Au-ag quantum dot nanozyme identified for multi-mode fluorescent, UV-vis and intelligent RGB monitoring and removal of toxic Hg2+ and S2- in food samples

To conveniently monitor and remove toxic Hg2+ and S2- in food samples, AuAg quantum-dot nanozyme (Au-Ag@FA QDs) was identified. The strong synergistic effect among folic acid (FA), Ag and Au endowed Au-Ag@FA QDs with superior peroxidase-mimic activity to accelerate 3,3',5,5'-tetramethylbenzidine (TMB) redox with Km/Vmax of 0.28 mmol·L-1/6.40 × 10-8 mol·L-1·s-1. Trace Hg2+ or S2- could selectively alter its peroxidase-like activity and inherent fluorescence performance, with obvious hyperchromic/"turn-on" fluorescent effect for Hg2+ or hypochromic/"turn-off" one for S2-. And red-green-blue (RGB) values analyzed from smartphones changed regularly with cHg2+ or cS2-. Under the optimized conditions, Au-Ag@FA QDs were successfully applied for multi-mode UV-vis, fluorescent, and RGB monitoring of Hg2+ or S2- in food samples. The detection limits were 7.38 × 10-7/5.74 × 10-8/4.93 × 10-6 g·L-1 and 1.99 × 10-6/4.48 × 10-8/5.79 × 10-6 g·L-1 respectively. Importantly, over 93.8 % Hg2+ or 90.5 % S2- could be removed by simple centrifugal-separation after detection. The selective recognition mechanisms to Hg2+ and S2- were also proposed.

CRISPR-Cas12a-regulated DNA adsorption on MoS2 quantum dots: Enhanced enzyme mimics for sensitive colorimetric detection of human monkeypox virus and human papillomavirus DNA

Diseases caused by viruses, such as monkeypox virus (MPXV) and human papillomavirus (HPV), pose serious threats to human health and safety. Although numerous strategies have been constructed for detecting MPXV and HPV DNA, most methods require either laborious procedures or complicated instruments involving skilled professionals. In this research, a CRISPR-Cas12a-mediated colorimetric detection platform for MPXV and HPV sensing was constructed for the first time by applying probe DNA to reprogram the catalytic properties of molybdenum disulfide quantum dots (MoS2 QDs). In the presence of MPXV or HPV targets, the CRISPR-Cas12a trans-cleavage activity is effectively motivated to decompose the probe DNA, leading to the suppression of enzymatic activity DNA enhancer adsorbed on MoS2 QDs, resulting in greatly decreased catalytic behaviors. The MoS2 QDs-DNA nanohybrids displayed prominent specificity and sensitivity, with detection limits at subpicomolar levels, as well as excellent stability and accuracy for determining MPXV and HPV DNA in human sera biosamples. Furthermore, the proposed colorimetric biosensing approach can be ensembled with a smartphone platform, allowing visible analysis of DNA targets. Taken together, this colorimetric strategy offers a novel diagnosis method for MPXV and HPV DNA detection, particularly favorable for highly endemic developing countries with restricted medical and instrumental support.

Eu MOF-enhanced FeNCD nanozymes for fluorescence and highly sensitive colorimetric detection of tetracycline

The constrained enzymatic activity and aggregation challenges encountered by small-sized nanozymes pose obstacles to their practical utility, necessitating a strategy to mitigate aggregation and boost enzymatic catalytic efficiency. In this work, a negatively charged Eu MOF was utilized as the encapsulation matrix, encapsulating the small-sized nanozymes FeNCDs into the Eu MOF to synthesize an FeNCDs@Eu MOF. The dispersibility of the encapsulated FeNCDs was increased, and owing to the negative charge of the FeNCDs@Eu MOF, electrostatic pre-concentration of the positively charged target molecule tetracycline (TC) was facilitated, thereby amplifying the enzymatic catalytic efficiency of the FeNCDs. The response of the FeNCDs to TC increased by nearly 6 times upon encapsulation. The TC detection limit (LOD) of the FeNCDs@Eu MOF-based sensor is as low as 11.63 nM. The incorporation of fluorescence detection expanded the linear range of the sensor, rendering it more suitable for practical sample detection.

