Abstract
Astrocyte cell differentiation to their characteristic starlike morphology with the expression of proteins in microdomains, critical for normal brain function, occurs naturally in-vivo but can be affected in pathological condition or in cell culture in-vitro. Analyzing the molecular composition and functional properties of astrocytes in a label-free manner with sub-micron spatial resolution can enable detailed insights into their role in brain physio-pathology. However, simultaneous insights into any structural, molecular, and functional features in unlabelled differentiated astrocytes, without perturbing their natural environment with exogenous tags, has been limited. Using mid-infrared photothermal imaging, an accumulation of α-helical signatures for the extended astrocyte processes is observed in differentiated astrocytes on a nanomaterials interface. At the same time, non-differentiated astrocytes feature a more diverse protein content, rich in β-sheets. Time-resolved photothermal diffusion measurements indicate a higher interfacial thermal resistance at the astrocyte processes, connecting protein structure with thermal relaxation dynamics experimentally within the same measurement, critical for energy transport and homeostasis. This photothermal multi-parameter characterization offers unique insights into what chemically and functionally determines healthy astrocytes, paving the way towards a deeper understanding of their differentiation mechanisms. This method allows for the detection of molecular, morphological, and functional signatures associated with pathological state of astrocytes ex-vivo.