Laser ablation-based fabrication of a microchip capillary electrophoresis device for antibiotic detection in dairy

The widespread use of antibiotics in dairy farming presents significant health risks to consumers, prompting the need for rapid on-farm testing solutions. Currently reported solutions utilize commercially available microfluidic devices, which are high in cost and limit accessibility. To address this issue, a laser-based fabrication method is presented for rapid prototyping of microfluidic devices without the need for dangerous chemical etchants. The proposed methodology uses pulsed ultraviolet laser ablation to fabricate a wide range of microfluidic channel geometries in two substrate materials: soda-lime glass and borosilicate glass. A comprehensive characterization of the laser ablation process is presented, reporting cut depth and surface roughness for both materials as functions of optical fluence, pulse frequency, and scanning velocity. Optical fluences ranging from 30 J/cm² to 185 J/cm², and pulse frequencies ranging from 20 kHz to 60 kHz are explored. In the optimized fabrication process, surface roughness as low as 2.14 microns is achieved, enabling the actuation of electroosmotic flow. A low-temperature glass-to-glass bonding procedure is used to enclose the fabricated channel, enabling the development of a fluid-tight microfluidic device. The refined fabrication process is used to develop a microchip capillary electrophoresis device paired with an ultraviolet-induced fluorescence spectroscopy sensor to detect antibiotic residues in milk. To maximize sample throughput, a citrate buffer background electrolyte is used. An industry-relevant application of the device is demonstrated through the detection and quantification of three fluoroquinolone-class antibiotics (ciprofloxacin, levofloxacin, and danofloxacin) in milk samples. A concentration response curve, limit-of-detection, and limit-of-quantification are reported for each analyte of interest to demonstrate the performance of the device. Limits of detection of 1.91 mM, 1.74 mM, and 3.71 mM are observed for ciprofloxacin, levofloxacin, and danofloxacin, respectively. The developed microchip capillary electrophoresis device, and associated fabrication method, shows promise for providing accessible sensors for on-farm analysis applications.