Fluorescence measurements on protein microarrays demand photodetectors with ultra-high sensitivity (down to the single photon level), low noise and parallel readout capability. In the frame of the NANOSPAD FP6 European project, a novel compact instrument capable of ultra-sensitive analysis of multiple proteins in a customized microarray has been designed and implemented. In order to obtain a very compact system, a monolithic 6 × 8 array of single photon avalanche diodes (SPAD) was developed. The SPAD detector technology combines the general advantages of silicon microelectronic devices (miniature size, ruggedness and reliability, low-voltage and low-power operation, insensitivity to magnetic fields, etc.) with very high sensitivity, due to the ability to detect single photons with high efficiency and low detector noise. For performing measurements of chemiluminescent microarrays, around this monolithic …