Human breath has been recognized as a complex yet predictive mixture of volatile organic compounds (VOCs) and inorganic gas species that can be utilized to non-invasively diagnose common diseases. Current laboratory techniques such as gas chromatography/mass spectrometry (GC/MS) and high-performance liquid chromatography (HPLC), are capable of VOC detection down to ppm concentrations. However, these methods are expensive, non-portable, require pre-processing of the exhaled VOCs, and expert operators, making them unsuitable for wide-spread use. Portable gas sensors have various advantages over other methods used in gas analysis, including ease of transportation, reduced treatment costs, fast results, and improved patient experience. Recent advancements in gas sensing technologies have enabled such devices to be used to diagnose, predict, and monitor a wide range of diseases and conditions, however, many challenges need still need to be addressed (i.e., sensitivity and selectivity) before they can be employed for such applications. Although nanotechnology has greatly improved the performance of gas sensor materials and their capacity to detect VOCs in human breath, issues around repeatability and accuracy remain, as well as adequateness due to the close proximity of the human body and the sensor device. This review focuses on how recent advancements in nanotechnology and solid-state materials have enabled VOC gas sensors to evolve into miniaturized, sensitive and selective devices for monitoring human breath in clinical applications. An introduction to the key aspects of breath analysis, including sources of VOCs in human breath and their role in disease diagnosis, is discussed. Furthermore, the current limitations and future prospects of such gas sensors for breath monitoring applications are also discussed in detail.

The chemical interaction of salicylic acid, formaldehyde, and sulfuric acid produced a disalicylic ligand (3,3′-dicarboxy-2,2′-dihydroxydiphenylmethane, DCM), which was then allowed to coordinate with copper (II) ions. The solid compounds’ chemical structures were determined using elemental analysis, UV-Vis, FT-IR, MS, ¹H-NMR, PXRD, SEM, TEM, magnetic studies, as well as molecular modeling based on DFT (density functional theory) calculations. It was proposed that the ligand coordinates in a tetradentate fashion with the copper ion to give a square-planar binuclear complex. A significant difference in the diffraction patterns between Cu(II)–DCM (amorphous) and DCM (crystalline) was displayed using an X-ray diffraction analysis. Spherical granules were identified throughout through morphology analysis using SEM and TEM. UV-Vis spectra were used to quantify the optical characteristics such as the energy gap, optical conductivity, refractive index, and penetration depth. The band gap values that lie within the semiconductor region suggested that the compounds could be used for electronic applications. The optimized structure of the synthesized Cu(II)–DCM complex was investigated using DFT and TD-DFT (time-dependent density functional theory) at the B3LYP/6-31G(d, p) level, with the LANL2DZ basis set for Cu in an ethanol solvent and the gas environment modeled by CPCM. The experimental data suggest a square-planar geometry of the Cu(II) binuclear complex. The theoretical calculations support the proposed structure of the compound. The cytotoxicity of the DCM against HCT–116 (human colon cancer) cells was tested, and the outcome exhibited good inhibitions of growth. A molecular docking (MD) examination was carried out to illustrate the binding mode/affinity of the prepared compounds (DCM and Cu(II)–DCM) in the active site of the receptor protein [CDK2 enzyme, PDB ID: 6GUE]. The compounds formed hydrogen bonds with the amino acid residues of the protein, increasing the binding affinity from −7.2 to −9.3 kcal/mol through the coordination process. The information from this current study, particularly the copper complex, is beneficial for exploring new compounds that have anticancer potential.

This study explores the synthesis of copper oxide nanoparticles (CuO NPs) via green and conventional methods, with emphasis on their performance in hydrogen evolution reactions (HERs). CuO NPs synthesized using okra extract (CuO_okra) and hydrazine hydrate (CuO_hyd) were characterized using XRD, FTIR, SEM, HRTEM, and electrochemical techniques. Structural analysis revealed that CuO_okra NPs have smaller crystallite sizes (39.8 nm) and higher defect densities than CuO_hyd NPs (56.8 nm), while CuO_hyd exhibited superior porosity and crystallinity. In HER studies, CuO_hyd outperformed CuO_okra, achieving a significantly lower overpotential (342.2 mV vs. 408.49 mV at 20 mA cm⁻²) and higher cathodic current density (15.9 vs. 11.3 mA cm⁻² at −1.3 V). Electrochemical impedance spectroscopy (EIS) further confirmed the superior catalytic activity of CuO_hyd NPs, showing minimal polarization resistance compared to CuO_okra.