Numerical Simulation of Pulsed NIR Laser-Tissue Photothermal Heating for Real Time Biosensing

V. Sukhotskiy, I.V.A.K. Reddy, A. Sangwan, P. Johari, J.M. Jornet, E.P. Furlani
University at Buffalo,
United States

Keywords: in-vivo biosensing, nanophotonics, photothermal modelling, pulsed laser heating


The past thirty years have shown a proliferation of biosensing technologies that pivot on advanced nanophotonic devices. In particular, label-free biological sample analysis devices that rely on surface plasmon resonance (SPR) have enabled diagnostics based on detection of low analyte concentrations in blood samples. Advances in fabrication and system integration have in turn led commercial SPR systems to emerge in the diagnostic, therapeutic and research areas [1]. Current SPR-based biosensing systems require a blood sample to be taken from a patient, prepared, and then analyzed in vitro using a bulky desktop SPR analysis device [2]. Similarly, the wearable fitness device market has grown aggressively in the last several years, paving the way for real-time sensing and data collection of heart rate, blood oxygenation levels, body temperature and blood pressure [3]. To date, no known systems have been able to integrate label-free SPR-based biosensing platforms with realtime sensing wearable devices. As an effort towards bridging the gap between these technologies, the Wearnet system (Fig. 1a) represents ongoing research in this area, and is based on the real-time nano-biosensing work done by Guo et al. [4]. The proposed WearNet system, composed of a wearable wrist band and an implanted SPR-enabled biochip, uses a near infrared (NIR) diode laser as a light and signal source to excite surface plasmons in the functionalized biochip implant, and relies on the reflected signal to travel back through the human tissue layers. SPR-based biosensing systems show promise to allow detect CYFRA 21-1 markers, which are correlated with lung cancer [5], however, to incorporate SPR sensing in-vivo, one of the major challenges is characterizing and understanding the limitations of the round-trip laser communication channel. Towards this goal, we demonstrate a parameterized 2D axisymmetric photothermal computational model, which can predict the intensity of the pulsed laser and the temperature increase inside human tissue layers (Fig. 1b). The finite element model uses P1 diffusion theory coupled with the Pennes bioheat equation, as well as wavelength-dependent bulk scattering and absorption parameters to explore the effect of key tunable parameters such as laser wavelength, pulse width, pulse frequency and optical penetration depth. The photothermal models presented here can be used toward rational design of the WearNet biosensing system by characterizing the human tissue response to the NIR laser as a communication channel. The models are validated using experimental measurements of polymer-based synthetic tissue. We discuss the models and the effect of the key tissue parameters on the signal fidelity and propose further work to enable rational design of the in vivo biosensing system to explore its feasibility.