Design Considerations for a Conventional Microscope based Microarray-Reader to Improve Sensitivity

An unmodified wide-field fluorescence microscope system equipped with a scientific grade CCD camera can be used to measure fluorescent signals in subnanoliter vials. The lowest detectable fluorescence signal in a 0.8nl vial of 200 × 200 × 20μm corresponds to a concentration of fluorescent molecules on the order of a nanomolar (10−9M ) for a dye such as Rhodamine. This paper will explain that the lowest detectable concentration is limited by one of the following instrumental factors: stray light, originating in the excitation path of the microscope system or readout noise in the photon detection part of the system. This paper will present a number of modifications to our wide-field microscope system to improve its performance in terms of the detection limit, under assumption that readout noise is the limiting factor.