Nitrogen-doped graphene quantum dots (N-GQDs) perturb redox-sensitive system via the selective inhibition of antioxidant enzyme activities in zebrafish

Graphene oxide quantum dots (GOQDs) induce behavioral disorders via the disturbance of kynurenine pathway in zebrafish larvae

The emergence of graphene quantum dots (GQDs) expands the use of graphene derivatives in nanomedicine for its direct therapeutic applications in treating neurodegeneration, inflammation, metabolic dysfunction, and among others. Nevertheless, the biosafety assessment of GQDs remains deficient mostly because of the diverse surface characteristics of the nanoparticles. Our prior work demonstrated that GQDs can induce strong thigmotactic effects in zebrafish larvae over a wide range of concentrations, yet the underlying metabolic mechanisms remain largely unknown. In this study, we conducted a further exploration about graphene oxide quantum dots (GOQDs) for its potential neurotoxic effect on the behaviors of zebrafish larvae by combining neurotransmitter-targeted metabolomics with locomotion analysis. After continuous exposure to a concentration gradient of GOQDs (12.5 - 25 - 50 - 100 - 200 μg/mL) for 7 days, the thigmotactic activities of zebrafish larvae were observed across all exposure concentrations relative to the control group, while the basal locomotor activities, including distance moved and average velocity, were significantly changed by low concentrations of GOQDs. Targeted metabolomics was performed using zebrafish larvae at 7 days post-fertilization (dpf) that were exposed to 12.5 and 200 μg/mL, both of which were found to perturb the kynurenine pathway by regulating the levels of kynurenine, 3-hydroxyanthranilic acid (3-HAA), and quinolinic acid (QA). Furthermore, the thigmotaxis of larval fish induced by GOQDs during exposure could be counteracted by supplementing Ro-61-8048, an agonist acting on kynurenine 3-monooxygenase (KMO). In conclusion, our study establishes the involvement of the kynurenine pathway in GOQDs-induced thigmotaxis, which is independent of the transcriptional modulation of glutamate receptor families.

Oxidative stress-induced neurotoxicity of quantum dots and influencing factors

Quantum dots (QDs) have significant potential for treating and diagnosing CNS diseases. Meanwhile, the neurotoxicity of QDs has garnered attention. In this review, we focus on elucidating the mechanisms and consequences of CNS oxidative stress induced by QDs. First, we discussed the pathway of QDs transit into the brain. We then elucidate the relationship between QDs and oxidative stress from in vivo and in vitro studies. Furthermore, the main reasons and adverse outcomes of QDs leading to oxidative stress are discussed. In addition, the primary factors that may affect the neurotoxicity of QDs are analyzed. Finally, we propose potential strategies for mitigating QDs neurotoxicity and outline future perspectives for their development.

Polyphenolic Carbon Quantum Dots with Intrinsic Reactive Oxygen Species Amplification for Two-Photon Bioimaging and In Vivo Tumor Therapy

Recent studies indicate that mitochondrial dysfunctions and DNA damage have a critical influence on cell survival, which is considered one of the therapeutic targets for cancer therapy. In this study, we demonstrated a comparative study of the effect of polyphenolic carbon quantum dots (CQDs) on in vitro and in vivo antitumor efficacy. Dual emissive (green and yellow) shape specific polyphenolic CQDs (G-CQDs and Y-CQDs) were synthesized from easily available nontoxic precursors (phloroglucinol), and the antitumor property of the as-synthesized probe was investigated as compared to round-shaped blue emissive CQDs (B-CQDs) derived from well-reported precursor citric acid and urea. The B-CQDs had a nuclei-targeting property, and G-CQDs and Y-CQDs had mitochondria-targeting properties. We have found that the polyphenol containing CQDs (at a dose of 100 μg mL-1) specifically attack mitochondria by excess accumulation, altering the metabolism, inhibiting branching pattern, imbalanced Bax/Bcl-2 homeostasis, and ultimately generating oxidative stress levels, leading to oxidative stress-induced cell death in cancer cells in vitro. We show that G-CQDs are the main cause of oxidative stress in cancer cells because of their ability to produce sufficient •OH- and 1O2 radicals, evidenced by electron paramagnetic resonance spectroscopy and a terephthalic acid test. Moreover, the near-infrared absorption properties of the CQDs were exhibited in two-photon (TP) emission, which was utilized for TP cellular imaging of cancer cells without photobleaching. The in vivo antitumor test further discloses that intratumoral injection of G-CQDs can significantly augment the treatment efficacy of subcutaneous tumors without any adverse effects on BalB/c nude mice. We believe that shape-specific polyphenolic CQD-based nanotheranostic agents have a potential role in tumor therapy, thus proving an insight on treatment of malignant cancers.

The Potentiating Effect of Graphene Oxide on the Arylhydrocarbon Receptor (AhR)-Cytochrome P4501A (Cyp1A) System Activated by Benzo(k)fluoranthene (BkF) in Rainbow Trout Cell Line

The increasing use of graphene oxide (GO) will result in its release into the environment; therefore, it is essential to determine its final fate and possible metabolism by organisms. The objective of this study was to assess the possible role of the aryl hydrocarbon receptor (AhR)-dependent cytochrome P4501A (Cyp1A) detoxification activities on the catabolism of GO. Our hypothesis is that GO cannot initially interact with the AhR, but that after an initial degradation caused by other mechanisms, small fractions of GO could activate the AhR, inducing Cyp1A. The environmental pollutant benzo(k)fluoranthene (BkF) was used for the initial activation of the AhR in the rainbow trout (Oncorhynchus mykiss) cell line RTL-W1. Pre-, co-, and post-exposure experiments with GO were performed and Cyp1A induction was monitored. The strong stimulation of Cyp1A observed in cells after exposure to GO, when BkF levels were not detected in the system, suggests a direct action of GO. The role of the AhR was confirmed by a blockage of the observed effects in co-treatment experiments with αNF (an AhR antagonist). These results suggest a possible role for the AhR and Cyp1A system in the cellular metabolism of GO and that GO could modulate the toxicity of environmental pollutants.

