Non-invasive detection of glucose in human urine using a color-generating copper NanoZyme

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

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

Silver-based bimetallic nanozyme fabrics with peroxidase-mimic activity for urinary glucose detection

The enhanced catalytic properties of bimetallic nanoparticles have been extensively investigated. In this study, bimetallic Ag-M (M = Au, Pt, or Pd) cotton fabrics were fabricated using a combination of electroless deposition and galvanic replacement reactions, and improvement in their peroxidase-mimicking catalytic activity compared to that of the parent Ag fabric was studied. The Ag-Pt bimetallic nanozyme fabric, which showed the highest catalytic activity and ability to simultaneously generate hydroxyl (•OH) and superoxide (O2•-) radicals, was assessed as a urine glucose sensor. This nanozyme fabric sensor could directly detect urinary glucose in the pathophysiologically relevant high millimolar range without requiring sample predilution. The sensor could achieve performance on par with that of the current clinical gold standard assay. These features of the Ag-Pt nanozyme sensor, particularly its ability to avoid interference effects from complex urinary matrices, position it as a viable candidate for point-of-care urinary glucose monitoring.

Rational design of cuprofullerene bipyridine nanozyme with high peroxidase-like activity for colorimetric sensing of bleomycin

The high catalytic activity of Cu-based nanozymes mainly depends on the efficient Fenton-like reaction of Cu+/ H2O2, but Cu+ cannot exist stably. Trying to find a material that can stably support Cu+ while promoting the electron cycle of Cu2+/Cu+ still faces serious challenges. C60 is expected to be an ideal candidate to solve this problem due to its unique structure and rich physicochemical properties. Here, we designed and synthesized a C60-doped Cu+-based nanozyme (termed as C60-Cu-Bpy) by loading high catalytic active site Cu+ onto C60 and coordinating with 2,2'-bipyridine (Bpy). The single crystal diffraction analysis and a series of auxiliary characterization technologies were used to demonstrate the successful preparation of C60-Cu-Bpy. Significantly, the C60-Cu-Bpy exhibited superior peroxidase-like activity during the catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). Then, the catalytic mechanism of C60-Cu-Bpy as peroxidase was elucidated in detail, mainly benefiting from the dual function of C60. On the one hand, C60 acted as a carrier to directly support Cu+, which has the ability to efficiently decompose H2O2 to produce reactive oxygen species. The other was that C60 acted as an electron buffer, contributing to promoting the Cu2+/Cu+ cycle to facilitate the reaction. Furthermore, a colorimetric sensor for the quantitative analysis of bleomycin was established based on the principle of bleomycin specific inhibition of C60-Cu-Bpy peroxidase-like activity, with satisfactory results in practical samples. This study provides a new strategy for the direct synthesis of Cu+-based nanozymes with high catalytic performance.

Current trends in colorimetric biosensors using nanozymes for detecting biotoxins (bacterial food toxins, mycotoxins, and marine toxins)

Biotoxins, predominantly bacterial food toxins, mycotoxins, and marine toxins, have emerged as major threats in the fields of seafood, other foods, feeds, and medicine. They have potential teratogenic, mutagenic, and carcinogenic effects on humans, occasionally triggering high morbidity and mortality. One of the apparent concerns relates to the increasing consumption of fast food resulting in the demand for processed food without adequate consideration of the toxins they may contain. Therefore, developing improved methods for detecting biotoxins is of paramount significance. Nanozymes, a type of nanomaterials exhibiting enzyme-like activity, are increasingly being recognized as viable alternatives to natural enzymes owing to their benefits, such as customizable design, controlled catalytic performance, excellent biocompatibility, and superior stability. The remarkable catalytic activity of nanozymes has led to their broad utilization in the development of colorimetric biosensors. This has emerged as a potent and efficient approach for rapid detection, enabling the creation of innovative colorimetric sensing methodologies through the integration of nanozymes with colorimetric sensors. In this review, recent development in nanozyme research and their application in colorimetric biosensing of biotoxins are examined with an emphasis on their characteristics and performance. The study particularly focuses on the peroxidase (POD) activity, oxidase (OXD) activity, superoxide dismutase (SOD), and catalase (CAT) activity of nanozymes in colorimetric biosensors. Ultimately, the challenges and future prospects of these assays are explored.

