The fluorescent carbon dot is a novel type of carbon nanomaterial. In comparison with semiconductor quantum dots and fluorescence organic agents, it possesses significant advantages such as excellent photostability and biocompatibility, low cytotoxicity and easy surface functionalization, which endow it a wide application prospect in fields of bioimaging, chemical sensing, environmental monitoring, disease diagnosis and photocatalysis as well. Biomass waste is a good choice for the production of carbon dots owing to its abundance, wide availability, eco-friendly nature and a source of low cost renewable raw materials such as cellulose, hemicellulose, lignin, carbohydrates and proteins, etc. This paper reviews the main sources of biomass waste, the feasibility and superiority of adopting biomass waste as a carbon source for the synthesis of carbon dots, the synthetic approaches of carbon dots from biomass waste and their applications. The advantages and deficiencies of carbon dots from biomass waste and the major influencing factors on their photoluminescence characteristics are summarized and discussed. The challenges and perspectives in the synthesis of carbon dots from biomass wastes are also briefly outlined.

Flavor is an important index to evaluate the sensory quality of tobacco. The process of fermentation is a key step in the production of aromatic substances in tobacco leaves and an important factor in improving their quality. Worldwide, reams of research show that chromatographic technology plays an irreplaceable role in the tobacco aromatic chemistry. Nevertheless, the degradation mechanism of latent aromatic compounds and the formation mechanism of characteristic aromatic substances have not been fully and systematically elucidated. In this study, the latest progress of basic methods, techniques, and research results of the separation, analysis, and identification of aromatic substances in fermented tobacco leaves were reviewed, and the next research and application directions were prospected. It is expected to provide theoretical reference for the study of molecular mechanism of tobacco flavor, reveal the degradation mechanism of potential aroma compounds, and help improve the quality of tobacco.

Recycling waste biomass into valuable products (e.g., nanomaterials) is of considerable theoretical and practical significance to achieve future sustainable development. Here, we propose a one-pot hydrothermal synthesis route to convert waste tobacco stems into biomass-based N, S-codoped carbon dots (C−dots) with the assistance of carbon black. Unlike most of the previously reported luminescent C−dots, these biomass-based C−dots showed a satisfactory stability, as well as an excitation-independent fluorescence emission at ~520 nm. Furthermore, they demonstrated a pH-dependent fluorescence emission ability, offering a scaffold to design pH-responsive assays. Moreover, these as-synthesized biomass-based C−dots exhibited a fluorescence response ability toward tetracycline antibiotics (TCs, e.g., TC, CTC, and OTC) through the inner filter effect (IFE), thereby allowing for the establishment a smart analytical platform to sensitively and selectively monitor residual TCs in real environmental water samples. In this study, we explored the conversion of waste tobacco stems into sustainable biomass-based C−dots to develop simple, efficient, label-free, reliable, low-cost, and eco-friendly analytical platforms for environmental pollution traceability analysis, which might provide a novel insight to resolve the ecological and environmental issues derived from waste tobacco stems.

Cancer cells are characterized by high viscosity, low pH and high levels of reactive oxygen species. Both pH and viscosity are key indicators which can respond to the microenvironment of cancer cells and are also important indicators for monitoring fatty liver. Based on this, we have constructed a hemicarbocyanine fluorescent probe (HTC) possessing a D–D′(π)–π–A structure using phenol as an electron donor (D), a thiophene moiety as an electron donor and a partial π bridge. The fluorescent probe HTC exhibits pH-responsive properties, and the fluorescence intensity of the probe at 627 nm gradually decreases and the fluorescence at 720 nm gradually increases with the increase of pH for pH = 7 to 10.5. Meanwhile, with an increase of viscosity the fluorescent probe HTC exhibited gradually enhanced fluorescence at 627 nm, thus revealing a response to the change of viscosity. In addition, the fluorescent probe HTC can target mitochondria for cellular fluorescence imaging, and co-localized fluorescence imaging with the commercial mitochondrial probe Mito-Tracker Green with a Pearson's coefficient of 0.91. We have utilized the properties of the fluorescent probe HTC, which exhibits a pH and viscosity response, and have applied it to monitor the change of pH or viscosity in cells and differentiate between normal and cancerous cells, as well as for the identification of non-alcoholic fatty liver mice. In addition, the probe is easily metabolized in mice and has good biocompatibility.