Luminescent quantum dots: Synthesis, optical properties, bioimaging and toxicity

Structural features regulated photoluminescence intensity and cell internalization of carbon and graphene quantum dots for bioimaging

Chapter 28 - Physical properties of quantum dots

ZnCl2 Enabled Synthesis of Highly Crystalline and Emissive Carbon Dots with Exceptional Capability to Generate O2⋅–

Recent advances in agricultural and marine waste-derived carbon dots for clean energy technologies

Carbon-based quantum dots and their nanocomposites have sparked immense interest for researchers as sensors due to their attractive physico-chemical properties caused by edge effects and quantum confinement. In this review article, we have discussed the synthesis and application of nanocomposites of graphene quantum dots (GQDs) and carbon quantum dots (CQDs). Different synthetic strategies for CQDs, GQDs, and their nanocomposites, are categorized as top-down and bottom-up approaches which include laser ablation, arc-discharge, chemical oxidation, ultrasonication, oxidative cleavage, microwave synthesis, thermal decomposition, solvothermal or hydrothermal method, stepwise organic synthesis, carbonization from small molecules or polymers, and impregnation. A comparison of methodologies is presented. The environmental application of nanocomposites of CQDs/GQDs and pristine quantum dots as sensors are presented in detail. Their applications envisage important domains dealing with the sensing of pollutant molecules. Recent advances and future perspective in the use of CQDs, GQDs, and their nanocomposites as sensors are also explored.

While previous research has primarily focused on nanoparticles larger than 20 nm for promoting migrasome formation, this study shifts the emphasis to nanoparticles smaller than 10 nm. Our findings reveal the significant impact of these sub-10 nm carbon-based quantum dots, specifically carbon quantum dots (CQD), graphene quantum dots (GQD), and graphitic oxide quantum dots (GOQDs), on migrasome formation, mitochondrial integrity, and platelet function. We establish a clear correlation between the application of these nanoparticles and the induction of migrasomes. Furthermore, our results indicate that CQD, GQD, and GOQDs enhance migrasome formation by upregulating phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), cholesterol, and GTP-RhoA. Additionally, these nanoparticles provide mitochondrial protection through a process called mitocytosis and promote increased platelet aggregation. This study represents a pioneering effort to connect various types of nanoscale graphene materials with the dynamic behavior of migrasomes, thereby advancing our understanding of nanoscale materials and their biological implications.Graphical Supplementary InformationThe online version contains supplementary material available at 10.1186/s12951-025-04010-9.

Silicon quantum dot is nanometer sized single crystalline silicon particles. It shows exotic luminescence properties such as size tuneablilty of luminescence band and quasi-direct electron-hole recombination resulting in efficient visible luminescence at room temperature, due to quantum confinement effects. Because of its environmental friendliness and low cost, the silicon quantum dot is a promising material for future light-emitting applications. Recently, a free-standing form of silicon quantum dot dispersed in solution, i.e., colloidal silicon quantum dots are intensively investigated due to their potential usefulness in solution based light emitting technology. The luminescence properties and solution dispersibility in silicon quantum dots are known to depend on the surface properties such as the coverage of surface termination and the kinds of surface terminated species.Various formation techniques for colloidal silicon quantum dot have been proposed, such as wet-chemical synthesis, plasma synthesis and high-temperature thermal processing. Pulsed-laser irradiation in liquid is one of the simplest top-down method for the formation of colloidal silicon quantum dots. By irradiating bulk crystalline silicon target with a high power pulsed-laser beam in liquid, silicon quantum dots are easily formed due to the ablation of silicon crystal and resultant condensation effect of ablated silicon at the liquid interface. An additional merit of this process is the easiness of surface termination control; because the nanocrystal surface formed by laser ablation actively reacts with molecules consisting of solution, one can control the surface termination by changing the kinds of solution. However, the control of the formed quantum dot size is still a challenging work and the size distribution of the quantum dots prepared by this process is usually wide.To overcome these issues, we developed a novel top-down pulsed laser irradiation technique for the formation of colloidal silicon quantum dots. We used an interconnected wire-nanostructure assembly, i.e., porous silicon (PSi), as a target material for the laser irradiation process, on behalf of bulk crystalline silicon target. PSi has beneficial properties for laser irradiation target such as low thermal conductivity and large surface areas. Because of these properties, the pulsed-laser irradiation of PSi target in organic solution allows us to generate the silicon quantum dots with relatively high preparation yields, and with various emission bands by changing irradiation conditions and the porosity of PSi. Furthermore, in our developed process, the formed dots are brighter than the original PSi target due to the stable organic terminations.Recently, we further improved our developed facile formation process of luminescent colloidal silicon quantum dots via porous silicon target. In the improved process, we employed electrochemically prepared PSi flakes, which purely consists of porous layer. The PSi flakes show extremely low thermal conductivity and heat capacity due to their intrinsic geometrical feature. Thus, even a low temperature thermal treatment as well as pulsed laser irradiation to PSi flakes in organic solution are efficiently converted porous silicon layer to colloidal silicon quantum dots. Furthermore, we succeeded in preparing silicon quantum dots dispersed in a polar and non-polar solvent depending on the ligands terminated on the dot surface by using different solutions. The present facile formation process of silicon quantum dots from PSi allows us to develop future top-down and low-cost mass production of luminescent colloidal silicon quantum dots.

