Photonic Crystal Enhanced Microscopy on a 2D Photonic Crystal Surface.

Digital-resolution biosensing based on resonant reflection from photonic crystals (PC) has demonstrated significant potential for detection of proteomic and genomic biomarkers in serology, infectious disease diagnostics, and cancer diagnostics. An important intrinsic characteristic of resonant metamaterial surfaces is that enhanced electromagnetic fields are not uniformly distributed, resulting in spatially variable light-matter interactions with nanoparticle tags that signal the presence of biomarker molecules. In this work, we compare the spatial uniformity of resonantly enhanced, surface-confined electromagnetic fields of a one-dimensional (1D) PC with a two-dimensional (2D) PC with fourfold symmetry. When illuminated with unpolarized light, the simultaneously excited electromagnetic fields of transverse electric and transverse magnetic modes of the 2D PC present equally strong but complementary spatial distribution, leading to a > 100% increased average near-field intensity accompanied with a > 50% compressed standard deviation compared to the 1D PC. Utilizing Photonic Resonator Absorption Microscopy (PRAM) to experimentally measure the absorption uniformity of ~80 nm gold nanoparticles distributed upon the PC surface, we observe a > 100% improvement of the signal uniformity when using the 2D PC. Overall, we demonstrate improvement in AuNP detection contrast, uniformity, and point spread function by PRAM performed upon a 2D PC surface.