymes

The aggravation of antibiotic resistance genes (ARGs) in the environment has posed a significant global health crisis. Accurate evaluation of ARGs levels in a facile manner is a pressing issue for environmental surveillance. Here, we demonstrate a unique dumbbell-shaped cascade nanozyme for visual/photoelectrochemical (PEC) dual-mode detection of ARGs. Gold nanoparticles (AuNPs) with tunable exposed facets are controllably anchored onto ZIF-8 dodecahedrons, exhibiting glucose oxidase (GOx)-like (ZIF-8@Au/G) and peroxidase (POD)-like (ZIF-8@Au/P) activities. Upon the occurrence of ARGs, an asymmetric cascade-amplified "dumbbell" configuration is spontaneously generated via target-induced DNA hybridization, comprising GOx-like ZIF-8@Au/G with capture DNA on one side and POD-like ZIF-8@Au/P with signal DNA on the opposite side. Such a cascade nano-system can efficiently oxidize colorless 2, 2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) into its green oxidation state and synergistically decompose H2O2, realizing colorimetric/PEC dual-mode ARGs detection with a detection limit of 0.112 nM. The applicability of the present bioassay is validated through measuring ARGs in real sludge samples. This work suggests the possibility to rationally design task-specific nanozymes and develop target-responsive nano-cascade assays for environmental monitoring.

Mn-based Prussian blue analogues: Multifunctional nanozymes for hydrogen peroxide detection and photothermal therapy of tumors

Nanozymes have the advantages of simple synthesis, high stability, low cost and easy recycling, and can be applied in many fields including molecular detection, disease diagnosis and cancer therapy. However, most of the current nanozymes suffer from the defects of low catalytic activity and single function, which limits their sensing sensitivity and multifunctional applications. The development of highly active and multifunctional nanozymes is an important way to realize multidisciplinary applications. In this work, Mn-based Prussian blue analogues (Mn-PBA) and their derived double-shelled nanoboxes (DSNBs) are synthesized by co-precipitation method. The nanobox structure of DSNBs formed by etching Mn-PBA with tannic acid endows Mn-PBA DSNBs with better peroxidase-like activity than Mn-PBA. A colorimetric method for the rapid and sensitive determination of H2O2 is developed using Mn-PBA DSNBs-1.5 as a sensor with a detection limit as low as 0.62 μM. Moreover, Mn-PBA DSNBs-2 has excellent photothermal conversion ability, which can be applied to the photothermal therapy of tumors to inhibit the proliferation of tumor cells without damaging other tissues and organs. This study provides a new idea for the rational design of nanozymes and the expansion of their multi-functional applications in various fields.

Nanozybiotics: Advancing Antimicrobial Strategies Through Biomimetic Mechanisms

Infectious diseases caused by bacterial, viral, and fungal pathogens present significant global health challenges. The rapid emergence of antimicrobial resistance exacerbates this issue, leading to a scenario where effective antibiotics are increasingly scarce. Traditional antibiotic development strategies are proving inadequate against the swift evolution of microbial resistance. Therefore, there is an urgent need to develop novel antimicrobial strategies with mechanisms distinct from those of existing antibiotics. Nanozybiotics, which are nanozyme-based antimicrobials, mimic the catalytic action of lysosomal enzymes in innate immune cells to kill infectious pathogens. This review reinforces the concept of nanozymes and provides a comprehensive summary of recent research advancements on potential antimicrobial candidates. Initially, nanozybiotics are categorized based on their activities, mimicking either oxidoreductase-like or hydrolase-like functions, thereby highlighting their superior mechanisms in combating antimicrobial resistance. The review then discusses the progress of nanozybiotics in treating bacterial, viral, and fungal infections, confirming their potential as novel antimicrobial candidates. The translational potential of nanozybiotic-based products, including hydrogels, nanorobots, sprays, bandages, masks, and protective clothing, is also considered. Finally, the current challenges and future prospects of nanozybiotic-related products are explored, emphasizing the design and antimicrobial capabilities of nanozybiotics for future applications.

