Real-Time Wireless Monitoring of Cell Proliferation and Detachment Based on pH-Responsive Conductive Polymer Dots.

In situ wireless monitoring for cell proliferation and detachment kinetics was conducted using pH-responsive zwitterionic polymer dots (Z-PDs), based on changes in electrochemical signals derived from Z-PD-coated substrates via the interaction of charges transferred between Z-PDs and cells. Z-PD-coated substrates were found to be a potent means to monitor and manipulate cell adhesion and detachment because of their high sensitivity over a wide range of pH conditions, and modification of the coated substrates was confirmed using a wireless system. At neutral pH, Z-PD-coated wireless sensors exhibited π-π stacking involving aromatic rings with hydrophobic interactions, thereby promoting cell proliferation; consequently, an increase in the measured resistance was observed. In contrast, Z-PD-coated substrates triggered by acidic and basic conditions promoted cell detachment, which induced an increase in the resistance compared with Z-PD substrates at pH 6.8, as a result of charges transferred to support Z-PD internalization through cell membranes after detachment. Therefore, as a wireless biosensor with excellent pH responsiveness that facilitates cell proliferation and detachment and whose electrochemical signals could be additionally acquired via a smartphone, Z-PD biosensors demonstrated a more favorable approach for monitoring cell-surface interactions than conventional optically based methods.

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.

pH-Responsive NIR-Absorbing Fluorescent Polydopamine with Hyaluronic Acid for Dual Targeting and Synergistic Effects of Photothermal and Chemotherapy.

In cancer therapy, optimizing tumor-specific delivery, tumor distribution, and cellular uptake of a drug is important for ensuring minimal toxicity and maximum therapeutic efficacy. This study characterized the therapeutic efficacy of a stimulus responsive and dual targeting nanocarrier for a bioimaging-guided photothermal and chemotherapeutic platform. Hyaluronic acid (HA) conjugated with triphenylphosphonium (TPP) and boronic acid (BA) diol-linked ß-cyclodextrin (ß-CD) forms an inclusion complex with paclitaxel (PTX), creating a shell-like composite on a core of carbonized fluorescent polydopamine nanoparticles (FNPs-pDA) applicable for photothermal therapy as well as bioimaging. The successful diol cross-linking between core@shells generates nanocarriers [FNPs-pDA@HA-TPP-CD-PTX] that can be used as an extracellular HA- and intracellular TPP-mediated dual targeting system. The carbonized FNPs-pDA was cross-linked with the boronic acid groups of HA-TPP-CD-PTX to promote the formation of boronate esters for pH-mediated photothermal activity, which have shown time dependent complete PTX release along with a photothermal mediated response. The in vitro dual bioimaging and photothermal-chemotherapeutic activities were compared between cancer and normal cells. Lysosomal escape and live/dead cells staining confocal images highlight the promise of this system, which might open up a new approach, a simple and versatile method for site-specific synergetic drug delivery.

Concentration-mediated multicolor fluorescence polymer carbon dots.

Polymer dots (PDs) showing concentration-mediated multicolor fluorescence were first prepared from sulfuric acid-treated dehydration of Pluronic® F-127 in a single step. Pluronic-based PDs (P-PDs) showed high dispersion stability in solvent media and exhibited a fluorescence emission that was widely tunable from red to blue by adjusting both the excitation wavelengths and the P-PD concentration in an aqueous solution. This unique fluorescence behavior of P-PDs might be a result of cross-talk in the fluorophores of the poly(propylene glycol)-rich core inside the P-PD through either energy transfer or charge transfer. Reconstruction of the surface energy traps of the P-PDs mediated through aggregation may lead to a new generation of carbon-based nanomaterials possessing a fluorescence emission and tunable by adjusting the concentration. These structures may be useful in the design of multifunctional carbon nanomaterials with tunable emission properties according to a variety of internal or external stimuli.

In Vitro and In Vivo Tumor Targeted Photothermal Cancer Therapy Using Functionalized Graphene Nanoparticles.

