Ultrasmall green-emitting carbon nanodots with 80% photoluminescence quantum yield for lysosome imaging

Multi-step strategies for synergistic treatment of urinary tract infections based on D-xylose-decorated antimicrobial peptide carbon dots

Urinary tract infections (UTIs) caused by Uropathogenic Escherichia coli (UPEC), often reoccur due to the formation of intracellular bacterial colonies (IBCs) and antibiotic resistance. Given the significance of YadC for UPEC infection in our previous study, we developed D-xylose-decorated ɛ-poly-L-lysine (εPL)-based carbon dots (D-xyl@εPLCDs) that can be traced, and employed multi-step approaches to elucidate the functional roles of D-xyl@εPLCDs in UPEC infection. Compared to undecorated particles, D-xyl@εPLCDs demonstrate YadC-dependent bacterial targeting and exhibit enhanced bactericidal activities both intracellularly and extracellularly. Moreover, pre-treatment of D-xyl@εPLCDs before infection blocked the subsequent adhesion and invasion of UPEC to bladder epithelial cells 5637. Increase of ROS production and innate immune responses were observed in bladder epithelial cells 5637 treated with D-xyl@εPLCDs. In addition, treatment of D-xyl@εPLCDs post-infection facilitated clearance of UPEC in the bladders of the UTI mouse model, and reduced ultimate number of neutrophils, macrophages and inflammatory responses raised by invaded bacteria. Collectively, we presented a comprehensive evaluating system to show that D-xyl@εPLCDs exhibits superior bactericidal effects against UPEC, making them a promising candidate for drug development in clinical UTI therapeutics.

Ultrabright Green-Emissive Nanodots for Precise Biological Visualization

Developing general methods to fabricate water-dispersible and biocompatible fluorescent probes will promote different biological visualization applications. Herein, we report a metal-facilitated method to fabricate ultrabright green-emissive nanodots via the one-step solvothermal treatment of rose bengal, ethanol, and various metal ions. These metal-doped nanodots show good water dispersity, ultrahigh photoluminescence quantum yields (PLQYs) (e.g., the PLQY of Fe-doped nanodots (FeNDs) was ∼97%), and low phototoxicity. Owing to the coordination effect of metal ions, the FeNDs realize glutathione detection with outstanding properties. Benefiting from the high endoplasmic reticulum (ER) affinity of the chloride group, the FeNDs can act as an ER tracker with long ER imaging capacity (FeNDs: >24 h; commercial ER tracker: ∼1 h) and superb photostability and can achieve tissue visualization in living Caenorhabditis elegans. The metal-doped nanodots represent a general nanodot preparation method and may shed new light on diverse biological visualization uses.

Effectively synthesized functional Si-doped carbon dots with the applications in tyrosinase detection and lysosomal imaging

There has been significant interest in the preparation and versatile applications of carbon dots (CDs) due to their immense potential value in sensors and imaging. In this work, silicon-doped green carbon dots (Si-CDs) with high quantum yield and rich epoxypropyl were effectively synthesized. Given the clinical diagnostic importance of abnormal levels of tyrosinase (TYR), sensitive detection of TYR is significant for clinical research. A fluorescence signal-off strategy with Si-CDs as probe was constructed to determine TYR based on the oxidation of dopamine by TYR. The detection ranges of this method were 0.01-1.5 and 10-30 U/mL with the detection limit of 0.0046 U/mL, the lower limit of quantification (LLOQ) was 0.01 U/mL, and TYR was successfully and accurately monitored in human serum. Additionally, due to the role of lysosomes in cellular regulatory processes, including TYR levels and fluorescence stability characteristics of Si-CDs in acidic conditions, it was envisaged to use Si-CDs as probe to establish real-time monitoring of lysosomes. According to fluorescence colocation analysis, Si-CDs had intrinsic lysosomal targeting ability to HepG2 and L-02 (with Pearson correlation coefficients were 0.90 and 0.91, respectively). The targeting of Si-CDs to lysosomes was due to the acidophilic effect of the epoxypropyl on its surface.

