Seeing is Sensing - External Observation of In Vivo Biological Gradient Field by Tracking Nanoswimmers

This work aims to demonstrate through computational analysis that, by monitoring the trajectory of externally manipulable nanoswimmers (NS), the in vivo biological gradient field (BGF) interacting with the NS can be indirectly observed. This observability is fundamental to the recently proposed framework of computational nanobiosensing (CONA) for "smart" cancer detection. We first present a novel NS propagation model to emulate the complex and chaotic NS kinetics inside the capillary network. Next, we propose an efficient control method that is able to employ the NS as in vivo sensors for the measurement of a specific BGF such as blood viscosity. The proposed method, based on the Linear Quadratic Regulator (LQR), effectively stabilizes the signal-to-noise ratio (SNR) induced by the Brownian motion of NS at a level above 10 dB to enhance the accuracy of viscosity estimation.