A multichannel fluorescence detection system for multi-lane DNA sequencer based on single photon counting is presented. The problem of elimination of the lane cross-talk caused by both optical and electronic cross-talk between the detection lanes is discussed. A novel method for elimination of the channel cross-talk is proposed. The calibration procedure for a DNA sequencer with lane cross-talk cancellation is described. Improvement in sensitivity of a DNA sequencer setup by introducing wide collection angle optical system is discussed.
We continue our work on the design and implementation of multi-channel single photon detection systems for highly
sensitive detection of ultra-weak fluorescence signals, for high-performance, multi-lane DNA sequencing instruments.
A fiberized, 32-channel single photon detection (SPD) module based on single photon avalanche diode (SPAD), model
C30902S-DTC, from Perkin Elmer Optoelectronics (PKI) has been designed and implemented. Unavailability of high
performance, large area SPAD arrays and our desire to design high performance photon counting systems drives us to
use individual diodes. Slight modifications in our quenching circuit has doubled the linear range of our system from
1MHz to 2MHz, which is the upper limit for these devices and the maximum saturation count rate has increased to 14
MHz. The detector module comprises of a single board computer PC-104 that enables data visualization, recording,
processing, and transfer. Very low dark count (300-1000 counts/s), robust, efficient, simple data collection and
processing, ease of connectivity to any other application demanding similar requirements and similar performance
results to the best commercially available single photon counting module (SPCM from PKI) are some of the features of
Single photon counting is the most sensitive method for detection of weak signals. However, it has rarely been used in DNA sequencing applications because of its complexity. We present a fiberized 16-channel single photon detection (SPD) module based on avalanche photo diodes (APD). The diodes are cooled at -20 °C and the average dark count is 700 c/s with APD operating at 10V over-voltage. The proposed system uses active quenching based on basic NAND gates and delay integrated circuits (ICs) and is compact in size, robust, easily portable and requires only 120Vac supply for its operation. The fiberization of the diodes using standard components allows the connection of this system to any other system using fibers with FC connectors with up to 400μm core diameters. Comparative performance with superior commercially available photon counting modules has been obtained. The SPD module has been successfully used for fluorescence detection of weak signals in a DNA sequencing instrument and hence the suitability of large active area APD model for DNA sequencing has been verified experimentally.