Deep Insight of Design, Mechanism, and Cancer Theranostic Strategy of Nanozymes

Since the discovery of enzyme-like activity of Fe3O4 nanoparticles in 2007, nanozymes are becoming the promising substitutes for natural enzymes due to their advantages of high catalytic activity, low cost, mild reaction conditions, good stability, and suitable for large-scale production. Recently, with the cross fusion of nanomedicine and nanocatalysis, nanozyme-based theranostic strategies attract great attention, since the enzymatic reactions can be triggered in the tumor microenvironment to achieve good curative effect with substrate specificity and low side effects. Thus, various nanozymes have been developed and used for tumor therapy. In this review, more than 270 research articles are discussed systematically to present progress in the past five years. First, the discovery and development of nanozymes are summarized. Second, classification and catalytic mechanism of nanozymes are discussed. Third, activity prediction and rational design of nanozymes are focused by highlighting the methods of density functional theory, machine learning, biomimetic and chemical design. Then, synergistic theranostic strategy of nanozymes are introduced. Finally, current challenges and future prospects of nanozymes used for tumor theranostic are outlined, including selectivity, biosafety, repeatability and stability, in-depth catalytic mechanism, predicting and evaluating activities.

Metal-free auxiliary pyrophosphate detection based on near-infrared carbon dots

The excessive use of pyrophosphate (PPi) anions as additives poses a serious threat to human health and the environment. Considering the current status of PPi probes, the development of metal-free auxiliary PPi probes has important applications. In this study, a novel near-infrared nitrogen and sulfur co-doped carbon dots (N,S-CDs) were prepared. The average particle size of N,S-CDs was 2.25 ± 0.32 nm with average height was 3.05 nm. The probe N,S-CDs showed a special response to PPi, and a good linear relationship was obtained with PPi concentrations ranging from 0 to 1 μM, with the limit of detection being 0.22 nM. Tap water and milk were used for practical inspection, and ideal experimental results were acquired. In addition, the probe N,S-CDs also showed good results in biological systems, such as cell and zebrafish experiments.

Melamine-Ag with dual functions of electrochemiluminescence luminophore and coreactant accelerators: Construction of MIP/M-Ag@MoS2-QDs sensing platform for specific detection of thiabendazole

A novel self-enhancement molecularly imprinted electrochemiluminescence (ECL) sensor (MIP/M-Ag@MoS₂-QDs/GCE) was constructed to detect thiabendazole (TBZ) in food. Melamine was used as template to chelate Ag⁺ to prepare composite nanomaterials (M-Ag). M-Ag possesses both ECL properties and coreactant catalytic properties, which can realize the self-enhancement of ECL luminophore. MoS₂-QDs with excellent edge activity and electrochemical reaction catalytic activity were used to accelerate the reaction rate of the microsystem and further enhance the ECL intensity. The specific detection method of TBZ was established by investigating the ECL response mechanism and specific recognition mechanism of MIP/M-Ag@MoS₂-QDs/GCE. The ECL intensity was proportioned to the lg C_(TBZ) in the linear range 5 × 10^-8 mol L^-1-5 × 10^-5 mol L^-1 with a limit detection of 1.42 × 10^-8 mol L^-1. The satisfactory recovery rate (83.57%-101.03%) was obtained in sample analysis, which was in good agreement with the analysis result of HPLC.

Dual Role of MoS2 Quantum Dots in a Cross-Dehydrogenative Coupling Reaction

Modern day research focuses on the development of greener and eco-friendlier protocols to fabricate biologically relevant targets with minimal waste generation. C-C bond formation reactions are of prime importance in this regard. In a typical photocatalytic hydrogen evolution reaction, three components are used, viz, catalyst, photosensitizer, and sacrificial amine donor. Among these, the photosensitizer and sacrificial amine donors are wasted at the end of the reaction. Considering these drawbacks, in this work, we have developed a methodology targeted at the utilization of sacrificial amine donors for C-H functionalization with MoS2 quantum dots (QDs) as the catalyst as well as the photosensitizer. QDs indeed emerged to be an active participant in the heterogeneous electron transfer process. This concept opens up new possibilities in the field of nanomaterial-based photomediated organic transformations without the aid of any external photosensitizers via a clean and sustainable protocol with no side product.

