NEAR-FIELD SURFACE-ENHANCED RAMAN IMAGING OF DYE-LABELED DNA WITH 100-NM RESOLUTION

Raman chemical imaging on a scale of 100 mn is demonstrated for the fi rst time. This is made possible by the combination of scanning near-fi eld optical microscopy (SNOM or NSOM) and surface-enhanced Raman scatt ering (SERS), using brilliant cresyl blue (BCB)-labeled DNA as a sampl e. SERS substrates were produced by evaporating silver layers on Teflo n nanospheres. The near-field SERS spectra were measured with an expos ure time of 60 s and yielded good signal-to-noise ratios (25:1). The d istinction between reflected light from the excitation laser and Raman scattered light allows the local sample reflectivity to be separated from the signal of the adsorbed DNA molecules. This is of general impo rtance to correct for topographic coupling that often occurs in near-f ield optical imaging. The presented data show a lateral dependence of the Raman signals that points to special surface sites with particular ly high SERS enhancement.