Guiding molecules with electrostatic forces in Surface Enhanced Raman   Spectroscopy (SERS)
  In Surface Enhanced Raman Scattering (SERS) the problem of drawing molecules to the places where surface plasmon resonance enhancements will produce signals is one of the most basic ones, and the initial obstacle to every application of the effect. We explore the possibility of using electrostatic forces as a means to "guide" charged molecules in solution toward SERS active substrates. We also show explicitly the possibility of selectively enhancing different types of dyes according to their charge, and we discuss briefly possible extensions for other applications where "electrostatic guiding" could be an option. 
Paul D. Lacharmoise, Eric C. Le Ru, Pablo G. Etchegoin