Designing CoS1.035 Nanoparticles Anchored on N-Doped Carbon Dodecahedron as Dual-Enzyme Mimics for the Colorimetric Detection of H2O2 and Glutathione

In recent years, the exploration of the nanozyme, an artificial enzyme with the structure and function of natural enzymes, has become a hot topic in this field. Although significant progress has been made, it is still a huge challenge to design nanozymes with multiple enzyme-like catalytic activities. In this work, we have successfully fabricated a colorimetric sensing platform to mimic peroxidase-like and oxidase-like activities by the CoS_1.035 nanoparticles decorated N-doped carbon framework porous dodecahedrons (abbreviated to CoS_1.035/N-C PDHs). And the catalytic mechanism of CoS_1.035/N-C PDHs toward the peroxidase-like and oxidase-like activities is systematically explored. The results display that CoS_1.035/N-C PDHs can catalyze the oxidation of the colorless substrate 3,3,'5,5'-tetramethylbenzidine (TMB) into blue oxidized TMB (ox-TMB) by disintegrating H₂O₂ or the physically/chemically absorbed O₂ into different ROS species (·OH or O₂ ^·-) in the presence or absence of H₂O₂. Therefore, on the basis of the dual-enzyme mimic activities of CoS_1.035/N-C PDHs, the bifunctional colorimetric sensing platform is established for H₂O₂ detection with a wide linear range of 0.5-120 μM and glutathione detection with a linear range of 1-60 μM, respectively. This work provides an efficient platform for dual-enzyme mimics, expanding the application prospect of Co-based chalcogenides as enzyme mimics in biosensing, medical diagnosis, and environment monitoring.

Metal-free colorimetric detection of pyrophosphate ions by the peroxidase-like activity of ATP

Pyrophosphate (P₂O₇^4-, PPi) plays a vital role in ecological environment. Its elevated levels in water bodies can lead to eutrophication. Hence, its detection is extremely significant. Whereas most of the existing methods for the actual detection of PPi may cause environmental pollution or suffer from operational complexity. In this study, we introduced a sensitive and selective method for detecting PPi based on the fact that PPi can inhibit the peroxidase-like activity of adenosine 5'-triphosphate (ATP). This strategy not only eliminated the complexity of material preparation (ATP is commercialized), but also addressed the general need for metal ions in detecting PPi. The dynamic range of PPi detection was 1.0-200 μM and the detection limit was 74 nM. In addition, this strategy had been successfully applied to the determination of PPi in tap water and lake water. This work extends the application of natural biological small molecule ATP in the analysis and provides an innovative thought for the metal-free detection of PPi.

FeMoO4 nanospheres-based nanozymatic colorimetry for rapid and sensitive pyrophosphate detection

Assays of pyrophosphate ion (PPi) are of remarkable biochemical significance due to their vital roles in the bioenergetic and metabolic processes or as disease indicators. Colorimetry is popular in the field of biosensing and detection because of its simplicity, speed and cost-effectiveness, but there is a lack of a suitable colorimetric probe. Herein, a novel colorimetric sensing platform has been established for the detection of pyrophosphate based on the FeMoO₄-H₂O₂-3,3',5,5'-tetra-methylbenzidine (TMB) system. Compared with most previously reported iron-based nanozymes, the as-obtained FeMoO₄ nanospheres with a rough surface possessed a much superior peroxidase-like catalytic activity (V_max = 28.47 × 10^-8 M s^-1) and substrate affinity (K_m = 0.174 mM) toward H₂O₂ catalysis. Due to the Fe(II) and PPi reaction, the presence of PPi could specifically restore blue oxidized TMB to colorless TMB, which led to a decrease in UV absorption at 652 nm. The absorbance change is proportional to the PPi concentration, with a linear detection range (from 0.5 to 25 μM) and a low detection limit of 0.3 μM (S/N = 3). Accordingly, its excellent selectivity and high sensitivity made it a potential colorimetric sensor for PPi analysis in actual water samples.

Iodide-enhanced Cu-MOF nanomaterials for the amplified colorimetric detection of Fe3

In this paper, a novel colorimetric strategy based on iodide ion (I^-) and Cu-MOF catalysis was developed for simple, low-cost, and naked-eye detection of Fe³⁺. Both I^- and MOFs display catalytic activity toward peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB). Adsorption and embedding of I^- in Cu-MOF generates Cu-MOF/I with a three-dimensional porous structure that exhibits higher specific surface area, providing more active sites to facilitate interaction with TMB, resulting in enhanced catalytic efficiency. Reports have shown that Fe³⁺ can oxidize TMB in the absence of H₂O₂. We found that as Fe³⁺ concentration increases, the color of the system gradually deepens and the UV absorption peak gradually increases, thus providing a colorimetric sensor for quantitative Fe³⁺ detection. The detection limit (LOD) obtained in the presence of I^- is 200 nM; however, in the absence of I^-, the LOD is approx. 10 μM. Thus, the sensing system is ideal for signal amplified analysis of Fe³⁺. In the presence of various interfering metal ions, the developed sensing system displays excellent selectivity. Additionally, the practical application to Fe³⁺ detection in real samples is explored.

