CHARACTERIZATION OF ISLAND FILMS AS SURFACE-ENHANCED RAMAN-SPECTROSCOPY SUBSTRATES FOR DETECTING LOW ANTITUMOR DRUG CONCENTRATIONS AT SINGLE-CELL LEVEL

Gold and silver vacuum-deposited island films were characterized by st udying deposition variables such as film thickness, evaporation rate, and substrate temperature. For both metals, these parameters were corr elated with the surface-enhanced Raman spectroscopy (SERS) effect and an increase in film thickness and low evaporation rates were shown to upshift the wavelength at maximum optical density (lambda(max)) and in crease the optical density of the substrates. In contrast, pre- and po stdeposition annealing of gold films led to the formation of substrate s that exhibited a downshift of lambda(max). Our spectral data also in dicated that silver films are substrates that are more suited for SERS applications where high frequency visible excitations are used. Measu rements on gold films classified them into two groups: thin Au films ( 10-50 Angstrom) well adapted for red excitations and thicker ones that are operative in the near infrared. SERS results, which were obtained from a single HL60 cell treated with micromolar drug quantities, plac ed on thin gold island films indicated that these island films could b e future promising substrates for SERS imaging at the cellular level. (C) 1998 John Wiley & Sons, Inc.