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Carbon-semiconductor hybrid quantum dots are classical carbon dots with core carbon nanoparticles doped with a selected nanoscale semiconductor. Specifically, on those with the nanoscale TiO 2 doping, denoted as C TiO2 -Dots, their synthesis and thorough characterization were reported previously. In this work, the C TiO2 -Dots were evaluated for their visible light-activated antibacterial function, with the results showing the effective killing of not only Gram-positive but also the generally more resistant Gram-negative bacteria. The hybrid dots are clearly more potent antibacterial agents than their neat carbon dot counterparts. Mechanistically, the higher antibacterial performance of the C TiO2 -Dots is attributed to their superior photoexcited state properties, which are reflected by the observed much brighter fluorescence emissions. Also considered and discussed is the possibility of additional contributions to the antibacterial activities due to the photosensitization of the nanoscale TiO 2 by its doped core carbon nanoparticles.

Carbon "quantum" dots or carbon dots (CDots) exploit and enhance the intrinsic photoexcited state properties and processes of small carbon nanoparticles via effective nanoparticle surface passivation by chemical functionalization with organic species. The optical properties and photoinduced redox characteristics of CDots are competitive to those of established conventional semiconductor quantum dots and also fullerenes and other carbon nanomaterials. Highlighted here are major advances in the exploration of CDots for their serving as high-performance yet nontoxic fluorescence probes for one- and multi-photon bioimaging in vitro and in vivo , and for their uniquely potent antimicrobial function to inactivate effectively and efficiently some of the toughest bacterial pathogens and viruses under visible/natural or ambient light conditions. Opportunities and challenges in the further development of the CDots platform and related technologies are discussed.

Carbon dots (CDots) have emerged to represent a highly promising new platform for visible/natural light-activated microbicidal agents. In this article, the syntheses, structures, and properties of CDots are highlighted, representative studies on their activities against bacteria, fungi, and viruses reviewed, and the related mechanistic insights discussed. Also highlighted and discussed are the excellent opportunities for potentially extremely broad applications of this new platform, including theranostics uses., Competing Interests: Competing Interests: The authors have declared that no competing interest exists., (© The author(s).)

Carbon dots (CDots) for their excellent optical and other properties have been widely pursued for potential biomedical applications, in which a more comprehensive understanding on the cellular behaviors and mechanisms of CDots is required. For such a purpose, two kinds of CDots with surface passivation by 3-ethoxypropylamine (EPA-CDots) and oligomeric polyethylenimine (PEI-CDots) were selected for evaluations on their uptakes by human cervical carcinoma HeLa cells at three cell cycle phases (G 0 /G 1 , S and G 2 /M), and on their different internalization pathways and translocations in cells. The results show that HeLa cells could internalize both CDots by different pathways, with an overall slightly higher internalization efficiency for PEI-CDots. The presence of serum in culture media could have major effects, significantly enhancing the cellular uptake of EPA-CDots, yet markedly inhibiting that of PEI-CDots. The HeLa cells at different cell cycle phases have different behaviors in taking up the CDots, which are also affected by the different dot surface moieties and serum in culture media. Mechanistic implications of the results and the opportunities associated with an improved understanding on the cellular behaviors of CDots for potentially the manipulation and control of their cellular uptakes and translocations are discussed., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Carbon dots (CDots) in a general structure of small carbon nanoparticles with various surface passivation schemes have emerged to represent a new class of carbon nanomaterials in now a rapidly advancing and expanding research field. Among various synthesis methods, the use of pre-processed and selected small carbon nanoparticles for deliberate chemical functionalization of the particle surface with organic molecules have produced high-performance and structurally better defined CDots. Specifically, small organic molecules 2,2'-(ethylenedioxy)bis(ethylamine) and 3-ethoxypropylamine were used for the effective surface passivation of the carbon nanoparticles via chemical functionalization to yield CDots that are brightly fluorescent and also structurally ultra-compact, amenable to various desired cell imaging applications. Thus, a systematic evaluation of these CDots on their cytotoxicity profiles is necessary, and performed in this study by using a diverse selection of cell lines. Also for fluorescence imaging, CDots were modified with their encapsulating selected organic dyes for much enhanced red/near-IR fluorescence emissions. These modified CDots with the dyes as guest were also evaluated for their cytotoxicity profiles. The results suggest that the CDots without and with the guest dyes are generally nontoxic to the selected cell lines, further supporting the notion that CDots can be used as high-performance yet nontoxic bioimaging agents.

