Highly selective preconcentration of ultra-trace cadmium by yeast surface engineering

The potential of selective cell-sorption for separation/preconcentration of ultra-trace heavy metals was exploited by surface engineering of Saccharomyces cerevisiae cells. The general idea is to display the cadmium-binding peptide on the cell surface in order to enhance the covalent interaction between cadmium and the yeast cells. By immobilizing the surface-engineered yeast cells onto cytopore (R) microcarrier beads for cadmium adsorption, we demonstrated that with respect to the native yeast 600-fold and 25-1000-fold improvements were observed respectively for the tolerance of ionic strength and the tolerant capability toward various metal cations after surface engineering. Based on these observations, a novel procedure for selective cadmium preconcentration was developed with detection by graphite furnace atomic absorption spectrometry (GFAAS), employing the engineered S. cerevisiae cell-loaded cytopore (R) beads as a renewable sorption medium incorporated into a sequential injection lab-on-valve system. The cadmium retained on the yeast cell surface was eluted with a small amount of nitric acid and quantified with GFAAS. Within a range of 5-100 ng L-1 and a sample volume of 1 mL, an enrichment factor of 30 was achieved along with a detection limit of 1.1 ng L-1, a sampling frequency of 20 h(-1) and a precision of 3.3% RSD at 50 ng L-1. The procedure was validated by analyzing cadmium in certified reference materials and a series of environmental water samples.