Ecotoxicological evaluation of functional carbon nanodots using zebrafish (Danio rerio) model at different developmental stages

Considering functional carbon nanodots (FCNs) are potential to be applied in many areas, their risk and toxicity to organisms are imperative to be evaluated. Thus, this study conducted acute toxicity test of zebrafish (Danio rerio) at embryonic and adult stage to estimate the toxicity of FCNs. Results show that the toxic effects of FCNs and nitrogen doped FCNs (N-FCNs) at their 10% lethal concentration (LC₁₀) values on zebrafish are expressed in developmental retardation, cardiovascular toxicity, renal damage and hepatotoxicity. There are interactive relationships between these effects, but the main reason should be ascribed to the undesirable oxidative damage induced by high doses of materials, as well as the biodistribution of FCNs and N-FCNs in vivo. Even so, FCNs and N-FCNs can promote the antioxidant activity in zebrafish tissues to cope with the oxidative stress. FCNs and N-FCNs are not easy to cross the physical barriers in zebrafish embryos or larvae, and can be excreted from intestine by adult fish, which proves their biosecurity to zebrafish. In addition, because of the differences in physicochemical properties, especially nano-size and surface chemical property, FCNs show higher biosecurity to zebrafish than N-FCNs. The effects of FCNs and N-FCNs on hatching rates, mortality rates and developmental malformations are dose-dependent and time-dependent. The LC₅₀ values of FCNs and N-FCNs on zebrafish embryo at 96 hpf are 1610 mg/L and 649 mg/L, respectively. According to the Acute Toxicity Rating Scale of the Fish and Wildlife Service, the toxicity grades of FCNs and N-FCNs are both defined as "practically nontoxic", and FCNs are "Relatively Harmless" to embryos because their LC₅₀ values are above 1000 mg/L. Our results prove the biosecurity of FCNs-based materials for future practical application.

Ecotoxicological and biochemical effects of di(2-ethylhexyl)phthalate on wheat (Jimai 22, Triticum aestivum L.)

Di(2-ethylhexyl)phthalate esters (DEHP) has attracted widespread attention due to its ecotoxicological effects on organisms. In this study, wheat seedlings were exposed to DEHP- contaminated soil with 4 concentration gradients (0, 1, 10, and 100 mg kg^-1, respectively) for 30 days. The growth index, physiological index, oxidative damage system, and gene expression of wheat seedlings were comprehensively measured and analyzed. The results revealed that DEHP could reduce the germination rate of wheat. Only the 100 mg kg^-1 treatment group significantly inhibited root length, but no effect on plant height. At the biochemical level, photosynthetic pigments of wheat seedlings were promoted first and then inhibited, while the soluble sugar content presented a trend of "inhibition - activation - inhibition". The antioxidant enzymes (SOD and POD) presented an approximate parabolic trend, while it was opposite for CAT. Whereas the corresponding antioxidant enzyme genes were up-regulated, and the Hsp70 heat-shock protein gene was down-regulated. Finally, integrated biological response index (IBR) analysis showed that the DEHP toxicity to wheat seedlings was dose dependent. Molecular docking indicated that DEHP could stably bind to GBSS and GST by intermolecular force. Overall, this study provided constructive insights for a comprehensive assessment of the toxicity risk of DEHP to wheat.

Graphene quantum dots (GQDs) induce thigmotactic effect in zebrafish larvae via modulating key genes and metabolites related to synaptic plasticity

Graphene quantum dots (GQDs) recently gain much attention for its medicinal values in treating diseases such as neurodegeneration and inflammations. However, owing to the high permeability of GQDs across the blood-brain barrier, whether its retention in the central nervous system (CNS) perturbs neurobehaviors remains less reported. In the study, the locomotion of zebrafish larvae (Danio rerio) was fully evaluated when administrated by two GQDs in a concentration gradient, respectively as reduced-GQDs (R-GQDs): 150, 300, 600, 1200, and 2400 g/L, and graphene oxide QDs (GOQDs): 60, 120, 240, 480, and 960 g/L. After exposure, the larvae were kept for locomotion analysis within one week's depuration. Substantial data showed that the basal locomotor activity of zebrafish larvae was not significantly changed by both two GQDs at low concentrations while weakened greatly with the increase of concentrations, and the total ATP levels of zebrafish larvae were also found to decrease significantly when exposed to the highest concentrations of GQDs. Next, the thigmotactic effect was observed to be remarkably induced in larvae by both two GQDs at any concentrations during exposure, and remained strong in larvae treated by high concentrations of R-GQDs after 7 days' depuration. To be noted, we found that GQDs affected the synaptic plasticity via downregulating the mRNA levels of NMDA and AMPA receptor family members as well as the total glutamine levels in zebrafish larvae. Together, our study presented robust data underlying the locomotor abnormalities aroused by GQDs in zebrafish larvae and indicated the potential adverse effects of GQDs on synaptic plasticity.

Pulmonary hazard identifications of Graphene family nanomaterials: Adverse outcome pathways framework based on toxicity mechanisms

Graphene-family nanomaterials (GFNs) are revolutionary new nanomaterials that have attracted significant attention in the field of nanomaterials, but the ensuing problems lie in the potential threats to public health and the ecosystem caused by these nanomaterials. From the perspective of GFN-related health risk assessments, this study reviews the current status of GFN-induced pathological lung events with a focus on the damage caused to different biological moieties (molecular, cellular, tissue, and organ) and the mechanistic relationships between different toxic endpoints. These multiple sites of damage were matched with existing adverse outcome pathways (AOPs) in an online knowledge base to obtain available molecular initiation events (MIEs), key events (KEs), and adverse outcomes (AOs). Among them, the MIEs were discussed in combination with the structure-activity relationship due to the correlation between toxicity and physical and chemical properties of GFNs. Based on the collection of information regarding MIEs, Kes, and AOs in addition to upstream and downstream causal extrapolation, the AOP framework for GFN-induced pulmonary toxicity was developed, highlighting the possible mechanisms of GFN-induced lung damage. This review intended to combine AOP with classic toxicological methods with a view to rapidly and accurately establishing a nanotoxicology infrastructure so as to contribute to public health risk assessment strategies through iteration from and animal models up to the population level.

