Comparison of Gold Nanoparticles Prepared Using Monobasic Sodium Citrate or Sodium Borohydride for Neomycin Determination in Saliva after Solid-Phase Extraction (SPE) on a Molecularly Imprinted Polymer (MIP)

Two distinct spherical gold nanoparticles (AuNPs) were compared for the spectrophotometric determination of neomycin in saliva. The AuNPs were produced using AuCl3 and monobasic sodium citrate (in water bath at 100 °C) under magnetic stirring (AuNPs-citrate) and using HAuCl4 and NaBH4, at room-temperature under mechanical agitation in a commercial reactor (AuNPs-H). Both AuNPs were spherical with diameters of 7.7 nm (AuNPs-H) and 26.1 nm (AuNPs-citrate) and the maximum wavelength of the localized surface plasmon resonance (LSPR) bands were at 511 nm (AuNPs-H) and 529 nm (AuNPs-citrate). Equivalent spectral extinctions were found despite the fact the large difference in concentrations of AuNPs in dispersions: 4.2 × 10−9 mol L−1 for the AuNPs-H and 8.7 × 10−11 mol L−1 for the AuNPs-citrate. Both AuNPs interacted with aminoglycosides (AMG), affecting intensity of the LSPR band as the concentration of AMG increased. The response of the AuNPs-H was more sensitive toward AMG covering the following ranges: 0.6–600 µg L−1 (gentamicin), 7.3–550 µg L−1 (neomycin) and 14–520 µg L−1 (kanamycin). AuNPs-H optical response was more robust in function of the pH with AuNPs-citrate response only observed in acid solution, favoring electrostatic interaction with AMG. Catalytic activity of AuNPs-H, in reducing the 4-phenolate ion, presented a higher rate constant (4.3 × 10−3 s−1) and was used as analytical probe to determine neomycin in saliva after solid phase extraction with a commercially available AMG imprinted polymer enabling quantification to 0.36 μg of the analyte.</p

Mechanisms of Tenebrescence and Persistent Luminescence in Synthetic Hackmanite Na₈Al₆Si₆O₂₄(Cl,S)₂

Synthetic hackmanites, Na₈Al₆Si₆O₂₄(Cl,S)₂, showing efficient purple tenebrescence and blue/white persistent luminescence were studied using different spectroscopic techniques to obtain a quantified view on the storage and release of optical energy in these materials. The persistent luminescence emitter was identified as impurity Ti³⁺ originating from the precursor materials used in the synthesis, and the energy storage for persistent luminescence was postulated to take place in oxygen vacancies within the aluminosilicate framework. Tenebrescence, on the other hand, was observed to function within the Na₄(Cl,S) entities located in the cavities of the aluminosilicate framework. The mechanism of persistent luminescence and tenebrescence in hackmanite is presented for the first time