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We demonstrate a higher sensitivity detection of proteins in a photonic crystal platform by including a deep subwavelength feature in the unit cell that locally increases the energy density of light. Through both simulations and experiments, the sensing capability of a deep subwavelength-engineered silicon antislot photonic crystal nanobeam (PhCNB) cavity is compared to that of a traditional PhCNB cavity. The redistribution and local enhancement of the energy density by the 50 nm antislot enable stronger light–molecule interaction at the surface of the antislot and lead to a larger resonance shift upon protein binding. This surface-based energy enhancement is confirmed by experiments demonstrating a nearly 50% larger resonance shift upon attachment of streptavidin molecules to biotin-functionalized antislot PhCNB cavities. 

Here we report a photonic crystal with a split ring unit cell shape that demonstrates an order of magnitude larger peak electric field energy density compared with that of a traditional photonic crystal. Split ring photonic crystals possess several subwavelength tuning parameters, including split ring rotation angle and split width, which can be leveraged to modify light confinement for specific applications. Modifying the split ring’s parameters allows for tuning of the peak electric field energy density in the split by over one order of magnitude and tuning of the air band edge wavelength by nearly 10 nm in the near infrared region. Designed to have highly focused optical energy in an accessible subwavelength gap, the split ring photonic crystal is well suited for applications including optical biosensing, optical trapping, and enhanced emission from a quantum dot or other nanoscale emitter that could be incorporated in the split.