Nanosized metal particles show specific physical and chemical properties that allow the creation of new composites materials, which are important for multiple applications in biology and medicine such as infections control. Metal nanoparticles, mainly copper, exhibit excellent inhibitory effect on Gram‐positive and Gram‐negative bacteria; therefore the exploration about the efficient, economical, and friendly environmental technics to synthesize inorganic nanoparticles is imperative. In this work a brief overview of the several methods is made including the comparison of the methods, mainly between sonochemical, microwave, and chemical routes. It allows determining the optimal parameters and technical conditions to synthesize copper nanoparticles with physical and chemical properties suitable for the oral bacterial inhibition.

Copper sulfide is a promising p-type inorganic semiconductor for optoelectronic devices such as solar cells, due its small band gap energy and its electrical properties. In this work nanocrystalline copper sulfide (Cu_xS), with two stoichiometric ratios (x = 2, 1.8) was obtained by one-pot synthesis at 220, 230, 240 and 260 °C in an organic solvent and amorphous Cu_xS was obtained in aqueous solution. Nanoparticle-like nucleation centers are formed at lower temperatures (220 °C), mixtures of morphologies (nanorods, nanodisks and nanoprisms) are seen at 230 and 240 °C, in which the nanodisks are predominant, while big hexagonal/prismatic crystals are obtained at 260 °C according to TEM results. A mixture of chalcocite and digenite phases was found at 230 and 240 °C, while a clear transition to a pure digenite phase was seen at 260 °C. The evolution of morphology and transition of phases is consistent to the electrical, optical, and morphological properties of the copper sulfide. In fact, digenite Cu_1.8S is less resistive (346 Ω/sq) and has a lower energy band gap (1.6 eV) than chalcocite Cu₂S (5.72 × 10⁵ Ω/sq, 1.87 eV). Low resistivity was also obtained in Cu_xS synthesized in aqueous solution, despite its amorphous structure. All Cu_xS products could be promising for optoelectronic applications.

Conducting polyaniline nanofibers (nf-PANI) were successfully synthesized by simple polymerization of aniline in presence of single and binary dopant agents. Strong hydrochloride acid (HCl), two weak organic acids (poly acrylic acid, PAA, 2-acrylamido-2-methyl-1-propanesulfonic acid, AMPSA) and one anionic surfactant (sodium dodecyl sulfate, SDS) were used to form the binary dopant agents. The binary dopant agent PAA modified the morphology of the single doped PANI, whereas AMPSA and SDS modified the dimensions of the nanofibers: the length size single nanofibers is reduced 1.72 times with binary-doped AMPSA and increased by a factor of 0.7 with SDS. The surface roughness of the films decreases when the dimensions of the nanofibers increase: PANI-SDS film is flatter than PANI-AMPSA film. In general, the conductivity of the single-doped PANI nanofibers (nf-PANI-HCl) was improved by one order of magnitude with binary dopant agents (HCI-PAA, HCl-AMPSA, HCl-SDS). The influence of the binary dopant agents in the nf-PANI-HCl properties is analyzed by Transmission Electron Microscope (TEM), Atomic Force Microscopy (AFM), UV-VIS absorption spectra, thermogravimetric analysis (TGA) and Fourier-Transform infrared spectra (FT-IR).