Preparation of carbon dot-based ratiometric fluorescent probes for cellular imaging from Curcuma longa.

This work derived biocompatible and stable probes based on fluorescent nanoparticles (FNPs) from a natural source, Curcuma longa. The multi-color fluorescence emissions from carbonized Curcuma longa (C-FNPs) obtained through defined dehydration conditions are soluble in water and have a small particle size (~17 nm). The surface passivation with polyethylene glycol (PEG) capped with amine groups in FNPs (P-FNPs) generated a probe with a higher quantum yield and longer fluorescence lifetime than obtained with C-FNPs. The X-ray photoelectron spectroscopy and X-ray diffraction spectra confirmed the associated chemical moieties of C-FNPs and P-FNPs. Furthermore, the prepared material showed non-toxic effects with almost 100% cell viability, even at high concentrations. In conclusion, fluorescence sensors from natural sources may be useful for numerous biomedical research applications.

Determination of Cancer Cell-Based pH-Sensitive Fluorescent Carbon Nanoparticles of Cross-Linked Polydopamine by Fluorescence Sensing of Alkaline Phosphatase Activity on Coated Surfaces and Aqueous Solution.

The tumor-specific sensitive fluorescence sensing of cellular alkaline phosphatase (ALP) activity on the basis of host-guest specific and pH sensitivity was conducted on coated surfaces and aqueous states. Cross-linked fluorescent nanoparticles (C-FNP) consisting of ß-cyclodextrin (ß-CD)/boronic acid (BA) and fluorescent hyaluronic acid [FNP(HA)] were conjugated to fluorescent polydopamine [FNP(pDA)]. To determine the quenching effect of this system, hydrolysis of 4-nitrophenyl phosphate (NPP) to 4-nitrophenol (NP) was performed in the cavity of ß-CD in the presence of ALP activated photoinduced electron transfer (PET) between NP and C-FNP. At an ALP level of 30-1000 U/L, NP caused off-emission of C-FNP because of their specific host-guest recognition. Fluorescence can be recovered under pH shock due to cleavage of the diol bond between ß-CD and BA, resulting in release of NP from the fluorescent system. Sensitivity of the assays was assessed by confocal imaging not only in aqueous states, but also for the first time on coated surfaces in MDAMB-231 and MDCK cells. This novel system demonstrated high sensitivity to ALP through generation of good electron donor/acceptor pair during the PET process. Therefore, this fluorescence sensor system can be used to enhance ALP monitoring and cancer diagnosis on both coated surfaces and in aqueous states in clinical settings.

Boronate-based fluorescent carbon dot for rapid and selectively bacterial sensing by luminescence off/on system.

Boronic acid, which can bind chemo-selectively and reversibly to diols, could be used for the early detection of bacteria through its affinity-binding reaction with diol groups on the bacterial cell wall. Herein, we describe the use of a diol-modified fluorescent probe (DYE) conjugated to a nanosensor consisting of phenylboronic acid-functionalized fluorescent carbon dot (FCD) to allow quenching via the Förster resonance energy transfer (FRET) process. Phenylboronic acid is well-known for its preferential affinity for diol-containing molecules through cyclic ester bond formation. Therefore, in the presence of glucose-containing bacteria, the DYE in the cyclic ester form will be released from the FCD and replaced by the bacterial cell forming a new cyclic boronate ester bond with the nanoparticle, inducing recovery of the fluorescence. Quantitatively, the system's detection performance at various bacterial concentrations (101-107 CFU/mL) reached ∼100% after 60 min, indicating that the high binding affinity of the diol moeity on the peptidoglycan (sugar)-rich bacteria was enough to displace the DYE from the boronic acid-functionalized FCD platform. Our facile and tunable fluorescence switch-on system was tested for its ability to detect bacteria in water from a contaminated river. Incredibly, the system was most successful in detecting bacteria in the contaminated river water, thus proving it to be a less expensive and more robust affinity biosensor for the detection of contaminating pathogens in various chemoselective ligand-based environments.

pH/Redox-Triggered Photothermal Treatment for Cancer Therapy Based on a Dual-Responsive Cationic Polymer Dot.

