Highly selective fluorescence detection of L-selenium-methylselenocysteine in selenium-enriched Cardamine violifolia.

ABSTRACT

A feasible and practicable "off-on" type of fluorescence strategy for highly selective screening of L-selenium-methylselenocysteine (L-SeMC) in selenium-enriched Cardamine violifolia was developed using g-C3N4-MnO2 nanocomposites as fluorescent probes. The g-C3N4 nanosheets can emit blue fluorescence at 320 nm excitation wavelength with a fluorescence quantum yield of 28%. When MnO2 was deposited onto g-C3N4 nanosheets, the fluorescence of the g-C3N4 nanosheets was quenched due to fluorescence resonance energy transfer (FRET). After the addition of L-SeMC, MnO2 was reduced to Mn2+, which eliminated FRET and fluorescence was restored. Based on this, a quantitative method for the determination of L-SeMC was established. The fluorescence intensity of g-C3N4-MnO2 nanocomposites showed a good linear relationship with the concentration of L-SeMC in the range of 0-45 µg mL-1, the limit of detection (LOD, 3σ/K) was 8.25 ng mL-1 and the correlation coefficient was 0.9904. Common selenium compounds such as SeO2, Na2SeO3, SeMet and SeCys caused weak fluorescence intensity, which means that the developed method is highly selective to detect L-SeMC in a series of selenium compounds. Meanwhile, the technique was evaluated by spiking L-SeMC standards in C. violifolia extraction solutions and with 9 C. violifolia extraction specimens, receiving excellent accordance with results from the commercially available atomic fluorescence spectroscopy method.