Quantum spectroscopy with undetected photons for biomolecular sensing in the mid-infrared

This research investigates the use of quantum spectroscopy with undetected photons for detecting proteins in the mid-infrared range. Classical Fourier-transform infrared spectroscopy serves as a reference to determine the mid-infrared absorption of protein samples, such as bovine serum albumin and N-terminal pro-brain natriuretic peptide.

This absorption data is then incorporated into a numerical model of a double-pass quantum interferometer. The study examines various parameters that affect the visibility of the interference pattern, including the length of the nonlinear crystal, the sample length, and the distance between the mirrors and samples. These factors are crucial in designing a quantum spectrometer with optimal image contrast at specific amide I-II spectral bands.

The simulations accurately reproduce the protein absorption features in the mid-IR region and demonstrate temperature-induced changes in protein secondary structure. This work offers practical design guidelines for future quantum bio-spectroscopy applications that employ only visible wavelength sources and detectors. The study's data is available upon request to the corresponding authors.

The research was supported by the Australian Research Council Centre of Excellence in Quantum Biotechnology and the Institute for Biomedical Materials and Devices at the University of Technology Sydney.