Photonic crystal biosensors operating in multiple domains: Coating material trade-offs

Abstract

Photonic crystals (PhCs), where the chip surface is periodically nanopatterned and coated with a high-refractive-index thin film to achieve guided mode resonance (GMR), are increasingly explored as label-free biosensors. This work investigates their operation beyond optical biosensing, focusing on simultaneous electrochemical and electrically assisted domains. In such platforms, the choice of coating material plays a decisive role in defining both functionality and inherent limitations. The ability to operate in multiple domains is studied here using transparent conductive oxides (TCOs) as a material example. Besides dual-domain functionality, TCOs may offer cross-domain effects, such as electro-optical modulation through free charge carrier distribution, enabling dynamic control of GMR. It has been found that, from the coating material perspective, fundamental trade-offs govern tunability, optical and electrochemical performance, and environmental robustness. This work presents a general perspective on coating material limitations in multifunctional PhC biosensors and outlines design guidelines for balancing optical and electrochemical requirements in multi-domain sensing platforms.