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Carbon dots (CDs), a kind of phototheranostic agent with the capability of simultaneous bioimaging and phototherapy [i.e. photodynamic therapy (PDT) or photothermal therapy (PTT)], have received considerable attention because of their remarkable properties, including flexibility for surface modification, high biocompatibility, low toxicity and photo‐induced activity for malignant tumor cells. Among numerous carbon sources, it has been found that natural biomass are good candidates for the preparation of CD phototheranostic agents. In this study, pheophytin, a type of Mg‐free chlorophyll derivative and also a natural product with low toxicity, was used as a raw carbon source for the synthesis of CDs by using a microwave method. The obtained hydrophobic CDs exhibited a maximum near‐infrared (NIR) emission peak at approximately 680 nm, and high singlet oxygen (1O2) generation with a quantum yield of 0.62. The self‐assembled CDs from the as‐prepared CDs with DSPE‐mPEG2000 retained efficient 1O2 generation. The obtained carbon dot assembly was not only an efficient fluorescence (FL) imaging agent but also a smart PDT agent. Our studies indicated that the obtained hydrophilic CD assembly holds great potential as a new phototheranostic agent for cancer therapy. This work provides a new route for synthesis of CDs and proposes a readily available candidate for tumor treatment. [ABSTRACT FROM AUTHOR]

During the past decade, increasing attention has been paid to fluorescent carbon dots (CDs) due to their unique photoluminescence (PL) properties. As synthetic methods gradually develop, many post‐functionalization strategies have been developed to enhance the PL of CDs. However, in most cases, the PL enhancement was less than 10‐fold with multistep modification processes. In this work, a facile and efficient post‐functionalization strategy was successfully applied to enhance the PL intensity of CDs dramatically up to 69 times by surfactants at room temperature for the first time. Furthermore, the mechanism of surfactant‐induced PL enhancement of CDs was investigated and in vivo bioimaging was performed. The results demonstrated that electrostatic/non‐electrostatic interactions between CDs and surfactants could effectively lower the vibration and rotation of CDs, increase radiative decay processes and, thus, enhance the PL of CDs. This finding may provide new insights into the strategies for enhancing the PL of CDs, further broadening their potential applications. Brighter Carbon Dots: The effect of different types of surfactants on the photoluminescence of carbon dots (CDs) was investigated. The results show that interactions between carbon dots and surfactants enhance the photoluminescence of CDs. [ABSTRACT FROM AUTHOR]

Abstract: Constructing complex nanoarchitectures via self‐assembly with nanoparticle building blocks is a practical strategy that produces nanostructures with properties that are absent in the individual unit. In this work, we used hydrophilic carbon dots (C‐dots) as building blocks to form C‐dot assemblies. Compared to the individual C‐dot, the self‐assembled C‐dots showed about 30 nm red‐shift of absorption, resulting in the 5.1% increasing of photothermal conversion efficiency upon a 671 nm laser irradiation. More importantly, the C‐dot assemblies enable them can be efficiently uptaken by cancer cells. Meanwhile, in vitro study demonstrated the C‐dot assemblies can efficiently kill cancer cells than that of individual C‐dot upon irradiation for 5 min at equivalent C‐dot concentration. Our study may provide a new strategy for the efficient photothermal therapy of cancer based on C‐dots. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Multifunctional liposomes with tumor targeted drug delivery and imaging. • Enhanced photoluminescence emission of carbon dots. • Enhanced anti-cancer efficacy of cinobufagin after loading into liposomes. Abstract Integrating the optical properties of near-infrared fluorescent carbon dots into liposomes may construct a multifunctional nano-system with the potential as a drug carrier, tracer and efficacy intensifier of the anticancer agent. In this study, the liposomes loaded with hydrophilic near-infrared carbon dots as a nano-carrier and tracer of lipophilic anticancer agent cinobufagin were developed. Prepared liposomes were characterized by particle size, morphology and entrapment efficiency. The drug release behavior, the tracer function, the anticancer effect and the side effect were investigated in vitro and in vivo. It was observed that the photoluminescence emission of carbon dots could be strongly enhanced up to 5 times by nano-liposomes. Due to this property, the bio-imaging of CDs + CB liposomes in vitro and in vivo could be clearly obtained. Our results also showed that the CDs + CB liposomes could be uptaken by cells (the lysosomes targeted) and delivered to the tumor site, and undoubtedly, the CDs + CB liposomes demonstrated sustained drug release, enhanced anticancer efficacy and low side effects in vivo. With the assistance of imaging function of CDs, the CDs + CB liposomes can easily display the distribution of drugs, which is very helpful for drug development and may open a novel avenue for drug delivery. [ABSTRACT FROM AUTHOR]

The distance-dependent based sensing mechanism, such as fluorescence resonance energy transfer (FRET) and surface plasmon resonance (SPR) absorption of gold nanoparticles, has been used widely in visual detection. In this work, we report another distance-dependent detection method for nucleoside triphosphates (NTPs) based on carbon dots (CDs) ( 1 O 2 donor) and 9, 10-diphenylanthracene-2-boronic acid (DABA, 1 O 2 acceptor). The CDs can generate singlet oxygen ( 1 O 2 ) which allows diffusion within 200 nm. Thus, the distance between CDs and DABA decreased through binding of NTPs (<200 nm), leading to absorption changes of DABA under light irradiation due to 1 O 2 trapping. This sensing system (CDs@DABA) has high selectivity for the detection of NTPs due to the double molecular recognition and a linear response in the 0–80 μM concentration range was accomplished with the detection limit as low as 4.35 μM. [ABSTRACT FROM AUTHOR]

Carbon dots (CDs) have emerged as promising nanomaterials for bioimaging-guided photodynamic therapy (PDT). However, designing red-emissive CDs (RCDs) with tunable type I and type II reactive oxygen species (ROS) generation to simultaneously meet PDT applications in aerobic and hypoxic scenarios still remain major challenges. Herein, three types of RCDs with maximum emission at approximately 680 nm are successfully prepared. It is noteworthy that they exhibit the adjustable ROS production with equal superoxide anion (via type I PDT) and incremental singlet oxygen (via type II PDT). Detailed structural and optical characterizations along with theoretical calculation reveal that the unique type I/II ROS formation mainly depends on the core sizes and surface states of RCDs, which determine their identical redox potentials and tapering energy gaps between singlet- and triplet states, respectively. Additionally, due to the inherent mitochondria targeting capability, RCDs enable themselves to induce cell programmed death via activating mitochondrion-mediated apoptotic pathways. This work exploits the unprecedented RCDs with tunable type I and type II ROS generation that could ensure highly efficient tumor eradication both in vitro and in vivo, even under the harsh tumor microenvironment, providing a new prospect for CDs as nanophotosensitizers to conquer the limitations of single type PDT. Red emissive carbon dots with tunable reactive oxygen species generation are prepared to achieve highly efficient fluorescence imaging-guided type I/II photodynamic therapy via activating mitochondrion-mediated apoptotic pathways of cancer cells, providing a new prospect for carbon dots as nanophotosensitizers to conquer the limitations of single type PDT. [Display omitted] [ABSTRACT FROM AUTHOR]