Nucleic acid aptamers: ideal reagents for point-of-care diagnostics?

Nucleic acid aptamers have many of the properties that make for effective reagents in point-of-care diagnostic devices and whilst superficially similar to antibodies as affinity reagents the scope for engineering them to fit this role is considerable. Synthesis of aptamers allows for the incorporation of functionality for both immobilisation and electrochemical signalling in a way that is compatible with the ‘strip’ type sensors familiar in enzyme sensors, such as those for glucose. Control of the structure of DNA aptamers through Watson–Crick base pairing allows for different electrochemical assay formats, whilst ferrocenes provide a versatile redox label and insights into the interactions between the aptamer and its target are obtained through both cyclic and square-wave voltammetries. Square-wave voltammetry in particular demonstrates good analytical utility. Two different approaches were used to assemble aptamer/redox probe structures on the surface of gold electrodes and both showed “signal on” behaviour (i.e. the current increases in the presence of analyte) although the two different methods appear to give quite distinct surface coatings.