Photoelectrochemical and optical applications of semiconductor quantum dots for bioanalysis

Semiconductor nanoparticles (NPs) or quantum dots (QDs) exhibit unique photophysical properties reflected by size-controlled fluorescence, high fluorescence quantum yields, and stability against photobleaching. These properties are utilized by applying the QDs as optical labels for the multiplexed analysis of immunocomplexes and DNA hybridization. Also, semiconductor QDs are used to probe biocatalytic transformations. The time-dependent replication or telomerization of nucleic acids, the oxidation of phenol derivatives by tyrosinase, and the hydrolytic cleavage of peptides by proteases are probed by using fluorescence resonance energy transfer or photoinduced electron transfer. The photoexcitation of semiconductor NP-biomolecule hybrids associated with electrodes enables the photoelectrochemical transduction of biorecognition events or biocatalytic transformations. This is exemplified with the generation of photocurrents by duplex DNA assemblies bridging CdS NPs to electrodes, and by the formation of photocurrents as a result of biocatalyzed transformations, or redox protein-mediated electron transfer in the presence of the NPs.