Suspended gold nanospheres have been synthesized via electrochemical method. UV-vis spectra and fluorescence emission spectra have been studied at room temperature. Numerical calculations based on quasi-static, scattering and local field theories were developed to describe these optical properties. With the increasing dielectric constant of surrounding medium from 1.0 to 2.0, both local field enhancement factor and absorption wavelength maximum red shift in a linear way. However, the wavelength maximum of scattering cross-section depends on the surrounding medium dielectric constant in a nonlinear fashion. (c) 2005 Elsevier B.V. All rights reserved.