Transformation of crystalline starch nanoparticles into highly luminescent carbon nanodots: Toxicity studies and their applications

Progress on the toxicity of quantum dots to model organism-zebrafish

In vivo toxicological studies are currently necessary to analyze the probable dangers of quantum dots (QDs) to the environment and human safety, due to the fast expansion of QDs in a range of applications. Because of its high fecundity, cost-effectiveness, well-defined developmental phases, and optical transparency, zebrafish has long been considered the "gold standard" for biosafety assessment of chemical substances and pollutants. In this review, the advantages of using zebrafish in QD toxicity assessment were explored. Then, the target organ toxicities such as developmental toxicity, immunotoxicity, cardiovascular toxicity, neurotoxicity, and hepatotoxicity were summarized. The hazardous effects of different QDs, including cadmium-containing QDs like CdTe, CdSe, and CdSe/ZnS, as well as cadmium-free QDs like graphene QDs (GQDs), graphene oxide QDs (GOQDs), and others, were emphasized and described in detail, as well as the underlying mechanisms of QDs generating these effects. Furthermore, general physicochemical parameters determining QD-induced toxicity in zebrafish were introduced, such as chemical composition and surface coating/modification. The limitations and special concerns of using zebrafish in QD toxicity studies were also mentioned. Finally, we predicted that the utilization of high-throughput screening assays and omics, such as transcriptome sequencing, proteomics, and metabolomics will be popular topic in nanotoxicology.

Preparation of solvent-free starch-based carbon dots for the selective detection of Ru3+ ions

A simple, green, and solvent-free pyrolysis method for the preparation of starch-based carbon dots (CDs) was developed. The CDs prepared at 300 °C exhibited a highest quantum yield of 21.0%, which was mainly due to the high degree of graphitisation of the CDs. The CDs were selective for the detection of Ru3+ ion solutions.

Turning waste into wealth: facile and green synthesis of carbon nanodots from pollutants and applications to bioimaging

In an effort to turn waste into wealth, Reactive Red 2 (RR2), a common and refractory organic pollutant in industrial wastewater, has been employed for the first time as a precursor to synthesize carbon nanodots (CNDs) by a facile, green and low-cost route, without utilization of any strong acids or other oxidizers. The detailed characterizations have confirmed that the synthesized CNDs exhibit good water dispersibility, with a mean particle size of 2.43 nm and thickness of 1-3 layers. Importantly, the excellent fluorescence properties and much reduced biotoxicity of the CNDs confer its potential applications in further biological imaging, which has been successfully verified in both in vitro (cell culture) and in vivo (zebrafish) model systems. Thus, it is demonstrated that the synthesized CNDs exhibit nice biocompatibility and fluorescence properties for bioimaging. This work not only provides a novel economical and environmentally friendly approach in recycling a chemical pollutant, but also greatly promotes the potential application of CNDs in biological imaging.

Mutated Shiitake extracts inhibit melanin-producing neural crest-derived cells in zebrafish embryo

The ability of natural extracts to inhibit melanocyte activity is of great interest to researchers. This study evaluates and explores the ability of mutated Shiitake (A37) and wildtype Shiitake (WE) extract to inhibit this activity. Several properties such as total phenolic (TPC) and total flavonoid content (TFC), antioxidant activity, effect on cell and component profiling were conducted. While having no significant differences in total phenolic content, mutation resulted in A37 having a TFC content (1.04 ± 0.7 mg/100 ml) compared to WE (0.86 ± 0.9 mg/100 ml). Despite that, A37 extract has lower antioxidant activity (EC50, A37 = 549.6 ± 2.70 μg/ml) than WE (EC50 = 52.8 ± 1.19 μg/ml). Toxicity tests on zebrafish embryos show that both extracts, stop the embryogenesis process when the concentration used exceeds 900 μg/ml. Although both extracts showed pigmentation reduction in zebrafish embryos, A37 extract showed no effect on embryo heartbeat. Cell cycle studies revealed that WE significantly affect the cell cycle while A37 not. Further tests found that these extracts inhibit the phosphorylation of Glycogen synthase kinase 3 β (pGSK3β) in HS27 cell line, which may explain the activation of apoptosis in melanin-producing cells. It was found that from 19 known compounds, 14 compounds were present in both WE and A37 extracts. Interestingly, the presence of decitabine in A37 extract makes it very potential for use in the medical application such as treatment of melanoma, skin therapy and even cancer.

