Photothermal effect-assisted reduced graphene oxide biosensor for amplification-free detection of miRNA

It remains a challenge to achieve high-sensitivity detection of tumor marker miRNA using optical refractive index (RI) sensors without nucleic acid amplification. This study proposes the photothermal effect-assisted reduced graphene oxide (rGO) biosensor that combines the photothermal effect of rGO with the rGO-based RI sensor for high-sensitivity detection of tumor marker miRNA-21. The rGO was functionalized with DNA probes capable of specifically hybridizing with the target miRNA-21. Quantitative detection of miRNA-21 was achieved by monitoring the RI change caused by the competitive hybridization of single-strand DNA (ssDNA)-functionalized AuNPs and target miRNA-21 with the DNA probes on the rGO surface. The presence of AuNPs disturbed the evanescent field on the rGO surface, thus achieving signal amplification. Furthermore, the localized photothermal effect heat induced by the interaction between rGO and pump light can effectively improve the hybridization kinetics of nucleic acid chains and achieve further signal amplification. The proposed biosensor had a high sensitivity toward the target miRNA-21, achieving a low detection limit of 4.05 fM without nucleic acid amplification. Its high specificity allowed for the recognition of single-base mismatches in miRNA-21. In addition, accurate quantification of low abundance miRNA-21 spiked into human urine samples was also successfully achieved. The photothermal effect-assisted rGO biosensor offers a promising approach for high-sensitivity detection of tumor marker miRNA without need for nucleic acid amplification.