Precise automated control of fluid volumes inside glass capillaries

A precise automated apparatus for controlling the position of small fluid s ample volumes inside glass capillaries has been developed as part of an aut omated system for handling submicroliter reaction volumes for genomic analy sis [1], [2], The apparatus uses a linear charge-coupled device (CCD) array , de motor, pneumatic pump, feedback controller, and a digital signal proce ssor (DSP) to detect the menisci and control in real-time the position of f luid in a clear glass capillary with a resolution of 50 mu m. This informat ion is used to infer fluid volumes and control aspiration and dispensing to within 15 nanoliters depending on the inner diameter of the capillary. A c omputer simulation was developed to determine the effect of thick- and thin -walled capillaries on the detected signals. This simulation showed that, w ith a geometry appropriate for the overall automated system, a capillary wi th an inner diameter greater than 0.6 times the outer diameter is optimal t o detect the presence of fluid inside the capillary. Thicker walled glass c apillaries may be employed if a focusing lens is placed between the light s ource and the capillary, This result was verified experimentally. [305].