A dual-function fluorescent probe for the detection of pH values and formaldehyde

A dual-function fluorescent probe (Probe 1) was developed in this work for the separate detection of pH value and formaldehyde (HCHO). Probe 1 could recognize HCHO and the pH value from the amino group. The colour of the probe solution was changed from grey blue to light blue with the increase in the pH value, and luminous intensity became larger with the increase in formaldehyde concentration. The curve function relationship between fluorescence intensity and the pH value was also determined. A smartphone containing a colour detector for imaging was used to record the values of the three primary colours (R value, G value, and B value) for the probe solution in formaldehyde. Importantly, there was a linear functional relationship between the B*R/G value with HCHO concentration. Therefore, the probe could be used as a rapid tool for the detection of formaldehyde. More importantly, Probe 1 was successfully used to detect formaldehyde in an actual distilled liquor sample.

Meticulously Designed Carbon Dots as Photo-Triggered RNA-Destroyer for Evoking Pyroptosis

An ideal photosensitizer for photodynamic therapy should not only possess high reactive oxygen species (ROS) generation efficiency but also maximize utilization of the in situ produced ROS species, where the latter is closely related to its intracellular location. However, rational design of such photosensitizer without tedious conjugation procedures remains a grand challenge. Here, we report the one-pot preparation of carbon dots (CDs)-based photosensitizer from levofloxacin and neutral red featuring both high 1O2 quantum yield (φΔ = 38.85%) and superior RNA selectivity. Moreover, the φΔ value shows a further 40% improvement and reaches 54.33% in response to RNA binding. Owing to these combined attributes, the CDs could exert great damage to the cellular RNA system (termed the RNA-destroyer) under extremely low dosage of light irradiation (15 mW cm-2, 1 min). It induces pyroptotic cell death and causes rapid release of different cytokines that served as molecular markers in photodynamic immunotherapy. This work represents the meticulously designed CDs with high ROS generation and utilization efficiency via good organization of the photosensitive and targeting modularity. Moreover, it is the first CDs-based pyroptosis inducer to the best of our knowledge.

Colorimetric detection of ozone in aqueous solution and imaging in living cells using a novel hemicyanine dye

Ozone (O3) is ubiquitous in the environment and exposure to high levels of O3 has been associated with various respiratory diseases, such as asthma, emphysema, and bronchitis. Therefore, it is necessary to develop a simple and efficient detection method for monitoring O3 in the environment and living cells. In this study, an intramolecular charge-transfer (ICT) compound was designed and synthesized based on a phenol-type hemicyanine dye and 4-bromo-1-butene, which could specifically detect O3 in aqueous solution. Due to the ICT process, the absorption spectrum, fluorescence spectrum, and color of the probe hemicyanine-butyl-3-enyl (HCB) changed significantly and thus the rapid and sensitive detection of O3 was realized. The interaction between O3 and the probe HCB could be completed within 40 min, and the detection limit of O3 was as low as 2.15 × 10-7 mol L-1. Finally, the proposed method was successfully applied to the visual detection of O3 in a simulated O3 environment and living cells.

Chiral dual-emission composite material fluorescein/CCQDs @ZIF-8 for highly efficient recognition of phenylenediamine isomers and their oxidized product

