Making Sense of Catalysis: The Potential of DNAzymes as Biosensors

DNA, long known as a carrier of genetic information, has recently revealed itself as a multifunctional entity. Using the powerful technique of in vitro selection, catalytic DNA molecules, known as DNAzymes or deoxyribozymes, have been isolated to catalyse numerous reactions using a range of metal-ion cofactors. Conjugation of these DNAzymes to an array of signalling platforms has led to the development of several DNAzyme-based sensor systems. By labelling DNAzymes and their nucleic acid substrates with fluorescent and quenching dyes, sensors have been designed to report the presence and concentration of specific metal ions with high sensitivity and specificity. By coupling DNAzyme activity to the aggregation state of gold nanoparticles, visual sensors have been designed that report the presence of a metal ion by a change in colour, eliminating the need for expensive detection equipment. Electrode-bound DNAzymes have been developed into electrochemical sensors offering high sensitivity and reduced background. The types of analyte that can be detected by DNAzymes have also been expanded by coupling DNAzymes to DNA aptamers that bind specific target molecules. These conjugates, called DNA aptazymes, have been developed to detect small molecules such as adenosine and adenosine triphosphate (ATP). Using an in vitro selection protocol with counter-selection steps, aptazymes that can detect molecules in complex mixtures have been isolated. This chapter will highlight innovative research that has been done to engineer DNAzyme-based sensors and discuss the prospects for using DNAzymes in future detection systems.