Applicability of OECD TG 201, 202, 203 for the aquatic toxicity testing and assessment of 2D Graphene material nanoforms to meet regulatory needs

Tests using algae and/or cyanobacteria, invertebrates (crustaceans) and fish form the basic elements of an ecotoxicological assessment in a number of regulations, in particular for classification of a substance as hazardous or not to the aquatic environment according to the Globally Harmonised System of Classification and Labelling of Chemicals (GHS-CLP) (GHS, 2022) and the REACH regulation (Registration, Evaluation, Authorisation and Restriction of Chemicals, EC, 2006). Standardised test guidelines (TGs) of the Organisation for Economic Co-operation and Development (OECD) are available to address the regulatory relevant endpoints of growth inhibition in algae and cyanobacteria (TG 201), acute toxicity to invertebrates (TG 202), and acute toxicity in fish (TG 203). Applying these existing OECD TGs for testing two dimensional (2D) graphene nanoforms may require more attention, additional considerations and/or adaptations of the protocols, because graphene materials are often problematic to test due to their unique attributes. In this review a critical analysis of all existing studies and approaches to testing used has been performed in order to comment on the current state of the science on testing and the overall ecotoxicity of 2D graphene materials. Focusing on the specific tests and available guidance's, a complete evaluation of aquatic toxicity testing for hazard classification of 2D graphene materials, as well as the use of alternative tests in an integrated approach to testing and assessment, has been made. This information is essential to ensure future assessments generate meaningful data that will fulfil regulatory requirements for the safe use of this "wonder" material.

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.

Abnormal neural differentiation in response to graphene quantum dots through histone modification interference

Graphene quantum dots (GQDs) have been broadly applied in biomedicine in recent years, and their environmental exposure and toxicological impacts have raised increasing concerns. The nanosafety assessment on the nervous system is one of the most important aspects, and potential effects of GQDs on neurodevelopment and the underlying mechanism are still elusive. In this study, the neural developmental toxicities of OH-GQDs and NH₂-GQDs were investigated using the mouse embryonic stem cells (mESCs). The results revealed that OH-GQDs significantly inhibited the ectoderm development, and reduced the neural precursor formation and neurogenesis during the neural differentiation of the mESCs. The exploration on the mechanism uncovered that the increased enrichment of H3K27me3 at the promoter region of the Smad6 gene was involved in histone modification-activated BMP signal pathway, which consequently influenced its regulatory effects on neural differentiation. Additionally, OH-GQDs elicited a stronger effect on inducing the imbalance of histone modification, and resulted in higher latency of neural differentiation disturbance than did NH₂-GQDs, suggesting surface functionalization-specific effects of GQDs on neurodevelopmental toxicity. This study would provide new insights in not only the adverse effects of GQDs on neurodevelopment, but also the influence from the chemical modification of GQDs on their bioactivities.

Effects of dietary lysolecithin on growth performance, serum biochemical indexes, antioxidant capacity, lipid metabolism and inflammation-related genes expression of juvenile large yellow croaker (Larimichthys crocea)

A 70-day feeding trial was conducted to investigate effects of dietary lysolecithin on growth performance, serum biochemical indexes, antioxidant capacity, lipid metabolism and inflammation-related genes expression of juvenile large yellow croaker (Larimichthys crocea) with initial weight of 6.04 ± 0.08 g. A formulated diet containing approximately 42% crude protein and 12.5% crude lipid was used as the control diet (CON). The other three experimental diets were formulated with supplementation of 0.2%, 0.4% and 0.6% lysolecithin based on the control diet, respectively. Results showed that weight gain rate (WGR) and specific growth rate (SGR) significantly increased in fish fed diets with lysolecithin compared with those in the control diet (P < 0.05). Fish fed diets with 0.4% and 0.6% lysolecithin had notably higher lipid content in muscle than that in the control diet (P < 0.05). When fish were fed diets with lysolecithin, serum high-density lipoprotein cholesterol (HDL-c) content was notably higher than that in the control diet (P < 0.05), while fish fed the diet with 0.6% lysolecithin had a significant lower serum low-density lipoprotein cholesterol (LDL-c) content than that in the control diet (P < 0.05). Meanwhile, serum aspartate transaminase (AST) and alanine transaminase (ALT) activities in fish fed diets with lysolecithin were remarkably lower than those in the control diet (P < 0.05). With the increase of dietary lysolecithin from 0.2% to 0.6%, mRNA expression of stearoyl-coenzyme A desaturase 1 (scd1), diacylglycerol acyltransferase 2 (dgat2) and sterol-regulatory element binding protein 1 (srebp1) showed decreasing trends. Furthermore, mRNA expression of carnitine palmitoyl transferase 1 (cpt1) and lipoprotein lipase (lpl) among each dietary lysolecithin treatment were significantly higher than those in the control diet (P < 0.05). In terms of inflammation, mRNA expression of tumor necrosis factor α (tnf-α) and interleukin-1 β (il-1β) were significantly down-regulated in fish fed diets with lysolecithin compared with those in the control diet (P < 0.05), while the mRNA expression of interleukin-10 (il-10) was significantly higher than that in the control diet (P < 0.05). In conclusion, dietary lysolecithin could promote the growth performance, improve hepatic lipid metabolism and regulate inflammation response in juvenile large yellow croaker, and the optimal supplement level of lysolecithin was approximately 0.4% in this study.

A new antioxidant made from a pterostilbene functionalized graphene nanocomposite as an efficient treatment for dry eye disease

Dry eye disease is a common condition that affects the eyes. It is caused by problems with the tear film and the tear dynamics. Dry eye can be caused by an increase in the amount of reactive oxygen species (ROS) in the corneal epithelium. The treatment for dry eye typically focuses on relieving the uncomfortable symptoms by using eye drops such as artificial tears, antibiotics, and by using anti-inflammatory/immunosuppressive agents such as cyclosporine, and lifitegrast. However, the recovery of patients with dry eye can take several years particularly if the symptoms are severe. This is because the present treatment approaches for dry eye are not based on its cause, e.g., the oxidative stress arising from the rapid increase in ROS. This work describes a new type of antioxidant made from pterostilbene (PS) and carboxyl-chitosan modified graphene (CG). The use of a hydrophilic two-dimensional CG nanosheet to improve the properties of PS is reported. Superior enhanced properties including better cellular permeability, long sustained release period (over 30 h), and antioxidant properties, were realized by using PS-CG. A hyperosmotic (HS) damaged human corneal epithelial cell (HCEC) model was used for antioxidant tests. This model has an intracellular ROS level 4 times more than that of a control group. The ROS content was declined efficiently to the same amount as normal cells in the PS-CG treated HS group. There was a significant decline in the content of lactate dehydrogenase (LDH) and the apoptosis rate of HCEC in the PS-CG treated HS group when compared to that seen in the HS model. Real-time polymerase chain reaction (PCR) and western blots (WB) were used to understand the antioxidant mechanism of PS-CG. The results showed that the antioxidant was working by activating the Keap1-Nrf2-ARE signalling pathway. In vivo testing testing using a dry eye mouse model suggested that the PS-CG acted as an efficient antioxidant. More tear production and healthier corneal and conjunctival epithelial cells were achieved when PC-CG was applied to this model. The use of PS-CG could be a new strategy for treating dry eye and other ocular diseases caused by ROS.

