A system for monitoring at least presence of a bioanalyte. The system comprises: a substrate having a skin contact surface, a microneedle outwardly protruding from the skin contact surface, a sensing complex positioned in the microneedle, and a circuit attached to the substrate. The sensing complex can comprise a nanostructure modified by a functional moiety covalently attached thereto, and an affinity moiety effective to react specifically with the bioanalyte to produce a reaction product. The circuit can apply voltage to the nanostructure and monitor changes in an electrical property of the nanostructure responsively to reaction between the reaction product and the functional moiety.
