Investigating sustainable and renewable sources of carbon quantum dots for utilization in food packaging systems: A review

With the continuous development of carbon-based materials, a variety of new materials have emerged one after another. Carbon Quantum Dots (CQDs) have succeeded in standing out from the crowd of new materials due to their better optical properties in biomedicine, ion detection, anti-counterfeiting materials and photocatalysis. In recent years, through the continuous exploration of CQDs, research scholars have found that the organic substances or heavy metals contained in traditional ones can cause irreversible harm to people and the environment. Therefore, the application of traditional CQDs in future studies will be gradually limited. Among various new materials, biomass raw materials have the merits of good biocompatibility, lower toxicity and green and environmental protection, which largely overcome the defects of traditional materials and have attracted many scholars to focus on the research and development of various biomass CQDs. This paper summarises the optical properties, fluorescence mechanisms, synthetic methods, functionalisation modulation of biomass CQDs and their relevant research progress in the fields of ion detection, bioimaging, biomedicine, biosensing, solar cells, anti-counterfeit materials, photocatalysis and capacitors. Finally, the paper concludes with some discussion of the challenges and prospects of this exciting and promising field of application.

Carbon quantum dots (CQDs) have emerged as a promising class of nanomaterials, distinguished by their unique optical and electronic properties, making them ideal candidates for catalyzing various organic synthesis reactions. This review provides a comprehensive overview of recent advancements in the application of CQDs as catalysts in organic transformations, with a focus on their synthesis, functionalization, and mechanisms of action. CQDs, also referred to as carbon dots (CQDs), are innovative zero-dimensional fluorescent carbon-based nanomaterials that have garnered significant global interest. The advantages of CQDs over traditional catalysts are noteworthy. They possess a high surface area, which facilitates increased interaction with reactants, and their surface chemistry can be easily tuned to optimize catalytic performance. Additionally, CQDs exhibit excellent stability under a wide range of reaction conditions, ensuring consistent catalytic activity. Their biocompatibility and low toxicity further enhance their appeal, positioning them as environmentally friendly and sustainable alternatives in chemistry. Due to their catalytic applications, CQDs are recognized for their remarkable optical properties, including strong fluorescence and water solubility, which allow them to be utilized in diverse fields, such as bioimaging, biosensing, and chemical sensing. Their eco-friendliness and simple synthesis methods make CQDs attractive for applications in nanomedicine, solar cells, drug delivery systems, and light-emitting diodes. The combination of these favorable characteristics positions CQDs as promising candidates for advancing technology across multiple domains, especially in medical and environmental applications. As research continues to uncover new functionalities and applications of CQDs, their role in catalysis and other fields is expected to expand, paving the way for innovative solutions to pressing challenges in organic synthesis and beyond.

Bacterial resistance to antibiotics have become one of the most severe threats in global public health, so the development of new-style antimicrobial agents is urgent. In this work, quaternized carbon quantum dots (qCQDs) with broad-spectrum antibacterial activity were synthesized by a simple green “one-pot” method using dimethyl diallyl ammonium chloride and glucose as reaction precursors. The qCQDs displayed satisfactory antibacterial activity against both Gram-positive and gram-negative bacteria. In rat models of wounds infected with mixed bacteria, qCQDs obviously restored the weight of rats, significantly reduced the death of rats from severe infection, and promoted the recovery and healing of infected wounds. Biosafety tests confirmed that qCQDs had no obvious toxic and side effects during the testing stage. The analysis of quantitative proteomics revealed that qCQDs mainly acted on ribosomal proteins in Staphylococcus aureus (Gram-positive bacteria) and significantly down-regulated proteins associated with citrate cycle in Escherichia coli (Gram-negative bacteria). Meanwhile, real-time quantitative PCR confirmed that the variation trend of genes corresponding to the proteins associated with ribosome and citrate cycle was consistent with the proteomic results after treatment of qCQDs, suggesting that qCQDs has a new antibacterial mechanism which is different from the reported carbon quantum dots with antibacterial action. Statement of significanceWith the development of the research on carbon quantum dots, the application of carbon quantum dots in the field of medicine has attracted extensive attention. In this paper, quaternized carbon quantum dots (qCQDs) with antimicrobial activity prepared by specific methods were studied, including antimicrobial spectrum, antimicrobial mechanism and in vivo antimicrobial application. The antimicrobial mechanism of qCQDs was studied by proteomics and RT-qRCR, and the different mechanisms of qCQDs against Gram-positive and Gram-negative bacteria were also found. This study provides a research foundation for the application of carbon quantum dots in antimicrobial field, and also expands the application range of carbon quantum dots in medicine field.