Self-assembly of cascade nanoenzyme glucose oxidase encapsulated in copper benzenedicarboxylate for wearable sweat-glucose colorimetric sensors with smartphone readout

BACKGROUND

With the advent of personalized medical approaches, precise and tailored treatments are expected to become widely accepted for the prevention and treatment of diabetes. Paper-based colorimetric sensors that function in combination with smartphones have been rapidly developed in recent years because it does not require additional equipment and is inexpensive and easy to perform. In this study, we developed a portable, low-cost, and wearable sweat-glucose detection device for in situ detection.

RESULTS

The sensor adopted an integrated biomimetic nanoenzyme of glucose oxidase (GOx) encapsulated in copper 1, 4-benzenedicarboxylate (CuBDC) (GOx@CuBDC) through a biomimetic mineralization process. CuBDC exhibited a peroxide-like effect, cascade catalytic effect with the encapsulated GOx, and increased the enzyme stability. GOx@CuBDC and 3,3,5,5-tetramethylbenzidine were combined to form a hybrid membrane that achieved single-step paper-based glucose detection.

SIGNIFICANCE AND NOVELTY

This GOx@CuBDC-based colorimetric glucose sensor was used to quantitatively analyze the sweat-glucose concentration with smartphone readings. The sensor exhibited a good linear relationship over the concentration range of 40-900 μM and a limit of detection of 20.7 μM (S/N = 3). Moreover, the sensor performed well in situ monitoring and in evaluating variations based on the consumption of foods with different glycemic indices. Therefore, the fabricated wearable sweat-glucose sensors exhibited optimal practical application performance.

Dual-mode detection of glucose based on pistol-like DNAzyme-mediated exonuclease-assisted signal cycle

Detecting glucose accurately and sensitively from clinical samples like tears and saliva is still difficult. We have created a sensor that can detect glucose with high sensitivity and accuracy by combining the use of glucose oxidase (GOx) to catalyze glucose, a pistol-like DNAzyme (PLDz) to transform the signal, gold nanoparticles (AuNPs) to enhance the optical properties and the exonuclease-III (Exo-III) to amplify the signal. As a result, the proposed method exhibits a low detection limit of 7.5 pM and a wide detection range covering seven orders of magnitude. The suggested dual-mode strategy provides a sensitive, precise and specific detection method for glucose. Another advantage is that the dual-mode technique significantly improves the precision and consistency of the measurements, demonstrating its immense potential for use in biomedical research and clinical diagnostics.

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.

Utilising the Nanozymatic Activity of Copper-Functionalised Mesoporous C3 N5 for Sensing Biomolecules

Designing unique nanomaterials for the selective sensing of biomolecules is of significant interest in the field of nanobiotechnology. In this work, we demonstrated the synthesis of ordered Cu nanoparticle-functionalised mesoporous C3 N5 that has unique peroxidase-like nanozymatic activity for the ultrasensitive and selective detection of glucose and glutathione. A nano hard-templating technique together with the in-situ polymerisation and self-assembly of Cu and high N-containing CN precursor was adopted to introduce mesoporosity as well as high N and Cu content in mesoporous C3 N5 . Due to the ordered structure and highly dispersed Cu in the mesoporous C3 N5 , a large enhancement of the peroxidase mimetic activity in the oxidation of a redox dye in the presence of hydrogen peroxide could be obtained. Additionally, the optimised Cu-functionalised mesoporous C3 N5 exhibited excellent sensitivity to glutathione with a low detection limit of 2.0 ppm. The strong peroxidase activity of the Cu-functionalised mesoporous C3 N5 was also effectively used for the sensing of glucose with a detection limit of 0.4 mM through glucose oxidation with glucose oxidase. This unique Cu-functionalised mesoporous C3 N5 has the potential for detecting various molecules in the environment as well as for next-generation glucose and glutathione diagnostic devices.