A rapid fluorescent aptasensor for point-of-care detection of C-reactive protein

In this paper, we report on a novel fluorescent aptasensor based on aptamers modified by both nitrogen-doped graphene quantum dots (N-GQDs) and gold nanoparticles (AuNPs) for the detection of C-reactive protein (CRP). FRET effect is utilized in our aptasensor by the change of aptamers conformation when binding with the target. An obvious fluorescence quench of the N-GQDs can be observed when CRP appears in the assay due to electron transfer between the donor and accepter. A detection limit of 0.2 ng/mL can be achieved by our sensor in PBS buffer which is much lower than the physiological CRP level in human serum. Also, CRP levels in different patients' serum are tested with our assay. Since our aptasensor is rapid (detection time less than 40 min), one-step and very simple to operate, we believe it has great potential to apply for point-of-care testing (POCT).

Chitosan Schiff bases-based polyelectrolyte complexes with graphene quantum dots and their prospective biomedical applications

Chitosan (Cs) bis-aldehyde Schiff base derivatives were synthesized by condensation of Cs with three bis-aldehydes namely; butane-1,4-diyl bis(4-formylbenzoate), N,N'-(butane-1,4-diyl)bis(2-(4-formylphenoxy)acetamide) and 4,4'-(butane-1,4-diylbis(oxy))dibenzaldehyde. The prepared Cs derivatives were blended with carboxymethyl chitosan(CMC) and graphene quantum dots (GQDs) to produce semi-IPNs polyelectrolyte complexes (PECs). and characterized with respect to their molecular structure and physio-chemical properties. The antibacterial activity against H. pylori (and in vitro Inosine 5'-monophosphate dehydrogenase IMPDH inhibitory assay) was evaluated. Additionally, a preliminary in vitro assessment for wound healing was performed against PECs in which wound closure percentages, and rates were investigated indicating an accelerated wound healing compared with untreated cells. The PEC based on Schiff base PEC containing amide linkage showed the highest wound healing ability. A minimal inhibitory concentration (MIC) was obtained for the PEC sample containing Cs Schiff base derived from 4,4'-(butane-1, 4-diylbis(oxy))dibenzaldehyde at a dose of 0.98 μg/ml inhibiting H. pylori growth by 100%. Additionally, the selected above-mentioned compound was selected to test its inhibitory activity against the HpIMPDH enzyme in addition to its selectivity towards the hIMPDH2 enzyme and was found to have promising activity against the HpIMPDH enzyme with IC₅₀ value of 0.65 μM, and to be safer and less active against the hIMPDH2 enzyme with IC₅₀ > 10 μM, reflecting its selectivity.

Multi-walled carbon nanotubes inhibit potential detoxification of dioxin-mediated toxicity by blocking the nuclear translocation of aryl hydrocarbon receptor

Despite numerous studies on effects of environmental accumulation of nano-pollutants, the influence of nanoparticles on the biological perturbations of coexisting pollutants in the environment remained unknown. The present study aimed at elucidating the perturbations of six environmental nanoparticles on detoxification of dioxin-induced toxicity at cellular level. We discovered that there was no remarkable difference in the cell uptake and intracellular distributions of these six nanoparticles. However, they have different effects on the detoxification of 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD). Multi-walled carbon nanotubes (MWCNTs) inhibited the translocation of aryl hydrocarbon receptor (AhR) from cytosol to the nucleus, leading to the downregulation of cytochrome P450 family 1 subfamily A member 1 (CYP1A1) and inhibition of detoxification function. These findings demonstrate that MWCNTs can impact the potential detoxification of dioxin-induced toxicity through modulating AhR signaling pathway. Co-exposures to MWCNTs and dioxin may cause even more toxicity than single exposure to dioxin or MWCNTs alone.

Nanomaterials-based photosensitizers and delivery systems for photodynamic cancer therapy

The increasing cancer morbidity and mortality requires the development of high-efficiency and low-toxicity anticancer approaches. In recent years, photodynamic therapy (PDT) has attracted much attention in cancer therapy due to its non-invasive features and low side effects. Photosensitizer (PS) is one of the key factors of PDT, and its successful delivery largely determines the outcome of PDT. Although a few PS molecules have been approved for clinical use, PDT is still limited by the low stability and poor tumor targeting capacity of PSs. Various nanomaterial systems have shown great potentials in improving PDT, such as metal nanoparticles, graphene-based nanomaterials, liposomes, ROS-sensitive nanocarriers and supramolecular nanomaterials. The small molecular PSs can be loaded in functional nanomaterials to enhance the PS stability and tumor targeted delivery, and some functionalized nanomaterials themselves can be directly used as PSs. Herein, we aim to provide a comprehensive understanding of PDT, and summarize the recent progress of nanomaterials-based PSs and delivery systems in anticancer PDT. In addition, the concerns of nanomaterials-based PDT including low tumor targeting capacity, limited light penetration, hypoxia and nonspecific protein corona formation are discussed. The possible solutions to these concerns are also discussed.

Respiratory exposure to graphene quantum dots causes fibrotic effects on lung, liver and kidney of mice

Graphene quantum dots (GQDs), as a novel graphene-based nanoparticle, presented a bright prospect in fields of biomedicine due to their excellent optical property. However, the biosafety assessment of GQDs is far behind their rapid development, which could restrict their wilder applications. This study focused on the potential adverse effects of two kinds of promising GQDs, i.e. nitrogen-doping graphene quantum dots (N-GQDs) and amino-modified graphene quantum dot (A-GQDs) on primary target organs of GNMs, including lung, liver and kidney. The intranasal instillation used here was to imitate the respiratory exposure of GQDs that is a commonly exposure route of GQDs in the environment. Although no severe damages associated with general health occurred in mice treated with GQDs, the fibrosis evidenced by statistically significant increases in the area of collagen I and TGF-ß1 and p-Smad3 expressions were observed in the lung, liver and kidney tissues. Interestingly, the fibrotic effect induced by GQDs could be effectively alleviated by a ferroptosis-specific inhibitor, which demonstrated a close relationship of fibrosis and ferroptosis. This study not only provides new insights on the toxicity mechanisms of GQDs, but also offers some efficient ways to control toxicity of GQDs, like dosage threshold and small molecular drugs.