As a new type of fluorescent nanomaterial, chiral carbon quantum dots (CCQDs) have the advantages of wide source, good water solubility and high chemical stability, and have been widely used in drug detection, bioimaging and chemical sensing. In this work, a chiral dual-emission hybrid material fluorescein/CCQDs@ZIF-8 (1) was synthesized by in-situ encapsulation strategy. Luminescence emission position of CCQDs and fluorescein are almost unchanged after the encapsulation into ZIF-8. The luminescent emissions of CCQDs and fluorescein can be observed to be located at 430 nm and 513 nm, respectively. When 1 is soaked in pure water, ethanol, dimethylsulfoxide, DMF, DMA and targeted substances solution for 24 h, 1 can maintain its structural stability. Photo-luminescent (PL) studies show that 1 can discriminate p-phenylenediamine (PPD) from m-phenylenediamine (MPD) and o-phenylenediamine (OPD), which can detect the presence of PPD with high sensitivity and selectivity (ratiomeric fluorescent probe with K_BH: 1.85 × 10³ M^-1 and detection limit: 8.51 μM). Further, 1 also effectively distinguish the oxidized product of these phenylenediamine(PD) isomers. 1 can be used as a "turn-off" fluorescent probe to detect oxidized product of PPD (ratiomeric fluorescent probe with K_SV: 6.82 × 10² M^-1 and detection limit: 0.112 mM) and a "turn-on" fluorescent probe to detect oxidized product of MPD (ratiomeric fluorescent probe: K_BH: 1.65 × 10³ M^-1 and detection limit: 35.03 μM) and oxidized product of OPD (ratiomeric fluorescent probe: K_BH: 2.40 × 10⁶ M^-1 and detection limit: 0.105 μM). Further, for the convenience of practical application, 1 can be developed as fluorescence ink and be prepared into a mixed matrix membrane. When the target substances are gradually added to the membrane, significant luminescence change with obvious color change can be observed.

A Lysosome-Targeted Near-Infrared Fluorescent Probe with Excellent Water Solubility for Surgery Navigation in Breast Cancer

To get a tumor-targeted contrast agent for imaging guide resection of tumors, we designed a novel fluorescent probe based on the heptamethine cyanine core, Cy7-MO, which has excellent water solubility and near-infrared photophysical and lysosomal targeting properties. The chemical structure of Cy7-MO was characterized by nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry. The toxicity of Cy7-MO was evaluated by cell counting kit-8. Then, a cellular-level study was conducted to evaluate the suborganelle localization in 4T1-Luc1 cells, and it was also used for surgical navigation in orthotopic breast tumor resection in vivo. The results showed that Cy7-MO was well targeted to lysosomes. Importantly, the Cy7-MO probe was found to be well tolerable and exhibited excellent biocompatibility. Moreover, the orthotopic breast tumor margin was clearly visualized through fluorescence guiding of Cy7-MO. Finally, the correct tumor tissues were completely removed, and a negative margin was obtained successfully, which demonstrated an enhanced precision of surgery.

Nanokit coupled electrospray ionization mass spectrometry for analysis of angiotensin converting enzyme 2 activity in single living cell

Angiotensin-converting enzyme 2 (ACE2) is not only an enzyme but also a functional receptor on cell membrane for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Here, the activity of ACE2 in single living cell is firstly determined using a nanokit coupled electrospray ionization mass spectrometry (nanokit-ESI-MS). Upon the insertion of a micro-capillary into the living hACE2-CHO cell and the electrochemical sorting of the cytosol, the target ACE2 enzyme hydrolyses angiotensin II inside the capillary to generate angiotensin 1-7. After the electrospray of the mixture at the tip of the capillary, the product is differentiated from the substrate in molecular weight to achieve the detection of ACE2 activity in single cells. The further measurement illustrates that the inflammatory state of cells does not lead to the significant change of ACE2 catalytic activity, which elucidates the relationship between intracellular ACE2 activity and inflammation at single cell level. The established strategy will provide a specific analytical method for further studying the role of ACE2 in the process of virus infection, and extend the application of nanokit based single cell analysis.

Novel Green Fluorescent Probe Stem From Carbon Quantum Dots for Specific Recognition of Tyrosinase in Serum and Living Cells

Tyrosinase (TYR), an important biomarker for melanoma, offered significant information early detection of melanoma and may decrease the likelihood of mortality. Therefore, this article constructed a highly sensitive and selective green fluorescent functionalized carbon quantum dots (TYR-CQDs) for tyrosinase (TYR) activity detection by one-step hydrothermal protocol utilizing catechol, citric acid and urea as precursors. The prepared TYR-CQDs illustrated excellent linear relationship and broad linear range with a low detection limit, which exhibited high accuracy and recovery in quantitative determination of TYR in human serum samples. Furthermore, the TYR-CQDs had successfully realized intracellular TYR detection owing to excellent biocompatibility, high anti-interference ability and good cellular imaging capability, suggesting the potential biomedical applications in early diagnosis of melanoma and other tyrosinase-related diseases.

