Enhanced fluorescence detection of miRNAs using one-dimensional photonic crystal-based biochips

In the last decade, among the various cerebral ischemia biomarkers, microRNAs (miRNAs, MW 7-10 kDa) have recently attracted the attention of researchers. These are short endogenous biomolecules of noncoding ribonucleic acids that negatively regulate gene expression. The presence of miRNAs in blood and the ability to measure their level in a non-invasive way, the so-called liquid biopsy approach, has opened new doors in the search for peripheral biomarkers for the diagnosis and prognosis of diseases such as hemorrhagic stroke. In order to perform liquid biopsy, Bloch surface waves supported by one dimensional photonic crystals are exploited to enhance and redirect the fluorescence arising from a sandwiched miRNA recognition assay. Besides, the sensing elements consist of disposable and low-cost plastic biochips coated with a 1DPC. The assay format consists of a first partial hybridization of an oligonucleotidic probe, immobilized onto the 1DPC surface in five regions, with the miRNA target (miR-16-5p, hemorrhagic stroke biomarker) to be revealed in a complex biological medium. The protocol is then completed with a second partial hybridization of the miRNA target with a second synthetic oligonucleotide conjugated with an organic dye. This last step permits to specifically introduce fluorescence where the sandwich assay is accomplished. Thanks to the present technique, we are able to detect miRNA target solutions with a limit of detection of 32 ng/mL in less than 60 minutes. In conclusion, since the recommended therapeutic window is very limited, biomarkers for cerebral ischemia/hemorrhage have the potential to speed-up diagnosis and the assignment of treatments.