Colorimetric determination of Pb2+ ions based on surface leaching of Au@Pt nanoparticles as peroxidase mimic

Dual nanozyme sensor enables rapid at-home cancer surveillance

Early detection of cancer is critical for improving patient survival rates, and current in vitro diagnostic methods show great potential, particularly for point-of-care applications. However, challenges such as time consumption, high costs, and reliance on sophisticated equipment limit their widespread use, especially in resource-limited regions. Here, we have developed a smartphone-assisted miniaturized analytic device that addresses these limitations, offering a portable, cost-effective solution for at-home, rapid cancer screening. Employing a hybrid nanozyme (AuNP@Cu2O-His) with a dual absorption design, this device enables reference-free radiometric quantification of multiple cancer biomarkers in serum down to femtomolar levels using aptamer-based recognition. Specifically, it achieves limits of detection (LOD) of 18.75 pg/mL for prostate-specific antigen (PSA), 110.31 pg/mL for alpha-fetoprotein (AFP), and 42.89 pg/mL for carcinoembryonic antigen (CEA), as determined by the 3σ/K method. Clinical sample analysis confirms the reliability of the device, with results closely matching clinical reports (relative errors below 6%). These findings highlight the potential of this robust, portable platform for early cancer detection in both clinical and resource-limited settings, enabling convenient and effective point-of-care diagnostics.

A colorimetric platform for sensitive sensing of Hg2+ and S2- based on Se-AuNPs with Hg2+-activated peroxidase-like activity

Herein, the selenium (Se) modified gold nanoparticles (Se-AuNPs) was synthesized using cerium doped carbon dots (Ce-CDs) as a reducing agent and template. As desired, Se-AuNPs displays enhanced peroxidase (POD)-like activity in the presence of Hg2+. The mechanism for the enhanced activity was attributed to the increased affinity between Se-AuNPs-Hg2+ and the substrate, in which Se and Au elements have a strong binding capacity to Hg2+, forming Hg-Se bonds and Au-Hg amalgam to generate more ·OH. This POD-like activity of Se-AuNPs-Hg2+ correlates with the colorimetric reaction by the catalytic reaction between 3,3',5,5'-tetramethylbenzidine (TMB) and H2O2. The oxidation of TMB was completely inhibited by the introduction of the reductive S2-. Based on the above findings, a strategy for the colorimetric detection of Hg2+ and S2- by Se-AuNPs was established with linear ranges of 0.33-66 μg/L and 0.625-75 μg/L, and low detection limits of 0.17 μg/L and 0.12 μg/L (3.3 δ/k), respectively. When the colorimetric probes for detection of Hg2+ and S2- was applied in environmental water samples, the recoveries were in the range of 90.3-108.0 %. This method will provide a new idea for the colorimetric detection strategy of Hg2+ due to the strong interaction between Hg and Se.

Tuning quantum dots emission on DNA tetrahedron/silica nanosphere/graphene oxide nanointerface for ratiometric fluorescence assay of Pb2+ in multiplex samples

BACKGROUND

Assembling framework nucleic acid (FNA) nanoarchitectures and tuning luminescent quantum dots (QDs) for fluorescence assays represent a versatile strategy in analytical territory. Rationally, FNA constructs could offer a preferential orientation to efficiently recognize the target and improve detection sensitivity, meanwhile, regulating size-dependent multicolor emissions of QDs in one analytical setting for ratiometric fluorescence assay would greatly simplify operation procedures. Nonetheless, such FNA/QDs-based ratiometric fluorescence nanoprobes remain rarely explored.