Nitrogen-doped graphene quantum dots induce ferroptosis through disrupting calcium homeostasis in microglia

Background

Along with the wild applications of nitrogen-doped graphene quantum dots (N-GQDs) in the fields of biomedicine and neuroscience, their increasing exposure to the public and potential biosafety problem has gained more and more attention. Unfortunately, the understanding of adverse effects of N-GQDs in the central nervous system (CNS), considered as an important target of nanomaterials, is still limited.

Results

After we found that N-GQDs caused cell death, neuroinflammation and microglial activation in the hippocampus of mice through the ferroptosis pathway, microglia was used to assess the molecular mechanisms of N-GQDs inducing ferroptosis because it could be the primary target damaged by N-GQDs in the CNS. The microarray data suggested the participation of calcium signaling pathway in the ferroptosis induced by N-GQDs. In microglial BV2 cells, when the calcium content above the homeostatic level caused by N-GQDs was reversed, the number of cell death, ferroptosis alternations and excessive inflammatory cytokines release were all alleviated. Two calcium channels of L-type voltage-gated calcium channels (L-VGCCs) in plasma membrane and ryanodine receptor (RyR) in endoplasmic reticulum (ER) took part in N-GQDs inducing cytosolic calcium overload. L-VGCCs and RyR calcium channels were also involved in promoting the excess iron influx and triggering ER stress response, respectively, which both exert excessive ROS generation and result in the ferroptosis and inflammation in BV2 cells.

Conclusion

N-GQDs exposure caused ferroptosis and inflammatory responses in hippocampus of mice and cultured microglia through activating two calcium channels to disrupt intracellular calcium homeostasis. The findings not only posted an alert for biomedical applications of N-GQDs, but also highlighted an insight into mechanism researches of GQDs inducing multiple types of cell death in brain tumor therapy in the future.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-022-00464-z.

Development of Graphene-Based Materials in Bone Tissue Engineaering

Bone regeneration-related graphene-based materials (bGBMs) are increasingly attracting attention in tissue engineering due to their special physical and chemical properties. The purpose of this review is to quantitatively analyze mass academic literature in the field of bGBMs through scientometrics software CiteSpace, to demonstrate the rules and trends of bGBMs, thus to analyze and summarize the mechanisms behind the rules, and to provide clues for future research. First, the research status, hotspots, and frontiers of bGBMs are analyzed in an intuitively and vividly visualized way. Next, the extracted important subjects such as fabrication techniques, cytotoxicity, biodegradability, and osteoinductivity of bGBMs are presented, and the different mechanisms, in turn, are also discussed. Finally, photothermal therapy, which is considered an emerging area of application of bGBMs, is also presented. Based on this approach, this work finds that different studies report differing opinions on the biological properties of bGBMS due to the lack of consistency of GBMs preparation. Therefore, it is necessary to establish more standards in fabrication, characterization, and testing for bGBMs to further promote scientific progress and clinical translation.

Graphene oxide toxicity in W1118 flies

The risk of graphene oxide (GO) exposure to various species has been greatly amplified in recent years due to its booming production and applications in various fields. However, a deep understanding of the GO biosafety lags its wide applications. Herein, we used W¹¹¹⁸ flies as a model organism to study GO toxicity at relatively low concentrations. We found that GO exposure led to remarkable weight loss, delayed development, retarded motion, and shortened lifespan of these flies. On the other hand, the GO influence on their sex ratio and the total number of pupae and adults were insignificant. The toxicological effect of GO was shown to be related to its serious compromise of the nutrient absorption in flies due to the severe damages in midguts. These damages were then attributed to the excessive accumulation of reactive oxygen species (ROS), which triggers the oxidative stress. These findings reveal the underlying mechanisms of GO biotoxicities in fruit flies, which might provide a useful reference to assess the risks of these newly invented nanomaterials likely never encountered by various species before.

Exploring graphene-based materials' genotoxicity: inputs of a screening method

Graphene-based materials (GBMs) are promising nanomaterials, and several innovations depend on their use. However, the assessment of their potential hazard must be carefully explored before entering any market. GBMs are indeed well-known to induce various biological impacts, including oxidative stress, which can potentially lead to DNA damage. Genotoxicity is a major endpoint for hazard assessment and has been explored for GBMs, but the available literature shows conflicting results. In this study, we assessed the genotoxicity of 13 various GBMs, one carbon black and one amorphous silica through a DNA damage response assay (using a human respiratory cell model, BEAS-2B). Concurrently, oxidative stress was assessed through a ROS production quantification (DCFH-DA assay using a murine macrophage model, RAW 264.7). We also performed a full physicochemical characterization of our samples to explore potential structure-activity relationships involving genotoxicity. We observed that surface oxidation appears linked to genotoxicity response and were able to distinguish several groups within our studied GBMs showing different genotoxicity results. Our findings highlight the necessity to individually consider each nanoform of GBMs since the tested samples showed various results and modes of action. We propose this study as a genotoxicity assessment using a high-throughput screening method and suggest few hypotheses concerning the genotoxicity mode of action of GBMs.

In situ immobilization of silver nanocrystals in carbon nanoparticles for intracellular fluorescence imaging and hydroxyl radicals detection

Silver nanoparticles (Ag NPs) have attracted extensive research interest in bioimaging and biosensing due to their unique surface plasmon resonance. However, the potential aggregation and security anxiety of Ag NPs hinder their further application in biomedical field due to their high surface energy and the possible ionization. Here, binary heterogeneous nanocomplexes constructed from silver nanoparticles and carbon nanomaterials (termed as C-Ag NPs) were reported. The C-Ag NPs with multiple yolk structure were synthesized via a one-step solvothermal route using toluene as carbon precursor and dispersant. The hydrophilic functional groups on the carbon layer endowed the C-Ag NPs excellent chemical stability and water-dispersity. Results showed that C-Ag NPs demonstrated excellent safety profile and excellent biocompatibility, which could be used as an intracellular imaging agent. Moreover, the C-Ag NPs responded specifically to hydroxyl radicals and were expected to serve as a flexible sensor to efficiently detect diseases related to the expression of hydroxyl radicals in the future.

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.