Tablet-Based Sensor: A Stable and User-Friendly Tool for Point-of-Care Detection of Glucose in Urine

The colorimetric detection of glucose in urine through enzymatic reactions offers a low-cost and non-invasive method to aid in diabetes management. Nonetheless, the vulnerability of enzymes to environmental conditions, particularly elevated temperatures, and their activity loss pose significant challenges for transportation and storage. In this work, we developed a stable and portable tablet sensor as a user-friendly platform for glucose monitoring. This innovative device encapsulates glucose oxidase and horseradish peroxidase enzymes with dextran, transforming them into solid tablets and ensuring enhanced stability and practicality. The enzymatic tablet-based sensor detected glucose in urine samples within 5 min, using 3,3',5,5'-tetramethylbenzidine (TMB) as the indicator. The tablet sensor exhibited responsive performance within the clinically relevant range of 0-6 mM glucose, with a limit of detection of 0.013 mM. Furthermore, the tablets detected glucose in spiked real human urine samples, without pre-processing, with high precision. Additionally, with regard to thermal stability, the enzyme tablets better maintained their activity at an elevated temperature as high as 60 °C compared to the solution-phase enzymes, demonstrating the enhanced stability of the enzymes under harsh conditions. The availability of these stable and portable tablet sensors will greatly ease the transportation and application of glucose sensors, enhancing the accessibility of glucose monitoring, particularly in resource-limited settings.

Fabric-Based Electrochemical Glucose Sensor with Integrated Millifluidic Path from a Hydrophobic Batik Wax

In recent years, measuring and monitoring analyte concentrations continuously, frequently, and periodically has been a vital necessity for certain individuals. We developed a cotton-based millifluidic fabric-based electrochemical device (mFED) to monitor glucose continuously and evaluate the effects of mechanical deformation on the device's electrochemical performance. The mFED was fabricated using stencil printing (thick film method) for patterning the electrodes and wax-patterning to make the reaction zone. The analytical performance of the device was carried out using the chronoamperometry method at a detection potential of -0.2 V. The mFED has a linear working range of 0-20 mM of glucose, with LOD and LOQ of 0.98 mM and 3.26 mM. The 3D mFED shows the potential to be integrated as a wearable sensor that can continuously measure glucose under mechanical deformation.

Electrochemical Synthesis of Shape‐controlled Cu−Ni Nanocomposite and its Application for Nonenzymatic Glucose Sensing at Nanomolar Level

The electrodeposition method was firstly applied to obtain uniform cube‐shaped copper nanoparticles on conductive glass (ITO), and then a layer of tiny nickel nanoparticles. A bimetallic composite electrode (Cu−Ni/ITO), characterized by TEM, XPS and XRD, was prepared to construct the non‐enzyme electrochemical glucose sensor with high catalytic activity. The catalytic performance of Cu−Ni/ITO had been greatly improved, probably due to the synergistic bimetallic catalysis effect. The electrode had a satisfactory linear response in the range of 2.5×10−7 M to 2.6×10−3 M, with detection limit as low as 67 nM. Besides, Cu−Ni/ITO had good anti‐interference ability and reproducibility, indicating the promising application for glucose detection in practical samples.

Platinum nanoparticles confined in metal-organic frameworks as excellent peroxidase-like nanozymes for detection of uric acid

High levels of uric acid (UA) in humans can cause a range of diseases, and traditional assays that rely on uric acid enzymes to break down uric acid are limited by the inherent deficiencies of natural enzymes. Fortunately, the rapid development of nanozymes in recent years is expected to solve the above-mentioned problems. Hence, we used a host-guest strategy to synthesize a platinum nanoparticle confined in a metal-organic framework (Pt NPs@ZIF) that can sensitively detect UA levels in human serum. Unlike previously reported free radical-catalyzed oxidation systems, its unique electron transfer mechanism confers excellent peroxidase-like activity to Pt NPs@ZIF. In addition, UA can selectively inhibit the chromogenic reaction of TMB, thus reducing the absorbance of the system. Therefore, using the peroxidase-like activity of Pt NPs@ZIF and using TMB as a chromogenic substrate, UA can be detected directly without relying on natural enzymes. The results showed a relatively wide detection range (10-1000 μM) and a low detection limit (0.2 μM). Satisfactory results were also obtained for UA in human serum. This study with simple operation and rapid detection offers a promising method for efficiently detecting UA in serum.

