1. A one-piece 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 free from intermediate image forming lenses, the large area imager further including: a computer configured to integrate a time period (t), and a (n) number of read-out frames with a frame time t/n, wherein the images are formed by integrating the images over the integrating time period (t), the large area imager configured to break the image integrating time period (t) into the (n) number of read-out frames to avoid noise saturation of the images; 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.