A facile strategy to construct versatile fluorescent probes for the detection of Au3+ and nitroaromatic

Colorimetric determination and recycling of gold(III) ions using label-free plasmonic H0.3MoO3 nanoparticles

A low-cost and environment-friendly sensor was developed for visual determination of gold ions (Au³⁺) by using label-free hydrogen doped molybdenum oxide (H_0.3MoO₃) nanoparticles as ratio probes. According to the characterization results of transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction, and Fourier transform infrared spectra, Au³⁺ is easily reduced to red Au nanoparticles (AuNPs) by blue H_0.3MoO₃ nanoparticles. The color change of the solution depends on the concentration of Au³⁺, which makes it possible to detect Au³⁺ visually. Under optimal experimental conditions of pH 4.6, H_0.3MoO₃ nanoparticles concentration of 0.075 mg·mL^-1, and reaction time of 7 min, the sensor offers a satisfactory determination range from 0.5 to 70 μM and a good determination limit of 0.45 μM for Au³⁺. The concentration of Au³⁺ as low as 10 μM can be directly distinguished through the naked eye. Additionally, the colorimetric probe has also been proved applicable in environmental water samples. More importantly, the resulting AuNPs have good stability and oxidase-like activity, which may be directly used in sensing, catalysis, energy, and other fields.

The chemical adsorption effect of surface enhanced Raman spectroscopy of nitrobenzene and aniline using the density functional theory

Nitrobenzene and Aniline are representatives of the nitro or amino compounds of benzene, mainly used in the manufacture of dyes, spices, medicines, and so on. Extensive use of Nitrobenzene and Aniline may cause pesticide residue pollution and have carcinogenic effects on organisms. In this paper, the Nitrobenzene and Aniline single molecules and their complexes with gold nanoparticles are studied theoretically by Raman spectroscopy, the surface-enhanced Raman spectroscopy (SERS) and the density functional theory (DFT) simulations. Selective binding of gold nanoparticles (AuNPs) to the analyte was used to study the molecular electrostatic potential (MEP), frontier molecular orbital (FMO) and the Raman activity spectra of Nitrobenzene and Aniline, as well as the Raman activity spectrum of the complexes. The most electronegative sites of Nitrobenzene and Aniline are found in the MEP and the hypothesis that these sites might be the adsorption sites of Nitrobenzene/Aniline molecules at the gold surface. At the same time, the MEP of the Nitrobenzene/Aniline complexes also prove the existence of the charge transfer effect between Nitrobenzene/Aniline and Au. The FMO energy gap of Nitrobenzene/Aniline is 0.18983 eV and 0.18953 eV, respectively, and which, after adding the Au₃ clusters, change to 0.03376 eV and 0.0797 eV, respectively, indicating that the Nitrobenzene/Aniline-Au₃ complexes have stronger chemical activities and are more prone to the charge transfer effects. The electrophilic indices of Nitrobenzene (0.17921 eV) and Aniline (0.05635 eV) are calculated and analyzed, as well as that of Nitrobenzene/Aniline-Au₃ complexes after adding the Au₃ atomic clusters, 0.80819 eV and 0.19819 eV, respectively. The obvious increasing trend in the electrophilic indices of the Nitrobenzene/Aniline-Au₃ complexes indicate their stronger biological activities and more prone to chemical reactions. The chemisorption of Nitrobenzene/Aniline and gold nanoparticles complexes is studied by the SERS, and the Raman formation of the complexes at different binding sites of Nitrobenzene/Aniline and Nitrobenzene/Aniline-Au₃ is well explained by the surface selection rule. The reason for the selective enhancement of the spectral peaks presented in the Raman activity spectrum is calculated, and the enhancement factor of the chemical enhancement due to the charge transfer effect is calculated as well. The reason for the peak offset in the SERS spectrum to the conventional Raman spectrum is explained.