Highly efficient carbon dots for quantitatively visualizing pH fluctuations in cells, zebrafish, mice and tumors

In vivo pH is closely related to complicated physiological and pathological processes. Quantitatively probing pH and visualizing pH variation via fluorescence (FL) imaging technique in living cells and organisms is crucial but difficult to accomplish. Herein, green fluorescent carbon dots (CDs) were synthesized, and their distinct advantages of extraordinarily high fluorescence quantum yield (FQY, 71.4%), unique photostability, high selectivity, sterling biocompatibility, appropriate pKa for biosensing, enable CDs to serve as pH-activatable probes for real time quantitative detection of continuous pH fluctuation in living cells, zebrafish, mice and tumors. We believe CDs are presently among the best-of-breed pH probes for comprehensive biomedical applications.

Multifunctional N,S-doped and methionine functionalized carbon dots for on-off-on Fe3+ and ascorbic acid sensing, cell imaging, and fluorescent ink applying

Fluorescent carbon dots (CDs) have been identified as potential nanosensors and attracted tremendous research interests in wide areas including anti-counterfeiting, environmental and biological sensing and imaging in considering of the attractive optical properties. In this work, we present a CDs based fluorescent sensor from polyvinylpyrrolidone, citric acid, and methionine as precursors by hydrothermal approach. The selective quantifying of Fe3+ and ascorbic acid (AA) are based on the fluorescent on-off-on process, in which the fluorescent quenching is induced by the coordination of the Fe3+ on the surface of the CDs, while the fluorescence recovery is mainly attributed to redox reaction between Fe3+ and AA, breaking the coordination and bringing the fluorescence back. Inspired by the good water solubility and biocompatibility, significant photostability, superior photobleaching resistance as well as high selectivity, sensitivity, and interference immunity, which are constructed mainly from the N,S-doping and methionine surface functionalization, the CDs have not only been employed as fluorescence ink in multiple anti-counterfeiting printing and confidential document writing or transmitting, but also been developed as promising fluorescence sensors in solution and solid by CDs doped test strips and hydrogels for effectively monitoring and removing of Fe3+ and AA in environmental aqueous solution. The CDs have been also implemented as effective diagnostic candidates for imaging and tracking of Fe3+ and AA in living cells, accelerating the understanding of their function and importance in related biological processes for the prevention and treatment specific diseases.

Electronic Supplementary Material

Supplementary material (fluorescence spectra: UV and Xe irradiation, TG, thermo stability, ionic strength, relationship between fluorescence responses at different concentrations of Fe3+ and AA, reaction time-dependent fluorescent responses; XPS spectra of CDs + Fe3+ and Fe3+@CDs + AA; structural characterization; equations about fluorescence lifetime, quantum yield and LOD; comparison of the CDs for the detection of Fe3+ and AA with reported methods; detection of Fe3+ and AA in real samples; absorption of Fe3+ in environmental samples and MTT assay results) is available in the online version of this article at 10.1007/s12274-022-5107-7.

Unprecedented Chiral Nanovaccines for Significantly Enhanced Cancer Immunotherapy

As a representative strategy for cancer immunotherapy, cancer nanovaccines have aroused enormous interest. Although various nanovaccines have been developed to promote immunogenicity and improve the therapeutic efficacy, chiral nanovaccines have been less explored as of yet. Chiral carbon dots (CDs) have similar size to proteins, abundant functional groups, and nanoscale chirality, which can not only carry and deliver antigens but also induce cellular and humoral immune responses and can play dual roles of nanovehicles and immune adjuvants. Herein, we demonstrate that the chiral nanovaccines (l/d-OVA) could be conveniently fabricated by utilizing chiral CDs as carriers and immune adjuvants and ovalbumin (OVA) as an antigen model. l/d-OVA nanovaccines could be effectively internalized by mouse bone-marrow-derived dendritic cells (BMDCs), boost BMDC maturation, efficiently cross-present to T cells, and suppress the growth of B16-OVA melanoma. This work illustrates the hopeful potential of chiral CDs as effective vectors for loading protein cargos and delivering them into cancer cells.

