1. A system for detecting the presence of tagged biological agents in a sample, the system comprising: a large area imager having an image forming surface, the imager being able to form digital or electronic images of the sample without the help of intermediate image forming lenses; a selectively positionable microscope and camera in viewing relation with the image forming surface; the camera is adapted to acquire an image through the microscope in the form of digital data; and the system or the imaging area is enclosed in a darkened environment to exclude any external photons; an electronic controller in communication with the imager, microscope, and camera, and configured to position at least one of the imager, microscope, and camera relative to each other in order to image selected regions of the image forming surface.