Confocal reader for biochip screening and fluorescence microscopy.

We developed a fluorescence reader for the sensitive detection of surface-generated fluorescence. The system is applicable for high resolution imaging as well as for the readout of large biochips. The surface of a microscope coverslip is scanned with a laser beam focused to a waist diameter of 500 nm (FWHM) by means of a single aspheric lens. Scanning large areas with a focused beam usually evokes the need of automatic control elements to adjust the laser spot to the designated position at the surface. Due to the special design of the reader, the focus keeps at the plane of the surface even when scanning large areas, obviating the requirement of any real time control. Thus the instrument is straightforward and inexpensive. Nevertheless it features a high sensitivity and high optical resolution. The versatility of the instrument is demonstrated by imaging cells and reading out a DNA-chip. The excellent sensitivity is shown by detecting single fluorescently labeled antibodies.