Modulation of the binding ability to biomacromolecule, cytotoxicity and cellular imaging property for ionic liquid mediated carbon dots

For the preparation of carbon dots (CDs), a variety of carbon sources and synthetic protocols are available which endow CDs with variable and unpredictable properties. In the present study, three CDs were developed with ionic liquid 1-butyl-3-methylimidazolium dicyanamide as the precursor through ethanol-thermal and hydrothermal strategies, termed as E-CDs and H-CDs, respectively. The features of these carbon dots, i.e., their physicochemical and optical properties, their interactions with bovine serum albumin (BSA) as well as their imaging capability were investigated with respect to the CDs prepared with microwave assisted approach (W-CDs). E-CDs and H-CDs were demonstrated to exhibit similar framework structures and optical properties, and they exhibited larger particle-sizes than that of W-CDs. In addition, the increase of ethanol-thermal and hydrothermal reaction time strengthened the quantum yields of the CDs and promoted their binding capability with BSA. E-CDs and H-CDs showed similar cytotoxicity on normal (LX-2) and cancer (SK-Hep-1) cells. We further found that these CDs may readily enter the cells within 5 min, while the fluorescence of hydrophilic E-CDs and H-CDs was very weak with respect to that of hydrophobic W-CDs in cell imaging. On the other hand, all the CDs exhibited little impact on the level of intracellular reactive oxygen species. The present study is conducive to guide the preparation of suitable carbon dots for different application scenarios.

Smart contact lens containing hyaluronate-rose bengal conjugate for biophotonic myopia vision correction

As the collagen layer weakens with increasing age or certain diseases such as keratoconus and myopia, the mechanical property of the collagen layer decreases with corneal deformation. To circumvent these problems, the corneal collagen has been crosslinked with the photosensitizer riboflavin under UV light after de-epithelialization. However, this treatment with riboflavin and UV light can cause notable damage to the eye. Here, the biocompatible rose bengal (RB) dye was conjugated to hyaluronic acid (HA) to enhance the corneal permeability, which can be activated by safe green light with a wavelength of 530 nm. Two-photon microscopy revealed the deep tissue penetration of the HA-RB conjugate in comparison with RB. Collagen fibrillogenesis, ex vivo tensile test, and ex vivo histological analysis confirmed the effective collagen crosslinking by HA-RB conjugate and the light irradiation. Furthermore, we developed a smart contact lens for on-demand HA-RB conjugate delivery from the reservoir embedded in the contact lens. Taken together, we could envision the feasibility of a smart contact lens for biophotonic myopia vision correction.

ZIF-based carbon dots with lysosome-Golgi transport property as visualization platform for deep tumour therapy via hierarchical size/charge dual-transform and transcytosis

The poor penetration of nanomaterials in solid tumours and difficulty in monitoring their penetration depth are major obstacles in their application for the treatment of solid tumours. Herein, pH-responsive carbon dots (ZCD) based on a zeolitic imidazolate framework (ZIF-8) were fabricated to achieve the deep delivery of the chemotherapeutic doxorubicin (DOX) via a hierarchical size/charge dual-transformation and transcytosis. The as-prepared ZCD accumulated in the solid tumour and the acidic tumour microenvironment further triggered its decomposition. Firstly, ZCD was decomposed by the weakly acidic extracellular microenvironment of the solid tumour, enabling it to transform into small and neutrally charged particles. Subsequently, these particles were endocytosed by lysosomes, and further disintegrated into smaller and positively charged particles, which could target the Golgi apparatus. Consequently, ZCD delivered DOX deep into the solid tumour via a size-shrinking strategy and Golgi-mediated transcytosis, thus significantly improving its antitumour efficacy. In addition, carbonization endowed ZCD with superior fluorescence property, which was enhanced in the acidic microenvironment, thus improving the sensitivity and accuracy of ex vivo monitoring of the penetration depth of the nanomedicine in real time. Collectively, our results confirmed that the carbon dots obtained via the direct carbonization of ZIF-8 simultaneously exhibited enhanced deep penetration into solid tumours and fluorescence, which could be monitored, and that the carbonization of functional materials is effective to enhance their fluorescence, and further broaden their applications.