Background: Carbon quantum dots (CDots) have recently been reported as a new class of visible light activated antimicrobial nanomaterials. This study reports the synergistic photoactivated antimicrobial interactions of CDots with photosensitizers on bacterial cells., Methods: The antimicrobial effects of the CDots with surface passivation molecules 2,2'-(ethylenedioxy)bis(ethylamine) in combination with photosensitizer methylene blue (MB) or toluidine blue (TB) at various concentrations were evaluated against Escherichia coli cells with and without 1-hour visible light illumination. The broth microdilution checkerboard method and isobologram analysis were used for determining if synergistic effect existed between CDots and MB or TB., Results: The results showed that CDots alone at a concentration of 5 μg/mL did not display antimicrobial effects, 1 μg/mL MB alone only decreased 1.86 log of viable cell numbers, but the combination treatment with 5 μg/mL CDots combined with 1 μg/mL MB completely inhibited bacteria growth, resulted in 6.2 log viable cell number reduction, suggesting synergistic interaction between the two. The antimicrobial effects of CDots/TB combination exhibited similarly synergistic effects on E. coli cells. These synergistic effects between CDots and MB or TB were further confirmed using the checkerboard microdilution methods, where the fractional inhibitory concentration index value (0.5) and the isobologram analyses. The synergistic interactions were also correlated to the increased generation of intracellular reactive oxygen species in E. coli cells upon the combination treatments of CDots/MB or CDots/TB., Conclusion: The study demonstrated the synergistic photoactivated antimicrobial effects of CDots in combination with other photosensitizers. Such synergistic effect may open new strategies for developing highly effective antimicrobial methods., Competing Interests: Disclosure The authors report no conflicts of interest in this work.

This study reported the first assessment of carbon dots' (CDots) antiviral activity to human norovirus virus-like-particles (VLPs), GI.1 and GII.4 VLPs. CDots with different surface passivation molecules, 2,2'-(ethylenedioxy)bis(ethylamine) (EDA)-CDots and 3-ethoxypropylamine (EPA)-CDots, were synthesized and evaluated. The results indicated both EDA- and EPA- CDots were highly effective to inhibit both strains of VLPs' bindings to histo-blood group antigens (HBGA) receptors on human cells at CDots concentration of 5 µg/mL, with EDA-CDots achieving 100% inhibition and EPA CDots achieving 85-99% inhibition. At low CDots concentration (2 µg/mL), positively charged EDA-CDots exhibited higher inhibitory effect (~82%) than non-charged EPA-CDots (~60%), suggesting the surface charge status of CDots played a role in the interactions between CDots and the negatively charged VLPs. Both types of CDots also exhibited inhibitory effect on VLP's binding to their respective antibodies, but much less effective than those to HBGA binding. After CDots treatments, VLPs remained intact, and no degradation was observed on VLPs' capsid proteins. Taken together, the observed antiviral effects of CDots on noroviruses were mainly through the effective inhibition of VLPs' binding to HBGA receptors and moderate inhibition of VLPs' binding to their antibodies, without affecting the integrity of viral capsid protein and the viral particle.

Carbon dots, generally defined as small carbon nanoparticles with various surface passivation schemes, have emerged as a new class of quantum-dot-like nanomaterials, with their optical properties and photocatalytic functions resembling those typically found in conventional nanoscale semiconductors. In this work, carbon dots were evaluated for their photoinduced bactericidal functions, with the results suggesting that the dots were highly effective in bacteria-killing with visible-light illumination. In fact, the inhibition effect could be observed even simply under ambient room lighting conditions. Mechanistic implications of the results are discussed and so are opportunities in the further development of carbon dots into a new class of effective visible/natural light-responsible bactericidal agents for a variety of bacteria control applications., Competing Interests: Notes The authors declare no competing financial interest.

