Fluorescent microscopy using localized excitation source with gold nanotriangles: A computational study

A new method for fluorescent microscopy has been proposed. Proposed method uses indirect excitation of fluorophores with nanometer localized illuminating source. Localized source is created at corners of gold nanotriangles which are deposited on glass substrate. Actually the combination of gold nanotriangle (deposited on glass) acts as active substrate (where species will be placed) for our proposed method. The structure will be scanned with a focused beam of laser (or combination of beams). Due to electric field enhancement in corners and edges of nanotringle (because of surface plasmons), third order nonlinear effect will be enhanced accordingly. Enhancement in third order nonlinearity will give the chance to third harmonic generation and four wave mixing at hot spots. Enhancement in nonlinear process will give the chance of localized source creation for excitation of fluorophores in near field region. In order to prove our claim, we have numerically analyzed interaction of light with gold nanotriangle deposited on glass substrate. Our method is based on solving Maxwell's equation in three dimensions, considering dispersion behaviour of permittivity and third order nonlinear susceptibility by nonlinear finite difference time domain method. Simulation results show that generated light is highly localized and its wavelength can be tuned by changing the excitation wavelength. As a result of omitting background noise and space dependency of excitation source, enhancement in spectral and spatial resolution of imaging system will result. (C) 2011 Elsevier B.V. All rights reserved.