We present a resonant-cavity-enhanced Single Photon Avalanche Diode (SPAD) fabricated on a reflecting siliconon-insulator (SOI) substrate. The substrate incorporates a two period distributed Bragg reflector fabricated using a commercially available double-SOI process. The resonant-cavity-enhanced (RCE) SPAD detectors have peak photon detection efficiencies ranging from 41% at 780nm to 32% at 850nm and time resolution of 35ps full-width at half maximum. Typical dark count rates of 500, 5000 and 100000 c/s were measured at room temperature with RCE SPADs having respectively 8, 20 and 50µm diameter.Fluorescence spectroscopy is nowadays widely used as analytical and research tool in several fields, such as chemistry, biology and materials science (see [1] for review). Miniaturized detectors with single-photon sensitivity are required in these applications to face the steady trend toward smaller sample volumes, lower excitation intensity and compact, low-cost analytical systems. Planar Single Photon Avalanche Diodes (SPADs) fabricated on double epitaxial silicon substrates offer the typical advantages of solid state devices (miniaturization, ruggedness, low voltage, low power, low cost, etc.) along with remarkably good photon timing resolution (< 35ps full width at half time) and high photon detection efficiency (PDE) in the visible range (~ 50% at 550nm)[2]. A shortcoming of planar SPADs is the relatively low PDE in the near infrared (NIR) range from 700 to 850nm (values from 25% to 12% are typical). Although this performance is much better than that of photomultiplier tubes, there is a general request for higher PDE in the NIR …