In the present study, a pH/redox-responsive cationic polymer dot (CD) was successfully prepared for a near-infrared (NIR)-mediated, simultaneously controllable photothermal temperature guided imaging off/on system to monitor therapeutic delivery. Carbonized disulfide cross-linked branched polyethyleneimine (bPEI) was conjugated with folic acid (FA) as a targeting moiety and partially formed an ionic complex with anionic indocyanine green (ICG) to afford a bPEI-based CD (ICG-CD). This was responsive to mild reductive (glutathione, GSH) and acidic tumor conditions, which enabled the simultaneous biodegradation of those hydrophobic and complex sites. The ICG-CD internalized readily into the cytoplasm of cancer cells by a FA receptor and cationic-mediated endocytosis in the off state, whereas if ICG-CD met intracellular GSH at high concentrations, GSH contributed partially to the recovery of fluorescence and was then internalized into acidic endosomes to induce complete restoration of fluorescence. This tumor-sensitive degradability of the CD not only facilitated ICG release in the tumor location but also allowed controllable photothermal therapy effects of nanoparticles under NIR irradiation, which resulted in improved cancer therapy. Taken together, the results indicate great potential in tumor targeting, intracellular imaging, and controllable therapeutic delivery through a fluorescence off/on assay under the pH/redox conditions of cancer cells.

Progress in internal/external stimuli responsive fluorescent carbon nanoparticles for theranostic and sensing applications.

In the past decade, fluorescent carbon nanoparticles (FNPs) prepared from natural resources and biomaterials have been attractive due to their various properties, such as unique optical properties, great biocompatibility, water dispersion, and facile surface functionalization. Depending on the properties of the carbon sources and the subsequent carbonization processes, internal/external stimuli responsive carbon nanoparticles have been generated that are useful for theranostic and sensing applications. In this review, we highlight the recent developments in the use of FNPs in nanomedicine in great detail, particularly for FNPs responding to internal stimuli, including redox, pH, and enzymes, and external stimuli, including temperature, light, and magnetic fields, for drug delivery and sensing applications. Furthermore, we hope to provide insight that could stimulate further research aiming for unparalleled useful applications. As a result, there are many possibilities that can be explored from this smart material.

Membrane and nucleus targeting for highly sensitive cancer cell detection using pyrophosphate and alkaline phosphatase activity-mediated fluorescence switching of functionalized carbon dots.

A specific membrane and nucleus targeted fluorescence OFF-ON-OFF system, using the dodecane/sulfobetaine group of functionalized carbon dots (CD) with a copper ion (Cu2+-CD) based on the presence of pyrophosphate (PPi) molecules and alkaline phosphatase (ALP) activity, for cancer cell detection was designed. The biosensor could be effectively transported from the cytosol to the nucleus in MDAMB cells, but not in MDCK cells due to the response to a change in pH by CD functionalized with zwitterionic groups. The biosensor also showed a membrane-selective regulated route for fusion of long alkyl chain grafted-CD on cell membranes. As a potential sensor, the fluorescence of the prepared Cu2+-CD was significantly quenched due to aggregation. In human cancer MDAMB cells, a nearly complete restoration of the fluorescence intensity of the Cu2+-CD was observed because of the high levels of intracellular PPi, which preferentially bound to Cu2+. After 10 min, in the MDAMB cells, re-quenching of the CD fluorescence occurred because of the high level of intracellular ALP, which can hydrolyze PPi and release the Cu2+ to re-aggregate the CD. In contrast to MDAMB cells, MDCK cells did not show an obvious response to the specific intracellular biomolecules, thus, enabling the biosensor to be used to distinguish between cancer and normal cells. In conclusion, this biosensor has the potential to be a simple and sensitive cancer diagnostic tool that can differentiate normal cells from cancer cells on coated surfaces and in aqueous states.

pH-Responsible fluorescent carbon nanoparticles for tumor selective theranostics via pH-turn on/off fluorescence and photothermal effect in vivo and in vitro.

