Three-in-One Detector by 3D Printing: Simultaneous Contactless Conductivity, Ultraviolet Absorbance, and Laser-Induced Fluorescence Measurements for Capillary Electrophoresis

We describe a 3-in-1 detector for simultaneous contactless
conductivity
(C4D), ultraviolet absorbance (UV-AD), and laser-induced
fluorescence (LIF) measurements on a single detection point for capillary
electrophoresis (CE). A key component of the detector was a rectangular
detector head that was assembled with four 3D-printed parts. Two parts
covering the detector head to function as a Faraday cage were fused
deposition modeling printed using an electrically conductive material.
The other two parts in between the conductive parts were stereolithography
(SLA) printed with high-resolution (50 μm) constructions on
the surface. After assembling the two SLA printed parts, several cavities
were built with the surface constructions. Two electrodes and a Faraday
shield for C4D were cast by injecting molten Wood’s
metal into the cavities. For UV-AD, a slit (100 μm width) was
created by putting together two grooves (50 μm depth) on the
surface of the SLA printed parts. A 255 nm UV-LED was used as the
light source. The effective path length and stray light for a 50 μm
id capillary were 39 μm and 13%, which were superior to those
of other reported 3D-printed AD detectors. Confocal LIF detection
was conducted by using an objective lens to focus the laser on the
capillary via a through-hole. The detector was used to detect model
analytes, including inorganic and organic ions, and fluorescein isothiocyanate
labeled amino acids in a signal-run CE separation. In detecting fluorescein,
LODs were 1.3 μM (C4D), 2.0 μM (UV-AD), and
1 nM (LIF). The calibration ranges covered from 0.01 μM to 500
μM.