Photonic crystal sensors' resonance wavelength is determined by the material's refractive index near the structure. Changes in analytes or samples at the sensor's center affect the local refractive index, causing a shift in the sensor's wavelength. OptiFDTD software can help simulate 2D photonic crystal sensors, but it's important to consider potential issues if the expected shift is not observed.

If you cannot observe a shift in resonance wavelength when changing samples, it may be due to an issue with the simulation setup or the photonic crystal design's sensitivity to refractive index changes. Consult experts in photonics simulations or optiFDTD software to provide insights, troubleshoot potential issues, and suggest alternative approaches. They can also validate simulation results and ensure the photonic crystal sensor design detects refractive index changes accurately.

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Thank you, Sulaf Waiss for your valuable suggestions.