Ready-to-use 3D printed electrochemical sensors with integrated bismuth precursors for trace metals monitoring

The development of tailor-made conductive filaments doped with functional materials represents an innovative approach toward the fabrication of ready-to-use electrochemical sensors via 3D printing in decentralized settings. In this work, 3D printable filaments integrating two types of bismuth precursors (bismuth citrate and bismuth oxide) were fabricated using a solvent-casting method. The filaments consist of polylactic acid as the polymeric base, carbon black as the conductive material, and bismuth precursors as functional materials. During the electrochemical preconcentration step, the integrated precursors are reduced in situ to bismuth particles on the sensor surface, yielding 3D printed Bi-based electrodes. The sensors were used as-printed, without any post-printing modification, for the direct simultaneous monitoring of Pb(II) and Cd(II) in water and fish samples. Additionally, the sensors were characterized using optical and electrochemical techniques, while the critical fabrication and operational parameters (such as bismuth precursor loading, preconcentration time and potential, effect of interferences) were systematically optimized. Both types of 3D printed Bi-based sensors exhibited favorable analytical performance, with sensors fabricated from the bismuth citrate-modified filament providing higher stripping signals and slightly lower limits of detection. This work demonstrates a versatile strategy for the fabrication of next-generation 3D printed electrochemical sensors that can be digitally produced in a decentralized manner and directly employed for on-site monitoring of heavy metal contaminants.