Multifunctional nanozymes for disease diagnosis and therapy

The development of nanotechnology has brought about groundbreaking advancements in diseases' diagnostics and therapeutics. Among them, multifunctional nanomaterials with enzyme-like activities (i.e., nanozymes) featured with high stability, large surface area for bioconjugation, and easy storage, offer unprecedented opportunities for disease diagnostics and treatment. Recent years have witnessed the great progress of nanozyme-based theranostics. To highlight these achievements, this review first introduces the recent advancements on nanozymes in biosensing and diagnostics. Then, it summarizes the applications of nanozymes in therapeutics including anti-tumor and antibacterial treatment, anti-inflammatory treatment, and other diseases treatment. In addition, several targeted strategies to improve the therapeutic efficacy of nanozyme are discussed. Finally, the opportunities and challenges in the field of diagnosis and therapy are summarized.

Ultra-trace Ag doped carbon quantum dots with peroxidase-like activity for the colorimetric detection of glucose

Carbon quantum dots (CQDs) have significant applications in nanozymes. However, previous studies have not elucidated the structure-activity relationship and enzyme mechanism. In this study, we employed a one-step microwave method to synthesize ultra-trace Ag-doped carbon quantum dots (Ag-CQDs). In the presence of hydrogen peroxide (H2O2), we used the oxidative coupling reaction of 3,3',5,5'-tetramethylbenzidine (TMB) to evaluate the intrinsic peroxidase-like activity, kinetics, and mechanism of Ag-CQDs. The trace amount of doped Ag (1.64 %) facilitated electron transfer from the CQDs interior to the surface. The electron transfer triggered the peroxide activity of CQDs, producing hydroxyl radical (·OH), which oxidized the colorless TMB to blue-colored TMB (oxTMB). By coupling with glucose oxidase (GOx), the Ag-CQDs/H2O2/TMB system has been used for colorimetric glucose determination. The system demonstrated a low detection limit (0.17 µM), wide linear range (0.5-5.5 µM), and satisfactory results when fruit juice was analyzed. This study reports a feasible method for the colorimetric detection of glucose by synthesizing ultra-trace Ag-doped carbon quantum dots with peroxidase-mimicking activity.

Perovskite hydroxide-based laccase mimics with controllable activity for environmental remediation and biosensing

Constructing relatively inexpensive nanomaterials to simulate the catalytic performance of laccase is of great significance in recent years. Although research on improving laccase-like activity by regulating ligands of copper (amino acids or small organic molecules, etc.) have achieved remarkable success. There are few reports on improving laccase-like activity by adjusting the composition of metal Cu. Here, we used perovskite hydroxide AB(OH)6 as a model to evaluate the relationship between Cu based alloys and their laccase-like activity. We found that when the Cu/Mn alloy ratio of the perovskite hydroxide A point is greater than 1, the laccase-like activity of the binary alloy perovskite hydroxide is higher than that of the corresponding single Cu. Based on the measurements of XPS and ICP-MS, we deduced that the improvements of laccase-like activity mainly attribute to the ratio of Cu+/Cu2+and the content of Cu. Moreover, two types of substrates (toxic pollutants and catechol neurotransmitters) were used to successfully demonstrated such nanozymes' excellent environmental protecting function and biosensing property. This work will provide a novel approach for the construction and application of laccase-like nanozymes in the future.

Al2O3-Stabilized Pt Nanozymes: Peroxidase Mimetics and Application in Glucose Detection

As promising alternatives for natural enzymes, much attention has been paid to nanozymes. And our recent study showed that the medium acid sites on the support are the active sites for the adsorption and oxidation of the substrate. Thus, in this work, due to the abundance of medium acid sites, Al2O3 was chosen as the support to prepare Pt/Al2O3 nanozymes. Through the Pt/Al2O3 samples, we further proved that the distribution of the Pt clusters and the amount of the medium acid sites can significantly influence the peroxidase-like activity. Then the Pt/Al2O3 sample was used for the detection of glucose. And as low as 0.96 μM glucose could be detected with a linear range from 5-60 μM via our method. This work showed the great potential applications of the easily prepared Pt/Al2O3 samples in varieties of simple, robust, and easy-to-make analytical approaches in the future.

