Solid-phase extraction of Cr(VI) with magnetic melamine–formaldehyde resins, followed by its colorimetric sensing using gold nanoparticles modified with p-amino hippuric acid

Cost-effective synthesis and application of Cu²⁺-doped melamine formaldehyde resin for enhanced tetracycline enrichment in environmental water

Tetracycline antibiotics (TCs) are typically present at low residue levels in environmental water, necessitating enrichment prior to analysis. In this study, a Cu2+-doped melamine formaldehyde resin (Cu-MFR) was synthesized to enhance the adsorption efficiency for TCs, leveraging the formation of stable Cu2+-TC complexes on the sorbent surface. Then it was used as an adsorbent in solid-phase extraction (SPE) for the enrichment of four TCs from water samples. The optimized parameters for Cu-MFR in the analysis of TCs in environmental water enabled linear detection ranges from 0.20 to 50 ng/mL, with relative recoveries ranging from 79.5 % to 97.6 % and relative standard deviations ≤ 10.0 %, using high-performance liquid chromatography-tandem high-resolution mass spectrometry (HPLC-HRMS). The limits of detection for the four TCs were determined to be between 0.11 and 0.16 ng/mL, indicating its potential for practical application in real sample analysis.

A review of the treatment technologies for hexavalent chromium contaminated water

The toxicity of hexavalent chromium (Cr(VI)) present in the environment has exceeded the current limits or standards and thus may lead to biotic and abiotic catastrophes. Accordingly, several treatments, including chemical, biological, and physical approaches, are being used to reduce Cr(VI) waste in the surrounding environment. This study compares the Cr(VI) treatment approaches from several areas of science and their competence in Cr(VI) removal. As an effective combination of physical and chemical approaches, the coagulation-flocculation technique removes more than 98% of Cr(VI) in less than 30 min. Most membrane filtering approaches can remove up to 90% of Cr(VI). Biological approaches that involve the use of plants, fungi, and bacteria also successfully eliminate Cr(VI) but are difficult to scale up. Each of these approaches has its benefits and drawbacks, and their applicability is determined by the research aims. These approaches are also sustainable and environmentally benign, thus limiting their effects on the ecosystem.

A Highly Sensitive Fluorescence and Screen-Printed Electrodes—Electrochemiluminescence Immunosensor for Ricin Detection Based on CdSe/ZnS QDs with Dual Signal

A sensitive dual-readout immunosensor for fluorescence and electrochemiluminescence (ECL) detection of ricin was established, which was combined with a streptavidin–biotin signal amplification system. CdSe/ZnS quantum dots with fine fluorescence and ECL properties were used as the dual-signal function probes of the sandwich immunocomplex. Under the optimum experimental conditions, the dual signal intensity increased significantly with the rise in ricin concentration. The fluorescence intensity of the senor exhibited a good liner relationship toward the ricin concentrations with 0.1~100 ng/mL and the limit of detection (LOD) was 81.7 pg/mL; taking ECL as the detection signal, the sensor showed a linear relationship with the ricin concentrations ranging from 0.01 ng/mL to 100 ng/mL and the LOD was 5.5 pg/mL. The constructed sensor with high sensitivity had been successfully applied to the detection of ricin in complex matrices with satisfactory recoveries. The proposed immunosensor model can be extended to the analysis and detection of others target proteins.

Morphology Adjustment and Optimization of CuS as Enzyme Mimics for the High Efficient Colorimetric Determination of Cr(VI) in Water

Metal sulfide is often utilized as a catalyzed material to form colorimetric response system for some heavy metal detection. While the aggregation effect and conventional morphology limited the catalyzed efficiency. Herein, a robust method based on morphology adjustment was proposed to improve the dispersibility and catalytic performance of CuS. The results demonstrated when the solvent ratio of ethylene glycol and dimethyl sulfoxide arrived at 3:1, it displayed an optimal structure which is like a patulous flower. Meanwhile, an optimal surface binding energy (ΔE) of 120.1 kcal/mol was obtained via theoretical calculation model. The flower-like structure caused a 2-fold increase in the catalytic level. Subsequently, the CuS was employed to make colorimetric detection of Cr(VI) in water. The assay results exhibited a linear range of the Cr(VI) from 60 to 340 nM, the limit of detection was 1.07 nM. In the practical tests for Qianhu lake water, the spiked recoveries were 93.6% and 104% with the RSD of 4.71% and 3.08%. Therefore, this CuS-based colorimetric method possesses a satisfactory application prospect for the Cr(VI) determination in water.

Surfactant stabilized gold nanomaterials for environmental sensing applications - A review

Surfactant stabilized Gold (Au) nanomaterials (NMs) have been documented extensively in recent years for numerous sensing applications in the academic literature. Despite the crucial role these surfactants play in the sensing applications, the comprehensive reviews that highlights the fundamentals associated with these assemblies and impact of these surfactants on the properties and sensing mechanisms are still quite scare. This review is an attempt in organizing the vast literature associated with this domain by providing critical insights into the fundamentals, preparation methodologies and sensing mechanisms of these surfactant stabilized Au NMs. For the simplification, the surfactants are divided into the typical and advanced surfactants and the Au NMs are classified into Au nanoparticles (NPs) and Au nanoclusters (NCs) depending upon the complexity in structure and size of the NMs respectively. The preparative methodologies are also elaborated for enhancing the understanding of the readers regarding such assemblies. The case studies regarding surfactant stabilized Au NMs were further divided into colorimetric sensors, surface plasmonic resonance (SPR) based sensors, luminescence-based sensors, and electrochemical/electrical sensors depending upon the property utilized by the sensor for the sensing of an analyte. Future perspectives are also discussed in detail for the researchers looking for further progress in that particular research domain.

Adsorptive colorimetric determination of chromium(VI) ions at ultratrace levels using amine functionalized mesoporous silica

There is an urgent need for a rapid, affordable and sensitive analytical method for periodic monitoring of heavy metals in water bodies. Herein, we report for the first time a versatile method for ultratrace level metal detection based on colorimetric sensing. The method integrates preconcentration using a nanomaterial with a colorimetric assay performed directly on the metal-enriched nanomaterial surface. This method circumvents the need for tedious sample pre-processing steps and the complex development of colorimetric probes, thereby reducing the complexity of the analytical procedure. The efficacy of the proposed method was demonstrated for chromium(VI) ions detection in water samples. Amine functionalized mesoporous silica (AMS) obtained from a one-pot synthesis was utilized as a pre-concentration material. The structural and chemical analysis of AMS was conducted to confirm its physico-chemical properties. The pre-concentration conditions were optimized to maximise the colorimetric signal. AMS exhibited a discernible colour change from white to purple (visible to the naked eye) for trace Cr(VI) ions concentration as low as 0.5 μg L^-1. This method shows high selectivity for Cr(VI) ions with no colorimetric signal from other metal ions. We believe our method of analysis has a high scope for de-centralized monitoring of organic/inorganic pollutants in resource-constrained settings.