RESULTS

We designed a sensitive and signal amplification-free fluorescence aptasensor for lead ions (Pb2+) that potentially cause extensive contamination to environment, cosmetic, food and pharmaceuticals. Red and green emission CdTe quantum dots (rQDs and gQDs) were facilely prepared. Moreover, silica nanosphere encapsulating rQDs served as quantitative internal reference and scaffold to anchor a predesigned FNA and DNA sandwich containing Pb2+ binding aptamer and gQD modified DNA signal reporter. On binding of Pb2+, the gQD-DNA signal reporter was set free, resulting in fluorescence quenching at graphene oxide (GO) interface. Owing to the rigid structure of FNA, the fluorescence signal reporter orderly arranged at the silica nanosphere could sensitively respond to Pb2+ stimulation. The dose-dependent fluorescence signal-off mode enabled ratiometric analysis of Pb2+ without cumbersome signal amplification. Linear relationship was established between fluorescence intensity ratio (I555/I720) and Pb2+ concentration from 10 nM to 2 μM, with detection limit of 1.7 nM (0.43 ppb), well addressing the need for Pb2+ routine monitoring. The designed nanoprobe was applied to detection of Pb2+ in soil, cosmetic, milk, drug, and serum samples, with the sensitivity comparable to conventional ICP-MS technique.

SIGNIFICANCE

Given the programmable design of FNA and efficient recognition of target, flexible tuning of QDs emission, and signal amplification-free strategy, the present fluorescence nanoprobe could be a technical criterion for other heavy metal ions detection in a straightforward manner.

Highly selective colorimetric determination of glutathione based on sandwich-structured nanoenzymes composed of gold nanoparticle-coated molecular imprinted metal-organic frameworks

A sandwich-structured composite nanoenzyme (NH2-MIL-101(Fe)@Au@MIP) was prepared using molecularly imprinted polymers, metal-organic frameworks, and gold nanoparticles and a highly selective glutathione (GSH) colorimetric sensor was constructed. The inner part of the composite nanoenzymes is a metal-organic framework loaded with gold nanoparticles (AuNPs), NH2-MIL-101(Fe)@Au, which has superior peroxidase-like activity compared with  NH2-MIL-101(Fe). This is due to the surface plasmon resonance effect of AuNPs. GSH can form strong Au-S bonds with AuNPs, which can significantly reduce the enzymatic activity of NH2-MIL-101(Fe)@Au, thereby changing the absorbance at 450 nm of the sensing system. The degree of change in absorbance is correlated with the concentration of GSH. In the outer part, the molecularly imprinted polymer with oxidized glutathione (GSSG) as a dummy template provided specific pores, which significantly improved the selectivity of the sensing system. The sensor showed good GSH sensing performance in the range 1 ~ 50 μM with a lower limit of detection (LOD) of 0.231 μM and good sensing performance in fetal bovine serum, indicating its high potential for clinical diagnostic applications.

Determination Methods of the Risk Factors in Food Based on Nanozymes: A Review

Food safety issues caused by foodborne pathogens, chemical pollutants, and heavy metals have aroused widespread concern because they are closely related to human health. Nanozyme-based biosensors have excellent characteristics such as high sensitivity, selectivity, and cost-effectiveness and have been used to detect the risk factors in foods. In this work, the common detection methods for pathogenic microorganisms, toxins, heavy metals, pesticide residues, veterinary drugs, and illegal additives are firstly reviewed. Then, the principles and applications of immunosensors based on various nanozymes are reviewed and explained. Applying nanozymes to the detection of pathogenic bacteria holds great potential for real-time evaluation and detection protocols for food risk factors.

Heterometallic nanomaterials: activity modulation, sensing, imaging and therapy

Heterometallic nanomaterials (HMNMs) display superior physicochemical properties and stability to monometallic counterparts, accompanied by wider applications in the fields of catalysis, sensing, imaging, and therapy due to synergistic effects between multi-metals in HMNMs. So far, most reviews have mainly concentrated on introduction of their preparation approaches, morphology control and applications in catalysis, assay of heavy metal ions, and antimicrobial activity. Therefore, it is very important to summarize the latest investigations of activity modulation of HMNMs and their recent applications in sensing, imaging and therapy. Taking the above into consideration, we briefly underline appealing chemical/physical properties of HMNMs chiefly tailored through the sizes, shapes, compositions, structures and surface modification. Then, we particularly emphasize their widespread applications in sensing of targets (e.g. metal ions, small molecules, proteins, nucleic acids, and cancer cells), imaging (frequently involving photoluminescence, fluorescence, Raman, electrochemiluminescence, magnetic resonance, X-ray computed tomography, photoacoustic imaging, etc.), and therapy (e.g. radiotherapy, chemotherapy, photothermal therapy, photodynamic therapy, and chemodynamic therapy). Finally, we present an outlook on their forthcoming directions. This timely review would be of great significance for attracting researchers from different disciplines in developing novel HMNMs.