We developed nanoparticles comprising a photothermal dye (IR825)-loaded carbonized zwitterionic polymer [FNP-I] as "switch-on" pH-responsive fluorescence probes to sense intracellular cancer cells and for near-infrared (NIR) controllable photothermal therapy (PTT) in vivo and in vitro. The fluorescent "off" of FNP-I was activated after reaching the cancer cell environment, where the zwitterionic compartment of FNP lost its hydrophobicity to induce PTT-mediated heat release of IR825 under NIR irradiation in the tumor. Approximately 100% of the IR825 was released from the FNP core to generate high thermal conversion to completely kill the cancer cells. Furthermore, after intravenous treatment of FNP-I into MDAMB-231-cell bearing mice, pH-responsive photothermal therapy was observed, achieving marked ablation of tumor cells with release of IR825 under tumor environment conditions. In addition, fluorescent signals were clearly found at the tumor site after 3 h, decreasing at the 6 h time point. The in vitro and in vivo detection system demonstrated good cellular uptake and biocompatibility as a potential imaging-guided photothermal therapy nanotool for cancer treatment. Interestingly, the synergism of the biosensor and PTT in single FNP-I platform led to more effective cancer cell killing than either monotherapy, providing a new approach for cancer treatment.

Redox-responsive FRET-based polymer dot with BODIPY for fluorescence imaging-guided chemotherapy of tumor.

Redox-responsive polymer dot (PD) were synthesized from disulfide cross-linked polymers in a carbonized process to allow quenching effects by loading of boron-dipyrromethene (BODIPY) onto the matrix. The disulfide linkage facilitated degradation of the PD system by intracellular glutathione (GSH), leading to fluorescence recovery by BODIPY and intracellular drug release. The paclitaxel release profile showed that approximately 100% of the drug escaped from the matrix in response to 10 mM GSH, whereas less than 10% was released in the absence of GSH. In vitro studies showed that quenching produced by BODIPY loading enabled visual monitoring of cancer cell death, as the quenching disappeared when BODIPY was released by GSH inside of cancer cells. The PD contain disulfide bonds representing a GSH-triggered ligand; thus, nanocarriers presented enhanced in vivo chemotherapeutic inhibition in xenograft tumor-bearing mice localized at the cancer location, guided by fluorescent off-on system tracking and measured by the release of BODIPY. This platform reacts to the redox level in sensitive manner and cancer cell death can be monitored by fluorescence, making this platform useful for bio-applications, particularly in vitro and in vivo therapy and diagnosis, while considering the cell physiological environment. This system may be useful for wider medical applications.

Dual-Responsive Carbon Dot for pH/Redox-Triggered Fluorescence Imaging with Controllable Photothermal Ablation Therapy of Cancer.

Herein we describe fluorescence resonance energy transfer (FRET) for a pH/redox-activatable fluorescent carbon dot (FNP) to realize "off-on" switched imaging-guided controllable photothermal therapy (PTT). The FNP is a carbonized self-crosslinked polymer that allows IR825 loading (FNP[IR825]) via hydrophobic interactions for cancer therapy. Fluorescence bioimaging was achieved by the internalization of FNP(IR825) into tumor cells, wherein glutathione (GSH) disulfide bonds are reduced, and benzoic imine groups are cleaved under acidic conditions. The release of IR825 from the FNP core in this system may be used to efficiently control PTT-mediated cancer therapy via its photothermal conversion after near-infrared (NIR) irradiation. In vitro and in vivo cellular uptake studies revealed efficient uptake of FNP(IR825) by tumor cells to treat the disease site. In this way we demonstrated in mice that our smart nanocarrier can effectively kill tumor cells under exposure to a NIR laser, and that the particles are biocompatible with various organs. This platform responds sensitively to the exogenous environment inside the cancer cells and may selectively induce the release of PTT-mediated cytotoxicity. Furthermore, this platform may be useful for monitoring the elimination of cancer cells through the fluorescence on/off switch, which can be used for various applications in the field of cancer cell therapy and diagnosis.

