Fluorescence microscopy has tackled many of the burning questions in cellular biology. Probing low-affinity cellular interactions remains one of the major challenges in the field to better understand cellular signaling. We introduce a novel approach the nanowire-aperture probe (NAP) to resolve biological signatures with a nanoscale resolution and a boost in light detection. The NAP takes advantage of the photonic properties of semiconductor nanowires and provides a highly localized excitation volume close to the nanowire surface. The probing region extends less than 20 nm into the solution, which can be exploited as a local light probe in fluorescence microscopy. This confined detection volume is especially advantageous in the study of cellular signaling at the cell membrane, as it wraps tightly around the nanowire. The nanowire acts as a local nanoaperture, both focusing the incoming excitation light and guiding photons emitted by the fluorophore. We demonstrate a 20-fold boost in signal-to-background sensitivity for single fluorophores and membrane-localized proteins in live cells. This work opens a completely new avenue for next-generation studies of live cells.