Colorimetric determination of cysteine based on Au@Pt nanoparticles as oxidase mimetics with enhanced selectivity

A H₂O₂-free colorimetric protocol based on urchin-like Au@Pt nanoparticles (Au@Pt NPs) has been developed for the sensitive and selective determination of cysteine (Cys). We verified the intrinsic oxidase-like activity of the Au@Pt NPs. They can act as artificial mimic oxidases to catalyse the oxidization of 3,3',5,5'-tetramethylbenzidine (TMB) with the assistance of dissolved oxygen, avoiding the use of H₂O₂ in the colorimetric determination of Cys. In addition, the discrimination of Cys from the other two biothiol analogues, homocysteine and glutathione, can be easily realized through a simple ageing process. HNO₃ is added to this colorimetric system to terminate the reaction by oxidizing ox-TMB (oxidized form of TMB) to diphenoquinone (DPQ), thus generating a characteristic absorption peak of DPQ at 450 nm. By recording the absorbance at 450 nm, interference from the aggregated Au@Pt NPs (absorption peak at 670 nm) when 650 nm (the characteristic absorption peak of ox-TMB) is used as the absorption wavelength can be eliminated. We investigated this H₂O₂-free colorimetric protocol and obtained high sensitivity, with a detection limit of 1.5 nM and relatively high selectivity. The analytical performance for real samples was further explored. The Au@Pt NP-based H₂O₂-free colorimetric protocol is of great significance for the sensitive and selective determination of Cys in practical samples in different scenarios.

Tannic Acid-Capped Gold Nanoparticles as a Novel Nanozyme for Colorimetric Determination of Pb2+ Ions

In this study, tannic acid-modified gold nanoparticles were found to have superior nanozyme activity and catalyze the oxidation reaction of 3,3′,5,5′-tetramethylbenzidine in the presence of hydrogen peroxide. Enhancing the catalytic activity of the nanozyme by Pb2+ ions caused by selectively binding metal ions by the tannic acid-capped surface of gold nanoparticles makes them an ideal colorimetric probe for Pb2+. The parameters of the reaction, including pH, incubation time, and concentration of components, were optimized to reach maximal sensitivity of Pb2+ detection. The absorption change is directly proportional to the Pb2+ concentration and allows the determination of Pb2+ ions within 10 min. The colorimetric sensor is characterized by a wide linear range from 25 to 500 ng×mL−1 with a low limit of detection of 11.3 ng×mL−1. The highly sensitive and selective Pb2+ detection in tap, drinking, and spring water revealed the feasibility and applicability of the developed colorimetric sensor.

Protein-Assisted Osmium Nanoclusters with Intrinsic Peroxidase-like Activity and Extrinsic Antifouling Behavior

Extensive studies have laid the groundwork for understanding peroxidase-like nanozymes. However, improvements are still required before their practical applications. On one hand, it is significant to explore highly reactive nanozymes. On the other hand, it is necessary to avoid fouling formed on the surface of nanozymes, which will affect their activity and the results of H₂O₂ sensors or H₂O₂-related applications. Herein, a strategy is reported to design osmium nanoclusters (Os NCs) with the existence of bovine serum albumin (BSA) through biomineralization. BSA-Os NCs were found to possess intrinsic peroxidase-like activity with a high specific activity (6120 U/g). Studies also found that the catalytic activity of BSA-Os NCs was better than those of reported protein-assisted metal nanozymes (e.g., BSA-Pt NPs and BSA-Au NCs). More significantly, BSA has been confirmed as a protective shell to give Os NCs extrinsic antifouling property in some typical ions (e.g., Hg²⁺, Ag⁺, Pb²⁺, I^-, Cr⁶⁺, Cu²⁺, Ce³⁺, S^2-, etc.), saline (0-2 M), or protein (0-100 mg/mL) conditions. Under optimal conditions, a colorimetric sensor was established to realize a linear range of H₂O₂ from 1.25 to 200 μM with a low detection limit of 300 nM. On this basis, remarkable features enable a BSA-Os NCs-based colorimetric sensor to detect H₂O₂ from complex systems with clear color gradients. Together, this work highlights the advantages of protein-assisted Os nanozymes and provides a paragon for peroxidase-like nanozymes in H₂O₂-related applications.

