Advanced Physical Research

Photoplethysmography is a non-invasive and portable optical sensing technique used for cardiovascular monitoring. However, its performance in wearable and textile-integrated systems may be limited by strong photon scattering in biological tissue, weak optical signals, motion-related disturbances, and the limited photo response of conventional photodetectors. This study presents a theoretical and conceptual framework for nano-enhanced PPG based on the integration of plasmonic light-field enhancement, nanoparticle-mediated control of photon transport, and photogating in graphene-quantum-dot heterostructures. A modified Beer-Lambert model and analytical diffusion-based calculations are used to examine the theoretical influence of nanoscale optical engineering on photon propagation and signal detection in scattering biological media. The proposed framework indicates that plasmonic nanostructures may enhance localized electromagnetic  elds, while QD/2D-material heterostructures may provide high internal photoconductive gain through long-lived carrier trapping and rapid carrier transport. Importantly, the predicted internal gain, potentially on the order of 10⁶-10⁷, should not be interpreted as an
equivalent improvement in the overall signal-to-noise ratio of a PPG system. When fundamental noise sources and practical measurement constraints are considered, the expected system-level SNR improvement is estimated to be approximately 10-25 dB under optimized conditions. These results represent theoretical predictions rather than experimentally validated device performance.