Evaluation of 3,4,4,9-trichlorocarbanilide to zebrafish developmental toxicity based on transcriptomics analysis

Triclocarban (TCC), considered an endocrine-disrupting, persistent, and bioaccumulating organic matter, has attracted a great deal of attention for its pollution and health risks. However, studies on its toxicological mechanism, especially for embryo development are limited. This article explores the cardiac developmental toxicity induced in zebrafish embryos after exposure to different TCC concentrations. First, liquid chromatography-tandem mass spectrometry was used in detecting TCC in embryos in vivo after exposure to various TCC. Results showed that embryonic TCC content reached 9.23 ng after exposure to 300 μg/L TCC, the heart rates of the embryos markedly decreased, heart abnormalities significantly increased. In addition, obvious pericardial effusion was observed in the larvae. Through transcriptome sequencing, 200 differential gene expression (DGE) patterns were detected in the TCC (300 μg/L) experimental and control groups. The results of GO function analysis and KEGG pathway of DGE showed that aryl hydrocarbon receptor (AhR) activation and cyp-related genes (cyp1a, cyp1b1 and cyp1c) were significantly up-regulated. these affected the normal development of zebrafish embryonic heart, tissue edema, and hemorrhage. TCC exhibited strong cardiac teratogenic effects and developmental toxicity, which is partly related to AhR activation. Transcriptome-based results are helpful in precisely determining the risk of TCC exposure. The potential mechanism between TCC and AhR should be further investigated.

A review on the cytotoxicity of graphene quantum dots: from experiment to simulation

Graphene quantum dots (GQDs) generate intrinsic fluorescence and improve the aqueous stability of graphene oxide (GO) while maintaining wide chemical adaptability and high adsorption capacity. Despite GO's remarkable advantages in bio-imaging, bio-sensing, and other biomedical applications, many experiments and simulations have focused on the biosafety of GQDs. Here, we review the findings on the biosafety of GQDs from experiments; then, we review the results from simulated interactions with biological membranes, DNA molecules, and proteins; finally, we examine the intersection between experiments and simulations. The biosafety results from simulations are explained in detail. Based on the literature and our experiments, we also discuss the trends toward GQDs with better biosafety.

Identification of potential circRNA-miRNA-mRNA regulatory networks in response to graphene quantum dots in microglia by microarray analysis

Along with the increasing application of graphene quantum dots (GQDs) in the fields of biomedicine and neuroscience, it is important to assess the probably adverse effects of GQDs in the central nervous system (CNS) but their underlying toxic mechanisms is still unclear. In this study, we evaluate the molecular mechanisms associated with circular RNAs (circRNAs) of nitrogen-doped GQDs (N-GQDs) and amino-functionalized GQDs (A-GQDs) damaging the cell viability and cellular structure in microglia by an integrative analysis of RNA microarray. The differentially expressed circRNA (DEcircRNAs)-miRNA- differentially expressed mRNA (DEmRNAs) regulatory networks were conducted in BV2 microglial cells treated with 25 µg/mL N-GQDs, 100 µg/mL N-GQDs and 100 µg/mL A-GQDs. Based on that, the protein-coding genes in each ceRNA network were collected to do bio-functional analysis to evaluate signaling pathways that were indirectly mediated by circRNAs. Some pathways that could play indispensable roles in the neurotoxicity of N-GQDs or both two kinds of GQDs were found. Low-dosed N-GQDs exposure mainly induced inflammatory action in microglia, while high-dosed N-GQDs and A-GQDs exposure both affect olfactory transduction and GABAergic synapse. Meanwhile, several classical signaling pathways, including mTOR, ErbB and MAPK, could make diverse contributions to the neurotoxicity of both two kinds of GQDs. These circRNAs could be toxic biomarkers or protective targets in neurotoxicity of GQDs. More importantly, they emphasized the necessity of comprehensive analysis of latent molecular mechanisms through epigenetics approaches in biosafety assessment of graphene-based nanomaterials.

Engineered N-doped graphene quantum dots/CoFe2O4 spherical composites as a robust and retrievable catalyst: fabrication, characterization, and catalytic performance investigation in microwave-assisted synthesis of quinoline-3-carbonitrile derivatives

Nitrogen-doped graphene quantum dots (N-GQDs), which are less than 10 nm in size, are an interesting member of the nanocarbon materials family. N-GQDs nanostructures have been broadly applied in various fields, such as drug-gene delivery systems, photocatalytic reactions, and catalysts, owing to their unique properties. However, N-GQDs have rarely been introduced as a catalyst in organic synthesis. Herein, CoFe₂O₄ nanocomposites with diverse morphologies are fabricated in various conditions (e.g. green routes, various pH adjusters, temperatures). Due to further active sites on the surface of the nanocomposites, morphology engineering can be effective in catalytic activities. Following the synthesis, the catalytic activity of the engineered CoFe₂O₄ nanocomposites was screened, and it presented the order of spherical > rod > prism > cubic. The uniform spherical morphology provides more accessible active sites. Then, the novel nano-sized N-GQDs/CoFe₂O₄ magnetic spherical composite was readily fabricated by a green, low-cost, and easy hydrothermal route. The engineered composite was applied as an efficient magnetic nanocatalyst for the MW-assisted one-pot synthesis of new and known quinoline-3-carbonitrile derivatives (83–96%) in the shortest reaction time (60–90 s). Furthermore, the green route, easy separation of the nanocatalyst, and reusability (7 runs) without noticeable loss of catalytic efficiency are other advantages.

Sustainable fabrication of spherical N-GQDs/CoFe₂O₄ nanocomposites as a novel magnetically retrievable catalyst for the synthesis of quinoline-3-carbonitrile derivatives has been developed.

Recent advances in the modification of carbon-based quantum dots for biomedical applications

Carbon-based quantum dots (CDs) are mainly divided into two sub-groups; carbon quantum dots (CQDs) and graphene quantum dots (GQDs), which exhibit outstanding photoluminescence (PL) properties, low toxicity, superior biocompatibility and facile functionalization. Regarding these features, they have been promising candidates for biomedical science and engineering applications. In this work, we reviewed the efforts made to modify these zero-dimensional nano-materials to obtain the best properties for bio-imaging, drug and gene delivery, cancer therapy, and bio-sensor applications. Five main surface modification techniques with outstanding results are investigated, including doping, surface functionalization, polymer capping, nano-composite and core-shell structures, and the drawbacks and challenges in each of these methods are discussed.

