Incident-angle dependence of fluorescence enhancement and biomarker immunoassay on gold nanohole array

We theoretically and experimentally investigate the influence of the incident angle of illumination on the fluorescence enhancement for two kinds of gold nanohole arrays – a gold nanohole array on glass substrate (Au-hole array), and a gold coated photoresist nanohole array (Au/PR-hole array). Our simulations show that the absorption spectra for the Au/PR-hole array vary substantially with angle of incidence, whereas the corresponding spectra for the Au-hole array are marginally affected. The experimental results reveal fluorescence enhancement up to 14 and 12 times for the Au-hole array at an incident angle of 70° and the Au/PR-hole array at an incident angle of 20°, respectively. Moreover, a model sandwich immunoassay for the detection of prostate specific antigen (PSA) shows about 3-fold higher sensitivity on Au/PR-hole array as compared to planar gold at 70°. To the best of our knowledge this is the first investigation reporting on the relationship between the incident angle and the fluorescence enhancement on gold nanohole arrays. Our findings provide a solid foundation for designing a highly efficient fluorescence detection system with oblique angular illumination.