Graphene quantum dot–guided growth of dendritic gold nanostructures for ultrasensitive electrochemical detection of miRNA-9 using a DNA capture probe in spiked human serum

A novel and ultrasensitive electrochemical biosensor was developed to detect miRNA-9 in human serum, based on dendritic gold nanostructure templated by graphene quantum dots (GQDs). Unlike conventional spherical nanoparticles commonly formed under GQD influence, fern leaf-like gold nanostructures (FLGNs) were electrodeposited in the presence of GQDs without the use of classical surfactants or shape-directing agents. This morphology arises from the dual role of GQDs as both complexing agents and soft templates, which modulate ion coordination and charge-transfer kinetics at the electrode interface. The resulting nanostructured surface exhibited a large electroactive area, efficient electron transfer, and anisotropic plasmonic features confirmed by UV–Vis spectroscopy and FESEM analyse. The sensing performance was achieved using a thiolated DNA capture probe-9 immobilized on the gold nanostructured electrode, enabling hybridization-based detection of the target miRNA-9 sequence via a ferro/ferricyanide redox probe. The sensor demonstrated an outstanding detection limit of 0.01 fM and a linear response over a concentration range of 100 aM to 1 nM. It also exhibited excellent selectivity and reliable performance in complex biological matrices, highlighting its potential for early-stage diagnosis. This surfactant-free, GQD-assisted synthesis strategy offers a facile route to anisotropic nanostructures and holds promise for the development of next-generation biosensors and diagnostic platforms.