The specifically synthesized and selected carbon dots of relatively high fluorescence quantum yields were evaluated in their fluorescence labeling of cells. For the cancer cell lines, the cellular uptake of the carbon dots was generally efficient, resulting in the labeling of the cells with bright fluorescence emissions for both one- and two-photon excitations from predominantly the cell membrane and cytoplasm. In the exploration on labeling the live stem cells, the cellular uptake of the carbon dots was relatively less efficient, though fluorescence emissions could still be adequately detected in the labeled cells, with the emissions again predominantly from the cell membrane and cytoplasm. This combined with the observed more efficient internalization of the same carbon dots by the fixed stem cells might suggest some significant selectivity of the stem cells toward surface functionalities of the carbon dots. The needs and possible strategies for more systematic and comparative studies on the fluorescence labeling of different cells, including especially live stem cells, by carbon dots as a new class of brightly fluorescent probes are discussed.

There has been much discussion on the need to develop fluorescent quantum dots (QDs) as ultracompact probes, with overall size profiles comparable to those of the genetically encoded fluorescent tags. In the use of conventional semiconductor QDs for such a purpose, the beautifully displayed dependence of fluorescence color on the particle diameter becomes a limitation. More recently, carbon dots have emerged as a new platform of QD-like fluorescent nanomaterials. The optical absorption and fluorescence emissions in carbon dots are not bandgap in origin, different from those in conventional semiconductor QDs. The absence of any theoretically defined fluorescence color-dot size relationships in carbon dots may actually be exploited as a unique advantage in the size reduction toward having carbon dots serve as ultracompact QD-like fluorescence probes. Here we report on carbon dots of less than 5 nm in the overall dot diameter with the use of 2,2'-(ethylenedioxy)bis(ethylamine) (EDA) molecules for the carbon particle surface passivation. The EDA-carbon dots were found to be brightly fluorescent, especially over the spectral range of green fluorescent protein. These aqueous soluble smaller carbon dots also enabled more quantitative characterizations, including the use of solution-phase NMR techniques, and the results suggested that the dot structures were relatively simple and better-defined. The potential for these smaller carbon dots to serve as fluorescence probes of overall sizes comparable to those of fluorescent proteins is discussed.

The emergence of photoluminescent carbon-based nanomaterials has shown exciting potential in the development of benign nanoprobes. However, the in vivo kinetic behaviors of these particles that are necessary for clinical translation are poorly understood to date. In this study, fluorescent carbon dots (C-dots) were synthesized and the effect of three injection routes on their fate in vivo was explored by using both near-infrared fluorescence and positron emission tomography imaging techniques. We found that C-dots are efficiently and rapidly excreted from the body after all three injection routes. The clearance rate of C-dots is ranked as intravenous > intramuscular > subcutaneous. The particles had relatively low retention in the reticuloendothelial system and showed high tumor-to-background contrast. Furthermore, different injection routes also resulted in different blood clearance patterns and tumor uptakes of C-dots. These results satisfy the need for clinical translation and should promote efforts to further investigate the possibility of using carbon-based nanoprobes in a clinical setting. More broadly, we provide a testing blueprint for in vivo behavior of nanoplatforms under various injection routes, an important step forward toward safety and efficacy analysis of nanoparticles.

In this study we report the effect of classical CdSe/ZnS quantum dots and novel spherical carbon dots on generation of singlet oxygen and other reactive oxygen species (ROS) in aqueous solutions in vitro. Free radicals were initiated either chemically using 2,2'-azodiisobutyramidine dihydrochloride (AAPH) or by radiation with a blue light source emitting 390-470 nm (peak 420 nm). Two reagents, dihydrorhodamine 123 (Dhr123) and singlet oxygen sensor green (SOSG), were used as radical probes. Quantum dots and carbon dots inhibited oxidation of the radical probes under decomposition of AAPH. However, when subjected to the blue light both the quantum dots and carbon dots induced oxidation of Dhr123 to a greater extent than SOSG in water. Generation of singlet oxygen was remarkably enhanced in deuterium oxide solutions while oxidation of Dhr123 remained unchanged. For comparison, traditional photosensitizer protoporphyrin IX mainly induced oxidation of SOSG in water. In conclusion, upon external radiation carbon dots or quantum dots generate reactive oxygen species acting as prooxidants. Carbon dots or quantum dots also scavenge free radicals that are generated chemically by an azo compound. Such dual properties of these nanoparticles can be used for photodynamic and photocatalytic or antioxidant applications.

