Solid-state fluorescence sensing is one of the most appealing detection techniques because of its simplicity and convenience in practical operation. Herein, we report the development of a red-emitting carbon dots (RCDs)-based material as a solid-state fluorescence sensor for the selective probing of gaseous ammonia. The RCDs were prepared by a low-cost, one-step carbonization method using sugar cane bagasse as the carbon precursor. The pristine RCDs were then directly coated on polyvinylidene fluoride membrane to produce a new fluorescence sensor capable of selectively distinguishing toxic gaseous ammonia from other analyte vapors through sensitive fluorescence quenching with a low detection limit. More importantly, the interfacial response mechanism occurring on the surface of the RCDs has been studied by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and Raman measurements. The results indicate that fluorescence quenching in the RCDs might result from ammonia-induced Michael addition through insertion of N into the CC group and deprotonation of the carboxyl group. To the best of our knowledge, this is the first report that provides clear insight into the mechanism of surface chemistry on CDs in the solid state.

A simple and effective glucose biosensor based on immobilization of glucose oxidase (GOD) in graphene (GR)/Nafion film was constructed. The results indicated that the immobilized GOD can maintain its native structure and bioactivity, and the GR/Nafion film provides a favorable microenvironment for GOD immobilization and promotes the direct electron transfer between the electrode substrate and the redox center of GOD. The electrode reaction of the immobilized GOD shows a reversible and surface-controlled process with the large electron transfer rate constant (k_s) of 3.42±0.08 s⁻¹. Based on the oxygen consumption during the oxidation process of glucose catalyzed by the immobilized GOD, the as-prepared GOD/GR/Nafion/GCE electrode exhibits a linear range from 0.5 to 14 mmol·L⁻¹ with a detection limit of 0.03 mmol·L⁻¹. Moreover, it displays a good reproducibility and long-term stability.

The photodegradation (λ=365 nm) of the biomolecule vitamin B₁₂, catalyzed by the photocatalyst TiO₂ nanoparticles (NPs), has been investigated in aqueous suspension. The photodegradation process of vitamin B₁₂ has been monitored by means of electronic absorption (Abs), Fourier-transform infrared (FT-IR), and resonance Raman (RR) spectroscopies, respectively. The results show that only under UV illumination in the presence of TiO₂ is there effective degradation, and the photocatalytic degradation of vitamin B₁₂ is strongly influenced by the amount of TiO₂ NPs, the pH, and the initial concentration of vitamin B₁₂. The photocatalytic reaction kinetics of vitamin B₁₂ conforms to a Langmuir-Hinshelwood isotherm model. Changes involving the three structural units of the carbon-metal bond C–Co, the organic corrin macrocycle combined with the benzimidazole nucleotide, and the inorganic CN in the vitamin B₁₂ molecule during the photocatalytic degradation are also discussed.