Prioritizing phthalate esters (PAEs) using experimental in vitro/vivo toxicity assays and computational in silico approaches

Phthalate esters (PAEs) pose prominent ecological risks owing to their multiplex toxicity potentials and ubiquitous detection in the environment. Therefore, this study aims to prioritize the individual and mixtures of six PAEs based on their toxicological implications using in vitro and vivo models exposed at environmentally relevant concentrations. Results were further confirmed using in silico Combination index (CI) and Independent action (IA), and molecular docking models. Among PAEs, DEHP revealed prominent in vitro/vivo toxicity followed by DEP, DBP, and DMP. Importantly, binary mixtures particularly C2-C6 and C11-C15 exhibited greater developmental toxicity, apoptosis, and perturbed the HPG pathway. The CI and IA models forecasted antagonistic and additive effects at Fa = 0.5 and Fa = 0.9 using in vitro Acinetobacter sp. Tox2. Conversely, in zebrafish, the IA model predicted mixture effects in the following order: additive > synergistic > antagonistic on the regulation of the HPG pathway, which was consistent with experimental results from Acridine Orange (AO) staining and apoptosis gene expression. Molecular docking for estrogen receptors (ERα, ERβ) revealed the highest binding energy scores for DEHP, compared to other PAEs. In short, our findings confirm that individual and mixtures of PAEs behave as xenoestrogens in the freshwater ecosystem with DEHP as a priority compound.

Theoretical Evaluation of DNA Genotoxicity of Graphene Quantum Dots: A Combination of Density Functional Theory and Molecular Dynamics Simulations

Owing to their unique morphology, ultrasmall lateral sizes, and exceptional properties, graphene quantum dots (GQDs) hold great potential in many applications, especially in the fields of electrochemical biosensors, bioimaging, drug delivery, gene delivery, etc. Their biosafety and potential genotoxicity to human and animal cells have been a growing concern in recent years. Especially, the potential DNA damage caused by GQDs is very crucial but still unclear. In this study, the effect of GQDs on DNA damage has been evaluated by a combination of molecular dynamics (MD) simulations and density functional theory. Our results demonstrate that the DNA damaging mechanism of GQDs depends on the size of GQDs. The small GQDs (seven benzene rings) tend to enter into the interior of DNA molecules and cause a DNA base mismatch. The relatively large GQDs (61 benzene rings) tend to adsorb onto the two ends of a DNA molecule and cause DNA unwinding. Due to the strong interaction between guanine (G) and GQDs, the effect of GQDs is much larger on G than on the other three bases (A, C, and T). In addition, the concentration of GQDs could also affect the results of DNA damaging.

Induction of ferroptosis in response to graphene quantum dots through mitochondrial oxidative stress in microglia

BACKGROUND

Graphene quantum dots (GQDs) provide a bright prospect in the biomedical application because they contain low-toxic compounds and promise imaging of deep tissues and tiny vascular structures. However, the biosafety of this novel QDs has not been thoroughly evaluated, especially in the central nervous system (CNS). The microarray analysis provides a hint that nitrogen-doped GQDs (N-GQDs) exposure could cause ferroptosis in microglia, which is a novel form of cell death dependent on iron overload and lipid peroxidation.

RESULTS

The cytosolic iron overload, glutathione (GSH) depletion, excessive reactive oxygen species (ROS) production and lipid peroxidation (LPO) were observed in microglial BV2 cells treated with N-GQDs, which indicated that N-GQDs could damage the iron metabolism and redox balance in microglia. The pre-treatments of a specific ferroptosis inhibitor Ferrostatin-1 (Fer-1) and an iron chelater Deferoxamine mesylate (DFO) not only inhibited cell death, but also alleviated iron overload, LPO and alternations in ferroptosis biomarkers in microglia, which were caused by N-GQDs. When assessing the potential mechanisms of N-GQDs causing ferroptosis in microglia, we found that the iron content, ROS generation and LPO level in mitochondria of BV2 cells all enhanced after N-GQDs exposure. When the antioxidant ability of mitochondria was increased by the pre-treatment of a mitochondria targeted ROS scavenger MitoTEMPO, the ferroptotic biological changes were effectively reversed in BV2 cells treated with N-GQDs, which indicated that the N-GQDs-induced ferroptosis in microglia could be attributed to the mitochondrial oxidative stress. Additionally, amino functionalized GQDs (A-GQDs) elicited milder redox imbalance in mitochondria and resulted in less ferroptotic effects than N-GQDs in microglia, which suggested a slight protection of amino group functionalization in GQDs causing ferroptosis.

CONCLUSION

N-GQDs exposure caused ferroptosis in microglia via inducing mitochondrial oxidative stress, and the ferroptotic effects induced by A-GQDs were milder than N-GQDs when the exposure method is same. This study will not only provide new insights in the GQDs-induced cell damage performed in multiple types of cell death, but also in the influence of chemical modification on the toxicity of GQDs.

Simultaneous Delivery of antimiR-21 and Doxorubicin by Graphene Oxide for Reducing Toxicity in Cancer Therapy

Graphene oxide (GO) has been studied by many researchers for its potential drug-delivery value. In order to reduce the side effects of anticancer drugs by decreasing the dosage and maintain the therapeutic effects, a dual drug-delivery system that used GO as a carrier and simultaneously loaded with antitumor drugs and antimir-21 was rationally designed for the cooperative treatment of tumors. Results obtained from our studies have found that MDA-MB-231 cells were inhibited in low Dox dose. The outcomes of confocal microscopy indicated that Dox and antimiR-21 could be released rapidly in cancer cells, which is good for killing cancer cells. In addition, qRT-PCR further demonstrated that miR-21 was silenced by antimiR-21. Consequently, GO has a great potential to codeliver chemotherapeutic drugs and gene drugs in cancer combination therapy for reducing toxicity.

Revisiting the cytotoxicity of quantum dots: an in-depth overview

Recently, medical research has been shifting its focus to nanomedicine and nanotherapeutics in the pursuit of drug development research. Quantum dots (QDs) are a critical class of nanomaterials due to their unique properties, which include optical, electronic, and engineered biocompatibility in physiological environments. These properties have made QDs an attractive biomedical resource such that they have found application as both in vitro labeling and in vivo theranostic (therapy-diagnostic) agents. Considerable research has been conducted exploring the suitability of QDs in theranostic applications, but the cytotoxicity of QDs remains an obstacle. Several types of QDs have been investigated over the past decades, which may be suitable for use in biomedical applications if the barrier of cytotoxicity can be resolved. This review attempts to report and analyze the cytotoxicity of the major QDs along with relevant related aspects.

