Temporally Resolved Fluorescence Spectroscopy of a Microarray-Based Vapor Sensing System

This paper describes a method to measure the complete fluorescence spectrum from numerous fluorescent microspheres in a microarray simultaneously during exposure to a vapor. The technique, called spectrally resolved sensor imaging (SRSI), positions a transmission grating directly in front of the microscope objective on a standard epi-fluorescence microscope. This modification produces a hybrid image on the CCD camera that contains a conventional fluorescence image in the zero-order diffracted light and a fluorescence spectral image in the first-order diffracted light. Three types of surface-functionalized silica microspheres were coated with a solvatochromic dye. The surface functionality on the microspheres influences the maximum emission wavelength of the dye and generates a fluorescence spectral signature that is used to identify each sensor type. These sensors were randomly distributed into a photolithographically fabricated microarray platform, and the spectral signature of each individual sensor was measured. The time resolution of spectral acquisition is short enough to capture dynamic changes in the fluorescence emission as a vapor is presented to the array. The ability to measure the entire fluorescence spectrum from each sensor simultaneously during a vapor exposure increases the dimensionality of the response data and significantly improves the classification accuracy of the system.