High sensitivity radiation detector for capillary electrophoresis

The authors have designed and fabricated a highly collimated, compact CdTe detector, specifically designed for measuring small radioactive sample volumes used in a capillary tube. The prototype detector was configured in a U-shape. The compact design has the advantage that it can be easily retrofitted to standard high-performance CE (capillary electrophoresis) apparatus, thereby providing additional high-sensitivity capabilities to these devices. The counting efficiency of the prototype detector was measured to be approximately 40%. Based on the detector efficiency and noise characteristics, it is estimated that the (noise-limited) minimum sample of ³²P-labeled DNA fragments that can be detected is of the order of 2 attomoles. This estimate was based on the measured noise count rate (3 cpm) and the assumption that an S/N ratio of three was needed to positively identify a peak above the background