Colorimetric sensing of iodide based on triazole-acetamide functionalized gold nanoparticles

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.

Urea-doped carbon dots as fluorescent switches for the selective detection of iodide ions and their mechanistic study

A facile and green strategy for the fabrication of fluorescent urea-doped carbon dots (N-CDs) has been explored. Significantly, the fluorescent N-CDs could recognize iodide ions (I⁻) with high selectivity, and their photoluminescence could be efficiently quenched by the addition of I⁻. The sensitivity analysis for I⁻ indicated a linear relationship in the range from 12.5 to 587 μM with the detection limit as low as 0.47 μM. Furthermore, the I⁻ induced fluorescence (FL) quenching mechanism was investigated employing a combination of techniques, including UV-vis/fluorescence spectroscopy, Density Functional Theory (DFT) calculation, TEM and time-resolved fluorescence decay measurements. The DFT calculation results demonstrated that the amino- and amide groups of N-CDs play a significant role in iodide recognition through the formation of multiple N–H⋯I⁻, C–H⋯I⁻ and C( Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O)N–H⋯I⁻ interactions with I⁻. The TEM experiment confirmed the aggregation process when I⁻ was added to the N-CDs solution. Moreover, the radiative decay rate of N-CDs, which was first measured and reported the kinetic behaviors of the FL-quenching process, decreased from 3.30 × 10⁷ s⁻¹ to 1.95 × 10⁷ s⁻¹ after the coordination with I⁻ ions. The reduced lifetime demonstrated that the excited energy dissipation led to a dynamic quenching process. Therefore, such carbon materials can function as effective fluorescent switches for the selective detection of I⁻ ions.

Urea-doped carbon dots (N-CDs) have been successfully fabricated for monitoring iodide ions; the reduced lifetime of N-CDs demonstrated that the excited energy dissipation led to a dynamic fluorescence quenching process.

Chitosan-derived hydrothermally carbonized materials and its applications: A review of recent literature

Chitosan (CS) is a linear polysaccharide biopolymer, one of the most abundant biowastes in the environment. This makes chitosan a potential material for a wide range of applications. To improve CS's properties, chitosan has to be chemically modified. Hydrothermal carbonization (HTC) is a sustainable process for converting chitosan to solid carbonized material. This article presents a review on the applications of hydrothermally treated chitosan in different fields such as water treatment, heavy metals adsorption, carbon dioxide capturing, solar cells, energy storage, biosensing, supercapacitors, and catalysis. Moreover, this review covers the impact of HTC process parameters on the properties of the produced carbon material. The diversity of applications indicates the great possibilities and multifunctionality of hydrothermally carbonized chitosan and its derivatives. The utilization of HTC-CS is expected to further expand as a result of the movement toward sustainable, environmentally-friendly resources. Thus, this review also recommends a few suggestions to improve the properties of HTC chitosan and its comprehensive applications.

Chemical sensing with Au and Ag nanoparticles

Noble metal nanoparticles (NPs) are ideal scaffolds for the fabrication of sensing devices because of their high surface-to-volume ratio combined with their unique optical and electrical properties which are extremely sensitive to changes in the environment. Such characteristics guarantee high sensitivity in sensing processes. Metal NPs can be decorated with ad hoc molecular building blocks which can act as receptors of specific analytes. By pursuing this strategy, and by taking full advantage of the specificity of supramolecular recognition events, highly selective sensing devices can be fabricated. Besides, noble metal NPs can also be a pivotal element for the fabrication of chemical nose/tongue sensors to target complex mixtures of analytes. This review highlights the most enlightening strategies developed during the last decade, towards the fabrication of chemical sensors with either optical or electrical readout combining high sensitivity and selectivity, along with fast response and full reversibility, with special attention to approaches that enable efficient environmental and health monitoring.

Colorimetric sensing of iodide ions based on unmodified gold nanoparticles and the distinctive antiaggregation-to-aggregation process

A highly sensitive and selective colorimetric analysis method based on unmodified gold nanoparticles (AuNPs) to detect iodide ions (I^- ) in solution in the presence of hexadecyl trimethyl ammonium bromide (CTAB) and mercury ions (Hg²⁺ ) has been successfully developed. Hg²⁺ could form a gold amalgam with AuNPs to protect AuNPs from CTAB-induced aggregation caused by the electrostatic attraction between CTAB and citrate ion-covered AuNPs. When a mixture of Hg²⁺ and I^- was added to the solution of AuNPs, the formation of the HgI₂ complex destroyed the protection of Hg²⁺ for AuNPs, which led to the aggregation of AuNPs accompanied with the change in colour of the solution from red to grey black and decrease in the absorbance of AuNPs at 520 nm. There was a good linear relationship between A_520nm and I^- concentration from 0 to 800 nM with a low limit of detection (LOD) of 4.2 nM. Furthermore, this simple and reliable colorimetric sensor has been applied successfully to the detection of I^- in practical samples.