<p>Quantum dots have applications in biomedical fields such as bio-imaging and drug delivery systems. This thesis describes research on silicon and germanium nanoparticles (quantum dots) synthesis and surface modification for biological applications. Purification methods of these quantum dots were also explored. In chapter 6 the application of silica nanoparticles into dry eye diagnosis was studied. The purpose of this research is to contribute the application of nanotechnology into biological fields. The crystalinity of the quantum dots was characterised by Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction analysis (SAED). The molecules on the surface of the quantum dots were characterised by Fourier Transform Infrared spectroscopy (FTIR) and Nuclear Magnetic Resonance (NMR). Silicon quantum dots were synthesised with a microemulsion system and various types of molecules were attached on the surface of the silicon quantum dots. However, some of the capping molecules which have oxygen atoms tend to form bonds between oxygen and silicon. Therefore, in the later chapter (chapter 4) various chemical reactions were conducted on the molecules attached to the silicon quantum dots. The silicon quantum dots were capped with diene molecules and one of the double bonds was left on the terminal end. The terminal end double bonds were converted to the functional groups which contain oxygen atoms to form peptide bonds. In this way it was confirmed that it can reduce the risk of oxygen atoms to be attached on the surface of the silicon quantum dots. The molecules on the surface of the silicon quantum dots were characterised mainly by FTIR and ¹H NMR. Optical properties and cyto-toxicity of these silicon quantum dots were also measured and analysed depending on the surface molecules. Two synthetic approaches were taken to produce germanium quantum dots. The first approach was the microemulsion system at room temperature. Different combinations of the surfactant and capping molecules were tested. For the second approach, high temperature bench top system was applied. In this method the bio-friendly molecules which have high boiling points were chosen as capping agents. The surface molecules were characterised by FTIR spectroscopy. In chapter 6 the synthesis of dye molecules conjugated silica nanoparticles was described. The purpose of this research is to produce biologically safe nanoparticles which can be applied in dry eye diagnosis. Three different dyes were used to conjugate with the silica nanoparticles. Only fluorescein isothiocyanate (FITC) succeeded in conjugating with the nanoparticles. Optical properties of this sample were measured and compared with the free dye molecule. Also the sample was applied in human eyes to analyse the tear film layer. An overall conclusion and future plans for the research were given in the last chapter.In this chapter, ideas of overcoming the problems and improving the techniques conducted in the research were described.</p>

