A chemiresistive biosensor based on a layered graphene oxide/graphene composite for the sensitive and selective detection of circulating miRNA-21.

In this study we developed a uniform, large-area, layered graphene composite of graphene oxide/graphene (GO/G) for the detection of circulating miRNA-21, a reliable biomarker for early cancer diagnosis. We prepared this layered composite of GO/G through low-damage plasma treatment of bilayer G. The top layer of G was oxidized (i.e., atomic layer oxidation) to form a GO layer, which acted as the bio-receptor, while retaining the properties of the bottom layer of G, which acted as an electrical response medium. With this structure, we fabricated a simple chemiresistive biosensor that could detect miRNA-21. The electrical resistance of the sensor varied linearly (R = 0.986) with respect to concentrations of the target miRNA-21 in the range from 10 pM to 100 nM in phosphate-buffered saline (PBS); the limit of detection was 14.6 pM. Hall measurements revealed that the mobility and concentration of the hole carriers both decreased upon increasing the target concentration, leading to the measured increase in resistivity of our chemiresistive biosensor. Furthermore, the sensor could discriminate the complementary target miRNA-21 from its single- and four-base-mismatched counterparts and another non-complementary miRNA. The ability to detect miRNA-21 in human serum albumin and bovine serum albumin was almost identical to that in PBS.