Infrared characterisation of fossils down to the nanoscale: Insights from an insect in amber

• O-PTIR and AFM-IR techniques achieve micrometric and nanometric lateral resolutions. • An extremely flat surface is necessary for accurate O-PTIR and AFM-IR analyses. • Only AFM-IR records fossil spectra with no to little contribution from amber. • These techniques can resolve micrometric chemical heterogeneity in ancient material. IR spectroscopy is a powerful tool for characterising the chemistry and chemical variability of organic remains in fossils. Optical-Photothermal InfraRed (O-PTIR) a