Sequential colorimetric sensing of cupric and mercuric ions by regulating the etching process of triangular gold nanoplates

Colorimetric and visual sensing of ferrous ion by Fenton reaction-stimulated etching of triangular gold nanoplates

In this study, a method for ultrasensitive sensing of Fe²⁺ based on Fenton reaction mediated etching of triangular gold nanoplates (Au NPLs) was developed. In this assay, the etching of Au NPLs by H₂O₂ was accelerated in the presence of Fe²⁺ due to the generation of superoxide free radical (O₂^·-) via Fenton reaction. With the concentration of Fe²⁺ increased, the shape of Au NPLs changed from triangular to sphere with the blue shifted localized surface plasmon resonance, accompanying a series of consecutive color changes from blue, bluish purple, purple, reddish purple and finally to pink. The rich color variations enable rapid visual quantitative determination of Fe²⁺ within 10 min. A good linear relationship between the peak shifts and the concentration of Fe²⁺ was obtained in the range of 0.035 to 1.5 μM (R² = 0.996). Favorable sensitivity and selectivity in the presence of other tested metal ions were achieved in the proposed colorimetric assay. The detection limits (3ơ/k) for Fe²⁺ was 26 nM by UV-vis spectroscopy, and the clearly discernible concentration of Fe²⁺ was as low as 0.07 μM by naked eyes. The recoveries of fortified samples in pond water and serum samples ranged from 96% to 106% with interday relative standard deviations <3.6% in all cases, demonstrating the applicability of the assay for measuring Fe²⁺ in real samples.

Colorimetric detection of Cu2+ based on the inhibition strategy for etching reaction of AgNCs

In this study, an efficient and simple colorimetric method for sensing of Cu²⁺ was established using inhibition effect of Cu²⁺ to the etching reaction of silver nanocubes (AgNCs) induced by H₂O₂. The etching reaction of AgNCs changes its morphology and absorbance with the visual appearance from yellow to colorless. On the contrary, the presence of Cu²⁺ can significantly inhibit the etching progress. Thus Cu²⁺ induces the obvious absorbance enhancement compared with AgNCs/H₂O₂ system. This design realizes colorimetric detection of Cu²⁺ based on the inhibition effect of etching reaction using AgNCs nanoprobe. The colorimetric response of AgNCs nanoprobe in ΔAbs_417.5 shows the linearity with the increasing concentrations of Cu²⁺ from 0.01 to 40 μM with good selectivity. The concentration limit of Cu²⁺ efficaciously discriminated by the naked eye is as low as 0.01 μM. Furthermore, the Euclidean distance (ED) of the difference map in RGB change before and after response with Cu²⁺ is applied for further visualization recognition of Cu²⁺. All the above results indicate the outstanding practicability and accuracy of the proposed assay for Cu²⁺ sensing.

Using a Dendritic Sensor as a Feasible Method for Detection of Copper in Water Samples

Due to the severe dangers of copper on human health, development of identification and measurement copper methods in aquatic environments as well as prevention transfer methods of these substances to water resources have received much attention. Among of this expansion, rapid, simple, safe, sensitive and economically viable detection methods are more considerable. In this paper, the sensor activity of the poly(amidoamine) dendrimer containing eight methoxy groups modified with naphthalimide fluorescent derivative is studied. The sensor potential of dendrimer-naphthalimide fluorescence was evaluated in various solvents with different polarities, and results indicated that the detection of cuprum cations (Cu²⁺) is possible at low concentration. Also, the fluorescence properties of dendrimer-naphthalimide system are measured in the presence of diverse metal cations. In light of above, from the obtaining results, it can be concluded that dendritic sensor can be used as a feasible method to detect of copper in water samples in low concentrations.

Gold and Silver Nanoparticle-Based Colorimetric Sensors: New Trends and Applications

Gold and Silver nanoparticles (AuNPs and AgNPs) are perfect platforms for developing sensing colorimetric devices thanks to their high surface to volume ratio and distinctive optical properties, particularly sensitive to changes in the surrounding environment. These characteristics ensure high sensitivity in colorimetric devices. Au and Ag nanoparticles can be capped with suitable molecules that can act as specific analyte receptors, so highly selective sensors can be obtained. This review aims to highlight the principal strategies developed during the last decade concerning the preparation of Au and Ag nanoparticle-based colorimetric sensors, with particular attention to environmental and health monitoring applications.