Sensitive detection of cancer and brain tissues using a miniaturized PT-symmetric nanophotonic biosensor based on exceptional points

In this study, a one-dimensional nanophotonic biosensor is introduced for the detection of cancer cells and tissues. The investigation focuses on three distinct multilayer structures designated S₁, S₂, and S₃ each characterized by unique symmetry properties. While S₁ and S₂ exhibit parity-time (PT) symmetry, S₃, a hybrid configuration, demonstrates augmented parity-time (APT) symmetry. The sensing mechanism is based on the appearance of exceptional points (EPs) in response to the presence of analytes, facilitating their precise and sensitive identification. Under identical operational conditions, three key phenomena are observed. First, by locating the exceptional point and utilizing the bidirectional transparency phenomenon, the structural parameters are optimized to maximize transmission at the refractive index corresponding to cancer cells and tissues. This enables accurate diagnosis by correlating the analyte's refractive index with the EP. Second, in structure S₃, a reduction in both layer thickness and porosity ratio results in a miniaturization effect, underscoring the influence of structural downsizing. Third, the implementation of APT symmetry in S₃ reduces the number of sampling parameters, enabling a more efficient and minimalistic sampling approach, referred to as a minor sampling technique. This approach minimizes the sample volume required for effective detection while maintaining measurement accuracy, offering promising implications across various sensing applications. As a whole, these outcomes propose a novel strategy for the identification of cell and tissue types through the exploitation of exceptional points, an area previously underexplored. Furthermore, the synergy between the miniaturization effect and an optimized sampling approach, significantly advances the prospects for developing high-precision biosensors.