Fig. 2

High resolution SEM and spectrally resolved intrinsic auto-cathodoluminescence images of a bovine collagen gel. a SE image (5.55 µm FOV, 10.8 nm pixel size), and b corresponding hyperspectral auto-CL image (43.2 nm pixel size, 550 nm spectral bandwidth, 20 ms pixel integration time). The bright particle in the center is residual gold remaining after sputtering, which emits CL above 800 nm, out of the detection range. c An overlay of three monochromatic auto-CL images, where selected blue, green, and red CL bands, marked in e, are centered at: 400 nm (50 nm bandwidth), 490 nm (100 nm bandwidth), and 650 nm (100 nm bandwidth), respectively. d Spectra projection showing auto-CL emission along a thick collagen fibril (1.73 µm distance, marked in the zoomed auto-CL image); each spectrum corresponds to a single pixel within the CL image (43.2 nm distance along the fibril). e Point spectra extracted from isolated fibrils and intersections of fibrils, showing CL spectral information specific to a molecular content. Scale bars in a, b and c are 2 µm. Scale bars in d are 500 nm