Design of Surface-Coatable NIR-Responsive Fluorescent Nanoparticles with PEI Passivation for Bacterial Detection and Killing.

The ability to quickly detect and kill bacteria is crucial in the realm of antibiotic resistance. In this study, we synthesized a detection probe consisting of polyethylenimine (PEI)-passivated polydopamine-based fluorescent carbon (FDA:PEI) nanoparticles, generating a cationic adhesive material for bacterial detection that is surface-coatable, photothermal, and antibacterial. The cationic FDA:PEI nanoparticles effectively bound to the anionic bacterial cell wall, resulting in a dramatic quenching effect visible in fluorescence spectra and confocal images. In this fluorescence on/off system, FDA:PEI nanoparticles showed similar bacterial detection abilities between aqueous- and solid-phase assays. Scanning electron microscopy clearly showed the attachment of FDA:PEI nanoparticles to the surface of bacteria, both in solution and as a coating on the surface of a polypropylene film. In addition to detection, this versatile material was found to have an antibacterial potential, via near-infrared irradiation to induce a heat release, killing bacteria by thermolysis. Thus, by exploiting the cationic and catechol moieties on the surface of polydopamine carbon dots, we developed a novel bacterial-detection platform that can be used in a broad range of conditions.

Preparation of dual-responsive hybrid fluorescent nano probe based on graphene oxide and boronic acid/BODIPY-conjugated polymer for cell imaging.

Here, we report a pH- and thermo-responsive fluorescent nanomaterial of functionalized reduced graphene oxide (rGO) with cross-linked polymer produced via catechol-boronate diol binding mechanism. When conjugated with the hydrophobic dye boron dipyrromethane (BODIPY), this material can act as a dual-responsive nanoplatform for cells imaging. 2-Chloro-3',4'-dihydroxyacetophenone (CCDP)-quaternized-poly(dimethylaminoethyl methacrylate-co-N-isopropylacrylamide) [C-PDN] was cross-linked with BODIPY and 4-chlorophenyl boronic acid (BA)-quaternized-poly(ethylene glycol)-g-poly(dimethylaminoethyl methacrylate-co-N-isopropylacrylamide) [BB-PPDN]. The GO was then reduced by the catechol group in the cross-linked polymer to synthesize rGO nanoparticles, which able to stabilize the quenching mechanism. This nanoplatform exhibits intense fluorescence at acidic pH and low fluorescence at physiological pH. Confocal laser scanning microscopy (CLSM) images shows bright fluorescence at lysosomal pH and total quench at physiological pH. Therefore, we have successfully developed a promising sensitive bio-imaging probe for identifying cancer cells.

Target-specific induced hyaluronic acid decorated silica fluorescent nanoparticles@polyaniline for bio-imaging guided near-infrared photothermal therapy.

We describe a novel synthesis method for silica nanoparticles, which involves a combination of these nanoparticles with targetable and nontargetable fluorescent dopamine-conjugated hyaluronic acid (HA-DA) via rational chemical dehydration. The resulting HA-decorated silica fluorescent nanoparticles, electrostatically linked to polyaniline (PANI) to form ionic complexes, possessed high fluorescence intensity and were monodisperse in solution, near-infrared light responsive, and amenable to specific labeling of cancer cell lines. When exposed to near-infrared irradiation, the fluorescent silica nanoparticles exerted photothermal cytotoxicity guided by bioimaging and distinguished malignant cancer cells from normal cells via receptor CD44. Different heating properties of nanoparticles depend on local interactions between different structures, and determination of their efficacy could lead to new thermal treatment options such as noninvasive photothermal therapy.