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The precise control of hydrogel shaping at high resolution is an intrinsic engineering challenge due to the low solid content of the material. Most of the approaches are based on lithographic mold, which becomes tricky to demold when the precision rises to micron and sub-micron range. In this work, a novel automated “electrodeposition + pulling” approach for rationally shaping chitosan hydrogel in 3D is reported. Taking advantage of the transient meniscus generated while pulling a sharpened metal wire out from a viscous solution, the process confines the electrodeposition of hydrogel simultaneously in it. Considering that the electrodeposition of hydrogel is driven by electrochemically generated OH− ions, the reaction engineering rationally and synergistically combines the mass transport of OH− ions, the gelification and the fluid mechanics in a dynamic process. With automation and mastering the process, the shape of hydrogel can be tuned, and it can be sharpened to below 1 µm at the tip with a desired length. Thus, it is demonstrated for electrochemical writing on 3D printed complex shaped surfaces. The sharpened hydrogel is in soft contact with the sample, allowing electrochemical deposition or etching reactions to be spatially localized in the contact area. By precisely pressing or stretching the hydrogel, the resolution can be tuned from a few to tens of microns just like traditional ink brushes, which may significantly improve the efficiency of writing. The work shows the power of electrochemical reaction engineering towards spatial control in 3D at micro and nano scale.

Herein, a &ldquo, nanonetwork&rdquo, modified electrode was fabricated based on multiwalled carbon nanotubes and CeO2 nanorods. Scanning electron microscopy, X-ray powder diffraction and zeta potential were employed to characterize this electrode. Multiwalled carbon nanotubes negatively charged and CeO2 nanorods positively charged form &ldquo, via electrostatic interaction. The performance of the CeO2 nanorods-based electrode remarkably improved due to the introduction of multiwalled carbon nanotubes. The detection of rifampicin (RIF) was used as a model system to probe this novel electrode. The results showed a significant electrocatalytic activity for the redox reaction of RIF. Differential pulse voltammetry was used to detect rifampicin, the reduction peak current of rifampicin linear with the logarithm of their concentrations in the range of 1.0 &times, 10&minus, 13&ndash, 1.0 &times, 6 mol/L, The linear equation is ip = 6.72 + 0. 46lgc, the detect limit is 3.4 &times, 14 mol/L (S/N = 3). Additionally, the modified electrode exhibits enduring stability, excellent reproducibility, and high selectivity. This strategy can be successfully used to detect trace rifampicin in samples with satisfactory results.

Electrode fabrication is one of the basic practices for electrochemists. Especially, microelectrodes are generally known as “hand-made” and their fabrication is often like an art. In this work, we report a new protocol for fabricating microelectrodes and multi-electrode probes based on recently matured 3D Fused Deposition Modeling (FDM) printing technique. The general concept is to print half of the insulating body in PETG, insert the (etched) metal or carbon wire(s) in the channel(s), and resume printing to complete the whole electrode. The printed electrodes are then sealed by heating and mechanically polished before use. The process requires only low-cost non-specialized facilities that can be easily equipped even in teaching laboratories. Single microelectrodes of Pt, C, Au, Ag, W and Cu with diameter below 5 µm are fabricated and examined by cyclic voltammetry and scanning electron microscopy. Furthermore, a multi-electrode probe consisting of W, Cu, Ag (oxidized to Ag/AgCl) and Pt is also printed and demonstrated for pH (potentiometric) and H2O2 (amperometric) sensing applications.