Label-free, sensitive colorimetric detection of mercury(II) by target-disturbed in situ seeding growth of gold triangular nanoprisms

Colorimetric detection of heavy metal ions with various chromogenic materials: Strategies and applications

Detection of heavy metal ions has drawn significant attention in environmental and food area due to their threats to the human health and ecosystem. Colorimetry is one of the most frequently-used methods for the detection of heavy metal ions owing to its simplicity, easy operation and rapid on-site detection. The development of chromogenic materials and their sensing mechanisms are the key research direction in the area of colorimetric method. Since each chromogenic material has their unique optical and chemical properties, they have totally different colorimetric sensing mechanisms. This review focuses on the chromogenic materials and their sensing strategies for the colorimetric detection of heavy metal ions. We divide the chromogenic materials into three types, including organic materials, inorganic materials, and other materials. As for each type of chromogenic material, we discuss their detailed sensing strategies, sensing performance, and real sample applications. Moreover, current challenges and perspectives related to the colorimetry of heavy metal ions are also discussed in this review. The aim of this review is to help readers to better understand the principles of colorimetric methods for heavy metal ions and push the development of rapid detection of heavy metal ions.

High-Throughput Color Imaging Hg2+ Sensing via Amalgamation-Mediated Shape Transition of Concave Cube Au Nanoparticles

Mercury, as one type of toxic heavy metal, represents a great threat to environmental and biological metabolic systems. Thus, reliable and sensitive quantitative detection of mercury levels is particularly meaningful for environmental protection and human health. We proposed a high-throughput single-particle color imaging strategy under dark-field microscopy (DFM) for mercury ions (Hg²⁺) detection by using individual concave cube Au nanoparticles as optical probes. In the presence of ascorbic acid (AA), Hg²⁺ was reduced to Hg which forms Au–Hg amalgamate with Au nanoparticles, altering their localized surface plasmon resonance (LSPR). Transmission electron microscopy (TEM) images demonstrated that the concave cube Au nanoparticles were approaching to sphere upon increasing the concentration of Hg²⁺. The nanoparticles underwent an obvious color change from red to yellow, green, and finally blue under DFM due to the shape-evolution and LSPR changes. In addition, we demonstrated for the first time that the LSPR of Au–Hg amalgamated below 400 nm. Inspired by the above-mentioned results, single-particle color variations were digitalized by converting the color image into RGB channels to obtain (green+blue)/red intensity ratios [(G+B)/R]. The concentration-dependence change was quantified by statistically analyzing the (G+B)/R ratios of a large number of particles. A linear range from 10 to 2000 nM (R² = 0.972) and a limit of detection (LOD) of 1.857 nM were acquired. Furthermore, many other metal ions, like Cu²⁺, Cr³⁺, etc., did not interfere with Hg²⁺ detection. More importantly, Hg²⁺ content in industrial wastewater samples and in the inner regions of human HepG2 cells was determined, showing great potential for developing a single-particle color imaging sensor in complex biological samples using concave cube Au nanoparticles as optical probes.

Copper nanoclusters with/without salicylaldehyde-modulation for multifunctional detection of mercury, cobalt, nitrite and cyanide ions in aqueous solution and bioimaging

The sensitive determination of multiple heavy metal ions and toxic anions is important in biological and environmental fields. Here we report a facile strategy to construct a multifunctional chemosensor for the detection of Hg²⁺, [Formula: see text]Co²⁺, and CN^- in aqueous solution based on the fluorescent copper nanoclusters (Cu NCs). It was interesting to find that salicylaldehyde (SA) could effectively modulate the fluorescence property and sensing behavior of Cu NCs. In the absence of SA, Cu NCs showed 'on-off' fluorescence responses at the addition of Hg²⁺ and [Formula: see text] under different quenching mechanisms. Upon the presence of SA, Cu NCs exhibited a strong intramolecular charge transfer emission at 500 nm, accompanied by the decrease of the initial fluorescence of Cu NCs at 430 nm. This fluorescence on-state of Cu NC-SA at 500 nm was found to be exclusively turned off by Co²⁺ and enhanced by CN^-. Spectroscopy results combined with thermodynamic analysis provided sufficient information to deduce the sensing mechanisms. Finally, the Cu NCs showed high biocompatibility and were able to be used for fluorescence bioimaging in living cells. This study provided a novel and simple strategy to construct the multifunctional chemosensors for bioanalytical applications.