Carbon-based "quantum" dots (or "carbon dots") are generally defined as surface-passivated small carbon nanoparticles that are brightly fluorescent. Apparently, the carbon particle surface passivation in carbon dots is critical to their fluorescence performance. An effective way to improve the surface passivation is to dope the surface of the precursor carbon nanoparticles with an inorganic salt, followed by the typical functionalization with organic molecules. In this work we passivated small carbon nanoparticles by a combination of the surface-doping with nanoscale semiconductors and the organic functionalization, coupled with gel column fractionation to harvest the most fluorescent carbon dots, which exhibited fluorescence emission quantum yields of up to 78%. Experimental and mechanistic issues relevant to potentially further improve the performance of carbon dots toward their being quantitatively fluorescent are discussed., (© The Royal Society of Chemistry 2011)

Semiconductor quantum dots and nanoparticles composed of metals, lipids or polymers have emerged with promising applications for early detection and therapy of cancer. Quantum dots with unique optical properties are commonly composed of cadmium contained semiconductors. Cadmium is potentially hazardous, and toxicity of such quantum dots to living cells, and humans, is not yet systematically investigated. Therefore, search for less toxic materials with similar targeting and optical properties is of further interest. Whereas, the investigation of luminescence nanoparticles as light sources for cancer therapy is very interesting. Despite advances in neurosurgery and radiotherapy the prognosis for patients with malignant gliomas has changed little for the last decades. Cancer treatment requires high accuracy in delivering ionizing radiation to reduce toxicity to surrounding tissues. Recently some research has been focused in developing photosensitizing quantum dots for production of radicals upon absorption of visible light. In spite of the fact that visible light is safe, this approach is suitable to treat only superficial tumours. Ionizing radiation (X-rays and gamma rays) penetrate much deeper thus offering a big advantage in treating patients with tumours in internal organs. Such concept of using quantum dots and nanoparticles to yield electrons and radicals in photodynamic and radiation therapies as well their combination is reviewed in this article.

We report that nanoscale carbon particles (carbon dots) upon simple surface passivation are strongly photoluminescent in both solution and the solid state. The luminescence emission of the carbon dots is stable against photobleaching, and there is no blinking effect. These strongly emissive carbon dots may find applications similar to or beyond those of their widely pursued silicon counterparts.

The optical properties of graphene-based nanomaterials have attracted much recent attention. This article provides an overview of recent advances in the study of linear and nonlinear optical transitions associated mostly with tailored energy bandgaps. In particular, the optical absorption characteristics and photoluminescence emissions due to various induced bandgaps and, in some cases, the formation of graphene quantum dots are highlighted. Nonlinear optical properties of these materials are reviewed with an emphasis on optical limiting through both nonlinear absorption and scattering mechanisms. [ABSTRACT FROM PUBLISHER]

Photoluminescence properties of carbon nanoparticles from different treatments in various suspensions were evaluated, and the results were in general agreement with those available in the literature. An interesting observation was that the quenching of luminescence emissions in the aqueous suspended carbon nanoparticles by aliphatic amines deviated from the classical Stern-Volmer behavior in a somewhat unusual fashion, exhibiting reversed quenching (increasing luminescence intensities) at very low quencher concentrations. The implication of the observation to the mechanistic framework that may account for photoluminescence emissions in both functionalized and naked carbon nanoparticles is proposed and discussed. On a évalué les propriétés de photoluminescence de nanoparticules de carbone obtenues par divers traitements dans des suspensions variées et les résultats obtenus sont généralement en accord avec eux qu'on retrouve dans la littérature. On a toutefois fait l'observation intéressante que la décroissance des émissions de luminescence des nanoparticules de carbone en suspension aqueuse, sous l'influence d'amines aliphatiques, dévie du comportement classique de Stern-Volmer d'une façon assez inhabituelle alors qu'elle présente une décroissance inversée (augmentation des intensités de luminescence) à des concentrations très faibles de désactivateur. On propose et on discute des implications de ces observations aux concepts mécanistiques qui pourraient expliquer les émissions de photoluminescence des nanoparticules nues ou fonctionnalisées. [ABSTRACT FROM AUTHOR]

