Selective colorimetric detection of Cr(iii) and Cr(vi) using gallic acid capped gold nanoparticles

Chromium Monitoring in Water by Colorimetry Using Optimised 1,5-Diphenylcarbazide Method

Chromium contamination of drinking water has become a global problem due to its extensive use in industry. The most commonly used methods for chromium detection in water are laboratory-based methods, such as atomic absorption spectroscopy and mass spectroscopy. Although these methods are highly selective and sensitive, they require expensive maintenance and highly trained staff. Therefore, there is a growing demand for cost effective and portable detection methods that would meet the demand for mass monitoring. Microfluidic detection systems based on optical detection have great potential for onsite monitoring applications. Furthermore, their small size enables rapid sample throughput and minimises both reagent consumption and waste generation. In contrast to standard laboratory methods, there is also no requirement for sample transport and storage. The aim of this study is to optimise a colorimetric method based on 1,5-diphenylcarbazide dye for incorporation into a microfluidic detection system. Rapid colour development was observed after the addition of the dye and samples were measured at 543 nm. Beer's law was obeyed in the range between 0.03-3 mg·L^-1. The detection limit and quantitation limit were found to be 0.023 and 0.076 mg·L^-1, respectively.

Cu(0) nanoparticle-decorated functionalized reduced graphene oxide sheets as artificial peroxidase enzymes: application for colorimetric detection of Cr(vi) ions

Graphene oxide sheets were functionalized by a “click” chemistry approach which was utilized for the decoration of Cu(0) nanoparticles for sensitive colorimetric detection of Cr(vi) ions.

New portable smartphone-based PDMS microfluidic kit for the simultaneous colorimetric detection of arsenic and mercury

A smartphone-based microfluidic platform was developed for point-of-care (POC) detection using surface plasmon resonance (SPR) of gold nanoparticles (GNPs). The simultaneous colorimetric detection of trace arsenic and mercury ions (As3+ and Hg2+) was performed using a new image processing application (app). To achieve this goal, a microfluidic kit was fabricated using a polydimethylsiloxane (PDMS) substrate with the configuration of two separated sensing regions for the quantitative measurement of the color changes in GNPs to blue/gray. To fabricate the microfluidic kit, a Plexiglas mold was cut using a laser based on the model obtained from AutoCAD and Comsol outputs. The colorimetric signals originated from the formation of nanoparticle aggregates through the interaction of GNPs with dithiothreitol - 10,12-pentacosadiynoic acid (DTT-PCDA) and lysine (Lys) in the presence of As3+ and Hg2+ ions. This assembly exhibited the advantages of simplicity, low cost, and high portability along with a low volume of reagents and multiplex detection. Heavy Metals Detector (HMD), as a new app for the RGB reader, was programmed for an Android smartphone to quantify colorimetric analyses. Compared with traditional image processing, this app provided significant improvements in sensitivity, time of analysis, and simplicity because the color intensity is measured through a new normalization equation by converting RGB to an Integer system. As a simple, real-time, and portable analytical kit, the fabricated sensor could detect low concentrations of As3+ (710 to 1278 μg L-1) and Hg2+ (10.77 to 53.86 μg L-1) ions in water samples at ambient conditions.

A sonochemical synthesis of cyclodextrin functionalized Au-FeNPs for colorimetric detection of Cr6+ in different industrial waste water

This paper describes a simple, selective and sensitive colorimetric sensing of Cr⁶⁺ ions using β-Cyclodextrin (β-CD) functionalized gold-iron nanoparticles (β-CD/Au-FeNPs). The sonochemically synthesized nanoparticles are winered in colour due to the SPR band of β-CD functionalized bimetalic nanoparticles Au-FeNPs. The capping and stabilizing of Au-FeNPs by redox β-CD is confirmed by FT-IR. The particles are spherical in shape and it posses the effective diameter of 18-20 nm. Under optimized conditions, in the presence of Cr⁶⁺ the wine red Au-FeNPs solution was turned to colourless, accompanying the broadening and red shifting of SPR band. The ratio between the absorbance wavelength at 573 nm to 535 nm (A₅₇₃/A₅₃₅) is linearly correlated with the Cr⁶⁺ concentrations ranging from 50 nM to 500 nM, with a detection limit of Cr⁶⁺ of 2.5 nM was achieved for the first time using β-CD/Au-FeNPs by spectrophotometry. The selectivity of the β-CD/Au-FeNPs towards other interfering metal ions. Finally the proposed method has been successfully employed for the determination of Cr⁶⁺ ion in various industrial waste water with good recoveries.

