Direct digital imaging of radio‐labeled two‐dimensional gel beta emissions using micro‐channel plate image enhancement

The use of autoradiography to record the distribution of radio‐labels such as tritium or 35 S in two‐dimensional (2‐D) gels has well known deficiencies: the film requires long exposures, has a nonlinear response curve, and has a restricted dynamic range. Autofluorography can improve upon each of these problems but only at the cost of resolution and quantitative accuracy. This paper demonstrates that a micro‐channel plate electron multiplier and a resistive anode position detector can detect and localize individual beta emissions from 35 S or tritium with at least 200 μm resolution. The locations of these beta emissions can be collected, converted to a 2‐D image, and displayed on a graphics terminal or integrated over spot areas for quantitative estimates of spot intensity. The collection process is rapid, linear, and has a dynamic range far greater than that of film. With the 35 S‐test gel (which required 40 h for an autoradiogram), strong spots can be integrated with better than ten percent accuracy with less than five minutes of data collection. Weak spots (those with less than 4 cpm) may require 80 min or more. Tritium gels require collection times an order of magnitude longer for equivalent quantitative accuracy.