Surface-enhanced resonance Raman scattering and near-infrared Fourier transform Raman scattering as in situ probes of ink jet dyes printed on paper

The characterization of ink Jet dyes and inks printed onto paper surfaces i s of importance for the development of ink jet ink formulations and for use in forensic science. Raman spectroscopy is an effective and informative pr obe for this purpose if problems associated with fluorescence are overcome. A comparison is made here between two effective techniques, surface-enhanc ed resonance Raman scattering (SERRS) and near-infrared Fourier transform R aman scattering (NIR-FTR). SERRS provides a good method for obtaining in si tu measurements using a visible laser system. It is fast (1-10 s accumulati ons) and requires very low laser powers (<1 mW). However, it requires the a ddition of a small dot of silver colloid to the paper surface In order to p roduce the enhancement. NIR-FTR is noninvasive: and simpler to use. However , much higher laser powers are required (>200 mW), and the spectral accumul ation time is significantly longer. Both methods overcome fluorescence effe ctively in most samples studied; however, each Is more effective than the o ther with selected inks and paper substrates. SERRS involves resonant enhan cement of the chromophore of the dye in contact with the silver surface, an d consequently it is the dye chromophore which is uniquely identified, With NIR-FTR, signals from the paper and the filler are also observed. Comparab le spectral patterns with clear, explicable differences are obtained from e ach method, indicating in particular that SERRS spectra can be interpreted without recourse to specific surface selection rules. The combination of th e two techniques provides some information on the electronic as well as the vibrational properties of the dyes in situ.