Electron microscopy is crucial for imaging biological ultrastructure at nanometer resolution. However, electron irradiation also causes specimen damage, reflected in structural and chemical changes that can give rise to alternative signals. Here, luminescence induced by electron-beam irradiation is reported across a range of materials widely used in biological electron microscopy. Electron-induced luminescence is spectrally characterized in two epoxy (Epon, Durcupan) and one methacrylate resin (HM20) over a broad electron fluence range, from 10⁻⁴ to 10³ mC cm⁻², both with and without embedded biological samples. Electron-induced luminescence is pervasive in polymer resins, embedded biomaterial, and occurs even in fixed, whole cells in the absence of resin. Across media, similar patterns of intensity rise, spectral red-shifting, and bleaching upon increasing electron fluence are observed. Increased landing energies cause reduced scattering in the specimen shifting the luminescence profiles to higher fluences. Predictable and tunable electron-induced luminescence in natural and synthetic polymer media is advantageous for turning many polymers into luminescent nanostructures or to fluorescently visualize (micro)plastics. Furthermore, these findings provide perspective to direct electron-beam excitation approaches like cathodoluminescence that may be obscured by these nonspecific electron-induced signals.

Nanomaterials can be identified in high-resolution electron microscopy images using spectrally-selective cathodoluminescence. Capabilities for multiplex detection can however be limited, e.g., due to spectral overlap or availability of filters. Also, the available photon flux may be limited due to degradation under electron irradiation. Here, we demonstrate single-pass cathodoluminescence-lifetime based discrimination of different nanoparticles, using a pulsed electron beam. We also show that cathodoluminescence lifetime is a robust parameter even when the nanoparticle cathodoluminescence intensity decays over an order of magnitude. We create lifetime maps, where the lifetime of the cathodoluminescence emission is correlated with the emission intensity and secondary-electron images. The consistency of lifetime-based discrimination is verified by also correlating the emission wavelength and the lifetime of nanoparticles. Our results show how cathodoluminescence lifetime provides an additional channel of information in electron microscopy.

Cellular complexity is unraveled at nanometer resolution using electron microscopy (EM), but interpretation of macromolecular functionality is hampered by the difficulty in interpreting grey-scale images and the unidentified molecular content. We perform large-scale EM on mammalian tissue complemented with energy-dispersive X-ray analysis (EDX) to allow EM-data analysis based on elemental composition. Endogenous elements, labels (gold and cadmium-based nanoparticles) as well as stains are analyzed at ultrastructural resolution. This provides a wide palette of colors to paint the traditional grey-scale EM images for composition-based interpretation. Our proof-of-principle application of EM-EDX reveals that endocrine and exocrine vesicles exist in single cells in Islets of Langerhans. This highlights how elemental mapping reveals unbiased biomedical relevant information. Broad application of EM-EDX will further allow experimental analysis on large-scale tissue using endogenous elements, multiple stains, and multiple markers and thus brings nanometer-scale 'color-EM' as a promising tool to unravel molecular (de)regulation in biomedicine.