The light source used for fluorescent microscopy is the sample itself, which fluoresces with visible light in response to electromagnetic excitation. Neighboring molecules can blur the target signal, so high-resolution imaging requires the observa- tion of a very small volume. Chong Xie et al. (pp. 3894-3899) propose an alternative to existing imaging techniques, which rely on highly confined standing light waves called evanescent waves to limit the illumination volume, but do not allow light to penetrate deep enough into cells to image the cell interior.
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