Nanozyme Applications: A Glimpse of Insight in Food Safety

Nanozymes own striking merits, including high enzyme-mimicking activity, good stability, and low cost. Due to the powerful and distinguished functions, nanozymes exhibit widespread applications in the field of biosensing and immunoassay, attracting researchers in various fields to design and engineer nanozymes. Recently, nanozymes have been innovatively used to bridge nanotechnology with analytical techniques to achieve the high sensitivity, specificity, and reproducibility. However, the applications of nanozymes in food applications are seldom reviewed. In this review, we summarize several typical nanozymes and provide a comprehensive description of the history, principles, designs, and applications of nanozyme-based analytical techniques in food contaminants detection. Based on engineering and modification of nanozymes, the food contaminants are classified and then discussed in detail via discriminating the roles of nanozymes in various analytical methods, including fluorescence, colorimetric and electrochemical assay, surface-enhanced Raman scattering, magnetic relaxing sensing, and electrochemiluminescence. Further, representative examples of nanozymes-based methods are highlighted for contaminants analysis and inhibition. Finally, the current challenges and prospects of nanozymes are discussed.

A Review on Metal- and Metal Oxide-Based Nanozymes: Properties, Mechanisms, and Applications

Since the ferromagnetic (Fe3O4) nanoparticles were firstly reported to exert enzyme-like activity in 2007, extensive research progress in nanozymes has been made with deep investigation of diverse nanozymes and rapid development of related nanotechnologies. As promising alternatives for natural enzymes, nanozymes have broadened the way toward clinical medicine, food safety, environmental monitoring, and chemical production. The past decade has witnessed the rapid development of metal- and metal oxide-based nanozymes owing to their remarkable physicochemical properties in parallel with low cost, high stability, and easy storage. It is widely known that the deep study of catalytic activities and mechanism sheds significant influence on the applications of nanozymes. This review digs into the characteristics and intrinsic properties of metal- and metal oxide-based nanozymes, especially emphasizing their catalytic mechanism and recent applications in biological analysis, relieving inflammation, antibacterial, and cancer therapy. We also conclude the present challenges and provide insights into the future research of nanozymes constituted of metal and metal oxide nanomaterials.

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.

A review on metal nanozyme-based sensing of heavy metal ions: Challenges and future perspectives

Large scale mining, manufacturing industries, exploitation of underground water, depletion of groundwater level, and uncontrolled discharge of industrial wastes have caused severe heavy metal ion pollution to the environment throughout the world. Therefore, the rapid detection of such toxic metal ions is inevitable. However, conventional methods require sophisticated instruments and skilled manpower and are difficult to operate in on-field conditions. Recently, metal nanozyme-based assays have been found to have the potential as an alternative to conventional methods due to their portability, simplicity, and high sensitivity to detect metal ion concentration to as low as parts per trillion (ppt). Metal nanozyme-based systems for heavy metal ions enable rapid and cheap screening on the spot with a very simple instrument such as a UV-vis absorption spectrophotometer and therefore, are convenient for use in field operations, especially in remote parts of the world. The sensing mechanism of a nanozyme-based sensor is highly dependent on its surface properties and specific interactions with particular metal ion species. Such method often encounters selectivity issues, unlike natural enzyme-based assays. Therefore, in this review, we mainly focus our discussion on different types of target recognition and inhibition/enhancement mechanisms, and their responses toward the catalytic activity in the sensing of target metal ions, design strategies, challenges, and future perspectives.