Determination of selenium nanoparticles in fermented dairy products

A single particle inductively coupled plasma mass spectrometry (sp-ICP-MS) method with improved sensitivity for determination of selenium nanoparticles (SeNPs) in lactic acid bacteria, bifidobacteria, and yeast was developed. The carbon-induced signal enhancement using 1% (v/v) methanol for preparation of sample dispersion led to decreasing detection limits from 61 nm to 47 nm in comparison to pure aqueous dispersion. Accuracy of SeNPs' size and number concentration determination were tested by adding artificially prepared SeNPs to the cells dispersion. While the found size of the SeNPs corresponded to original value, the number concentration recovery ranged from 46 to 102%. The repeatability of SeNPs size measurement was 0.6-15% and of number concentration determination 2.5-54%. The spherical and ovoid shaped SeNPs with average diameter in range of 60-261 nm and number concentration of 2.4 x 10(9)-1.6 x 10(11) mL(-1) located both extracellularly and intracellularly was found by transmission electron microscopy and sp-ICP-MS in cell cultures growing in medium containing 10 mg L-1 of sodium selenite. Bio-synthesized SeNPs were stable for one week in aqueous dispersion and their stability was prolonged to one month by addition of hydrochloric acid (pH = 1.5). Moreover, the possibility of analyzing SeNPs in enzymatic extracts intended for speciation analysis of organic selenium species was proven to be suitable also for SeNPs characterization. Thus, a way to share sample preparation procedure with different types of analyses was demonstrated.