Wireless Capsule for Autofluorescence Detection

Variations in tissue autofluorescence (AF) can be exploited to detect early signs of intestinal cancer, however current endoscopic AF systems are only able to inspect the oesophegus and large intestine. We present the design, fabrication and testing of a pill capable of inducing and detecting AF from mammalian intestinal tissue. The prototype comprises an application specific integrated circuit (ASIC), illumination LED, optical filters to minimize sensor response to crosstalk from the illumination wavelength, a pulse counter/control unit and a radio transmitter. The ASIC contains a single photon avalanche diode detector (SPAD), and integrate high voltage charge pump (up to 37.9 V) power supply. The SPAD operates above its breakdown voltage to operate in Geiger mode, and exhibits a detection efficiency peak at 465 nm, sufficiently close to human tissue autofluorescence's peak of 520±10 nm. The ASIC was fabricated using a commercial high-voltage CMOS process. The complete device uses only 21.4 mW.