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An effective, selective, and multicolor colorimetric assay for Cu2+ detection based on the regulation of peroxidase-like nanozyme-mediated etching of gold nanorods (Au NRs) is proposed. Cu2+-creatinine complex is selected as the nanozyme that exhibits excellent peroxidase-like activity even in the case of low concentration of Cu2+, which can catalyze 3,3,5,5-tetramethylbenzidine (TMB) to produce oxidized TMB (TMB+) in the presence of hydrogen peroxide, and TMB+ is oxidized to generate TMB2+ after adding H+, and the TMB2+ can etch Au NRs. The determination of Cu2+ is achieved based on the blue shift of the longitudinal localized surface plasmon resonance peak of Au NRs. Under the optimal conditions, the developed colorimetric assay exhibits high sensitivity for the detection of Cu2+ (limit of detection is 0.034 μM) with a wide linear range of 0.05–4.0 μM (R2 = 0.987). The solution shows a rainbow-like color in response to the increase of Cu2+ concentration, which can realize the semi-quantitative detection of Cu2+ by naked eyes. In addition, the developed method exhibits excellent selectivity for Cu2+-detection. The established method was used for the determination of Cu2+ in lake water, soil, and normal human serum with satisfactory recovery of spiked samples. [ABSTRACT FROM AUTHOR]

A bisubstrate colorimetric system was developed for rapid and multi-color assay of copper ion (Cu2+). Cu2+-triethylamine (Cu2+-TEA) complex with the peroxidase-like activity can catalyze the 3,3′,5,5′-tetramethylbenzidine (TMB) to produce oxidized TMB (TMB+, color in blue) and dopamine (DA) to oxidized DA (oxDA, color in orange) in the presence of hydrogen peroxide, which can obtain a three-color colorimetric result due to the couple of complementary colors of blue and orange. The determination of Cu2+ is achieved based on the absorbance value at 460 nm of the composite peak of TMB+ and oxDA. After systematically optimizing the reaction conditions, the developed bisubstrate colorimetric method exhibits high sensitivity for the detection of Cu2+ (limit of quantitation (LOQ) is 0.0625 μM) with a wide linear range of 0.0625–8.0 μM (R2 = 0.991). Meanwhile, the reaction solution shows an orange, brown, and green color change with the increase in Cu2+ concentration, which can realize the semi-quantitatively detection by the naked eyes. Furthermore, TMB was also used as a single substrate for Cu2+ detection with a linear range of 0.5–9.0 μM (R2 = 0.994), and the LOQ is determined to be 0.5 μM. The LOQ of bisubstrate system is 8 times lower than that of single substrate system, indicating a higher sensitivity for the detection of Cu2+ using the bisubstrate colorimetric system. In addition, the developed bisubstrate colorimetric method exhibits excellent selectivity for Cu2+ detection, which was applied in the determination of Cu2+ in lake water and soil samples, and satisfactory spiked recoveries were obtained. [Display omitted] • Cu2+-triethylamine (TEA) complex exhibits excellent peroxidase-like activity. • A bisubstrate (TMB + dopamine) colorimetric sensor is developed based on Cu2+-TEA complex. • The developed senor displays three-color change for the detection of Cu2+. • The bisubstrate sensor shows a higher sensitivity than that of single substrate. [ABSTRACT FROM AUTHOR]

This work describes a simple and reliable colorimetric method based on the gold nanoparticles without any modification, which can realize the rapid, sensitive, and quantitative detection of lead (Pb2+) and copper (Cu2+) ions, providing a reference for monitoring metal ions in the environmental water. When Pb2+ was added to the gold nanoparticles solution containing a low concentration of L‐Cysteine, the combination of Pb2+ and L‐Cysteine can induce the aggregation of gold nanoparticles. On the contrary, Cu2+ can catalyze the oxidation of L‐Cysteine and destroy the formation of the Au‐S bond between L‐Cysteine and gold nanoparticles, thereby preventing the aggregation of gold nanoparticles. As the ultraviolet‐visible spectrum of gold nanoparticle solution is closely related to their aggregation status, the Cu2+ and Pb2+ can be determined. The calibration curves, which are constructed based on ratios of the absorbance at 650 nm and 520 nm of gold nanoparticles, display good linearity in the range of 50.0−2.5 × 103 nM for Pb2+ and 25.0−300.0 nM for Cu2+, respectively. The limits of quantitation of Pb2+ and Cu2+ are determined to be 50.0 and 25.0 nM, respectively. In addition, the spiked recoveries of Pb2+ and Cu2+ in real water samples are 94.6−112.5 and 87.3−114.7% with a relative standard deviation of less than 6.3%, respectively. [ABSTRACT FROM AUTHOR]

The formation of Pb-O bond between Pb SP 2+ sp and L-Cysteine can induce significant aggregation of Au NPs (blue color), conversely, Cu can catalyze the oxidation of Cysteine and prevent the aggregation of Au NPs (pink color). DOI: 10.1002/sscp.202200019 The cover picture shows that the lead ion (Pb SP 2+ sp ) and copper ion (Cu SP 2+ sp ) in lake water are detected by UV-Vis analysis using gold nanoparticles (Au NPs) as the colorimetric probe. [Extracted from the article]