In Situ Assembly of Nanomaterials and Molecules for the Signal Enhancement of Electrochemical Biosensors

The physiochemical properties of nanomaterials have a close relationship with their status in solution. As a result of its better simplicity than that of pre-assembled aggregates, the in situ assembly of nanomaterials has been integrated into the design of electrochemical biosensors for the signal output and amplification. In this review, we highlight the significant progress in the in situ assembly of nanomaterials as the nanolabels for enhancing the performances of electrochemical biosensors. The works are discussed based on the difference in the interactions for the assembly of nanomaterials, including DNA hybridization, metal ion-ligand coordination, metal-thiol and boronate ester interactions, aptamer-target binding, electrostatic attraction, and streptavidin (SA)-biotin conjugate. We further expand the range of the assembly units from nanomaterials to small organic molecules and biomolecules, which endow the signal-amplified strategies with more potential applications.

One-component nano-metal-organic frameworks with superior multienzyme-mimic activities for 1,4-dihydropyridine metabolism

Although a number of nanozymes have been developed, it is still difficult to develop single-component nanozyme with overall high multienzyme-like activities. In this study, the nanosized metal-organic frameworks (nano-MOFs) FePCN (PCN stands for porous coordination network) was synthesized by integrating zirconium and iron ions with different catalytic property on single-component MOFs and exhibited superior intrinsic multienzyme-like activities, namely oxidase-, peroxidase- and phosphatase-mimicking activity. The catalytic active sites of oxidase- and peroxidase-, and phosphatase-like activity of FePCN were Fe-centers and Zr-O clusters, respectively. Based on the intrinsic oxidase-like activity and the similarity of molecular structures between cytochrome P450 oxidase (CYP) cofactors and the organic linker in FePCN, FePCN exhibited high CYP-like activity to catalyze the oxidation of hypotensive drug 1,4-dihydropyridine (1,4-DHP) into diethyl 2,6-dimethylpyridine-3,5-dicarboxylate (DDPD) and the yield of DDPD reached over 80%. Moreover, as peroxidase- and phosphatase-mimics, FePCN was successfully applied to detecting H₂O₂ under neutral condition and catalyzing the dephosphorylation of adenosine triphosphate (ATP), respectively. This study provides a feasible way for rational design one-component nanomaterials as multienzyme-mimics.

Fe(III)-mediated reversible catalytic activity of MoS2 nanozymes for bisphosphonate drug sensing

Peroxidase-like activity of MoS₂ quantum dots (QDs) can be reversibly regulated by means of Fe³⁺/alendronate sodium (ALDS)-induced aggregation/disaggregation of the QDs in solution. Specifically, Fe³⁺ can selectively aggregate the MoS₂ QDs and thus greatly enhance their peroxidase-like activity, while such enhancement can be inhibited in the presence of ALDS owing to the competitive coordination of ALDS with Fe³⁺. By regulating the enzyme-like activity of MoS₂ QDs, different colorimetric signal of a typical substrate of horseradish peroxidase, 3,3΄,5,5΄-tetramethylbenzidine, can be measured in the presence of H₂O₂. Based on this mechanism, we develop a colorimetric approach for the determination of ALDS and further applied in quality control of pharmaceutical products, utilizing either smartphone or UV-vis spectrometer as a readout. This detection method is rapid and selective, where derivatization of ALDS before detection is not needed. Such a smartphone-based colorimetric detection platform is promising to be applied in point-of-care testing at home, small clinics, or underdeveloped regions.

Platinum-Copper Bimetallic Colloid Nanoparticle Cluster Nanozymes with Multiple Enzyme-like Activities for Scavenging Reactive Oxygen Species