Highly Selective Detection of Iodide in Biological, Food, and Environmental Samples Using Polymer-Capped Silver Nanoparticles: Preparation of a Paper-Based Testing Kit for On-Site Monitoring

This work describes a facile synthesis of polymer-capped silver nanoparticles at room temperature. Chitosan oligosaccharide lactate-capped silver nanoparticles (COL-AgNPs) show the surface plasma resonance (SPR) band at 400 nm. The color of the COL-AgNPs was observed to be brownish yellow. The synthesized COL-AgNPs are stable for 5 months. The COL-AgNPs were characterized by UV-vis, X-ray diffraction, high-resolution transmission electron microscopy (HR-TEM), mass, and Fourier transform infrared spectral techniques. The obtained COL-AgNPs are monodispersed, and the range of the particle diameter was calculated to be 16.37 ± 0.15 nm by HR-TEM. We have utilized the COL-AgNPs as a probe to sense iodide (I^-). The SPR band of COL-AgNPs was decreased after the addition of iodide, and the color of the solution changed to colorless. Based on the decreases in SPR band absorbance, the concentration of iodide was calculated. The detection limit was found to be 108.5 × 10^-9 M (S/N = 3). Other interferences (825- and 405-fold) did not interfere with the detection of 1.48 × 10^-6 M iodide. The sensing mechanism was also discussed. Finally, we have successfully applied our sensing system for the detection of iodide in tap water, river water, pond water, blood serum, urine, and food samples. Good recoveries are obtained with spiked iodide in the real samples. Importantly, we have developed a paper-based kit using wax-printed paper for the on-site monitoring of iodide. The developed paper-based kit absorbance was validated with the microplate reader. To the best of our knowledge, this is the first report that used six different real samples for the detection of iodide and development of the paper-based kit for on-site monitoring.

Carbon Quantum Dots Prepared with Chitosan for Synthesis of CQDs/AuNPs for Iodine Ions Detection

Water-soluble and reductive carbon quantum dots (CQDs) were fabricated by the hydrothermal carbonization of chitosan. Acting as a reducing agent and stabilizer, the as-prepared CQDs were further used to synthesize gold nanoparticles (AuNPs). This synthetic process was carried out in aqueous solution, which was absolutely "green". Furthermore, the CQDs/AuNPs composite was used to detect iodine ions by the colorimetric method. A color change from pink to colorless was observed with the constant addition of I- ions, accompanied by a decrease in the absorbance of the CQDs/AuNPs composite. According to the absorbance change, a favorable linear relationship was obtained between ΔA and I- concentration in the range of 20⁻140 μM and 140⁻400 μM. The detection limit of iodide ions, depending on the 3δ/slope, was estimated to be 2.3 μM, indicating high sensitivity to the determination of iodide. More importantly, it also showed good selectivity toward I- over other anion ions, and was used for the analysis of salt samples. Moreover, TEM results indicated that I- ions induced the aggregation of CQDs/AuNPs, resulting in changes in color and absorbance.

Nanodiamonds conjugated to gold nanoparticles for colorimetric detection of clenbuterol and chromium(III) in urine

Nanodiamonds were modified such that they carry thiol groups (ND-thiol). Gold nanoparticles were reacted with ND-thiol to obtain a highly stable conjugate of the type ND@AuNPs. Both ND-thiol and the ND@AuNPs were characterized by SEM, TEM, AFM, DLS, zeta potential, XPS, XRD, UV-Vis, Raman, FTIR and cytotoxicity studies. Their biocompatibility was confirmed via an MTT assay with HeLa cells. At a pH value of 6, the ND@AuNPs represent a colorimetric probe that can be used to selectively detect the illegally used β-adrenergic drug clenbuterol (CLB) and the pollutant chromium(III). Detection can be performed visually by monitoring the color change from wine red to purple blue, or by colorimetric measurement of the so-called SPR peaks at 651 and 710 nm. The color changes are due to aggregation, and this is confirmed by TEM and DLS data. The involvement of surface functional groups that assist in analyte recognition was verified by FTIR. The detection limits are 0.49 nM for CLB, and 0.37 nM for Cr(III). The ND@AuNPs were successfully applied to the determination of Cr(III) and CLB in spiked human urine samples. Notably, the low interference by other ions in the detection of Cr(III) in tap and lake water is confirmed by ICP-MS analyses. Graphical abstract Nanodiamonds carrying thiol groups (ND-Thiol) were conjugated to gold nanoparticles, and the resulting ND@AuNPs are shown to be viable probes for the colorimetric detection of sub-nanomolar levels of clenbuterol (CLB) and Cr(III) ions, with demonstrated applicability to real water and urine samples.

Pyridoxal conjugated gold nanoparticles for distinct colorimetric detection of chromium(iii) and iodide ions in biological and environmental fluids

We developed pyridoxal conjugated gold nanoparticles (CAPy-AuNPs) for the selective colorimetric detection of Cr³⁺ and iodide ions in an aqueous medium.