Despite the tremendous progress that photothermal therapy (PTT) has recently achieved, it still has a long way to go to gain the effective targeted photothermal ablation of tumor cells. Driven by this need, we describe a new class of targeted photothermal therapeutic agents for cancer cells with pH responsive bioimaging using near-infrared dye (NIR) IR825, conjugated poly(ethylene glycol)-g-poly(dimethylaminoethyl methacrylate) (PEG-g-PDMA, PgP), and hyaluronic acid (HA) anchored reduced graphene oxide (rGO) hybrid nanoparticles. The obtained rGO nanoparticles (PgP/HA-rGO) showed pH-dependent fluorescence emission and excellent near-infrared (NIR) irradiation of cancer cells targeted in vitro to provide cytotoxicity. Using intravenously administered PTT agents, the time-dependent in vivo tumor target accumulation was exactly defined, presenting eminent photothermal conversion at 4 and 8 h post-injection, which was demonstrated from the ex vivo biodistribution of tumors. These tumor environment responsive hybrid nanoparticles generated photothermal heat, which caused dominant suppression of tumor growth. The histopathological studies obtained by H&E staining demonstrated complete healing from malignant tumor. In an area of limited successes in cancer therapy, our translation will pave the road to design stimulus environment responsive targeted PTT agents for the safe eradication of devastating cancer.

Target delivery and cell imaging using hyaluronic acid-functionalized graphene quantum dots.

This work demonstrates the way to achieve efficient and target specific delivery of a graphene quantum dot (GQD) using hyaluronic acid (HA) (GQD-HA) as a targeting agent. HA has been anchored to a GQD that accepts the fascinating adhesive properties of the catechol moiety, dopamine hydrochloride, conjugated to HA, which was confirmed by X-ray photoelectron spectroscopy. Transmission electron microscopy revealed a particle size of ∼20 nm, and the fluorescence spectra revealed significant fluorescence intensity even after the anchoring of HA. The prepared GQD-HA was applied to CD44 receptor overexpressed tumor-bearing balb/c female mice, and the in vivo biodistribution investigation demonstrated more bright fluorescence from the tumor tissue. In vitro cellular imaging, via a confocal laser scanning microscope, exhibited strong fluorescence from CD44 overexpressed A549 cells. Both in vivo and in vitro results showed the effectiveness of using HA as targeting molecule. The loading and release kinetics of the hydrophobic drug doxorubicin from a GQD under mildly acidic conditions showed that a GQD can be considered as a novel drug carrier, while the nontoxic behavior from the MTT assay strongly supports the identification of GQD-HA as a biocompatible material.

Temperature and pH-tunable fluorescence nanoplatform with graphene oxide and BODIPY-conjugated polymer for cell imaging and therapy.

This paper demonstrates the development of pH and thermo-responsive fluorescent nanoparticles, which are composed of graphene oxide (GO) with BODIPY conjugated PEG, to trigger the detection of cancer cells through imaging based on intracellular accommodation. Responsiveness to pH is studied using atomic force microscopy and apparent thickness differences are seen with changes in pH. Confocal images of the nanoparticles (NPs) exhibit remarkably bright fluorescence at lysosomal pH, while no fluorescence is observed under a physiological environment, making the NPs a novel fluorescent probe. The NPs are able to accumulate the hydrophobic anticancer drug DOX due to the hydrophobic surface of GO and show excellent drug release behavior. Therefore, the NPs developed are novel candidates for a fluorescent probe to identify cancer cells and a drug carrier for cancer therapy.

Investigation of space charge distribution of low-density polyethylene/GO-GNF (graphene oxide from graphite nanofiber) nanocomposite for HVDC application.

