Transition metal complexes based aptamers as optical diagnostic tools for disease proteins and biomolecules

Abstract Aptamers are powerful recognition elements that can bind a large number of target molecules, including metal ions, small molecules, proteins, enzymes, even complex targets like cancer cells, etc., with high affinity and specificity. Hence, aptamer-based biosensors (hereafter named “aptasensors”) have been extensively utilized in the field of clinical diagnostics and biomedical applications. In contrast to organic luminophores and quantum dots, luminescent transition metal complexes offer many desirable and wide-ranging properties, including tunable emission throughout the visible to NIR regions, long lifetime with a large Stockes shift, high quantum yield, good thermal, chemical and photochemical stability and metabolic inertness for biosensing applications. The incorporation of biomolecules or lipophilic entities into the metal complexes could overcome problems associated with membrane permeability and uptake by cells. Especially, Ru(II) and Ir(III) complexes are promising candidates for these potential applications. This review describes an overview of recent progress in the emerging area of aptasensors utilizing Ru(II) and Ir(III) transition metal complexes. To date, though aptasensors have been used in a wide variety of detection techniques, we have focused mainly on the luminescence approach in this article. Numerous aptasensors have illustrated promising detection results, even in complicated biological environments. If more rigorous research is continued on this area, it is hoped that in the future transition metal complexes based aptamers may show tremendous applications in biomedical research, especially diagnostics, imaging and drug delivery.