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Diagnostic assays utilizing fluorescent reporters in the context of low abundance biomarkers for cancer and infectious disease can reach lower limits of detection through efficient collection of emitted photons into an optical sensor. In this work, we present the rational design, fabrication, and application of one-dimensional photonic crystal (PC) grating interfaces to accomplish a cost-effective prism-free, metal-free, and objective-free platform for augmentation of fluorescence emission collection efficiency. Guided mode resonance (GMR) of the PC is engineered to match the laser excitation (532 nm) and emission maximum (580 nm) of the radiating dipoles to arrive at optimized conditions. The photo-plasmonic hybrid nano-engineering using silver nanoparticles presented >110-fold steering fluorescence enhancement enabling placement of the sample between the excitation source and detector that are in a straight line. From the experimental and simulation inferences, we propose a radiating GMR model by scrutinizing the polarized emission properties of the hybrid substrate, in accordance with the radiating plasmon model. The augmented fluorescence intensity realized here with a simple detection instrument provides sub-nanomolar sensitivity to provide a path toward point-of-care scenarios. 

Abstract 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, the spatial uniformity of resonantly enhanced, surface‐confined electromagnetic fields of a 1D PC is compared with a 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, a >100% improvement of the signal uniformity is observed when using the 2D PC. Overall, improvement in AuNP detection contrast, uniformity, and point spread function is demonstrated by PRAM performed upon a 2D PC surface.