4-Aminothiophenol functionalized gold nanoparticles as colorimetric sensors for the detection of cobalt using UV–Visible spectrometry

A Simple Aptamer SERS Sensor Based on Mesoporous Silica for the Detection of Chlorpyrifos

Chlorpyrifos is an organophosphorus insecticide, which can be used to control a variety of chewing and piercing mouthparts pests in agricultural production. It can destroy the normal nerve impulse conduction by inhibiting the activity of acetylcholinesterase or cholinesterase in the nerves, causing a series of poisoning symptoms. In order to achieve the quantitative analysis of chlorpyrifos residues in agricultural products, an aptamer-controlled signal molecule release method was developed in this study. The signal molecule 4-ATP of surface-enhanced Raman spectroscopy (SERS) was loaded into aminated mesoporous silica nanoparticles (MSNs-NH2) prepared by the one pot method, and then coated with an aptamer of chlorpyrifos through electrostatic interaction. The specific binding of the aptamer and chlorpyrifos led to the release of 4-ATP, and the amount of 4-ATP released was positively correlated with the amount of chlorpyrifos. Finally, the standard curve of chlorpyrifos quantitative detection based on SERS was established. Meanwhile, Ag-carrying mesoporous silica (Ag@MSNs) was prepared as the reinforcement substrate for SERS detection. The results showed that there was a good linear correlation between the Raman intensity and the concentration of chlorpyrifos at 25−250 ng/mL, and the limit of detection (LOD) was 19.87 ng/mL. The recoveries of chlorpyrifos in the apple and tomato samples were 90.08−102.2%, with RSD < 3.32%. This method has high sensitivity, specificity, reproducibility and stability, and can be used for the quantitative detection of chlorpyrifos in the environment and agricultural products.

A Novel Imidazole Bound Schiff Base as Highly Selective "Turn-on" Fluorescence Sensor for Zn2+ and Colorimetric Kit for Co2

An imidazole based Schiff base (2-[(1H-imidazole-2-ylmethylene)-amino]-4-methyl-phenol) (IMP), with an imine unit, has been designed and characterized by various standard methods. The evaluation of the probe as a fluorogenic sensor for Zn²⁺ and a chromogenic sensor for Co²⁺ has been rationalized in terms of the PET mechanism. In the presence of Zn²⁺, a light yellow colored solution of IMP with maximum absorption of 364 nm becomes bright yellow with maximum absorption of 410 nm and a measurable fluorescent signal at 612 nm with bathochromic enhancement. The sensitivity of the fluorescent based assay (6.78 × 10^-9 M) for Zn²⁺ is far below the limit in the World Health Organization (WHO) guidelines for drinking water (7.6 × 10^-5 M) and therefore it is capable of being a practical system for the monitoring of Zn²⁺ concentrations in aqueous samples. Moreover, IMP showed a highly selective colorimetric response to Co²⁺ by displayed an obvious pink color upon addition of metal solution immediately without any interference from other ions. These results provide a new approach for selectively recognizing the two most important trace elements in the human body simultaneously, for Zn²⁺ by emission spectra and Co²⁺ by the naked eye.

Lansoprazole-Based Colorimetric Chemosensor for Efficient Binding and Sensing of Carbonate Ion: Spectroscopy and DFT Studies

The new benzimidazole based receptor Lansoprazole has been used to detect carbonate anion by naked-eye and Uv-Vis spectroscopy. This receptor revealed visual changes withCO 3 2 - anion in ethanol. No detectable color changes were observed upon the addition of any other tested anions. The lansoprazole chemosensor selectively recognizesCO 3 2 - ion over the other interference anions in the ethanol, followed by deprotonation and reflected 1:1 complex formation between the receptor and the carbonate ion. Lansoprazole exhibits splendid selectivity toward carbonate ion via a visible color change from colorless to yellow with a detection limit of 57 μM. The binding mode ofCO 3 2 - to receptor L is supported by Density Functional Theory calculation. Moreover, this receptor shows a practical visible colorimetric test strip for the detection of carbonate ions. The transition states calculation demonstrates the occurrence of reaction from L to L-CO 3 2 - after overcoming an energy barrier of 10.1 kcal/mol, and there is considerable interaction energy between L andCO 3 2 - (94.9 kJ/mol), both of which confirmed that receptor L has high sensitivity and selectivity to the carbonate ion. The theoretical studies were performed to acquire an electronic description of the complexation mechanism byCO 3 2 - as well as to study bonding and structure in the complex. The optimized structures and binding mechanisms were supported with a high correlation and agreement by spectroscopy and DFT calculations.

