Using multi-material fused deposition modeling (FDM) for one-step 3D printing of microfluidic capillary electrophoresis with integrated electrodes for capacitively coupled contactless conductivity detection

Abstract

For the first time, the fused deposition modeling (FDM) 3D printing method was used to fabricate a microchip capillary electrophoresis (MCE) with channel dimensions (58 × 65 µm) below 100 µm. Moreover, electrodes to conduct capacitively coupled contactless conductivity detection (C4D) were integrated into the MCE using three conductive thermoplastic filaments containing graphene, carbon black, and copper. After optimizing the parameters for multi-material printing, the MCE-C4D device was fabricated in a single (one step) 3D printing process using an FDM 3D printer equipped with two extrusion nozzles. An optimization design method allowed finding that the distance (gap) between the electrodes of around 1 mm provided the maximum response of the C4D. The optimized frequency of the excitation signal applied in the C4D electrodes depended on the composition of the conductive filament used to print the electrodes. The optimized frequencies for the electrodes printed with thermoplastic polymers containing copper and carbon black were 268 and 384 kHz, respectively. The MCE-C4D successfully separated and detected a mixture of K+, Na+, and Li+ with good resolution, efficiency, precision, linearity, and limits of detections (LOD) of 10.2, 11.6, and 14.1 µmol L-1, respectively.