Electrochemical modulation of remote fluorescence imaging at an ordered opto-electrochemical nanoaperture array.

An array of nanometer-sized apertures capable of electrochemically modulating the fluorescence of a model analyte is presented. The device, which combines near-field optical methods and ultramicroelectrode properties in an array format, is based on an etched coherent optical fiber bundle. Indeed, the fabrication steps produced an ordered array where each optical nanoaperture is surrounded by a ring-shaped gold nanoelectrode. The chronoamperometric behavior of the array shows stable diffusion-limited quasi-steady-state response. The model analyte, tris(2,2'-bipyridine) ruthenium, emits fluorescence in the Ru(II) state, but not in the oxidized Ru(III) state. Fluorescence is excited by visible light exiting from each nanoaperture since light is confined to the tip apex by the gold coating. A fraction of the isotropically emitted luminescence is collected by the same nanoaperture, transmitted by the corresponding fiber core and eventually detected by a charge-coupled device (CCD) camera. The array format provides a fluorescence image resolved at the nanometric scale which covers a large micrometric area. Therefore the high-density array plays a bridging role between these two fundamental scales. We established that the opto-electrochemical nanoapertures are optically independent. Fluorescence of the sample collected by each nanoaperture is modulated by changing the potential of the nanoring electrodes. Reversible electrochemical switching of remote fluorescence imaging is performed through the opto-electrochemical nanoaperture array itself. Eventually this ordered structure of nanometer light sources which are electrochemically manipulated provides promising photonic or electro-optical devices for various future applications. For example, such an array has potential in the development of a combined SNOM-electrochemical nanoprobe array to image a real sample concomitantly at the nanometer and micrometer scale.