Design and analysis of surface plasmon resonance optical sensor for determining cobalt ion based on chitosan-graphene oxide decorated quantum dots-modified gold active layer

In this study, the incorporation of surface plasmon resonance (SPR) spectroscopy with novel chitosan-graphene oxide/cadmium sulphide quantum dots (CdS QDs) active layer for cobalt ion (Co²⁺) detection has been developed. The interaction of different Co²⁺ concentrations with the novel modified active layer was monitored using the SPR technique. From the SPR results, detection range, sensitivity, full width at half maximum (FWHM), detection accuracy (DA) and signal-to-noise ratio (SNR) have been analysed. The results showed the detection range of this optical sensor was 0.01 to 10 ppm, and it was saturated for higher concentration of Co²⁺. The sensitivity obtained was 0.1188 ppm^-1 for low concentration of Co²⁺ ranged from 0.01 to 1 ppm. The FWHM and DA were consistent for all concentration of Co²⁺, while the SNR of the SPR signal increased with the Co²⁺ concentration. The SPR angle shifts were also fitted using Langmuir, Freundlich and Sips (Langmuir-Freundlich) isotherm models, where Sips model fitted the best with the binding affinity of 0.939 ppm^-1. The results proved that the novel chitosan-graphene oxide/CdS QDs modified gold thin film can detect Co²⁺ via SPR spectroscopy.

Low-temperature phyto-synthesis of copper oxide nanosheets: Its catalytic effect and application for colorimetric sensing

The last decade has seen a remarkable detonation in modifying chemical processes for nanomaterial synthesis to make them 'green'. Owing to the unique properties of nanomaterial and with regard to environmental issues, in this study, a new alternative and fast eco-friendly approach for the synthesis of copper oxide nanosheets (CuO-NSs) using Terminalia catappa (Indian almond) leaf extract as a renewable and non-toxic reducing agent and efficient stabilizer was reported. It is noteworthy to mention that the present fabrication process can open up the possibility of fast, low cost and high efficiency synthesis of CuO nanostructures with an interesting morphology of nanosheets at ambient temperature and pressure. Optimization of important factors such as pH, the quantity of leaf extract, copper precursor concentration, incubation time and temperature on the formation of CuO-NSs were investigated. The formation of bioreduced CuO-NSs was certified by UV-Vis spectroscopy, XRD, TEM analysis and FT-IR spectroscopy. Due to good stability, and excellent catalytic activity of the synthesized CuO-NSs, they are exerted to degrade of MB dye in water as a model color pollutant in the presence of NaBH₄ at room temperature. Furthermore, color properties of CuO nanostructures aid us to apply these biosynthesized nanomaterials in the design of optical sensors for detection of Fe²⁺ and Fe³⁺ ions. In view of many advantages of the current optical sensors based on CuO-NSs, such as eco-friendly, cost-effective, and straightforward design, the sensing system presents a potential application in environmental science.

Sensitive and selective colorimetric nitrite ion assay using silver nanoparticles easily synthesized and stabilized by AHNDMS and functionalized with PABA

Nitrite ions (NO₂ ^-), as one of the important inorganic anions, exhibit considerable effects towards the environment and human health. Moreover, over intake of this anion may cause dangerous diseases. Herein, we successfully fabricated silver nanoparticles (AgNPs) using 4-amino-5-hydroxynaphthalene-2, 7-disulphonic acid monosodium salt (AHNDMS) and functionalized them with p-aminobenzoic acid (PABA), and used the functionalised AgNPs as a sensitive and selective colorimetric sensor for nitrite ions. The structure of the as-prepared pure AgNPs was experimentally characterized by different characterizations methods, namely, UV-vis, FT-IR, CV, DPVs, SEM, TEM, and XRD. Additionally, the nitrite ion sensitively and selectively changes the brownish yellow color of the dispersed AgNPs to pinkish red, indicating aggregation of AgNPs, with a detection limit of 0.016 ppm (0.348 μM) and 0.0069 ppm (0.149 μM) by the naked-eye and by UV-vis spectroscopy, respectively. The color change suggested that the aggregation of AgNPs was induced by nitrite-selective diazo-coupling. UV-vis spectra show the disappearance of the absorbance at 474 nm and appearance of a new peak at 532 nm, presumably due to the conversion of AgNPs to silver ions. Moreover, the studies of interference in the proposed sensor confirm its selectivity in the presence of anions as well as cations. Furthermore, linearity was observed between the absorption and the concentration of nitrite ions. More importantly, the proposed sensor was practicably applied for the determination of nitrite in different water samples, such as distilled water, river water, and tap water.