The optical properties and solar energy conversion applications of carbon quantum dots: A review

The demand for more healthy foods with longer shelf life has been growing. Food packaging as one of the main aspects of food industries plays a vital role in meeting this demand. Integration of nanotechnology with food packaging systems (FPSs) revealed promising promotion in foods’ shelf life by introducing novel FPSs. In this paper, common classification, functionalities, employed nanotechnologies, and the used biomaterials are discussed. According to our survey, FPSs are classified as active food packaging (AFP) and smart food packaging (SFP) systems. The functionality of both systems was manipulated by employing nanotechnologies, such as metal nanoparticles and nanoemulsions, and appropriate biomaterials like synthetic polymers and biomass-derived biomaterials. “Degradability and antibacterial” and “Indicating and scavenging” are the well-known functions for AFP and SFP, respectively. The main purpose is to make a multifunctional FPS to increase foods’ shelf life and produce environmentally friendly and smart packaging without any hazard to human life.

Extensive application of carbon quantum dots (CQDs) enlarges its concentration in sewage treatment system. The response of nitrifying sludge to CQDs after long-term exposure was investigated. Results showed that CQD concentrations of 0-100mg/L presented positive effect to enzymes involved in nitrification, accelerating NH4+-N degradation and NO2--N transformation. The oxidation rate of NO2--N was significantly improved from 3.14 to 7.91mg/(L h) under the stress of 100mg/L CQDs. Besides, CQDs stimulated the production of sludge biomass and kept the stability of sludge settleability. Additionally, CQDs were mainly captured by loosely bound extracellular polymeric substances, reducing aromatic-like protein. Microbes alleviated CQD stress by secreting tryptophan-like protein and polysaccharides. After few CQDs entered cells, intracellular antioxidant defense was activated. Total antioxidant capacity level was heightened at least 31%. The activities of superoxide dismutase and catalase were enhanced at relatively low and high CQD concentration levels. Hence, microbial metabolic pathways, microbial community, and nitrifying bacteria were not significantly affected by CQDs. The findings of this work provide new insight for understanding the environmental implication of CQDs in the biological treatment system.

Advances in lubricants are vital to the pursuit of energy efficiency and sustainable development. It is well known that the essence of lubricating oil is lubricant additives, especially the friction-reducing and anti-wear additives. Carbon quantum dots (CQDs), a novel zero-dimensional carbon-based nanomaterial, have attained growing expectations in material and chemical sciences because of their extraordinary properties such as low toxicity and environmentally friendly, high chemical and thermal stability, and good designability. Since their discovery, CQDs have shown great potential in many applications including sensors, medicine, photovoltaic devices, biology, and tribology. The latest application of CQDs as the high-performance friction-reducing and anti-wear additives has garnered increasing attention. With the in-depth study, CQDs have gradually exhibited their excellent tribological properties, especially acted as additives in lubricating base oils. This paper has reviewed the progress in the research and development of CQDs-based lubricant additives by introducing lots of successful applications of CQDs-based additives in the present work and then highlighted the friction-reducing and anti-wear property, superiority, as well as the lubrication mechanism of CQDs as an additive, along with some discussion on challenges and perspectives in this significant and promising field. Finally, we offered a series of suggestions for developing the next-generation high-performance CQDs-based lubricant additives. This work presented the carbon quantum dots as the lubricant additives of lubricating base oils.

