Raman is not an appropriate way to estimate size, although the Raman signal of any adsorbed molecules may be enhanced due to the SERS effect at 785nm. However, a SERS enhancement at 785nm is usually indicative of aggregation of spherical gold nanoparticles.
Furong Tian, et al., Analytical Methods, 6, 9116-9123(2014)
UV/vis spectroscopy is an indirect indication of size, but more direct measurements such as Light scattering, AFM or SEM/TEM would be preferable.