Smartphone-based device for rapid and single-step detection of piRNA-651 using anti-DNA:RNA hybrid antibody and enzymatic signal amplification.

P-element-induced wimpy testis (PIWI)-interacting RNAs (piRNAs/piRs) are a class of small noncoding RNAs that play a crucial role in regulating various biological processes, including carcinogenesis. One specific piRNA, piR-651, has been reported to be overexpressed in both human blood serum and solid cancer tissues, that can be used a viable biomarker in cancer diagnosis. Early diagnosis of cancer can help reduce the burden of the disease and improve survival rates. In the present work, we report for the first time a smartphone-based colorimetric biosensor for highly sensitive and specific detection of piR-651 thanks to an enzymatic signal amplification, which yielded high colorimetric intensities. Indeed, a heteroduplex DNA:RNA was formed in the presence of piR-651 with the capture DNA probe immobilized on the magnetic beads for easy magnetic separation. Then, a HRP tethered to anti-DNA:RNA (S9.6) was used to reveal the DNA-RNA heteroduplex formed by catalyzing the oxidation of TMB substrate into colorimetric TMBox , which absorbs at 630 nm. The absorbance is positively proportional to the piR-651 concentrations. On the other hand, the colorimetric product of the assay can be photographed with a smartphone camera and analyzed using ImageJ software. Using a smartphone and under optimal conditions, the biosensor responded linearly to the logarithm of piRNA-651 from 8 fM to 100 pM with a detection limit of 2.3 fM and discriminates against other piRNAs. It was also successfully applied to the determination of piRNA-651 levels in spiked human serum.