Cadmium-free quantum dot-based theranostics

The nature of carbon quantum dot (CD) luminescence is still broadly investigated based on different CD synthesis processes. This study aims at investigating the effect of microwave power on optical characteristics of CDs using microwave radiation techniques. CDs are synthesized with citric acid as a source of carbon and urea as a passivation agent. CDs have been successfully synthesized, and an increase in the CD burn-off percentage was observed with an increase in the microwave power. The TEM test results show that the dimensions of the CDs resulted are in the range of 3.4–9.5 nm with an average size of 6 nm at 450 W. The results of the FTIR functional group structural analysis show that a CD has N—H and O—H stretching bonds. According to the results of UV–Vis analysis, the CDs have absorption peaks at 335 nm and 407 nm, which indicates a π → π* electronic transition from the C=C bond and an n → π* transition from the C=O bond. Using the Tauc-plot method, the CD energy bandgap values were found to be 2.47 eV, 2.51 eV, 2.51 eV, 2.52 eV, and 2.53 eV at CD 300, CD 450, CD 600, CD 850, and CD 1000, respectively. The optical multichannel analyzer test results show that the peak emission waves produced by CDs are 536 nm and 532 nm with the strongest bright green light at CD 1000. Time-resolved photoluminescence testing shows that the CD decay time generally ranges from 5 ns. Overall, an increase in the microwave power causes an increase in the percentage of burn-off, energy bandgap, absorption intensity, and CD emission intensity.

Carbon quantum dots (CQDs) have attracted intense research interest due to their unique physicochemical properties and broad application potential. CQDs are a new class of ultrasmall fluorescent carbon nanoparticles (<10 nm) that exhibit bright photoluminescence, broad excitation spectra, high quantum yields (QYs), and excellent photostability. Structurally, they consist of graphitic sp2/sp3-hybridized carbon with amorphous or nanocrystalline cores. Unlike conventional semiconductor quantum dots (SQDs), which often contain toxic group II–VI, III–VI, or IV–VI elements, CQDs offer a safer and more environmentally friendly alternative for biomedical and cosmetic applications. This review summarizes recent advances in green-chemistry approaches for CQD synthesis, including top-down, bottom-up, waste-derived, and surface-functionalization methods. Particular attention is given to natural carbon sources, which provide low-cost, sustainable, and eco-friendly routes for scalable production. The optical, electronic, and toxicological properties of CQDs are discussed to clarify their performance and safety profiles. Special emphasis is placed on their emerging roles in wound healing and cosmetic formulations, which remain underexplored despite their promising potential. To our knowledge, this is the first comprehensive review focusing on the current progress, key challenges, and future perspectives of CQDs in beauty and personal care applications.

Glioblastoma (GBM), classified as a grade IV glioma, poses a significant challenge in the medical field due to the lack of efficient early detection techniques and targeted treatment options. This review addresses this critical unmet need by evaluating the transformative potential of carbon quantum dots (CQDs) and graphene quantum dots (GQDs), along with their biofunctionalized derivatives. These advanced nanomaterials offer remarkable opportunities to revolutionize the diagnosis and treatment of GBM at the cellular level. The excellent biocompatibility, stability, and adjustable surface properties of biofunctionalized GQDs (bGQDs) and biofunctionalized CQDs (bCQDs) create a strong foundation for the targeted management of GBM. Careful surface modifications enable selective toxicity toward GBM cells while preserving the health of normal cells. This approach enhances penetration through the blood–brain barrier and targets tumor cell nuclei precisely. Furthermore, the photophysical properties of bCQDs and bGQDs make them suitable for innovative anticancer treatments, including photodynamic and photothermal therapies. By incorporating anticancer agents and receptor-mediated targeting systems within bCQDs and bGQDs, therapeutic effectiveness is significantly improved through enhanced drug delivery and increased tumor specificity. Developing sensitive and selective biosensors for GBM using bCQDs and bGQDs as fluorescent and electrochemical sensing platforms enables real-time monitoring of disease progression. This review emphasizes the promising future of fluorescent CQDs and GQDs as powerful alternatives to traditional GBM management strategies, paving the way for more effective and personalized approaches in nanomedicine.Clinical trial number Since this study is a review, it is not eligible for submission to the clinical trial registry.

