A cam-based laser-induced fluorescence scanner for capillary array electrophoresis

Capillary array electrophoresis (CAE) is an important high throughput analytical technique. Laser-induced fluorescence (LIF) has been the dominant detection method for CAE owing to its low limit of detection (LOD) and wide linear dynamic range (LDR). Linear LIF scanners were first used in CAE because linear motions of an objective match well with a common planar array of capillaries. A problem with linear scanners is that the motor is required accelerating/decelerating so that all capillaries can be properly scanned, which makes motion control complicated and reduces the duty cycle. Rotary scanners were developed to overcome this problem. While rotary scanners have been successfully applied in CAE, the capillaries have to be arranged in a circular format, which can be inconvenient in some cases. In this report, we describe a cam-based LIF scanner as an alternative technique for CAE detection. In this system, a rotary motor is mechanically linked with a capillary holder via a cam. During operation, the motor carries the cam in a rotary motion that drives an array of capillaries on the holder to move back and forth across the objective for fluorescence detection. Using this design, the capillaries can be parallel-arranged in a plane while the motor acceleration/deceleration is avoided. To demonstrate the feasibility of this approach, we constructed a prototype instrument with a constant-velocity scanning distance of ∼10 mm, a scanning frequency of 3 Hz and a duty cycle of ∼70%. The scanner exhibited a LOD of 69 pM of fluorescein and a LDR of 3.5 orders of magnitude. Multiplexed capillary SDS-PAGE was performed on this scanner for protein separations.