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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.
U. C. Fischer (1986) studied this question.