Submicrometer aperture in a thin metal film as a probe of its microenvironment through enhanced light scattering and fluorescence

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Abstract
The concept of surface-enhanced spectroscopy is applied to the detection of small changes in the optical properties of the microenvironment of a single small scattering object. Apertures of a diameter of 0.18–0.48 μm in thin films of silver or gold supported by a glass slide are used as microprobes to detect the properties of an adjacent liquid. Resonant conditions for enhanced light scattering are obtained, which allow for a very sensitive measurement of refractive-index differences of the order of 10−4 in a small volume determined by the aperture size. Enhanced quenching of scattering from an aperture by dissolved dye molecules is introduced as a new type of surface-enhanced spectroscopy. Conditions were found that lead to an enhancement of fluorescence intensity of a Rhodamine solution in the probe volume by a factor of 40. It is suggested that these enhanced processes be used to detect time-dependent processes in the vicinity of the apertures such as fluctuations in the population of the small number of dye molecules within the probe volume of the apertures.