An implantable nanosensor includes a stent to be implanted inside a fluid conduit. The stent has a well in a surface of the stent. The implantable nanosensor further includes a nanoscale-patterned sensing substrate disposed in the well. The nanoscale-patterned sensing substrate is to produce an optical scattering response signal indicative of a presence of an analyte in a fluid carried by the fluid conduit when interrogated by an optical stimulus signal.