Deep Tissue Sensing of Chiral Molecules using Polarization Enhanced Photoacoustics

TL;DR

This paper introduces PAPEORS, a novel photoacoustic polarization system that enables deep-tissue sensing of chiral molecules, overcoming scattering limitations of traditional methods and allowing for non-invasive, in-vivo applications at depths around 3.5 mm.

Contribution

The paper presents the first development of a photoacoustic polarization system for deep-tissue chiral molecule sensing, extending in-vivo capabilities beyond 1 mm depth.

Findings

Achieved detection limit of 80 mg/dL for glucose in serum samples.

Demonstrated deep-tissue sensing at depths of about 3.5 mm.

System can be miniaturized for point-of-care use.

Abstract

Chiral molecule sensing is currently performed using chromatography, electrophoresis, enzymatic-assays, mass spectrometry, and chiroptical sensing techniques. Currently polarimetry is the only method having in-vivo sensing capabilities, while other techniques analyze chiral molecules in body fluids. Polarimetry demonstrated in-vivo performance upto depths of 1 mm while using UV-Visbile light, beyond which light scattering tends to be dominant. We hypothesize that photoacoustic sensing while operating at the Near-Infrared (NIR)-II window can allow for deep-tissue sensing, due to reduced scattering/autofluorescence effects. Herein, a Photoacoustic based Polarization Enhanced Optical Rotation Sensing (PAPEORS) system was developed for the first time to estimate optical rotation parameter using the recorded PA signals at larger depths. This optical rotation was then used to correlate with the chiral molecular concentration at depths of about 3.5 mm. Experimental evaluations were performed with aqueous glucose solution, naproxen drug, and serum-based glucose samples. PAPEORS has achieved a detection limit of 80 mg/dL using circular incidence polarization with serum-based glucose samples. Further ex-vivo experiments were performed to demonstrate the ability of PAPEORS for deep-tissue sensing, which can be extended for in-vivo chiral molecular sensing. PAPEORS uses single wavelength for sensing chiral biomolecules, hence can be miniaturized, allowing for many point-of-care applications.