Design of the purpose-made microscope is an important part for this research. While similar to experimental setups for visible wavelength Raman imaging,2,3 our system has several unique features. For excitation, the microscope uses the 257 nm cw line from a frequency-doubled laser (Coherent, Inc.), suitable for resonant excitation of nucleotide bases.30 Even with desiccated samples, we used a high NA glycerin-immersion objective lens (Carl Zeiss, Inc. ) for excitation and scattering light collection from the sample with the smallest possible excitation focal volume. The excitation intensity is adjusted to μm2 by an ND filter. A shutter is used for controlling the duration of sample exposure to avoid photodegradation of the sample. Rayleigh scattering is rejected by an edgefilter, and the frequency-processed light is then dispersed by a holographic grating (Princeton Instruments, Inc. ). We measured the spectra by a back-illuminated CCD (Princeton Instruments, Inc. SPEC-10 2KBUV). Grating dispersion is calibrated with the laser line (), and Raman bands of boron nitride () and acetonitrile (). For imaging, a piezo-electric stage (PI, Inc.) raster-scanned the sample with a 0.5 μm step. Each spectrum is acquired with 0.75 s sample exposure, and all optics are necessarily made of quartz or .