Colorimetric determination of Hg2+ based on the mercury-stimulated oxidase mimetic activity of Ag3PO4 microcubes

Hg2+ detection and information encryption of new [1+1] lanthanide cluster

The sensing of heavy metal ion and information encryption are two very important research areas. Therefore, developing multi-functional materials capable of sensing heavy metal ions and encrypting information is highly important. In this work, three [1 + 1] lanthanide clusters [Ln(TFBA)3(dmp) (H2O)2]2 (Ln = Tb3+Tb1+1, Eu3+Eu1+1, Gd3+Gd1+1, HTFBA = 2,3,4,5-tetrafluorobenzoic acid, dmp = 4,7-dimethyl-1,10-phenanthroline) were designed and synthesized. Among them, Tb1+1 shows excellent luminescence sensing towards Hg2+ (Ex = 350 nm, Em = 545 nm). Results demonstrates the sensing with high selectivity, strong anti-interference, 20-s response time, high accuracy, excellent linear relationship in 0-20.0 μM, and a very low limit of detection (0.02 ppb). Furthermore, paper strips based on Tb1+1 is fabricated for visual detection of Hg2+ in real samples of tap water, lake water, human urine, and human serum. More interestingly, a new method for confidentiality of information is realized through multi-color anti-counterfeiting patterns with the [1 + 1] lanthanide cluster ink, based on the luminescence "on-off" sensing towards Hg2+.

Silver nanoparticles deposited carbon microspheres nanozyme with enhanced peroxidase-like catalysis for colorimetric detection of Hg2+ in seafood

Novel methods for high-performance detection of Hg²⁺ in seafood are critical for ensuring food safety and human health. Herein, Ag nanoparticles (Ag NPs) were successfully deposited on carbon microspheres (CMs) to form Ag NPs-CMs nanocomplex. The proposed Ag NPs-CMs could oxidize colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidation state TMB (oxTMB) in the presence of hydrogen peroxide (H₂O₂) and had a significant UV-vis absorption peak at 652 nm. The excellent peroxidase-like activity was attributed to the increased electrostatic attraction of CMs and the catalytic synergistic effect. After adding Hg²⁺, the catalytic activity of Ag NPs-CMs was specifically enhanced and the Michaelis-Menten constant (K_m) decreased from 0.067 to 0.052 mmol/L due to the formation of Ag-Hg amalgam which produced more superoxide anions (O₂^•-) and hydroxyl radicals (•OH). The linear response ranges for Hg²⁺ were 2~833 nmol/L and 2.5~40 μmol/L, with the low detection limit of 1.10 nmol/L. This method was applied to detect Hg²⁺ in seafood with satisfactory recoveries of 95.65~106.56%. A hydrogel kit was designed for portable detection of Hg²⁺, and the response range was 0.5~5 μmol/L. This work provides a reliable method for visual Hg²⁺ detection in seafood as well as a feasible strategy for the design of high-performance nanozymes.

An electrochemiluminescence immunosensor with double co-reaction accelerators based on Ag3PO4@EuPO4-AgNP for detecting squamous cell carcinoma antigen

This study aimed to design a sandwich electrochemiluminescence (ECL) immunosensor with double co-reaction accelerators for sensitively detecting squamous cell carcinoma antigen (SCCA). First, silver orthophosphate (Ag3PO4) nanoparticles were modified on the surface of EuPO4 nanowires to improve their poor dispersibility/solubility. At the same time, EuPO4 was used as a co-reaction accelerator to catalyze S2O82- to produce more intermediates (SO4•-), significantly enhancing the ECL signal of Ag3PO4. Ag nanoparticles (AgNP) modified on Ag3PO4@EuPO4 composite nanomaterials were used not only as linkers of luminescence groups and biomarkers but also as a co-reaction accelerator to effectively enhance ECL signal. The designed ECL immunosensor displayed several advantages, including good stability and reproducibility. Under the optimal conditions, its linear range in detecting SCCA was 0.0001-50 ng·mL-1, the detection limit was 25 fg·mL-1 (S/N = 3), the recovery was 96.6-100.4%, and the relative standard deviation was less than 4.8%. It was successfully applied to detect SCCA in human serum.

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.

Colorimetric detections of iodide and mercuric ions based on a regulation of an Enzyme-Like activity from gold nanoclusters

A simple colorimetric method was developed for sensitive and selective detections of I^- and Hg²⁺. Histidine stabilized gold nanoclusters (His-AuNCs) were synthesized and catalyzed the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to a blue product. As a strong ligand toward gold, iodide (I^-) attached to the surface of the His-AuNCs and significantly enhanced the oxidase-like activity of the His-AuNCs. Based on this enhancement, a sensitive colorimetric response toward I^- was obtained. Furthermore, the strong interaction between Hg²⁺ and I^- was adopted for an indirect Hg²⁺ detection. Under the optimal conditions, the platform presented high selectivity for the determinations of I^- and Hg²⁺ in the ranges 0.02-1 µM and 0.05-0.8 µM, with detection limits as 3.3 nM and 8 nM respectively. This colorimetric assay was successfully applied for analysis of real samples.

Rapid color-fading colorimetric sensing of Hg in environmental samples: regulation mechanism from DNA dimension

It was found that dimension change of aptamer DNA significantly weakened the mimicking activity of gold nanozyme, which was contrary to previous research. Based on this, a rapid colorimetric method for the detection of low concentrations of mercury in environmental media was fabricated. It was observed that 40 nM Hg²⁺ causes color changes in solution. The detection limit of absorbance measurements was estimated to be 9.3 × 10^-11 M. The assay was fast and could complete a single test in half an hour. The detection results for real environment samples confirmed the reliability of the colorimetric analysis in practical application. The proposed assay provides an alternative method for real-time monitoring of mercury in the environment. In particular, the charge effect on the affinity of nanozyme consummated the DNA regulation mechanism for the simulated enzyme activity.