Carbon Nanotube Fiber-Based Flexible Microelectrode for Electrochemical Glucose Sensors

Electrochemical sensors are gaining significant demand for real-time monitoring of health-related parameters such as temperature, heart rate, and blood glucose level. A fiber-like microelectrode composed of copper oxide-modified carbon nanotubes (CuO@CNTFs) has been developed as a flexible and wearable glucose sensor with remarkable catalytic activity. The unidimensional structure of CNT fibers displayed efficient conductivity with enhanced mechanical strength, which makes these fibers far superior as compared to other fibrous-like materials. Copper oxide (CuO) nanoparticles were deposited over the surface of CNT fibers by a binder-free facile electrodeposition approach followed by thermal treatment that enhanced the performance of non-enzymatic glucose sensors. Scanning electron microscopy and energy-dispersive X-ray analysis confirmed the successful deposition of CuO nanoparticles over the fiber surface. Amperometric and voltammetric studies of fiber-based microelectrodes (CuO@CNTFs) toward glucose sensing showed an excellent sensitivity of ∼3000 μA/mM cm², a low detection limit of 1.4 μM, and a wide linear range of up to 13 mM. The superior performance of the microelectrode is attributed to the synergistic effect of the electrocatalytic activity of CuO nanoparticles and the excellent conductivity of CNT fibers. A lower charge transfer resistance value obtained via electrochemical impedance spectroscopy (EIS) also demonstrated the superior electrode performance. This work demonstrates a facile approach for developing CNT fiber-based microelectrodes as a promising solution for flexible and disposable non-enzymatic glucose sensors.

Biosynthesis of bifunctional silver nanoparticles for catalytic reduction of organic pollutants and optical monitoring of mercury (II) ions using their oxidase-mimic activity

In this study, an aqueous extract of Sclerocarya birrea leaves was used as a reducing agent to synthesize silver nanoparticles (AgNPs). The synthesis was carried out at room temperature and was both rapid and simple. Different characterization techniques such as UV/visible spectroscopy, surface-enhanced Raman spectroscopy, X-ray diffraction, and focused ion beam scanning electron microscopy were used to confirm the formation of AgNPs. The synthesized nanoparticles exhibited catalytic activity for the reduction of 4-nitrophenol, methyl orange, methylene blue, and rhodamine 6G. The catalytic activity was monitored by measuring the UV/visible absorbance spectra of the compounds using sodium borohydride as a reducing agent and found to be high. Additionally, the particles displayed oxidase-like activity. In the presence of AgNPs, 3, 3', 5, 5'-tetramethylbenzidine (TMB) which is colorless was transformed to oxidized TMB, which is blue, using dissolved oxygen as the oxidant. In the presence of Hg2+, the oxidase-like activity was enhanced. On the basis of this observation, an assay for the analysis of Hg2+ was developed. The linear range of the calibration curve is wide (0-600 µM) and the limit of detection (LOD) is low, as small as 34.8 nM. The method is strongly selective towards Hg2+. Tap water obtained from the laboratory where these experiments were carried out was used to study the feasibility of the method in real sample analyses.

Au@bovine serum albumin nanoparticle-based acid-resistant nanozyme quartz crystal microbalance sensing of urine glucose

A robust, efficient and sensitive quartz crystal microbalance (QCM) for glucose detection has been constructed using Au@bovine serum albumin (Au@BSA) nanoparticles as an active layer. The nanoparticles serve as tandem nanozymes and their stability over natural enzymes enable the sensor to show a wider linear dynamic range between 0.05 and 15 mM, a higher acid-resistance (pH 2.0-8.0) and heat-resistance (35-60 °C) than conventional glucose oxidase (GOx)-based sensors. The sensor has been further applied to measure glucose content in artificial urine directly without dilution, where the recovery of 99.6-105.2% and the relative standard deviations (RSDs) below 0.88% confirm a good reproducibility for the measurement results. In addition, the developed Au@BSA QCM sensor can retain 95% of its initial activity after 40 days of storage. Overall, the Au@BSA sensor shows better comprehensive performance than the commercial sensor strips for urine glucose analysis and provides a promising approach in a more precise and robust manner.

Recent Advances in Construction and Application of Metal-Nanozymes in Pharmaceutical Analysis

Nanozymes, made of emerging nanomaterials, have similar activity to natural enzyme and exhibit promising applications in in the fields of environment, biology and medicine, and food safety science. In recent years, with the deep finding and research to nanozymes by researchers, its application in field of pharmaceutical analysis has emerged gradually, possessing great significance in drug safety evaluation and quality control. This review summarizes the construction of metal nanozymes, strategies to improve their performance and their application in pharmaceutical detection and analysis, especially in detection of target analytes consisting of small molecule medicine macromolecule, toxic and others, which proposes theoretical foundation for development of nanozymes in this field. At the same time, it also provides opportunities and challenges for the construction and application of new nanozymes.