Graphene quantum dot based materials for sensing, bio-imaging and energy storage applications: a review

Graphene quantum dots (GQDs) are an attractive nanomaterial consisting of a monolayer or a few layers of graphene having excellent and unique properties. GQDs are endowed with the properties of both carbon dots (CDs) and graphene. This review addresses applications of GQD based materials in sensing, bioimaging and energy storage. In the first part of the review, different approaches of GQD synthesis such as top-down and bottom-up synthesis methods have been discussed. The prime focus of this review is on green synthesis methods that have also been applied to the synthesis of GQDs. The GQDs have been discussed thoroughly for all the aspects along with their potential applications in sensors, biomedicine, and energy storage systems. In particular, emphasis is given to popular applications such as electrochemical and photoluminescence (PL) sensors, electrochemiluminescence (ECL) sensors, humidity and gas sensors, bioimaging, lithium-ion (Li-ion) batteries, supercapacitors and dye-sensitized solar cells. Finally, the challenges and the future perspectives of GQDs in the aforementioned application fields have been discussed.

Graphene quantum dots (GQDs) are an attractive nanomaterial consisting of a monolayer or a few layers of graphene having excellent and unique properties.

Dispersed graphene materials of biomedical interest and their toxicological consequences

Graphene is one-atom thick nanocarbon displaying a unique honeycomb structure and extensive conjugation. In addition to high surface area to mass ratio, it displays unique optical, thermal, electronic and mechanical properties. Atomic scale tunability of graphene has attracted immense research interest with a prospective utility in electronics, desalination, energy sectors, and beyond. Its intrinsic opto-thermal properties are appealing from the standpoint of multimodal drug delivery, imaging and biosensing applications. Hydrophobic basal plane of sheets can be efficiently loaded with aromatic molecules via non-specific forces. With intense biomedical interest, methods are evolving to produce defect-free and dispersion stable sheets. This review summarizes advancements in synthetic approaches and strategies of stabilizing graphene derivatives in aqueous medium. We have described the interaction of colloidal graphene with cellular and sub-cellular components, and subsequent physiological signaling. Finally, a systematic discussion is provided covering toxicological challenges and possible solutions on utilizing graphene formulations for high-end biomedical applications.

Antioxidant Activity of Graphene Quantum Dots Prepared in Different Electrolyte Environments

Antioxidants can reduce or inhibit damage such as oxidative decay caused by elevated levels of free radicals. Therefore, pursuing antioxidants with excellent properties has attracted more and more attention. Graphene quantum dots (GQDs) are considered a promising material because of their good free radical scavenging activity, low toxicity, and excellent water solubility. However, their scavenging efficiency, antioxidant mechanism, and effective control methods need to be improved. Herein, in order to further reveal the antioxidant mechanism of GQDs, the role of electrolytes in improving the antioxidant activity of GQDs is explored. In addition, 1,1-diphenyl-2-picrazine (DPPH∙), hydroxyl (∙OH), and superoxide (∙O₂⁻) free radicals are used to evaluate the antioxidant activity of the as-prepared GQDs. Combined with transmission electron microscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, and cyclic volt–ampere characteristic curves, the effects of an electrolytic environment on the surface functional groups, charge transfer capability, and defect states of GQDs are obtained. The antioxidant mechanism of GQDs and how to improve their antioxidant activity are further elucidated.

Band gap tuning and surface modification of carbon dots for sustainable environmental remediation and photocatalytic hydrogen production - A review

Energy and water are the two major issues facing the modern mankind. Providing freshwater requires energy and producing energy uses water. In the present-day scenario, both these routes face growing problems and limitations. Energy crisis has risen due to the depletion of fossil fuels that cause pollution to water bodies making the water unusable for human consumption. In this regard, semiconductor nanocrystals with luminescent properties or carbon quantum dots (CQDs) are the newly developed nanomaterials whose distinctive photo-physical characteristics are focusing to a new generation of robust materials and sensors for sustainable development. In this review, advances in surface and band gap modification of CQDs to improve the activity of nanomaterials will be discussed with special reference to some specific CQDs exhibiting special optical properties for water treatment/splitting applications. Recent advances on CQDs nanocomposites including their applications in photodegradation of organic pollutants, sensing of heavy metal ions in water and water splitting are discussed critically to narrate the future prospects in this field. Challenges and limitations for further improvement are covered to provide smart choices for creating sustainability of benign environment and economic benefits.

Antimicrobial Activity and Mechanism of Functionalized Quantum Dots

An essential characteristic of quantum dots (QDs) is their antimicrobial activity. Compared with conventional antibiotics, QDs not only possess photoluminescence properties for imaging and photodynamic therapy but also have high structural stability. To enhance their antimicrobial efficiency, QDs usually are functionalized by polymers, including poly(ethylene glycol), polyethyleneimine, and poly-l-lysine. Also, QDs conjugated with polymers, such as poly(vinylpyrrolidone) and polyvinylidene fluoride, are prepared as antimicrobial membranes. The main antimicrobial mechanisms of QDs are associated with inducing free radicals, disrupting cell walls/membranes, and arresting gene expression. The different mechanisms from traditional antibiotics allow QDs to play antimicrobial roles in multi-drug-resistant bacteria and fungi. Since the toxicity of the QDs on animal cells is relatively low, they have broad application in antimicrobial research as an effective alternative of traditional antibiotics.

Dextran Aldehyde in Biocatalysis: More Than a Mere Immobilization System

Dextran aldehyde (dexOx), resulting from the periodate oxidative cleavage of 1,2-diol moiety inside dextran, is a polymer that is very useful in many areas, including as a macromolecular carrier for drug delivery and other biomedical applications. In particular, it has been widely used for chemical engineering of enzymes, with the aim of designing better biocatalysts that possess improved catalytic properties, making them more stable and/or active for different catalytic reactions. This polymer possesses a very flexible hydrophilic structure, which becomes inert after chemical reduction; therefore, dexOx comes to be highly versatile in a biocatalyst design. This paper presents an overview of the multiple applications of dexOx in applied biocatalysis, e.g., to modulate the adsorption of biomolecules on carrier surfaces in affinity chromatography and biosensors design, to serve as a spacer arm between a ligand and the support in biomacromolecule immobilization procedures or to generate artificial microenvironments around the enzyme molecules or to stabilize multimeric enzymes by intersubunit crosslinking, among many other applications.