Optical system for detection of signal in fluorescent immunoassay

An optical system for delivering excitation light to a chemical sensor and receiving an optical signal from the sensor, comprising:

• a focusing lens for focusing said excitation light;
• a planar mirror having a reflective side, a non-reflective side, and a hole for passing a predetermined portion of said excitation light from said focusing lens through said mirror;
• a region for exciting and coupling fluorescence from an analyte, said region capable of receiving excitation light through said hole and of directing said fluorescence to said reflective side of said mirror;
• imaging means for optically imaging the portion of said fluorescence reflected by said mirror to form an image of said region, said imaging means having an image plane;
• an optical stop having a substantially circular aperture in the image plane of said imaging means for blocking undesired light from said imaging means and passing desired light from said imaging means;
• and
• a detector situated in a path of said desired light emerging from said aperture in said optical stop;
• said mirror being angled for directing substantially all fluorescence from said region into said imaging means.