Ultrasensitive detection of vitamin B6 using functionalised CdS/ZnS core–shell quantum dots

A simple and sensitive method for the determination of vitamin B6 was developed based on the fluorescence quenching of l-cysteine capped CdS/ZnS quantum dots (QDs). The synthesised QDs were characterised using UV–vis absorption spectroscopy, fluorescence spectroscopy, FT-IR spectroscopy and transmission electron microscopy. The influence factors on the determination of vitamin B6 were investigated and the optimum conditions were determined. Under optimum conditions, the fluorescence intensity of l-cysteine capped CdS/ZnS QDs was linearly proportional to vitamin B6 over a concentration range from 0.05 mg L−1 to 6.5 mg L−1 with a correlation coefficient of 0.9946. The detection limit of this system was 0.015 mg L−1. The quenching mechanism was studied using the UV–vis absorption and fluorescence spectroscopy. The fluorescence of these core–shell QDs is quenched effectively by the vitamin B6 without obvious shift in maximum photoluminescence wavelength. Similarly, there is no obvious shift observed in the absorption spectra of l-cysteine capped CdS/ZnS QDs before and after adding the different concentrations of vitamin B6. This confirmed that quenching phenomenon in this system is possibly attributed to the effective electron transfer from QDs to vitamin B6. The proposed method was employed to detect vitamin B6 in the pharmaceutical sample with satisfactory results.