Smartphone-based portable electrochemical biosensing system for detection of circulating microRNA-21 in saliva as a proof-of-concept

Circulating microRNAs (miRNAs) are effective cancer biomarkers that are highly stable in body fluids enabling noninvasive detection. Portable, low-cost and efficient biosensing systems is crucial for early on-site diagnosis, especially in resource-limited settings. Present work deals with the development of a smartphone-based biosensing system for electrochemical detection of circulating microRNA-21 (miR-21) biomarker in saliva as a proof-of-concept. The smartphone-based biosensing system composed of a disposable screen-printed biosensor modified with reduced graphene oxide/gold (rGO/Au) composite, a circuit board for detection and a Bluetooth-enabled smartphone equipped with specially designed Android application. The hybridization between miR-21 target and ssDNA probe on the rGO/Au-modified electrode resulted in the decrease in peak current with increase in miR-21 target concentration. The smartphone-based biosensing system showed comparable performance with commercial electrochemical workstation, for miR-21 detection in the concentration range of 1 × 10⁻⁴ M to 1 × 10^-12 M with correlation coefficient (r²) of 0.99. In addition to good selectivity in discriminating mismatched and non-target sequences, the biosensing system also showed acceptable recovery rate ranging from 96.2%–107.2 % in spiked artificial saliva. The smartphone-based biosensing system is envisioned to be able to realize rapid and highly sensitive detection of circulating miRNA biomarker in body fluid for point-of-care testing in remote areas.