Sago starch nanocrystal-stabilized Pickering emulsions: Stability and rheological behavior

This study presents the isolation of SNC from sago starch and its performance as proficient particle emulsifier. It highlights the impact of SNC on the stability and rheological properties of oil-in-water (o/w) emulsions. The percentage yield of the SNC obtained was equivalent to 25 ± 0.1% (w/w) with particle diameters ranging from 25 to 100 nm. A series of Pickering emulsion at different ratios of oil (5%-35% v/v) and SNC (1%-4% w/v) was prepared for further investigations. The mean droplet diameter of emulsions obtained was ranged from 19.12 to 35.96 μm, confirming the effects of both SNC and oil content on the droplet's diameter distribution. Formulations with 4.0 wt% of SNC exhibited the maximum stability against coalescence. Results obtained have justified that the SNC can be used as an alternative solid emulsifier in producing stable emulsion with desired properties for various applications.

Comprehensive spectroscopic studies of synergism between Gadong starch based carbon dots and bovine serum albumin

Carbon dots (C-dots) were used to study the binding mechanisms with serum protein, bovine serum albumin (BSA) by using two notable binding systems known as non-covalent and covalent interaction. Interaction between C-dots and BSA were estimated by Stern-Volmer equation and Double Log Regression Model (DLRM). According to the fluorescent intensity, quenching of model carrier protein by C-dots was due to dynamic quenching for non-covalent and static quenching for covalent binding. The binding site constant, K_A and number of binding site, for covalent interaction is 1754.7L/mol and n≈1 (0.6922) were determined by DLRM on fluorescence quenching results. The blue shift of the fluorescence spectrum, from 450nm to 421nm (non-covalent) and 430nm (covalent) and suggested that both the microenvironment of C-dots and protein changed in relation to the protein concentration. The fluorescence intensity results show that protein structure has a significant role in Protein-C-dots interactions and type of binding influence physicochemical properties of C-dots differently. Understanding to this bio interface is important to utilize both quantum dots and biomolecules for biomedical field. It can be a useful guideline to design further applications in biomedical and bioimaging.

Transcriptomic response and perturbation of toxicity pathways in zebrafish larvae after exposure to graphene quantum dots (GQDs)

Graphene quantum dots (GQDs) are widely used for biomedical applications. Previously, the low-level toxicity of GQDs in vivo and in vitro has been elucidated, but the underlying molecular mechanisms remained largely unknown. Here, we employed the Illumina high-throughput RNA-sequencing to explore the whole-transcriptome profiling of zebrafish larvae after exposure to GQDs. Comparative transcriptome analysis identified 2116 differentially expressed genes between GQDs exposed groups and control. Functional classification demonstrated that a large proportion of genes involved in acute inflammatory responses and detoxifying process were significantly up-regulated by GQDs. The inferred gene regulatory network suggested that activator protein 1 (AP-1) was the early-response transcription factor in the linkage of a cascade of downstream (pro-) inflammatory signals with the apoptosis signals. Moreover, hierarchical signaling threshold determined the high sensitivity of complement system in zebrafish when exposed to the sublethal dose of GQDs. Further, 35 candidate genes from various signaling pathways were further validated by qPCR after exposure to 25, 50, and 100 μg/mL of GQDs. Taken together, our study provided a valuable insight into the molecular mechanisms of potential bleeding risks and detoxifying processes in response to GQDs exposure, thereby establishing a mechanistic basis for the biosafety evaluation of GQDs.