Direct, non-amplified detection of microRNA-134 in plasma from epilepsy patients
Biofluid-based molecular biomarkers support clinical decision-making around diagnosis, prognosis and treatment for various diseases. MicroRNAs (miRNAs) have emerged as important regulators of gene expression in the brain and levels of miR-134 have been found to be elevated in experimental and human epilepsy. Here we show direct detection of miR-134 in human plasma without the need for PCR amplification using platinum nanoparticles (PtNPs) that are region-selectively decorated with probe strand nucleic acids. The nanoparticles were produced by electrodeposition using nanoscale defects within self-assembled monolayers of dodecanethiol. The template breaks the symmetry of the particle allowing one side to be selectively modified with the probe and leaving the other clean and capable of catalytically reducing hydrogen peroxide. The detection electrode was functionalised with single-stranded capture miRNA, miRNA that is complementary to miR-134 but leaves a section of the target available to bind the nucleic acid sequence bound to the PtNPs. Thus, electrocatalytic nanoparticles become confined on the electrode surface only when the target is present. Significantly, the relatively large current associated with the binding of small numbers of nanoparticles and their small area of occupation leads to attomolar limits of detection and a wide dynamic range without the need for molecular, e.g., PCR amplification. Using plasma samples from healthy volunteers and epilepsy patients we show highly linear correlation in miR-134 measurement to results with Taqman-based PCR. The present study demonstrates rapid and simple detection of miRNA that if developed further could provide simple point-of-care devices for detection of epilepsy biomarkers.