Carbon Dots in Biomedicine: A Review

Despite the rapid development of science and technology, the effective treatment of cancer still threatens human life and health. However, the success of cancer treatment is closely related to early diagnosis, identification, and effective treatment. In recent years, with the strengthening of the development and research of nanomaterials for cancer diagnosis and treatment, researchers have found that carbon dots (CDs) have the advantages of wide absorption, excellent biocompatibility, diverse imaging characteristics, and photostability and are widely used in various fields, such as sensing, imaging, and drug/gene transportation. Recently, researchers also discovered that CDs could be used as an effective photosensitizer to generate active oxygen or convert light energy into heat under the stimulation of the external lasers, making them have the effects of photothermal and photodynamic therapy for cancer. In this review, we first outline the single-modal and multimodal imaging analysis of CDs in cancer cells. After introducing diversified imaging functions, we focused on the design and the latest research progress of CDs in phototherapy and introduced in detail the strategies of CDs in phototherapy treatment and the challenges faced by clinical applications. We hope that this overview can provide important insights for researchers and accelerate the pace of research on CDs in imaging-guided phototherapy treatment.

Nitrogen-doped carbon quantum dots as fluorescent nanosensor for selective determination and cellular imaging of ClO. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2022;271:120941. [PMID: 35114635 DOI: 10.1016/j.saa.2022.120941]

The carbon nanomaterial based fluorescent probes have been widely applied in biological imaging. In the current research, we propose an interesting strategy for selective sensing of hypochlorite (ClO^-) by a water-soluble and highly fluorescent nanosensor based on the N-doped carbon quantum dots (CDs) which was fabricated by a facile and environmental friendly hydrothermal approach from polyvinyl pyrrolidone, L-arginine and tryptophan. The structural characteristics of the probe were measured by multitudinous methods which proved the nanometer spherical structure of the probe and the successfully N-doping. Fluorescent investigation demonstrated that the probe is not only highly stable under interferences of pH, ionic strength, and irradiation, but also significantly selective toward ClO^- amongst a variety of attractive bioactive species through the fluorescent quenching process which was correlative with the concentration of ClO^- and linearly in the range of 0.1-50 μmol·L^-1 with the sensitivity of 0.03 μmol·L^-1. The probe can also be further illustrated in a prospective application for determination of ClO^- in environmental water through both solution response and filer paper sensing. Moreover, the positive biocompatibility and ignorable cytotoxicity made the probe a promising effective agent for detection and visualizing ClO^- in living cells which can facilitate the understanding the oxidative stress from the overexpressing ClO^-.

An insight into the potentials of carbon dots for in vitro live-cell imaging: recent progress, challenges, and prospects

Carbon dots (CDs) are a strong alternative to conventional fluorescent probes for cell imaging due to their brightness, photostability, tunable fluorescence emission, low toxicity, inexpensive preparation, and chemical diversity. Improving the targeting efficiency by modulation of the surface functional groups and understanding the mechanisms of targeted imaging are the most challenging issues in cell imaging by CDs. Firstly, we briefly discuss important features of fluorescent CDs for live-cell imaging application in this review. Then, the newest modulated CDs for targeted live-cell imaging of whole-cell, cell organelles, pH, ions, small molecules, and proteins are elaborately discussed, and their challenges in these fields are explained.

