Bionanotechnology for single-cell analysis

The cell is the smallest structural unit of biological life. These microscopic systems perform functions as diverse as energy metabolism, intra- and intercellular signalling by chemical and electrical means, and self-reproduction. Thousands of different biochemical and electrical processes are simultaneously performed with the aid of nanometre-sized proteins and information stored in DNA. Multiple processes interconnect, giving rise to complicated biological phenomena. Therefore measurement of biomolecules in intact live cells provides more relevant knowledge of their physiological function than biochemical assays carried out with purified molecules in test tubes. Several measurement techniques for single-cell analysis, developed in the past decades, have the sensitivity and resolution to monitor a small number of biomolecules within a single cell. For example with patch clamp and related techniques, one can measure electric current passing through an ion channel to study the behaviour of a single protein molecule. Electrochemical methods such as amperometry and voltammetry allow measurement of about one hundred zepto moles of oxidisable chemicals secreted from a single cell. Various fluorescence techniques reveal the dynamics of intracellular signals such as free Ca ²⁺ in a single cell. Newer application of nanotechnological measurements with high spatio-temporal resolution on single-cell analysis is certainly a promising area of both bionanotechnology and cell biology. In this review we will introduce several experimental approaches that have contributed to our understanding of cell functions.