Herein, we report an eco-friendly and simple fluorescent nitrogen-doped carbon quantum dot (N-CQD) biosensor which was synthesized via a hydrothermal method using erhanediamine (EDA) and citric acid (CA) as precursors. The surface functionalization of N-CQDs exhibited a bright blue emission under the excitation wavelength of 350 nm. The obtained N-CQDs were characterized by atomic force microscopy (AFM), Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, and transmission electron microscopy. It was found that the surface of the CQDs was successfully functionalized. After that, as-prepared N-CQDs were further applied in Fe(III) detection. Spectroscopic data indicated that fluorescent carbon-based nanomaterials displayed a sensitive response to Fe ³⁺ in the range of 0.5–1000 μ M as a fluorescence sensor in real environmental samples. Furthermore, the results also showed that a novel N-CQD nanomaterial could be employed as an ideal fluorescent Fe(III) probe.

Titanium dioxide-polyaniline/polyamide 6 (TiO₂-PANI/PA6) composite nanofibers were prepared by in situ polymerization of aniline in the presence of PA6 nanofibers and a sputtering-deposition process with a high purity titanium sputtering target. TiO₂-PANI/PA6 composite nanofibers and PANI/PA6 composite nanofibers were fabricated for ammonia gas sensing. The ammonia sensing behaviors of the sensors were examined at room temperature. All the results indicated that the ammonia sensing property of TiO₂-PANI/PA6 composite nanofibers was superior to that of PANI/PA6 composite nanofibers. TiO₂-PANI/PA6 composite nanofibers had good selectivity to ammonia. It was also found that the content of TiO₂ had a great influence on both the morphology and the sensing property of TiO₂-PANI/PA6 composite nanofibers.

We report a room-temperature ammonia sensor with extra high response values and ideal flexibility, including polyaniline (PANI)-coated titanium dioxide-silicon dioxide (TiO ₂ -SiO ₂ ) or copper oxide-titanium dioxide-silicon dioxide (CuO-TiO ₂ -SiO ₂ ) composite nanofibers. Such flexible inorganic TiO ₂ -SiO ₂ and CuO-TiO ₂ -SiO ₂ composite nanofibers were prepared by electrospinning, followed by calcination. Then, in situ polymerization of aniline monomers was carried out with inorganic TiO ₂ -SiO ₂ and CuO-TiO ₂ -SiO ₂ composite nanofibers as templates. Gas sensing tests at room temperature indicated that the obtained CuO-TiO ₂ -SiO ₂ /PANI composite nanofibers had much higher response values to ammonia gas (ca. 45.67–100 ppm) than most of those reported before as well as the prepared TiO ₂ -SiO ₂ /PANI composite nanofibers here. These excellent sensing properties may be due to the P-N, P-P heterojunctions and a structure similar to field-effect transistors formed on the interfaces between PANI, TiO ₂ , and CuO, which is p-type, n-type, and p-type semiconductor, respectively. In addition, the prepared free-standing CuO-TiO ₂ -SiO ₂ /PANI composite nanofiber membrane was easy to handle and possessed ideal flexibility, which is promising for potential applications in wearable sensors in the future.

Camphor sulfonic acid (CSA)-doped polyamide 6/polyaniline (PA6/PANI) composite nanofibers were fabricated using in situ polymerization of aniline under different CSA concentrations (0.02, 0.04, 0.06, 0.08 and 0.10 M) with electrospun PA6 nanofibers as templates. The structural, morphological and ammonia sensing properties of the prepared composite nanofibers were studied using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), four-point probe techniques, X-ray diffraction (XRD) and a home-made gas sensing test system. All the results indicated that the CSA concentration had a great influence on the sensing properties of CSA-doped PA6/PANI composite nanofibers. The composite nanofibers doped with 0.02 M CSA showed the best ammonia sensing properties, with a significant sensitivity toward ammonia (NH₃) at room temperature, superior to that of the composite nanofibers doped with 0.04–0.10 mol/L CSA. It was found that for high concentrations of CSA, the number of PANI–H⁺ reacted with NH₃ would not make up a high proportion of all PANI–H⁺ within certain limits. As a result, within a certain range even though higher CSA-doped PA6/PANI nanofibers had better conductivity, their ammonia sensing performance would degrade.