Rose Bengal-Derived Ultrabright Sulfur-Doped Carbon Dots for Fast Discrimination between Live and Dead Cells

The discrimination between dead and live cells is crucial for cell viability evaluation. Carbon dots (CDs), with advantages like simple and cost-effective synthesis, excellent biocompatibility, and high photostability, have shown potential for realizing selective live/dead cell staining. However, most of the developed CDs with the live/dead cell discrimination capacity usually have low photoluminescence quantum yields (PLQYs) and excitation wavelength-dependent fluorescence emission (which can cause fluorescence overlap with other fluorescent probes and make dual-color live/dead staining impossible), and hence, developing ultrabright CDs with excitation wavelength-independent fluorescence emission property for live/dead cell discrimination becomes an important task. Here, using a one-pot hydrothermal method, we prepared ultrasmall (∼1.6 nm), ultrabright (PLQY: ∼78%), and excitation wavelength-independent sulfur-doped carbon dots (termed S-CDs) using rose bengal and 1,4-dimercaptobenzene as raw materials and demonstrated that the S-CDs could rapidly (∼5 min) and accurately distinguish dead cells from live ones for almost all the cell types including bacterial, fungal, and animal cells in a wash-free manner. We confirmed that the S-CDs could rapidly pass through the dead cell surfaces to enter the interior of the dead cells, thus visualizing these dead cells. In contrast, the S-CDs could not enter the interior of live cells and thus could not stain these live cells. We further verified that the S-CDs presented better biocompatibility and higher photostability than the commercial live/dead staining dye propidium iodide, ensuring its bright application prospect in cell imaging and cell viability assessment. Overall, this work develops a type of CDs capable of realizing the live/dead cell discrimination of almost all the cell types (bacterial, fungal, and animal cells), which has seldom been achieved by other fluorescent nanoprobes.

F,N-Doped carbon dots as efficient Type I photosensitizers for photodynamic therapy

Photodynamic therapy (PDT) is a promising and emerging method for the treatment of cancer. Usually, Type II PDT is used in the clinic, and mainly involves three key elements: a photosensitizer, molecular oxygen and laser light. However, it is known that tumor tissue is deficient in oxygen molecules which is why Type I PDT is mostly preferred in the therapy of tumors in which the hypoxic tissue plays a major role. Fluorescent carbon dots (CDs) have shown great potential in cancer theranostics, acting as bioimaging agents and photosensitizers. Herein, we have synthesized novel kinds of fluorine and nitrogen co-doped carbon dots (F,NCDs) that emit bright green fluorescence under ultra-violet light. The F,NCDs have excellent water solubility and low cytotoxicity. They can generate hydroxyl radicals (˙OH) and superoxide anions (˙O2-) under LED light (400-500 nm, 15 mW cm-2) irradiation, making them ideal photosensitizers for Type I PDT. Furthermore, upon using the HepG2 cell line as an in vitro model, the F,NCDs exhibit a better cell imaging effect and higher PDT efficiency than the control sample of CDs without F and N doping. This work has illustrated that the F,NCDs are promising in achieving the image-guided PDT of cancers, usually in a hypoxia tumor microenvironment.

Antimicrobial carbon-dot–stabilized silver nanoparticles

Carbon-dot–stabilized silver nanoparticles (CD–AgNPs) with high stability and low toxicity exhibit good antibacterial activity and broad-spectrum performance.

Chiral Carbon Dots-Enzyme Nanoreactors with Enhanced Catalytic Activity for Cancer Therapy

As a class of functional proteins, enzymes possess inherent insignificant features, for instance, mediocre stability and membrane impermeability and reduced enzymatic activity after modification, which partly limit their biomedical applications. Thus, it is indispensable to exploit robust nanoreactors with high enzymatic activity and good stability and cell permeability. Here, the chiral carbon dots (CDs)-glucose oxidase (GOx) nanoreactors named LGOx and DGOx were constructed by the coassembly of GOx with L/D-CDs, respectively. L/DGOx can significantly enhance the activity of GOx and improve the efficient delivery of GOx to cancer cells. Moreover, these nanoreactors can generate hydrogen peroxide to efficaciously kill cancer cells and restrain tumor growth, and DGOx exhibits higher enzymatic activity than LGOx. According to our understanding, this is the first report about utilizing chiral CDs as vectors to construct effective CDs-enzyme nanohybrids for cancer therapy, which is envisioned to be a versatile strategy for multitudinous biomedical applications.

