Molybdenum Disulfide Quantum Dots as a Photoluminescence Sensing Platform for 2,4,6-Trinitrophenol Detection

Transition metal chalcogenides, especially molybdenum disulfide (MoS₂), have recently attracted wide attention from researchers as graphene-analogous materials. However, until now, little literature has reported the synthesis of photoluminescent MoS₂ materials and their applications in analytical chemistry. We herein presented a facile bottom-up hydrothermal route for the synthesis of photoluminescent MoS₂ quantum dots (QDs) by using sodium molybdate and cysteine as precursors. The prepared MoS₂ QDs were characterized by transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, photoluminescence spectroscopy, and UV–vis spectroscopy. The MoS₂ QDs were then used as photoluminescent probes to construct a photoluminescence (PL) quenching sensor for detection of 2,4,6-trinitrophenol (TNP). The TNP sensor presented a wide linear range from 0.099 to 36.5 μM with a high detection limit of 95 nM. Furthermore, the sensor displayed a high sensitivity toward TNP over other structurally similar compounds like 2,4,6-trinitrotoluene, p-chlorophenol, phenol, and 2,6-di-<i>tert</i>-butyl-4-methylphenol. To understand the origin of the high sensitivity, we assessed the emission wavelength-dependent PL quenching behavior of MoS₂ QDs by the above five compounds using Stem–Volmer equation in detail. The results showed that the novel approach we put forward can satisfactorily explain the interaction mechanisms between MoS₂ QDs and the five compounds, and the high sensitivity for TNP very likely originated from a combination of the PL resonance energy transfer, electronic energy transfer, and electrostatic interactions between MoS₂ QDs and TNP. Finally, the sensor was successfully applied for detection of TNP in water samples and test papers

Competitive Interactions of Ionic Surfactants with Salbutamol and Bovine Serum Albumin: A Molecular Spectroscopy Study with Implications for Salbutamol in Food Analysis

The effect of ionic surfactants, sodium dodecyl sulfate (SDS) and <i>N</i>-cetyl-<i>N</i>,<i>N</i>,<i>N</i>-trimethylammonium bromide (CTAB), on the interaction between β-agonist salbutamol (SAL) and bovine serum albumin (BSA) was investigated with the use of fluorescence spectroscopy (FLS) and chemometrics methods [multivariate curve resolution-alternating least-squares (MCR-ALS) and parallel factor analysis algorithm (PARAFAC)]. It was found that the binding constant of SAL to BSA in the presence of CTAB was much larger than that without this ligand. The ligand/BSA stoichiometry was 4:1, that is, (CTAB)₄–BSA, and was 2:1 with the ligand, that is, (SAL)₂–BSA. These results were obtained from the concentration profiles extracted by MCR-ALS for all three reactants. Quantitative information on the complex CTAB–BSA–SAL species was obtained with the resolution of the excitation–emission fluorescence three-way data matrices by PARAFAC. This research has implications for the analysis of SAL in food and might be performed in laboratories associated with organizations such as the U.S. Food and Drug Administration (FDA) and the International Olympic Committee (IOC)

A Near-Infrared Reflectance Spectroscopy Method for Direct Analysis of Several Chemical Components and Properties of Fruit, for Example, Chinese Hawthorn

Near-infrared spectroscopy (NIRS) calibrations were developed for the discrimination of Chinese hawthorn (<i>Crataegus pinnatifida</i> Bge. var. <i>major</i>) fruit from three geographical regions as well as for the estimation of the total sugar, total acid, total phenolic content, and total antioxidant activity. Principal component analysis (PCA) was used for the discrimination of the fruit on the basis of their geographical origin. Three pattern recognition methods, linear discriminant analysis, partial least-squares-discriminant analysis, and back-propagation artificial neural networks, were applied to classify and compare these samples. Furthermore, three multivariate calibration models based on the first derivative NIR spectroscopy, partial least-squares regression, back-propagation artificial neural networks, and least-squares-support vector machines, were constructed for quantitative analysis of the four analytes, total sugar, total acid, total phenolic content, and total antioxidant activity, and validated by prediction data sets

Label-Free Fluorescence Sensing of Lead(II) Ions and Sulfide Ions Based on Luminescent Molybdenum Disulfide Nanosheets

Fluorescent molybdenum disulfide (MoS₂) nanosheets were synthesized hydrothermally by employing sodium molybdate and thiourea as the starting materials. Lead­(II) ion was introduced as a chemical dopant into the fluorescent nanosheets for the first time, and it was found that the fluorescence of the doped MoS₂ nanosheets showed a considerable enhancement compared with that of initial MoS₂ nanosheets, implying that lead­(II)-doping into the MoS₂ nanosheets could result in an increase in the fluorescence quantum yield. In parallel, we exploited the lead­(II)-induced fluorescence enhancement of MoS₂ nanosheets to design a green and facile fluorescent “turn on” nanosensor for lead­(II) detection. Moreover, we found that the fluorescent intensity of the doped MoS₂ nanosheets was drastically quenched by the successive addition of sulfide ions. Hence, the “turn off” process was used to fabricate a green fluorescence quenching sensor for detection of sulfide ions. Finally, we elucidated the origin of the lead­(II)-induced fluorescence enhancement and sulfide-induced fluorescence reduction by using various analytical techniques like scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and UV–vis spectroscopy. The work not only opens a door for the further development of new approaches for the preparation of various fluorescent layered transition metal dichalcogenides with high quantum yields but also provides a versatile and sustainable sensing platform for ion detection

One-Pot Aqueous Synthesis of Nucleoside-Templated Fluorescent Copper Nanoclusters and Their Application for Discrimination of Nucleosides

A facile, one-pot synthetic method has been proposed to prepare water-soluble fluorescent copper nanoclusters (CuNCs) templated by nucleosides. The nucleoside-templated fluorescent CuNCs were further characterized by using various analytical techniques, such as transmission electron microscopy, X–ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and fluorescence spectroscopy. The role of various reactants such as ascorbic acid, nucleoside, and citrate buffer in the synthesis process of fluorescent CuNCs was explored. The results showed that nucleoside and ascorbic acid were very likey to respectively act as a stabilizer and a reductant to form nanoclusters, and citrate buffer acted as both pH regulator solution and a reducing agent. The fluorescence spectra of various nucleoside-templated CuNCs were finally combined with multivariate chemometrics analysis for discrimination of different nucleosides