An Encyclopedic Compendium on Chemosensing Supramolecular Metal-Organic Gels

Chemosensing, an interdisciplinary scientific domain, plays a pivotal role ranging from environmental monitoring to healthcare diagnostics and (inter)national security. Metal-organic gels (MOGs) are recognized for their stability, selectivity, and responsiveness, making them valuable for chemosensing applications. Researchers have explored the development of MOGs based on different metal ions and ligands, allowing for tailored properties and sensitivities, and have even demonstrated their applications as portable sensors such as paper-based test strips for practical use. Herein, several studies related to MOGs development and their applications in the chemosensing field via UV-visible or luminance along with electrochemical approach are presented. These papers explored MOGs as versatile materials with their use in sensing bio or environmental analytes. This review provides a foundational understanding of key concepts, methodologies, and recent advancements in this field, fostering the scientific community.

Ag-Cu filled nanonets with ultrafine dual-nanozyme active units for neurotransmitter biosensing

Ag and Cu based nanostructures serve as advanced functional materials for biomedical applications, due to their unique properties. Here, we proposed a novel neurotransmitter biosensing method based on Ag-Cu composite nanozyme, synthesized through the soft film plate method. Supported by the soft film template, the Ag-Cu nanozymes were stably kept to an ultrafine 2D structure with high monodispersity, which provided a large specific surface area and sufficient binding sites, leading to controllable and improved dual-nanozyme activities over similar-sized mono-Ag and mono-Cu, and up to 4.95 times of natural enzyme-level. The multi-path enzymatic reaction processes catalyzed by Ag-Cu composite nanozymes were firstly theoretically discussed in detail, according to the theoretical redox potential of redox couples in the reaction systems. On this basis, the Ag-Cu filled nanonets based neurotransmitter biosensing is successfully applied in rapid detection for glutathione and dopamine, possessing a linear range of 10∼100 μM and 1-10 μM, and a detection limit of 3.01 μM and 0.29 μM, respectively, which exhibited superior performance for biomedical purposes over most commercially available products in speed and precision.

Diagnosis of Mycobacterium tuberculosis using palladium-platinum bimetallic nanoparticles combined with paper-based analytical devices

In this study, we demonstrate that palladium-platinum bimetallic nanoparticles (Pd@Pt NPs) as the nanozyme, combined with a multi-layer paper-based analytical device and DNA hybridization, can successfully detect Mycobacterium tuberculosis. This nanozyme has peroxidase-like properties, which can increase the oxidation rate of the substrate. Compared with horseradish peroxidase, which is widely used in traditional detection, the Michaelis constants of Pd@Pt NPs are fourteen and seventeen times lower than those for 3,3',5,5'-tetramethylbenzidine and H2O2, respectively. To verify the catalytic efficiency of Pd@Pt NPs, this study will execute molecular diagnosis of Mycobacterium tuberculosis. We chose the IS6110 fragment as the target DNA and divided the complementary sequences into the capture DNA and reporter DNA. They were modified on paper and Pd@Pt NPs, respectively, to detect Mycobacterium tuberculosis on a paper-based analytical device. With the above-mentioned method, we can detect target DNA within 15 minutes with a linear range between 0.75 and 10 nM, and a detection limit of 0.216 nM. These results demonstrate that the proposed platform (a DNA-nanozyme integrated paper-based analytical device, dnPAD) can provide sensitive and on-site infection prognosis in areas with insufficient medical resources.