Nanozyme-based cascade SPR signal amplification for immunosensing of nitrated alpha-synuclein

A self-assembled nanozyme of iron porphyrin mediated supramolecular modified gold nanoparticles (FpA) was fabricated to determine nitrated alpha-synuclein as the Tyr 39 residue (nT39 α-Syn) of a potential biomarker for early diagnosis of Parkinson's disease (PD). Mechanically, localized surface plasmon resonance (LSPR) and the mass effect caused by catalytic deposition of the nanozyme contributed to a cascade signal amplification strategy. The sensor allowed a signal amplification and selective nT39 α-Syn bioanalysis with a 1.34-fold enhancement by cascade amplified SPR signal and double specific recognition. The detection limit was 1.78 ng/mL in the detection range of 7-240 ng/mL. Benefiting from the excellent immunosensor, this method can distinguish healthy people and PD patients using actual samples. Overall, this strategy provides a nanozyme-based biosensing platform for the early diagnosis of PD and can be applied to detect other protein biomarkers, such as PD-L1.

π-Conjugated Copper Phthalocyanine Nanoparticles as Highly Sensitive Sensor for Colorimetric Detection of Biomarkers

Though numerous nanomaterials with enzyme-like activities have been utilized as probes and sensors for detecting biological molecules, it is still challenging to construct highly sensitive detectors for biomarkers using polymeric materials. Benefiting from the π-d delocalization effect of electrons, excellent metal-chelating property, high electron transferability, and good chemical stability of π-conjugated phthalocyanine, the design of the copper phthalocyanine-based conjugated polymer nanoparticles (Cu-PcCP NPs) as a colorimetric sensor for a variety of biomarkers is reported. The Cu-PcCP NPs are synthesized through a simple microwave-assisted polymerization, and their chemical structures are thoroughly characterized. The colorimetric results of Cu-PcCP NPs demonstrate excellent peroxidase-like detecting activity and also great substrate selectivity than most of the reported Cu-based nanomaterials. The Cu-PcCP NPs can achieve a detection limit of 4.88 μM for the H₂ O₂ , 4.27 μM for the L-cysteine, and 21.10 μM for the glucose via a cascade catalytic system, which shows comparable detecting sensitivity as that of many earlier reported enzyme-like nanomaterials. Moreover, Cu-PcCP NPs present remarkable resistance to harsh conditions, including high temperature, low pH, and excessive salts. These highly specific π-conjugated copper-phthalocyanine nanoparticles not only overcome the current limitation of polymeric material-based sensors but also provide a new direction for designing next-generation enzyme-like nanomaterial-based colorimetric biosensors.

Enzyme Encapsulation by Facile Self-Assembly Silica-Modified Magnetic Nanoparticles for Glucose Monitoring in Urine

Silica nanoparticles hold tremendous potential for the encapsulation of enzymes. However, aqueous alcohol solutions and catalysts are prerequisites for the production of silica nanoparticles, which are too harsh for maintaining the enzyme activity. Herein, a procedure without any organic solvents and catalysts (acidic or alkaline) is developed for the synthesis of silica-encapsulated glucose-oxidase-coated magnetic nanoparticles by a facile self-assembly route, avoiding damage of the enzyme structure in the reaction system. The encapsulated enzyme was characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive spectrometry, and a vibrating sample magnetometer. Finally, a colorimetric sensing method was developed for the detection of glucose in urine samples based on the encapsulated glucose oxidase and a hydrogen peroxide test strip. The method exhibited a good linear performance in the concentration range of 20~160 μg mL⁻¹ and good recoveries ranging from 94.3 to 118.0%. This work proves that the self-assembly method could be employed to encapsulate glucose oxidase into silica-coated magnetic particles. The developed colorimetric sensing method shows high sensitivity, which will provide a promising tool for the detection of glucose and the monitoring of diabetes.

