Hyperspectral imaging and time-resolved spectroscopy of photoexcited processes in biomolecules

Abstract

This work has two main focuses, the study of ultrafast phenomena on biomolecules and the development of optical setups for hyperspectral imaging. The project was developed in partnership with the university Politecnico di Milano, as part of a Ph.D. sandwich internship. We performed pump-probe measurements and also ab initio calculations to study the photophysical and photochemical processes of three aromatic amino acids: tryptophan, tyrosine, and phenylalanine. The results reveal ultrafast electron transfer from singlet to triplet states and photoproducts formation. We complemented the photoexcitation amino acid studies with linear absorption and photoluminescence measurements. In parallel, we developed two optical setups for hyperspectral imaging using a birefringent interferometer. Both setups allow us to obtain images that have not only the spatial but also the spectral information point by point in the image. The Ąrst one was designed for macro applications and the other for microscopic applications. The technique brings a novel way to acquire the hyperspectral images, based on an interferometric gadget called TWINS (Translating-Wedge-based Identical pulses eNcoding System). The TWINS is used to generate two replicas of the spectral information emitted by the sample, e. g. the reĆectance or photoluminescence, one delayed in respect to the other. Then the interference pattern is generated by projecting the replicas to a common polarization and precisely controlling the delay between them that are detected by a camera. After computing the Fourier transform of the interferogram, we access the spectrum at each point of the image. With the hyperspectral camera, projected for macroscopic applications, we explored its potential in art and conservation, and with the hyperspectral microscope, we explored applications to study biological samples.