Pollutants and contaminants are commonly found in the environment, affecting the air, soil, food, and drinking water. Consequently, the development of novel purification technologies and efficient detection devices for these pollutants is crucial. Many conventional procedures are labor-intensive, costly, require advanced skills, and are generally inconvenient because of their susceptibility. However, detection methods utilizing quantum dots (QDs) can overcome these conventional limitations, such as lengthy detection times and cumbersome processes. This paper seeks to delineate several categories of quantum dots, including metal-based quantum dots, graphene quantum dots (GQDs), and carbon quantum dots (CQDs). This also encapsulates the developments in quantum dot-based detection of environmental contaminants, including antibiotics, heavy metals, pesticides, and viruses, along with the applications of quantum dots in chemical gas sensing. In addition, the environmental issues and toxicity of the QDs were examined. In this review, QDs are presented as a rapidly evolving platform with transformative potential for environmental sensing and pollutant detection, provided their lifecycle impacts are carefully managed and innovative, and less toxic designs are advanced.

Carbon-based quantum dots (CbQDs), encompassing carbon quantum dots (CQDs) and graphene quantum dots (GQDs), are an emerging class of nanomaterials with strong potential to serve as multifunctional fuel additives for compression ignition (CI) engines. This is the first focused critical review to consolidate and evaluate the combustion, performance, and emissions impacts of CbQDs in diesel-based fuels. Compared to broader carbonaceous nanomaterials, CbQDs offer unique advantages, including tunable surface functionality, nanoscale dispersion stability, and catalytic radical-generation potential. The review systematically analyzes experimental findings on the influence of CQDs and GQDs on ignition delay, fuel reactivity, brake-specific fuel consumption (BSFC), brake thermal efficiency (BTE), and key exhaust emissions including carbon monoxide (CO), unburned hydrocarbons (UHC), particulate matter (PM), and nitrogen oxides (NOx). Results indicate that CbQDs can reduce BSFC and emissions of CO, UHC, and PM by up to 6.8%, 31%, 45% and 90% respectively, while enhancing BTE by up to 6.6% depending on formulation and dosing. However, NOx behavior remains formulation-dependent and often presents trade-offs. Despite encouraging outcomes, the review identifies major gaps in mechanistic understanding, standardization, and real-world validation. Key directions for future work are proposed, including deeper diagnostics, techno-economic analysis, and environmental risk assessments to support scalable deployment. This synthesis offers essential guidance for researchers and developers advancing next-generation, nanotechnology-enhanced diesel engine technologies.

Currently, graphene has attracted much attention in the fields of bioimaging, biolabeling and drug delivery. Theoretical and experimental studies have shown that the graphene quantum dots (GQDs) are expected to show good optical properties due to their quantum confinement and edge effect. In this report, using the electrochemical assay the fluorescent GQDs with a diameter between 5 and 10 nm could be obtained via electrolysing graphite in alkaline condition and with hydrazine hydrate as a reducing agent at room temperature. The structure of the GQDs was confimed by means of transmission electron microscope (TEM) and atomic force microscope (AFM). The finding showed that the GQDs have an uniform size, and most of them are separate graphene. The GQDs mainly consist of single layer with less than 1 nm. Their features and properties were characterized by fourier transform infrared spectroscopy (FTIR), photoluminescence spectra (PL), UV-visible spectroscopy (UV-vis) and X-ray diffraction (XRD). The results indicated that the GQDs have bright yellow luminescence with a 14 % quantum yield, which is higher than that of traditional carbon quantum dots reported previously. When they were excited by different excitation wavelengths, the intensity of photoluminescence increased to the maximum, and then decreased gradually. The fluorescent emission peak of the GQDs remained unshifted, suggesting a novel kind of quantum dots different from those of graphene oxide quantum dots depending excitation wavelengths. The luminescence of GQDs arises from the graphene modified with the phthalhydrazide-like groups and hydrazide groups at the edge. The highly fluorescent GQDs have high water solubility, good photostability and biocompatibility, indicating that the GQDs can easily enter the cells. By incorporating the GQDs with A549 (lung cancer) and MCF-7 (breast cancer) cells through MTT assay, the newly obtained GQDs exhibited low cytotoxicity with an advantage of strong photoluminescence in the cells, and thus the GQDs might be used as a bioimaging marker in tumor cell imaging.