Fabrication of high-performance artificial antioxidant enzyme (AAE) systems based on a single nanozyme possessing multi-enzymatic activities is fascinating but challenging. Here, polyvinylpyrrolidone (PVP)-platinum-copper nanoparticle clusters (PVP-PtCuNCs) are prepared by a facile one-pot chemical coreduction method. PVP-PtCuNCs possess efficient superoxide dismutase (SOD)-like, peroxidase (POD)-like, and catalase (CAT)-like activities, and the multi-enzymatic activities depend on the bimetal component and cluster structure. Compared with individual platinum nanoparticle clusters (PVP-PtNCs), PVP-PtCuNCs can effectively eliminate reactive oxygen species (ROS) including superoxide anions, hydrogen peroxide, and hydroxyl radicals. The doping of copper not only reduces the usage of Pt content but also improves the catalytic efficiency and versatility effectively through the synergistic effect of bimetal components and the nanocluster structure. The results not only demonstrate that a single bimetallic nanozyme has the potential as an efficient AAE system in the biomedical application but also demonstrate that traditional concepts of structure-activity relationships can be used to fabricate nanozymes with the desired multi-enzymatic activities.

Reversible regulation of enzyme-like activity of molybdenum disulfide quantum dots for colorimetric pharmaceutical analysis

Regulating the catalytic activity of nanozymes is significant for their applications in various fields. Here, we demonstrate a new strategy to achieve reversible regulation of the nanozyme's activity for sensing purpose. This strategy involves the use of zero-dimensional MoS₂ quantum dots (MQDs) as the building blocks of nanozymes which display very weak peroxidase (POD)-like activity. Interestingly, such POD-like activity of the MQDs largely enhances in the presence of Fe³⁺ while diminishes with the addition of captopril thereafter. Further investigations identify the mechanism of Fe³⁺-mediated aggregation-induced enhancement of the POD-like activity and the inhibitory effect of captopril on the enhancement, which is highly dependent on their concentrations. Based on this finding, a colorimetric method for the detection of captopril is developed. This sensing approach exhibits the merits of simplicity, rapidness, reliability, and low cost, which has been successfully applied in quality control of captopril in pharmaceutical products. Moreover, the present sensing platform allows smartphone read-out, which has promising applications in point-of-care testing devices for clinical diagnosis and drug analysis.

•

A new post-synthesis strategy is developed to achieve reversible regulation of nanozyme's activity.

•

Fe³⁺-mediated aggregation can enhance the peroxidase-like activity of MoS₂ quantum dots more than 10 times.

•

Quality control of captopril in pharmaceutical products is realized by manipulating nanozyme's catalytical activity.

•

This sensing approach allows smartphone read-out, which has promising applications in point-of-care testing.

A turn-on luminescence probe based on amino-functionalized metal-organic frameworks for the selective detections of Cu2+, Pb2+ and pyrophosphate

A "turn-on" fluorescent probe based on amino-functionalized metal-organic frameworks (MOF-5-NH₂) is developed for the detection of Cu²⁺, Pb²⁺ and pyrophosphate (P₂O₇^4-, PPi). The fluorescence emission of fluorescent materials obtained by one-step synthesis is attributed to organic ligands. Cu²⁺ and Pb²⁺ coordinate with the amino group on the surface of the MOF-5-NH₂, which is ascribed to the host-guest electron transfer between analyte and probe, giving rise to the fluorescence quenching. After adding PPi, the intense affinity between Cu²⁺ and PPi remove Cu²⁺ from the MOF-5-NH₂, blocking of the electron transfer process, and the fluorescence can be recovered. The limit of detection is 0.057, 0.25 and 0.32 μmol L^-1 for the detection of Cu²⁺, Pb²⁺ and PPi, respectively. This turn-on mode based fluorescent probe shows preferable sensitivity and specificity to detect Cu²⁺, Pb²⁺ and PPi. These results demonstrate that the fluorescent MOF-5-NH₂ as a sensing platform displays remarkably performance.

Nanozymes for Environmental Pollutant Monitoring and Remediation

Nanozymes are advanced nanomaterials which mimic natural enzymes by exhibiting enzyme-like properties. As nanozymes offer better structural stability over their respective natural enzymes, they are ideal candidates for real-time and/or remote environmental pollutant monitoring and remediation. In this review, we classify nanozymes into four types depending on their enzyme-mimicking behaviour (active metal centre mimic, functional mimic, nanocomposite or 3D structural mimic) and offer mechanistic insights into the nature of their catalytic activity. Following this, we discuss the current environmental translation of nanozymes into a powerful sensing or remediation tool through inventive nano-architectural design of nanozymes and their transduction methodologies. Here, we focus on recent developments in nanozymes for the detection of heavy metal ions, pesticides and other organic pollutants, emphasising optical methods and a few electrochemical techniques. Strategies to remediate persistent organic pollutants such as pesticides, phenols, antibiotics and textile dyes are included. We conclude with a discussion on the practical deployment of these nanozymes in terms of their effectiveness, reusability, real-time in-field application, commercial production and regulatory considerations.

