Affordable equipment to fabricate laser-induced graphene electrodes for portable electrochemical sensing.

Graphene-based materials present unique properties for electrochemical applications, and laser-induced conversion of polyimide to graphene is an emerging route to obtain a high-quality material for sensing. Herein we present compact and low-cost equipment constructed from an open-source 3D printer at which a 3.5-W visible (449 nm) laser was adapted to fabricate laser-induced graphene (LIG) electrodes from commercial polyimide, which resulted in electron transfer kinetic (k0) of 5.6 × 10-3 cm s-1 and reproducibility calculated by relative standard deviation (RSD < 5%) from cyclic voltammograms of [Fe(CN)6]3-/4- using 5 different electrodes. LIG electrodes enabled the simultaneous voltammetric determination of uric acid (+ 0.1 V vs. pseudo-reference) and nitrite (+ 0.4 V vs pseudo-reference), with limit of detection (LOD) values of 0.07 and 0.27 µmol L-1, respectively. Amperometric measurements for the detection of H2O2 (applying + 0.0 V vs. Ag|AgCl|KCl(sat.)) after Prussian blue (PB) modification and ciprofloxacin (applying + 1.2 V vs. Ag|AgCl|KCl(sat.)) were performed under flow conditions, which confirmed the high stability of LIG and LIG-PB surfaces. The LOD values were 1.0 and 0.2 µmol L-1 for H2O2 and ciprofloxacin, respectively. The RSD values (< 12%) obtained for the analysis using three different electrodes attested the precision of LIG electrodes manufactured in two designs. No sample matrix effects on the determination of ciprofloxacin in milk samples were observed  (recoveries between 84 and 96%). The equipment can be built with less than $300 and each LIG electrode costs less than $0.01.

Copper(II) complexes based on thiosemicarbazone ligand: Preparation, crystal structure, Hirshfeld surface, energy framework, antiMycobacterium activity, in silico and molecular docking studies.

Considering the promising previous results on the remarkable activity exhibited by cobalt(III) and manganese(II) thiosemicarbazone compounds as antibacterial agents, the present study aimed to prepare and then evaluate the antibacterial activity of two different types of Cu(II) complexes based on a 2-acetylpyridine-N(4)-methyl-thiosemicarbazone ligand (Hatc-Me), a monomer complex [CuCl(atc-Me)] and a novel dinuclear complex [{Cu(µ-atc-Me)}2µ-SO4]. The compounds were characterized by infrared spectra, ultraviolet visible and CHN elemental analysis. In addition, the crystalline structures of the complexes were determined by single-crystal X-ray diffraction. In both cases, the Schiff base ligand coordinated in a tridentate mode via the pyridine nitrogen, imine nitrogen and sulfur atoms. The two Cu(II) atoms in the dimer are five coordinate, consisting of three NNS-donor atoms from the thiosemicarbazone ligand connected by a sulfate bridge. The Hirshfeld surface and energy framework of the complexes were additionally analyzed to verify the intermolecular interactions. The biological activity of the Cu(II) salts, the free ligand and its Cu(II) complexes was evaluated against six strains of mycobacteria including Mycobacterium tuberculosis. The complexes showed promising results as antibacterial agents for M. avium and M. tuberculosis, which ranged from 6.12 to 12.73 µM. Furthermore, molecular docking analysis was performed and the binding energy of the docked compound [{Cu(µ-atc-Me)}2µ-SO4] with M. tuberculosis and M. avium strains were extremely favorable (-11.11 and - 14.03 kcal/mol, respectively). The in silico results show that the complexes are potential candidates for the development of new antimycobacterial drugs.