3D-printed lab-in-a-syringe voltammetric cell based on a working electrode modified with a highly efficient Ca-MOF sorbent for the determination of Hg(II)

This work combines, for the first time, 3D-printing technology and a highly efficient metal organic framework (Ca-MOF) as an electrode modifier to produce a novel fully integrated lab-in-a-syringe device for the sensitive determination of Hg(II) by anodic stripping voltammetry. The specific Ca-MOF ([Ca(H₄L)(DMA)₂]·2DMA where H₆L is the N,N’-bis(2,4-dicarboxyphenyl)-oxalamide and DMA is the N,N-dimethylacetamide) shows an exceptional Hg(II) sorption capability over a wide pH range and its mechanism is elucidated via spectroscopic and X-ray diffraction studies. The voltammetric lab-in-a-syringe device is fabricated through a single-step process using a dual extruder 3D printer and is composed of a vessel integrating two thermoplastic conductive electrodes (serving as the counter and pseudo-reference electrodes) and of a small detachable 3D-printed syringe loaded with a graphite paste/Ca-MOF mixture (which serves as the working electrode). After optimization of the fabrication and operational variables, a limit of detection of 0.6 μg L⁻¹ Hg(II) was achieved, which is comparable or lower than that of existing sensors (plastic 3D-printed, gold and MOF-based electrodes). The adoption of 3D printing technology in combination with the highly efficient Ca-MOF enables the fabrication of a simple, low-cost and sensitive electrochemical sensor for Hg(II), which is suitable for on-site applications.