To improve the sensitivity of protein microarray, a prism surface replaces the surface of the common microscope slide.The protein targets arrayed on the surface are hybridized and labelled by fluorescent probes. Evanescent excitation occurs when the convergent laser reaches the surface, and a photomultiplier tube detects the emitted fluorescent signal. A two-dimensional actuator scans the whole surface to achieve planar laser excitation and fluorescence collection. The penetration depth of the evanescent field into the protein targets is only some hundred nanometers and can be controlled by different incident angle of the laser beam, so the undesired background signals are reduced dramatically and the detection sensitivity is improved by a factor of 50 to 100 comparing to confocal excitation. This approach can detect low abundance analytes without signal amplification.