Substrate-Free Untagged Detection of miR393a Using an Ultrasensitive Electrochemical Biosensor

[Image: see text] Rapid and sensitive detection of numerous regulatory pathways in growth and development processes and defensive responses in plant–pathogen interactions caused by miRNA has been the current interest of agricultural scientists. Herein, an uncomplicated ultrasensitive electrochemical biosensor was fabricated to detect miR393a, as its detection is of vital importance for plant diseases. A streptavidin-coated screen-printed carbon electrode (SPCE) was fabricated and characterized by scanning electrochemical microscopy, scanning electron microscopy, surface plasmon resonance, and cyclic voltammetry. The two-dimensional (2D) structure and chemical functionality of the streptavidin-coated SPCE render it a superior platform for loading a modified probe via a 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide–N-hydroxysuccinimide linker. This biorecognition platform is capable of efficiently using its excellent conductivity, greater surface area, and effective electrochemical execution due to its synergistic effect between streptavidin and carbon electrodes. The biosensor showed a good linear response (R(2) = 0.96) to miR393a concentrations ranging from 100 nM to 100 fM. This streptavidin-based biosensor is highly sensitive to the minimum concentration of miR393a, lowest detection limit, and ultrasensitivity under optimized conditions, i.e., 100 fM, 0.33 fM, and 33.72 μA fM(–1) cm(–2), respectively. In addition, remarkable recoveries could be obtained to confirm the feasibility of this assay in plant disease samples. The fabricated technology could offer a selective, adaptable, and farmer-friendly strategy for the timely detection of miRNA of plant samples.