Near-Infrared Light-Triggered Lysosome-Targetable Carbon Dots for Photothermal Therapy of Cancer

Photothermal therapy (PTT) has inherent advantages in the treatment of hypoxic tumors due to its optically controlled selectivity on tumor ablation and oxygen-independent nature. The subcellular organelle-targeting capability and photothermal conversion efficiency (PCE) at near-infrared (NIR) wavelength are the key parameters in the assessment of the photothermal agent (PTA). Here, we report that carbon dots (CDs) prepared by the hydrothermal treatment of coronene derivatives show a high PCE of 54.7% at 808 nm, which can be attributed to the narrow band gap and the presence of amounts of continuous energy bands on CDs. Moreover, the vibrations in the layered graphite structures of the CDs also increase the rate of nonradiative transition and thus enhance the PCE. Furthermore, the CDs also possess excellent photostability, biocompatibility, and cell penetration capability and could mainly accumulate in the lysosomes. These experiment results have proved that the CDs are suitable as an efficient NIR light-triggered PTA for efficient PTT against cancer.

One-step fabrication of functional carbon dots with long wavelength emission for gene delivery and bio-imaging

As a new-type of fluorescent material, carbon dots (CDs) are promising nanoscale reagents with the potential to integrate the functions of bio-imaging and gene/drug delivery. Most of the reported CDs for nucleic acid delivery only emitted short-wavelength (blue and green) fluorescence, making them unsuitable for in vivo application. Herein, a one-step solvothermal method was applied to prepare CDs with long wavelength emission from low molecular weight PEI and rhodamine dyes for both bio-imaging and gene delivery. The structure of the CDs was confirmed by several analytical methods including ¹H NMR, FT-IR, TEM, and XPS. The results showed that the CDs possess excellent fluorescence properties, which enable their application in both in vitro and in vivo bio-imaging. Meanwhile, the CDs could also be used for the intracellular tracking of the gene delivery process. In vitro transfection results revealed that the CDs possessed high transfection efficiency, which was up to 162 times higher than that of the "golden standard" transfection reagent PEI 25 kDa. Besides, these CDs also exhibited better serum tolerance and lower cytotoxicity than PEI. A mechanistic study suggested that the CD/DNA complexes may release the nucleic acid cargo more effectively. This work provides a new method to prepare multi-functional CDs with non-viral gene delivery and long wavelength bio-imaging abilities.

Rationally designed upconversion nanoparticles for NIR light-controlled lysosomal escape and nucleus-based photodynamic therapy

Cell nucleus-based photodynamic therapy is a highly effective method for cancer therapy, but it is still challenging to design nucleus-targeting photosensitizers. Here, we propose the "one treatment, multiple irradiations" strategy to achieve nucleus-based photodynamic therapy using the photosensitizer rose bengal (RB)-loaded and mesoporous silica-coated upconversion nanoparticles with the surface modification of amine group (UCNP/RB@mSiO₂-NH₂ NPs). After implementation into cancer cells, the rationally designed UCNP/RB@mSiO₂-NH₂ NPs could be specifically accumulated in the acidic lysosomes due to their amino group-decorated surface. Upon a short-term (3 min) irradiation of 980 nm near-infrared light, the reactive oxygen species produced by RB through the Förster resonance energy transfer between the upconversion nanoparticles and RB molecules could effectively destroy lysosomes, followed by the release of the UCNP/RB@mSiO₂-NH₂ NPs from the lysosomes. Subsequently, these released UCNP/RB@mSiO₂-NH₂ NPs could be transferred into the cell nucleus, where a second 980 nm light irradiation was conducted to achieve the nucleus-based photodynamic therapy. The rationally designed UCNP/RB@mSiO₂-NH₂ NPs showed excellent anticancer performance in both two-dimensional and three-dimensional cell models using the "one treatment, multiple irradiations" strategy.