Chitosan polymer matrix-derived nanocomposite (CuS/NSC) for non-enzymatic electrochemical glucose sensor

In this study, N and S co-doped chitosan polymer matrix-derived composite (CuS/NSC) was synthesized via a one-step hydrothermal technique using a low-cost copper complex of chitosan polymer. Cyclic voltammetry and chronoamperometry revealed excellent electrocatalytic performance. The glucose sensor exhibited a linear range of 160 μM to 11.76 mM, a low detection limit 2.72 μM and a sensitivity of 13.62 mA mM^-1 cm^-2 with an excellent linear response. Furthermore, the sensor also displayed selectivity for glucose over potential interfering agents and exhibited a satisfactory recovery percentage using real sample in human serum. The results demonstrate that, CuS/NSC is an efficient nanocomposite material for non-enzymatic glucose sensors and is applicable for glucose detection in biological fluids.

Flexible Biosensors Based on Colorimetry, Fluorescence, and Electrochemistry for Point-of-Care Testing

With the outbreak and pandemic of COVID-19, point-of-care testing (POCT) systems have been attracted much attention due to their significant advantages of small batches of samples, user-friendliness, easy-to-use and simple detection. Among them, flexible biosensors show practical significance as their outstanding properties in terms of flexibility, portability, and high efficiency, which provide great convenience for users. To construct highly functional flexible biosensors, abundant kinds of polymers substrates have been modified with sufficient properties to address certain needs. Paper-based biosensors gain considerable attention as well, owing to their foldability, lightweight and adaptability. The other important flexible biosensor employs textiles as substrate materials, which has a promising prospect in the area of intelligent wearable devices. In this feature article, we performed a comprehensive review about the applications of flexible biosensors based on the classification of substrate materials (polymers, paper and textiles), and illustrated the strategies to design effective and artificial sensing platforms, including colorimetry, fluorescence, and electrochemistry. It is demonstrated that flexible biosensors play a prominent role in medical diagnosis, prognosis, and healthcare.

L-Cysteine as an Irreversible Inhibitor of the Peroxidase-Mimic Catalytic Activity of 2-Dimensional Ni-Based Nanozymes

The ability to modulate the catalytic activity of inorganic nanozymes is of high interest. In particular, understanding the interactions of inhibitor molecules with nanozymes can bring them one step closer to the natural enzymes and has thus started to attract intense interest. To date, a few reversible inhibitors of the nanozyme activity have been reported. However, there are no reports of irreversible inhibitor molecules that can permanently inhibit the activity of nanozymes. In the current work, we show the ability of L-cysteine to act as an irreversible inhibitor to permanently block the nanozyme activity of 2-dimensional (2D) NiO nanosheets. Determination of the steady state kinetic parameters allowed us to obtain mechanistic insights into the catalytic inhibition process. Further, based on the irreversible catalytic inhibition capability of L-cysteine, we demonstrate a highly specific sensor for the detection of this biologically important molecule.

Photothermometric analysis of bismuth ions using aggregation-induced nanozyme system with a target-triggered surface cleaning effect

The development of nanozyme-based photothermometric sensing for point-of-care testing (POCT) heavy metal ions is of great significance for disease diagnosis and health management. Considering the low catalytic activity of most nanozymes at physiological pH, we found bismuth ions (Bi³⁺) could effectively enhance the peroxidase (POX)-like activity of cetyltrimethylammonium bromide and citrate-capped octahedral gold nanoparticle (CTAB/Cit-AuNP) nanozymes. It is mainly based on Bi³⁺ ions being able to trigger the surface cleaning effect of CTAB/Cit-AuNPs. Because the more active Bi³⁺ ions could effectively bind with citrate on the gold surface and competitively destroy the electrostatic interaction between citrate and CTAB, resulting in the removal of CTAB ligands from the gold surface. Without the ligand protection, CTAB/Cit-AuNPs aggregated immediately, and further resulted in a significant activation of the POX-like activity of AuNP nanozymes. Based on this principle, we introduced the enzyme substrate 3,3',5,5'-tetramethylbenzidine (TMB) into this aggregation-induced nanozyme system, and rationally designed a photothermometric platform to quickly and sensitively detect Bi³⁺ ions by using the good photothermal effect of the oxidation product of TMB (oxTMB). The developed photothermometric method only using a common thermometer has a limit of detection (LOD) as low as 45.7 nM for POCT analysis of Bi³⁺ ions. This study not only provides a more accurate understanding of the aggregation-induced nanozymes based on the surface cleaning principle, but also shows the potential applications of aggregation-induced nanozymes in the POCT field.