Direct Detection of Beta Particles on a Microfluidic Chip using Position Sensitive APDs

A new device is being developed that will allow imaging of the distribution of charged particles in microfluidic circuits, using position sensitive avalanche photodiodes (PSAPD). Microfluidic chips are an emerging technology that will facilitate the synthesis and study of new molecular imaging probes. These poly-dimethylsiloxane (PDMS) chips are low in cost to custom design and produce, and their development/prototyping cycles are relatively short. They can contain a variety of microcircuitry and microwells for manipulating nanoliter volumes of solutions. The new imaging device will be created by direct contact of a PSAPD detector with the fluidic layer of a PDMS chip and will provide 2-dimensional images of the distribution of beta emitting radiolabeled probes on the chip. Furthermore, the new device will also be capable of quantifying small amounts of these radiolabeled probes over time. The PSAPD will be used for the direct detection of positrons and other charged particles. Preliminary studies were performed in our laboratory to test the feasibility of detecting small amounts of radioactive positron emitting fluorodeoxyglucose (FDG) in a prototype device. Results have shown that sensitivities as low as 56 plusmn 0.1 pCi in a 4 mm² ROI (14 pCi/mm²) and line pair spatial resolution of 0.5 mm can be achieved.