A Portable Device for miRNAs Detection Based on a Gold-Nanoparticle Ratiometric Colorimetric Strategy

MicroRNAs (miRNAs) have recently emerged as a new class of biomarkers for disease diagnosis and play vital roles in physiological and pathological processes. Here, a novel fiber-optic prototype that allows synchronized optical transmittance measurements at different wavelengths has been designed and fabricated for selective and sensitive miRNAs detection based on a ratiometric colorimetric strategy. The proposed measurement method automatically adjusts the output light power through the LEDs, minimizing eventual differences in brightness and potential losses through the optical fiber without the need expensive optical components. The prototype has been validated for the detection of miRNAs identified as biomarkers of bovine mastitis in dairy cattle. Observation of the color changes from red to blue of the AuNP solution, and therefore on the transmittance signal, caused by miRNA-induced gold nanoparticles (AuNPs), aggregation has been used for rapid detection of such genetic biomarker. The equipment designed and constructed is portable, being the main parameters of the measurement managed with a smartphone, and it could be potentially employed with any other biosensor whose detection strategy is based on changes in the distance between AuNPs.