Fluorophore signal and detection enhancement in nanowire biosensors

Semiconductor nanowires have been demonstrated as an efficient platform for fluorescence-based biosensors. Here, we study theoretically how GaP nanowires (i) enhance the excitation intensity at the position of fluorophores attached to the nanowire sidewall, (ii) enhance the probability to collect photons emitted from the fluorophores by directing them preferentially into the numerical aperture of collection objective, and (iii) through the Purcell effect increase the quantum yield of fluorophores. We find that the optimum diameter depends strongly on the fluorophore emission wavelength. In addition to an overall signal-detection scheme, we model imaging-based detection of the fluorescence.