Dresden 2026 – scientific programme

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BP: Fachverband Biologische Physik

BP 33: Bioimaging

BP 33.8: Talk

Thursday, March 12, 2026, 17:15–17:30, BAR/0205

Phase Analysis of Photothermal Signal Enables Sub-Cellular Chemical Mapping of Complex Biological Systems — •Felix Hermann Patzschke and Frank Cichos — Molecular Nanophotonics Group, Peter Debye Institute for Soft Matter Physics, Leipzig University, Linnéstraße 5, 04103 Leipzig

Optically probed Photothermal Infrared (O-PTIR) microscopy is a powerful technique for label-free chemical imaging at sub-micron resolution, promising for cell and tissue analysis. However, the mechanism of signal generation is complex, suffering from the dynamic crosstalk between background and target heating. This lack of a rigorous, quantitative understanding of these dynamics currently forces users to sacrifice either chemical specificity or spatial resolution.

We conducted systematic experiments on defined nanoscale structures to motivate and validate a quantitative theoretical model based on the transient heat equation. This model reveals that the phase of the photothermal signal, a dynamic quantity often neglected, contains essential, localized information.

This phase directly encodes the time delay associated with thermal wave propagation, allowing for precise quantification of sub-cellular structural detail through effective thermal distance, even when the amplitude signal is insufficient to resolve closely-spaced features. By leveraging the full phase and amplitude response, we overcome existing spatial resolution limits, achieving enhanced, label-free chemical mapping for next-generation bioimaging, using existing hardware.

Keywords: Photothermal Detection; Mid-IR Spectroscopy; Superresolution Imaging