ABSTRACT
Silicon quantum dot has become an attractive nanomaterial due to their excellent biocompatibility and optical performance. However, poor water-solubility of the traditional silicon quantum dot limits its wide application. In this study, we reported the synthesis of water-soluble silicon quantum dots with imidazole groups by using hydrothermal method, in which N-trimethysilylimidazole was used as a precursor of silicon. Compared with sodium borohydride, ascorbic acid, bovine serum protein, cysteine and citric acid, the as-prepared silicon quantum dots offered the strongest fluorescence intensity when sodium citrate was used as the reducing agent and stabilizer for the synthesis. The reaction could complete within 2 h at 220℃. The obtained silicon quantum dots showed good water-solubility with an average particle size of 2. 6 nm, and the result of infrared spectroscopic analysis verified the existence of free imidazole groups on the surface. By means of the investigation of the fluorescence quenching behavior of copper ions towards the silicon quantum dots at different temperatures, we found that the degree of fluorescence quenching increased with the increase of temperature. There results proved that the fluorescence decrease belongs to static quenching. Namely, the interaction of Cu2+ with imidazole groups on the surface of silicon quantum dots formed stable complex. In addition, the resonance light scattering analysis also showed that the fluorescence quenching process was accompanied by the agglomeration of particles. Based on the fluorescence quenching behavior of silicon quantum dots, we established a method for the fluorescent detection of Cu2+. When the concentration of Cu2+was in the range of 0. 04-2400 μmol/L, the fluorescence intensity would linearly decrease with the increase of Cu2+ concentration, and the detection limit (S/N=3) reached 1. 29×10-8 mol/L. The method provided high sensitivity, selectivity and reproducibility, and was successfully applied to the determination of trace copper in fruits and vegetables.
ABSTRACT
In the presence of hydrochloric acid, tetraethoxysilicane was hydrolyzed and formed silica sol. Non-labeled immunosensor was fabricated by droping the mixture solution of the silica sol and antibody of aflatoxin B_1 on the surface of glassy carbon electrode. In this work, a Fe(CN)_6~(3-/4-) phosphate buffer solution) was employed as base solution for investigating cyclic voltammetry(CV) and electrochemical impedance spectroscopic(EIS) performances of the sensor, respectively. The experimental results t indicated that because of the complex formed by the immunoreaction hindered the diffusion of Fe(CN)_6~(3-/4-) on the electrode surface, the redox peak current of the immunosensor in CV obviously decreased, and its electron transfer impedance linearly) increased with increasing the concentration of aflantoxin B_1(AFB). When the medium acidit and incubation) time were pH 6.5 and 20 min, respectively, the biggest electron transfer impedance changed value before and after the immunoreaction was obtained. Under the optimal conditions, a linear range to concentration of aflatoxin B_1 was 1-10 μg/L with a detection limit of 0.1 μg/L(S/N=3). Proposed method is of high sensitivity and stability, it has been successfully applied to determine AFB_1 in maize, rice and peanut.