Quantum Spectroscopy with Undetected Photons for Biomolecular Sensing in the Mid-Infrared

TL;DR

This paper proposes a quantum spectroscopy method using undetected photons for biomolecular sensing in the mid-infrared, demonstrating potential for non-invasive protein analysis with optimized design parameters.

Contribution

It introduces a practical quantum spectrometer design that captures protein absorption features in the mid-IR using visible light sources and detectors.

Findings

Simulated visibility spectra match protein absorption features in mid-IR.

Temperature effects on protein secondary structure are detectable.

Design rules for future quantum bio-spectroscopy are established.

Abstract

We investigate quantum spectroscopy with undetected photons for protein detection in the mid-infrared spectral region. Classical Fourier-transform infrared spectroscopy of protein samples (bovine serum albumin and N-terminal pro-brain natriuretic peptide) is used as reference to define the sample's mid-infrared absorption, which is then embedded in a numerical model of a double-pass quantum interferometer. We analyse parameters that influence visibility of the interference pattern formed by the signal beams, including the length of nonlinear crystal, sample length and mirror-sample distance. This leads us to a practical quantum spectrometer design with optimal image contrast at the specific amide I-II spectral bands. The simulated visibility spectra reproduce nearly identically the protein absorption features in the mid-IR and reveal temperature-induced changes to the protein secondary structure. Overall, this provides practical design rules for future quantum bio-spectroscopy applications that use only visible wavelength sources and detectors.