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On–off–on fluorescent sensors based on emerging carbon nanoparticles (CNPs) or carbon dots (CDs) have attracted extensive attention for their convenience and efficiency. In this study, dumped silkworm excrement was used as a novel precursor to prepare fluorescent nitrogen-doped CNPs (N-CNPs) through hydrothermal treatment. The obtained N-CNPs showed good photoluminescent properties and excellent water dispersibility. Thus, they were applied as fluorescence “on–off–on” probes for the detection of Fe(III) and biothiols. The “on–off” process was achieved by adding Fe(III) into N-CNP solution, which resulted in the selective fluorescence quenching, with the detection limit of 0.20 μM in the linear range of 1–500 μM. Following this, the introduction of biothiols could recover the fluorescence efficiently, in order to realize the “off–on” process. By using glutathione (GSH) as the representative, the linear range was in the range of 1–1000 μM, and the limit of detection was 0.13 μM. Moreover, this useful strategy was successfully applied for the determination of amounts of GSH in fetal calf serum samples.

The current licensed adjuvant alum is found to be insufficient to induce cellular immune responses and a balanced Th1/Th2 ratio, which are desirable against cancers and microbial infections. Hence, it is encouraged to develop adjuvants which can simultaneously improve cell-mediated and humoral immune responses of the antigen and possess a favorable Th1/ Th2 balance. Herein, quaternized cationic carbon dots derived from biquaternary ammonium salt (BQAS-CDs) were newly prepared, and their adjuvanticity and biocompatibility were preliminarily explored in vivo. The developed BQAS-CDs are enriched in quaternary ammonium groups on the surface, which enable them to bind to and aggregate with the negatively charged ovalbumin (OVA). The resulting BQAS-CDs + OVA nanocomplexes dramatically enhance the uptake of antigen by the antigen-presenting cells (APCs). Compared to the conventional adjuvant alum, the BQAS-CDs + OVA nanocomplexes significantly increase the anti-OVA IgG2a and IgG2b levels and keep the level of the OVA-specific IgG1 antibody, inducing both robust Th1-and Th2-type immune responses. Furthermore, they stimulate the proliferation of OVA-specific CD4 + and CD8 + T cells. No significant alterations were observed in the hematological and histological parameters of BQAS-CDs + OVA-immunized recipients. These findings suggest the potential benefits of BQAS-CDs as an alternative adjuvant in the future.

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