Cu²⁺ functionalized N-acetyl-L-cysteine capped CdTe quantum dots as a novel resonance Rayleigh scattering probe for the recognition of phenylalanine enantiomers

A fluorescence nanoprobe of N-Acetyl-L-Cysteine capped CdTe QDs for sensitive detection of nitrofurazone

A method was established for detecting the content of nitrofurazone (NFZ) by fluorescence quenching of N-Acetyl-L-Cysteine (NAC) coated cadmium telluride quantum dots (CdTe QDs). By means of transmission electron microscopy (TEM) and multispectral methods such as fluorescence and ultraviolet visible spectra (UV-vis), the synthesized CdTe QDs were characterized. The quantum yield (φ) of CdTe QDs was measured as 0.33 by reference method. The CdTe QDs had a better stability, the RSD of fluorescence intensity was 1.51% in three months. NFZ quenching the emission light of CdTe QDs was observed. The analyses of Stern-Volmer and time-resolved fluorescence suggested the quenching was static. The binding constants (K_a) between NFZ and CdTe QDs were 1.14 × 10⁴ (293 K), 0.74 × 10⁴ (303 K) and 0.51 × 10⁴ (313 K) L mol^-1. The hydrogen bond or van der Waals force was the dominated binding force between NFZ and CdTe QDs. The interaction was further characterized by UV-vis absorption as well as Fourier transform infrared spectra (FT-IR). Using fluorescence quenching effect, a quantitative determination of NFZ was carried out. The optimal experimental conditions were studied and determined as following: pH was 7 and contact time was 10 min. The effects of reagent addition sequence, temperature and the foreign substances including some metals (Mg²⁺; Zn²⁺; Ca²⁺; K⁺; Cu²⁺), glucose, bovine serum albumin (BSA) and furazolidone on the determination were studied. There was a high correlation between the concentration of NFZ (0.40 - 39.63 μg mL^-1) and F₀/F with the standard curve F₀/F = 0.0262c + 0.9910 (r = 0.9994). The detection limit (LOD) reached 0.04 μg mL^-1 (3S₀/S). The contents of NFZ in beef and bacteriostatic liquid were detected. The recovery of NFZ was 95.13% - 103.03% and RSD was 0.66% - 1.37% (n = 5).

β-Cyclodextrin-Immobilized Ni/Graphene Electrode for Electrochemical Enantiorecognition of Phenylalanine

In this work, a Ni/graphene (Ni/G) electrode was designed and fabricated by plasma-enhanced chemical vapor deposition (PECVD) for the ultrasensitive recognition of d- and l-phenylalanine. Through a single-step PECVD process, the Ni/G electrode can achieve better hydrophilicity and larger catalytic surface area, which is beneficial for the electrochemical recognition of bio-objects. After surface modification with β-cyclodextrin, the Ni/G electrode can distinguish d-phenylalanine from l-phenylalanine according to a 0.09 V peak shift in differential pulse voltammetry tests. Moreover, this Ni/G electrode achieved a detection limit as low as 1 nM and a wide linear range from 1 nM to 10 mM toward l-phenylalanine, with great storage stability and working stability.

Chiral recognition of phenylglycinol enantiomers based on N-acetyl-l-cysteine capped CdTe quantum dots in the presence of Ag. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2017;183:23-29. [PMID: 28432917 DOI: 10.1016/j.saa.2017.04.014]

In this study, a novel method for chiral recognition of phenylglycinol (PG) enantiomers was proposed. Firstly, water-soluble N-acetyl-l-cysteine (NALC)-capped CdTe quantum dots (QDs) were synthesized and experiment showed that the fluorescence intensity of the reaction system slightly enhancement when added PG enantiomers to NALC-capped CdTe quantum dots (QDs), but the R-PG and S-PG could not be distinguished. Secondly, when there was Ag⁺ presence in the reaction system, the experiment result was extremely interesting, the PG enantiomers cloud make NALC-capped CdTe QDs produce different fluorescence signal, in which the fluorescence of S-PG+Ag⁺+NALC-CdTe system was significantly enhanced, and the fluorescence of R-PG+Ag⁺+NALC-CdTe system was markedly decreased. Thirdly, all the enhanced and decreased of the fluorescence intensity were directly proportional to the concentration of R-PG and S-PG in the linearly range 10^-5-10^-7mol·L^-1, respectively. So, the new method for simultaneous determination of the PG enantiomers was built too. The experiment result of the method was satisfactory with the detection limit of PG can reached 10^-7mol·L^-1 and the related coefficient of S-PG and R-PG are 0.995 and 0.980, respectively. The method was highly sensitive, selective and had wider detection range compared with other methods.

Measurement analysis of two radials with a common-origin point and its application

In spectral analysis, a chemical component is usually identified by its characteristic spectra, especially the peaks. If two components have overlapping spectral peaks, they are generally considered to be indiscriminate in current analytical chemistry textbooks and related literature. However, if the intensities of the overlapping major spectral peaks are additive, and have different rates of change with respect to variations in the concentration of the individual components, a simple method, named the 'common-origin ray', for the simultaneous determination of two components can be established. Several case studies highlighting its applications are presented.