The conformational behavior of multivalent tris(imidazolium)cyclophanes in the hybrids with metal (pseudo)halides or polyoxometalates

Three 3D imidazole or benzimidazole-bearing cages as trivalent cationic templates react with metal (pseudo)halides or polyoxometalates to obtain a series of different organic–inorganic hybrids in which the cages exhibit breathing behavior of expansion and contraction.

Metal free MoS2 2D sheets as a peroxidase enzyme and visible-light-induced photocatalyst towards detection and reduction of Cr(vi) ions

Two-dimensional molybdenum disulphide (MoS₂) sheets were prepared by using a simple thermal decomposition method.

Synthesis of highly fluorescent Cu/Au bimetallic nanoclusters and their application in a temperature sensor and fluorescent probe for chromium(iii) ions

Bimetallic nanoclusters (BNCs) have attracted great attention due to their cooperative electronic, optical, and catalytic properties. Here, a novel one-step synthetic method is presented to prepare highly fluorescent bimetallic copper–gold nanoclusters (Cu/Au BNCs) in ambient conditions by using glutathione (GSH) as both the reducing agent and the protective layer preventing the aggregation of the as-formed NCs. The resultant Cu/Au BNCs are uniformly dispersed, with an average diameter of 1.5 nm, and it exhibits emission at 450 nm with excitation at 380 nm. Interestingly, the fluorescence signal of the Cu/Au BNCs is reversibly responsive to the environmental temperature, and it shows good sensitivity in the range of 20–70 °C (F = −23.96T + 3149.2 (R = 0.94)). Furthermore, it was found that the fluorescence of Cu/Au BNCs was quenched selectively by Cr³⁺, and a detection method was further developed with detection linear range from 50 nM to 1 mM (F = −174.85[Cr³⁺] + 1686.69 (R = 0.98)) and high sensitivity (LOD = 10 nM, S/N = 3).

The Cu/Au BNCs have been successfully synthesized as a temperature sensor and it successful detection Cr³⁺.

Kinetic Discrimination of Metal Ions Using DNA for Highly Sensitive and Selective Cr3+ Detection

Most metal sensors are designed for a strong binding affinity toward target metal ions, and the underlying principle relies on binding thermodynamics. The kinetic aspect of binding, however, was rarely explored for sensing. In this work, the binding kinetics of 19 common or toxic metal ions are compared based on a fluorescence quenching assay using DNA oligonucleotides as ligands. Among these metals, Cr³⁺ shows uniquely slow fluorescence quenching kinetics, and the quenched fluorescence cannot be recovered by EDTA or sulfide. Most other metals quenched fluorescence instantaneously and can be fully recovered by these metal chelators. Various factors such as DNA sequence and length, chelating agent, pH, and fluorophore type were studied to understand the binding mechanism, leading to a unique two-stage binding model for Cr³⁺. This system has a wide dynamic range of up to 50 μM Cr³⁺ and a low limit of detection of 80 nM. It is also useful for measuring Cr³⁺ in lake water. This work proposes a new metal sensor design by monitoring binding kinetics with Cr³⁺ being a primary example.

A new Tb(iii)-functionalized layer-like Cd MOF as luminescent probe for high-selectively sensing of Cr3+

A new layer-like metal–organic framework {[Cd₄(NDIC)₄·5DMF·H₂O]DMF}_n (NDIC = 5-(5-norbonene-2,3-dicarboximide) isophthalic acid) was synthesized by solvothermal method.

Hydrothermal synthesis of nitrogen and boron doped carbon quantum dots with yellow-green emission for sensing Cr(vi), anti-counterfeiting and cell imaging

Nitrogen and boron co-doped carbon quantum dots with great stability in high-salt conditions and good photostability are prepared through hydrothermal method and utilized for fluorometric detection of Cr(vi), anti-counterfeiting and cell imaging.