Carbon dots, generally small carbon nanoparticles with various forms of surface passivation, have achieved the performance level of semiconductor quantum dots in the green spectral region, but their absorption and fluorescence in red/near-IR are relatively weaker. Conceptually similar to endofullerenes, host-guest carbon dots were designed and prepared with red/near-IR dyes encapsulated as guest in the carbon nanoparticle core. Beyond the desired enhancement in optical properties, the host-guest configuration may significantly broaden the field of carbon dots. [ABSTRACT FROM AUTHOR]

Carbon dots (CDots) are strongly absorptive over the visible spectrum, with the effective photon-harvesting driving rich excited state processes and properties. In this work, spectroscopic probing of these processes and properties is coupled with the evaluation of the photoinduced bactericidal function of CDots, aimed toward making correlations among the findings from the former and those from the latter on the inactivation of bacterial pathogens. Within the general mechanistic framework for CDots, the observed effective and efficient antibacterial activities of the CDots under visible light are attributed to major contributions by the initially photo-generated electrons and holes that are trapped at passivated surface defect sites of the dots, in addition to the traditional reactive oxygen species (ROS) produced in the emissive excited states from the recombination of the redox pairs. Such major contributions to the inactivation of the bacteria by the separated redox species in CDots can not be quenched by ROS scavengers commonly used in the study of photodynamic effects with classical molecular photosensitizers, thus making light-activated CDots uniquely potent antimicrobial agents. The characteristic features of photoexcited CDots and their related mechanistic implications are discussed in reference to the similar behaviors and mechanistic model of conventional semiconductor quantum dots. Image 1 [ABSTRACT FROM AUTHOR]

Carbon “quantum” dots or carbon dots, generally defined as small carbon nanoparticles with various surface passivation schemes, have emerged to represent a rapidly advancing and expanding research field. A wide variety of technological applications of carbon dots have been pursued, including especially their uses as fluorescence probes or sensors. In the work reported here, carbon dots obtained from the surface chemical functionalization of small carbon nanoparticles with 2,2′-(ethylenedioxy)bis(ethylamine) (EDA) were selected as structurally compact and defined fluorescence probes, and their interactions with nitrotoluene compounds were studied on the basis of fluorescence quenching in steady-state and time-resolved measurements. The fluorescence quenching of the carbon dots by the nitrotoluenes, which are commonly used as signature compounds for nitroaromatic explosives, was found to be extremely efficient in ambient solution, though still at the very upper-limit of diffusion-control. There were some static quenching contributions at high nitrotoluene quencher concentrations, especially for the compound that is more electron deficient, which could be rationalized in terms of some near-neighbor charge transfer interactions. Mechanistic implications of the results and the potential for carbon dots to serve as highly sensitive fluorescence probes in the detection of nitroaromatic explosives are discussed. [ABSTRACT FROM AUTHOR]

A simple yet consequential modification was made to the popular carbonization processing of citric acid - polyethylenimine precursor mixtures to produce carbon dots (CDots). The modification was primarily on pushing the carbonization processing a little harder at a higher temperature, such as the hydrothermal processing condition of around 330 °C for 6 h. The CDots thus produced are comparable in spectroscopic and other properties to those obtained in other more controlled syntheses including the deliberate chemical functionalization of pre-processed and selected small carbon nanoparticles, demonstrating the consistency in CDots and reaffirming their general definition as carbon nanoparticles with surface passivation by organic or other species. Equally significant is the finding that the modified processing of citric acid - polyethylenimine precursor mixtures could yield CDots of record-setting fluorescence performance, approaching the upper limit of being quantitatively fluorescent. Thus, the reported work serves as a demonstration on not only the need in selecting the right processing conditions and its associated opportunities in one-pot syntheses of CDots, but also the feasibility in pursuing the preparation of quantitatively fluorescent CDots, which represents an important milestone in the development and understanding of these fluorescent carbon nanomaterials. [ABSTRACT FROM AUTHOR]

