Plasmon-enhanced biosensors for microRNA analysis and cancer diagnosis

MicroRNAs are a class of reliable biomarkers for noninvasive detection of a variety of diseases, including cancers. This is because miRNA, especially exosome miRNAs, can stably circulate in the blood and are consequently indicative of the development and progression of typical cancer cells. Among a variety of tools for miRNA analysis, plasmon-enhanced biosensors have attracted special interests due to their remarkable sensing properties. It originates from the principle that local surface plasmon resonance occurs when the dimensions of a metallic nanostructure are shorter than the wavelength of the incident light, leading to collective but non-propagating oscillations of free electrons that generates intriguing optoelectronic properties. This article presents a review of recent progress in miRNA detection based on plasmon-enhanced optical sensing, including surface enhanced Raman scattering, plasmon-enhanced fluorescence, and plasmon-enhanced electrochemiluminescence. The article is focused on the molecular sensing mechanisms and the assembling strategies of the nanomaterial substrates to plasmonically enhance optical outputs of miRNAs. In particular, this paper discusses different methods of enzyme-mediated or enzyme-free amplification and substrate-enhanced sensing, and highlights the potential of plasmon-enhanced optical sensors for multiplexed analysis of complex biological samples, as well as for point-of-care testing for the onset of typical cancers.