Implementation of X-ray microscopy and micro-XANES analysis for investigations of the cellular uptake and cellular metabolism of transition metals

Micro-SRIXE (synchrotron-radiation-induced X-ray emission) and micro-XAS (X-ray absorption spectroscopy) were used to probe the uptake of exogenous metals by cells. The high flux and the sub-micron resolution of the hard X-ray microprobe, offer the experimenter the ability to obtain highly sensitive spatial and structural information of cellular elements. In this work the uptake of carcinogenic Cr(VI) was compared with that of a relatively non-toxic Cr(III) complex by micro-SRIXE mapping of whole cells. High intracellular Cr concentrations were observed in Cr(VI)-treated cells, while no significant Cr uptake was observed for Cr(Ill)-treated cells, as is consistent with uptake studies performed by other techniques. Micro-XANES analysis of Cr(V)- and Cr(VI)-treated cells showed that the predominant oxidation product following cellular metabolism was Cr(III). As shown by X-ray microscopic analysis of thin-sectioned cells, however, the reduction of Cr(VI) to Cr(III) did not occur at a fast enough rate to exclude Cr entry into the cell nucleus.