Development of extremely stable dual functionalized gold nanoparticles for effective colorimetric detection of clenbuterol and ractopamine in human urine samples

New glutamic acid (Glu) and polyethylenimine (PE) functionalized ultra-stable gold nanoparticles (PE-Glu-AuNPs) were developed via a simple NaBH₄ reduction method. The low toxicity and biocompatibility of PE-Glu-AuNPs were confirmed via an MTT assay in Raw 264.7 cells. Excitingly, PE-Glu-AuNPs were found to be extremely stable at room temperature up to six months and were utilized in an effective colorimetric naked eye assay of clenbuterol (CLB) and ractopamine (RCT) at pH 5. It was found that the selective assay of CLB and RCT is not affected by any other interferences (such as alanine, phenylalanine, NaCl, CaCl₂, threonine, cysteine, glycine, glucose, urea and salbutamol). Furthermore, the detection of these β-agonists can be visually accomplished through change color from wine red to purple blue. Notably, the aggregation induced detection of CLB and RCT was well confirmed through transmission electron microscopy (TEM) and dynamic light scattering (DLS) studies. DLS investigations, clearly showed, that in the presence of CLB and RCT, the initial size of PE-Glu-AuNPs (12.8 ± 8.6 nm) was changed to 84.8 ± 52.3 and 79.5 ± 47.8 nm, respectively, via aggregation. Furthermore, the colorimetric assays of CLB and RCT with PE-Glu-AuNPs were effective starting from CLB and RCT concentrations of 200 nM and 400 nM, respectively, and could be visualized using the naked eyes. Remarkably, UV-vis titrations of PE-Glu-AuNPs with CLB and RCT could be used to well estimate their sub nanomolar detection limits (LODs) via standard deviation and linear fittings. The contribution of surface functional groups that support the analyte recognition was confirmed by fourier-transform infrared spectroscopy (FTIR) analysis. Moreover, the CLB and RCT assays with PE-Glu-AuNPs were supported by examination of human urine samples.

Biological response of HeLa cells to gold nanoparticles coated with organic molecules

In this work, gold nanospheres functionalized with low weight organic molecules (4-aminothiphenol and cysteamine) were synthesized in a one-step method for their in vitro cytotoxic evaluation on HeLa cells. To enhance the biocompatibility of the cysteamine-capped GNPs, BSA was used due to its broad PH stability and high binding affinity to gold nanoparticles. Besides, the widely reported silica coated gold nanorods were tested here to contrast their toxic response against our nanoparticles coated with organic molecules. Our results shown, the viability measured at 1.9×10^-5M did not show significant differences against negative controls for all the samples; however, the metabolic activity of HeLa cells dropped when they were exposed to silica gold nanorods in the range of concentrations from 2.9×10^-7M to 3.0×10^-4M, while in the cases of gold nanospheres, we found that only at concentrations below 1.9×10^-5M metabolic activity was normal. Our preliminary results did not indicate any perceivable harmful toxicity to cell membrane, cytoskeleton or nucleus due to our nanospheres at 1.9×10^-5M. Additional test should be conducted in order to ensure a safe use of them for biological applications, and to determine the extent of possible damage.

A new water-soluble heteronuclear PdII–AuI pincer complex as two-photon luminescent probe for biological Co2+ detection

A new water-soluble heteronuclear Pd^II–Au^I pincer complex was synthesized and investigated for biological Co²⁺ detection.

A simple and novel system for colorimetric detection of cobalt ions

A simple and novel method for the colorimetric detection of Co(2+) was developed based on controlling the oxidation level of methylene blue (MB). After a complex was formed between MB, 2-aminothiophenol (ATP) and copper nitrate (MB-ATP-Cu(2+)), the sensing of Co(2+) showed high selectivity. The mechanism of sensing has also been discussed.