Biocompatible Folic-Acid-Strengthened Ag-Ir Quantum Dot Nanozyme for Cell and Plant Root Imaging of Cysteine/Stress and Multichannel Monitoring of Hg2+ and Dopamine

To boost the enzyme-like activity, biological compatibility, and antiaggregation effect of noble-metal-based nanozymes, folic-acid-strengthened Ag-Ir quantum dots (FA@Ag-Ir QDs) were developed. Not only did FA@Ag-Ir QDs exhibit excellent synergistic-enhancement peroxidase-like activity, high stability, and low toxicity, but they could also promote the lateral root propagation of Arabidopsis thaliana. Especially, ultratrace cysteine or Hg2+ could exclusively strengthen or deteriorate the inherent fluorescence property with an obvious "turn-on" or "turn-off" effect, and dopamine could alter the peroxidase-like activity with a clear hypochromic effect from blue to colorless. Under optimized conditions, FA@Ag-Ir QDs were successfully applied for the turn-on fluorescence imaging of cysteine or the stress response in cells and plant roots, the turn-off fluorescence monitoring of toxic Hg2+, or the visual detection of dopamine in aqueous, beverage, serum, or medical samples with low detection limits and satisfactory recoveries. The selective recognition mechanisms for FA@Ag-Ir QDs toward cysteine, Hg2+, and dopamine were illustrated. This work will offer insights into constructing some efficient nanozyme sensors for multichannel environmental analyses, especially for the prediagnosis of cysteine-related diseases or stress responses in organisms.

The Nanozyme Revolution: Enhancing the Performance of Medical Biosensing Platforms

Nanozymes represent a class of nanosized materials that exhibit innate catalytic properties similar to biological enzymes. The unique features of these materials have positioned them as promising candidates for applications in clinical sensing devices, specifically those employed at the point-of-care. They notably have found use as a means to amplify signals in nanosensor-based platforms and thereby improve sensor detection limits. Recent developments in the understanding of the fundamental chemistries underpinning these materials have enabled the development of highly effective nanozymes capable of sensing clinically relevant biomarkers at detection limits that compete with "gold-standard" techniques. However, there remain considerable hurdles that need to be overcome before these nanozyme-based sensors can be utilized in a platform ready for clinical use. An overview of the current understandings of nanozymes for disease diagnostics and biosensing applications and the unmet challenges that must be considered prior to their translation in clinical diagnostic tests is provided.

Nanoplasmonic biosensors for multicolor visual analysis of acetylcholinesterase activity and drug inhibitor screening in point-of-care testing

The monitoring of acetylcholinesterase (AChE) activity and the screening of its inhibitors are significance of the diagnosis and drug therapy of nervous diseases. A metal ions-mediated signal amplification strategy was developed for the highly sensitive and multicolor assay of AChE activity and visually screening its drug inhibitors. After the specific reaction between AChE and acetylthiocholine (ATCh), the hydrolysis product thiocholine (TCh) can directly and decompose the α-FeOOH nanorods (NRs) to release amounts of Fe2+, which was regarded as Fenton reagent to efficiently catalyze H2O2 to produce ·OH. Then, the as-formed ·OH can further largely shorten the gold nanobipyramids (Au NBPs), generating a series of palpable color variations. The linear range for AChE activity was 0.01-500.0 U/L with the limit of detection as low as 0.0074 U/L. The vivid visual effects could be easily distinguished for the multicolor assay of AChE activity by naked eye in visible light. To achieve the point-of-care testing, Au NBPs were further assembled on polymeric electrospun nanofibrous films (ENFs) surface as test strips for the easy-to-use test of AChE activity by RGB values with a smartphone. Fascinatingly, this proposed strategy can be used for the visual screening AChE inhibitors or non-inhibitors. Comparing with the clinical drugs (rivastigmine tartrate, and donepezil), some natural alkaloids such as evodiamine, caffeine, camptothecin, and berberine hydrochloride were selected as inhibitor modes to confirm the drug screening capability of this method. This proposed strategy may have great potential in the other disease-related enzymatic biomarkers assay and the rapid screening of drug therapy.