Homogeneous assay based on the pre-reduction and selective cation exchange for detection of multiple targets by atomic spectrometry

In view of the high sensitivity and good selectivity, chemical vapor generation atomic spectrometry (CVG-AS) and inductively coupled plasma mass spectrometer (ICP-MS), especially low-cost atomic fluorescence spectrometry (AFS) have been widely used in bioassay. However, the existing AS method is mostly based on heterogeneous strategies, and can't detect multiple targets in one system. In this study, we present the discovery and mechanism study of a phenomenon of Hg²⁺ pre-reduction that the concentration of Hg²⁺ decreased when it was mixed with the reductants (ascorbic acid (AA), SnCl₂, or NaBH₄/KBH₄) over long-time reaction (hours) by CVG-AFS and ICP-MS. A homogeneous Cu²⁺ assay method was developed based on the competition reaction of Cu²⁺ and Hg²⁺ for consuming AA, and its application in the detection of pyrophosphate (PPi) and alkaline phosphatase (ALP) was investigated based on the PPi complexation with Cu²⁺, and ALP hydrolyzation of PPi using CVG-AFS as a representative detector. Subsequently, in order to further verify the applicability of the system, cation exchange reaction (CER) was utilized here based on the selectively recognize Ag⁺ and C-Ag⁺-C by CuS nanoparticles (NPs). As the exchanged Cu²⁺ from CuS NPs can be sensitively and selectively detected via above-mentioned Cu²⁺ assay method, this strategy can be extended for the Ag⁺, DNA and prostate specific antigen (PSA) detection based on base complementary pairing and the specific recognition of aptamer. Under the optimal experimental conditions, the system showed high sensitivity for the detection of Cu²⁺, PPi, ALP, Ag⁺, DNA, and PSA, with limit of detections (LODs) of 0.12 nmol L^-1, 25 μmol L^-1, 0.025 U/L, 0.2 nmol L^-1, 0.05 nmol L^-1, and 0.03 ng/mL, respectively. The method was successfully used to determination Cu²⁺, ALP, and PSA in human serums, showing similar results with those of ICP-MS and kits methods.

Simply translating mercury detection into a temperature measurement: using an aggregation-activated oxidase-like activity of gold nanoparticles

A new household thermometer-based POCT analysis for mercury based on the aggregation-activated oxidase-like activity of gold nanoparticles.

One-pot synthesis of luminol–gallium nanoassemblies and their peroxidase-mimetic activity for colorimetric detection of pyrophosphate

Luminol–Ga nanoassemblies exhibit peroxidase-mimetic activity. Colorimetric detection of PPi is developed owing to the formation of a complex between PPi and Ga³⁺.

Zinc ion-triggered aggregation induced emission enhancement of dual ligand co-functionalized gold nanoclusters based novel fluorescent nanoswitch for multi-component detection

Herein, a zinc ion (Zn²⁺)-triggered aggregation induced emission enhancement (AIEE) fluorescence "on-off-on" nanoswitch was fabricated for inorganic pyrophosphate (PPi) and inorganic pyrophosphatase (PPase) activity detection. Dual ligand functionalized Au NCs were utilized as the substrate of the AIEE nanoswitch. The introduction of Zn²⁺ can cause Au NCs aggregated along with the enhanced fluorescence. After the addition of PPi, aggregated Au NCs disaggregated along with decreased fluorescence due to the competitive combination between PPi and Zn²⁺ (on-off). When PPase was introduced, PPi was hydrolyzed and release Zn²⁺, resulting in aggregated Au NCs along with enhanced fluorescence again (off-on). On the basis of this, highly selective and sensitive detection PPi (liner range from 0.1 to 300 μM) and PPase activity (liner range from 0.1 to 10 mU) can be achieved. The detection limits are 0.04 μM for PPi and 0.03 mU for PPase, respectively. Furthermore, the as-prepared Zn²⁺-triggered AIEE nanoswitch was successfully used for quantitative analysis of PPase activity in human serum with satisfactory spiked recoveries, and applied for the inhibitors screening.

Smartphone-based colorimetric assay of antioxidants in red wine using oxidase-mimic MnO2 nanosheets

A smartphone-based colorimetric method is developed for the determination of total antioxidants in red wine using oxidase-mimic MnO₂ nanosheets as probes.