Portable genotyping system: Four-colour microchip electrophoresis

Abstract

In the field of genomic research, the microcapillary electrophoresis (MCE) plays a key role, allowing a small reagent use but requiring the ability to detect luminescences down to a few photons per second. Very high sensitivity detectors are therefore required, rising the systems’ final costs and reducing their diffusion. There is a strong request to develop compact and low cost systems. The state of the art for MCE-based DNA analysis instruments is the use of photomultiplier tubes (PMTs) or CCDs, but either have some drawbacks. As for the PMTs, they cannot be integrated, so detection of the four bases can occur only using four different PMTs, increasing size and cost. As for the CCDs, even if they are commonly used, they are not the best solution regarding simplicity and cost. A valid alternative is single photon avalanche diodes (SPADs). Such devices present high quantum efficiency (higher than PMTs), with the possibility to integrate several detectors on a single chip, even with custom geometries, retaining low fabrication costs and high sensitivity. The strong potential of planar SPAD technology for DNA analysis has already been demonstrated in previous works. Here we present the first genotyping system based on a custom array of four SPADs, purposely designed to be used in conjunction with Beckman-Coulter markers. The module size is 19 cm ( L), 12.5 cm ( W), 15 cm ( H), including high voltage section, detectors and optical system: at the best of our knowledge, this is the most compact four-colour genotyping system in literature.