Time-resolved ICP-MS measurement of metals in single-cell algae

Abstract

Complete text of publication follows. It is crucial to characterize the metal contents of individual biological cells since metals play an important role in different biological processes. In this study, a new method for single-cell measurement using time-resolved ICP-MS was developed. C. vulgaris, a single-cell alga, was used as a model. The algal cells in the original aliquot were introduced into the ICP using conventional solution nebulization. The metals in each cell produce a plume of gaseous analyte ions in the ICP. The plume was detected as a current spike in the mass spectrometer. ICP-MS current spikes corresponding to individual algal cells were readily detected. The frequency of the spikes is proportional to the number density of the cells in the sample. A cell counting method, based on the number of the spikes of 25Mg in an ICP-MS temporal profile, was developed and verified by hemacytometry. The intensity of each spike is related to the quantity of the analyte ions in each cell. Mg, Mn, and Cu were readily measured. The detection limit was ∼106 analyte ions per cell. The ratio of Mg, Mn, and Cu in the cells was 35.6 : 1.3 : 1.0. Analyte ions adsorbed on the cells can be measured directly without separation of the algae from the metal solution. The technique has been applied to the study of metal ions-algae interactions at cellular level. The authors kindly acknowledge the financial support from the Department of Chemistry and the CRCG of The University of Hong Kong.