Carbon quantum dot-induced developmental toxicity in Daphnia magna involves disturbance of symbiotic microorganisms

Hydrothermal synthesis of carbon quantum dots (CQDs) from biomass is a green and sustainable route for CQDs applications in various fields. However, one of the major problems is the low CQDs yield because the traditional hydrothermal treatment would produce large amounts of hydrochar byproduct. In this work, we present a novel, facile, and effective method for large-scale synthesis of CQDs from biomass-derived carbon including hydrochar and carbonized biomass through mild oxidation (NaOH/H2O2 solution). An ultrahigh CQDs yield of 76.9 wt % can be obtained, which is much higher than those obtained from traditional hydrothermal and strong acid oxidation processes. Furthermore, the CQDs have excellent quantum yield (QY) that is higher than (or comparable to) those from other methods. In addition, the CQDs have uniform size (∼2.4 nm) and their surface states can be regulated to significantly improve the QY by adjusting the concentration of oxidants. The CQDs displayed excellent sensitivity for Pb2+ detection along with good linear correlation ranging from 1.3 to 106.7 μM. These advantages, together with low cost, sustainability, and green process, make this approach have great potential in the synthesis and applications of CQDs in large scale.

Carbon quantum dots, which produce good fluorescence, are potential for many applications, including biomedical applications. In biomedical researches, many quantum dots have been utilized and explored under the two-photon emission mechanism. This mechanism allows living tissue to survive from the excitation laser used in the procedure. The study on the two-photon emission mechanism of carbon quantum dots is rarely done by other researchers. Therefore, in this work, we focused on synthesizing carbon quantum dots from urea and trisodium citrate and studying their optical properties under one-photon and two-photon emission mechanisms. We found that using higher photon energy, we were able to excite carbon quantum dots to get emissions at lower photon energy. Cyan until green emission colours were observed under the one-photon mechanism. Furthermore, we also found that carbon quantum dots can emit fluorescence at higher photon energy when they were excited using lower photon energy. This was the evidence that carbon quantum dots were also able to be excited using the two-photon mechanism. From absorbance and photoluminescence spectra, we were able to predict the energy band level of the carbon quantum dots. This work could give further clues for the application of carbon quantum dots in biomedical applications.

Biomedical application of carbon quantum dots: A review

A new method of carbon quantum dots (CQDs) fluorescent imaging for human serum proteins detection after polyacrylamide gels electrophoresis (PAGE) is established. Polyacrylamide gel electrophoresis is one of the most general and powerful technique to separate complex biosamples, and it is widely used in molecular biology, biochemistry and medicine. With the evolution of clinical proteomics, the development of a novel method to detect serum proteins after PAGE with high resolution and high sensitivity is of great significant. As far as we know, the carbon quantum dots have not been applied in the detection of serum proteins after PAGE. The fluorescent carbon quantum dots were synthesized by a one-step microwave pyrolysis method: glycerol and phosphate buffer (7.1 mmolL -1 , pH 7.4) (φ=70%) was mixed evenly, and then put the solu- tion into the advanced microwave digestion system and heated for 14 min (750 W), the colorless solution turned to yellow after reaction. The yellow solution was diluted into the incubation solution with HOAc-NaOAc buffer (80 mmolL -1 , pH 2.7), and then used for staining serum proteins. The emission and excitation spectra of carbon quantum dots were measured, and the excitation wavelength allowed the use of an ultraviolet lamp at 365 nm for the fluorescent imaging. In order to inves- tigate the performance of CQDs fluorescent imaging, the dilution of human serum samples separated by electrophoresis was used for detection, and was compared with traditional method of CBB-R250 staining and silver staining. The results sug- gested that CQDs based on fluorescent imaging could effectively detect human serum proteins with high sensitivity and resolution. The sensitivity of CQDs imaging was higher than CBB staining and comparable to silver staining. Therefore, the CQDs fluorescent imaging could be an inexpensive, time-saving, pollution-free and convenient method with high sensitivity and resolution for the detection of human serum proteins. It demonstrates the CQDs fluorescent imaging technology has great significant prospects in the development of biotechnology and nanotechnology. Keywords carbon quantum dot; polyacrylamide gel electrophoresis; protein; fluorescent imaging