Fluorescent carbon ‘quantum’ dots are generally obtained by deliberate chemical functionalization of carbon nanoparticles or by ‘one-pot’ carbonization processing. For brightly fluorescent carbon dots with optoelectronic polymers, a hybrid approach was developed to use pre-processed and selected carbon nanoparticles as precursor for surface passivation by poly(9-vinylcarbazole) (PVK) in one-pot thermochemical processing, thus taking advantage of the more controllable feature from the deliberate functionalization and also the versatility associated with the one-pot synthesis. The PVK-carbon dots were characterized by optical spectroscopy, microscopy, and other techniques. The broad applicability of the hybrid approach is discussed. [ABSTRACT FROM AUTHOR]

Carbon ‘quantum’ dots or carbon dots have emerged as a new class of luminescent nanomaterials. While photoluminescence properties of carbon dots had targeted optical imaging and related usage, their unique excited state redox processes responsible for the luminescence emissions may find potentially significant optoelectronic applications. In this regard, we investigated the electroluminescence properties of the carbon dots integrated into multilayer light emitting diode devices. The devices emitted white light with a slight blue color, visible to naked eyes, thus validating the expectation that carbon dots may potentially serve as a new platform for electroluminescent nanomaterials. [ABSTRACT FROM AUTHOR]

Carbon “quantum” dots(or carbon dots) have emergedas a new class of optical nanomaterials. Beyond the widely reportedbright fluorescence emissions in carbon dots, their excellent photoinducedredox properties that resemble those found in conventional semiconductornanostructures are equally valuable, with photon–electron conversionapplications from photovoltaics to CO2photocatalytic reduction.In this work we used gold-doped carbon dots from controlled synthesisas water-soluble catalysts for a closer examination of the visible-lightphotoconversion of CO2into small organic acids, includingacetic acid (for which the reduction requires many more electronsthan that for formic acid) and, more interestingly, for the significantlyenhanced photoconversion with higher CO2pressures overan aqueous solution of the photocatalysts. The results demonstratethe nanoscale semiconductor-equivalent nature of carbon dots, withexcellent potential in energy conversion applications. [ABSTRACT FROM AUTHOR]

Photoluminescent nanomaterials continue to garner research attention becauseof their many applications. For many years, researchers have focused on quantum dots (QDs) of semiconductor nanocrystals for their excellent performance and predictable fluorescence color variations that depend on the sizes of the nanocrystals. Even with these advantages, QDs can present some major limitations, such as the use of heavy metals in the high-performance semiconductor QDs. Therefore, researchers continue to be interested in developing new QDs or related nanomaterials. Recently, various nanoscale configurations of carbon have emerged as potential new platforms in the development of brightly photoluminescent materials. [ABSTRACT FROM AUTHOR]

• Carbon dots (CDots) exploit unique properties of small carbon nanoparticles; • Carbon/semiconductor hybrid dots substantially expand the CDots platform; • Carbon/TiO 2 dots in different compositions/configurations can be designed and prepared; • The hybrid dots can be explored for different photoexcited state properties; • The hybrid dots can serve as effective photodynamic antibacterial agents. Carbon/TiO 2 hybrid dots with the general configuration of nanoscale carbon domains incorporated with TiO 2 nanoparticles of different sizes (8 and 25 nm in diameter) were prepared and characterized, and their optical and photodynamic properties were studied. The properties were found to be affected dramatically by the relative sizes and configurations of the nanoscale carbon domains and TiO 2 nanoparticles in the hybrid dots, as reflected by the observed major difference in their photodynamic inactivation of bacteria under visible light. Mechanistic implications of the results are discussed. [ABSTRACT FROM AUTHOR]