The increase in national energy consumption has forced us to intensify renewable energy utilization. Solar panel is one optional answer for that purpose. Unfortunately, the product resistance and photon absorption from silicon-based solar cells are still not good enough. Carbon quantum dots (CQD) could be an alternative advanced material that can be utilized to maximize the performance of solar panels. Therefore, researchers are interested in finding out how to manufacture CQD from the synthesis of rice husk waste composite as an advanced solar cell and analyze its potential to maximize solar panel photon energy absorption. Researchers use mixed study that applies literature review methods (as part of the descriptive research aspect) and causal comparative research methods (as part of the quantitative aspect). Based on previous research, rice husk waste was pre-processed by washing using de-ionized water (DI water) to remove residue, then baked and blended into powder, and cleaned using HCl as impurities remover. The hydrothermal process was carried out at 190 oC for 12 hours to synthesize CQD which functioned by amino and carboxyl. For further purification, CQD was dialyzed against DI water in cellulose. Super-dense material due to quantum level compression, makes CQD have a higher resistance when compared to silicon as solar cells. In addition, the absorption of photon energy that can be done by CQD solar cells has a higher percentage when compared to conventional solar cells. However, in this paper, the researchers did not make CQD and only analyzed through modeling which became the research gap in this paper.

The pursuit of sustainable development refers to meet the present needs while safeguarding the resources for future generations ensuring the well-being of human societies. Nanoscience is contributing significantly to the field of public healthcare by delivering a number of cutting-edge technological applications and products related to healthcare. Carbon quantum dots (CQDs), carbon-based nanomaterials, are gaining recognition for their potential health benefits worldwide. The current study aims to review the applications of CQDs in the biomedical field based on existing literature. The methodology used is the collection of the literature studies from authoritative sources such as Google Scholar, PubMed, and ResearchGate, with keywords ‘Carbon quantum dots in healthcare, biosensing, bioimaging, gene therapy, treatment, and theranostics’. The retrieved literature was comprehensively analyzed to construct the detailed review which suggests that CQDs have demonstrated remarkable potential across various domains, from disease treatment to biosensing, gene delivery, drug delivery, and bioimaging thus helping to achieve the 3rd goal of sustainable development. In addition to CQDs synthesized by chemical processes, natural CQDs developed by green chemistry from natural sources are gaining accreditation due to their evidenced potential health benefits. This article has reviewed the versatile applications of Carbon Quantum Dots (CQDs) in the biomedical field and discussed the possible contributions to achieve sustainable healthcare for the first time, suggesting CQDs as a potential target for future research and development. However, there are some limitations of CQDs including complex surface modification, toxicity, limited clinical translation which requires more attention in order to improve their healthcare applicability.

Background: Nanoparticles have been widely used in dentistry due to their numerous physical and biological benefits. Carbon quantum dots (CQD) are used in many biological applications due to their small size and low cytotoxicity. It is expected to improve the surface properties of tooth enamel against acid dissolution when applied at low concentrations. The objective: This study evaluated the effect of CQD solution on the microhardness and surface characteristics of sound and demineralized enamel surfaces. Material and Methods: The solution was prepared with laser ablation and then examined with UV light (325 mm). The distribution, size, and dimensions of particles were analyzed using field emission scanning electron microscopes and transmission electron microscopes. Forty solid teeth (the first upper premolar) were prepared and divided into four groups (n=10). Group 1 (control group), Group 2 (Sound + CQD), Group 3 (Sound + CQD + Demineralization) and Group 3 (Sound+ Demineralization + CQD). The sample was immersed in the test solution for 4 minutes at 37 °C. The enamel microhardness was tested using Vickers microhardness testers, and the morphological characteristics were observed under a scanning electron microscope. Results: The CQD particles appear to be sphere-shaped with diameters of 2-10 nm and blue cyan light. After application of CQDs, the average microhardness value increased significantly (p<0.001) compared to the control group. Demineralized enamel (group 4) recorded a higher microhardness (p=0.006) than sound enamel (group 3) after CQD application. The treated surface was smooth and homogeneous, with a better crystal structure and closed pores than the untreated surface. Conclusion: The addition of CQDs had a profound effect on the sound surface hardness and demineralized enamel with enhanced morphological properties, which is considered an effective method for the prevention of dental disease.