This paper reported a research on space charge distribution in low-density polyethylene (LDPE) nanocomposites with different types of graphene and graphene oxide (GO) at low filler content (0.05 wt%) under high DC electric field. Effect of addition of graphene oxide or graphene, its dispersion in LDPE polymer matrix on the ability to suppress space charge generation will be investigated and compared with MgO/LDPE nanocomposite at the same filler concentration. At an applied electric field of 80 kV/mm, a positive packet-like charge was observed in both neat LDPE, MgO/LDPE, and graphene/LDPE nanocomposites, whereas only little homogenous space charge was observed in GO/LDPE nanocomposites, especially with GO synthesized from graphite nano fiber (GNF) which is only -100 nm in diameter. Our research also suggests that dispersion of graphene oxide particles on the polymer matrix plays a significant role to the performance of nanocomposites on suppressing packet-like space charge. From these results, it is expected that nano-sized GO synthesized from GNF can be a promising filler material to LDPE composite for HVDC applications.

Spiropyran-conjugated pluronic as a dual responsive colorimetric detector.

Novel spiropyran-conjugated Pluronic [polyethylene oxide (PEO)-b-polypropylene oxide (PPO)-b-polyethylene oxide (PEO)] micelles are developed as a new colorimetric detector showing photo- or thermo-switchable behavior. Facile conjugation of spiropyran to Pluronic was confirmed by (1)H NMR, UV-Vis, and Fluorescence spectroscopy. A switchable photoluminescence is found depending on the irradiation with either UV or visible light, and temperature resulting from structural isomerization of spiropyran between spiropyran (SP) and merocyanine (MC) form. Cytotoxicity of the spiropyran-conjugated Pluronic (SP-PL) was evaluated following an MTT assay, whereas photo responsiveness of spiropyran within the micelles was determined by confocal laser scanning microscopy.

Blood compatible graphene/heparin conjugate through noncovalent chemistry.

Blood compatible graphene/heparin conjugate is simply formulated through noncovalent interaction between chemically reduced graphene and heparin. Charge repulsion of negatively charged heparin on graphene plates renders hydrophobic graphene to be solublized in aqueous media without any precipitation or aggregation even after 6 months. Unfractioned heparin (UFH) with higher molecular weight was effective for graphene solubilization while low molecular weight heparin (LMWH) was not. Noncovalently interacting heparin chains on graphene plates preserve their anticoagulant activity after conjugation with graphene. Graphene/UFH conjugate shows much enhanced anti factor Xa (FXa) activity of 29.6 IU/mL compared with pristine graphene oxide (GO; 1.03 IU/mL).

Mineralized Soft and Elastic Polymer Dot Hydrogel for a Flexible Self-Powered Electronic Skin Sensor.

We propose an integrated, self-powered, flexible electronic skin device containing an alginate-derived polymer dot (A-PD)-incorporated mineralized hydrogel-based energy storage unit and a chitosan-derived n-type carbon dot (N-CD)-based solar cell for an energy-harvesting unit. This study demonstrates a unique architecture of mineralized hydrogel comprising A-PD-incorporated poly(acrylic acid) (PAA)/CaCO3/laponite containing soft and sensitive layers, deposited with a polyaniline electrode to serve as an energy storage unit. The self-assembly was achieved through the ionic cross-linking between A-PD and PAA driven by the mineralization process, resulting in excellent dimensional stability and improved mechanical properties of the hydrogel. The sp2 carbon-rich A-PD enhances the electrochemical performance and the overall photon-to-electrical conversion and storage efficiency for self-powered devices by the formation of the bridge of electrons between the ionized polymer and metal ion. The capacitive sensor developed in this study exhibits high sensitivity in detecting small pressure changes, such as the falling of small water droplets. The self-powered sensing device can detect and monitor various human motions continuously by harvesting light energy from outdoor sunlight. Furthermore, the energy-autonomous device exhibits unique responses for handwriting characters stably and repeatedly. The proposed system may be applicable to human-machine interfaces, biomonitoring systems, secure communication, and wearable devices.

Selective redox-responsive theragnosis nanocarrier for breast tumor cells mediated by MnO2/fluorescent carbon nanogel.

A redox-responsive fluorescent carbon nanogel (FCN) was designed as a bioimaging probe for targeted drug delivery to cancer cells. FCN was synthesized by the carbonization of disulfide cross-linked hyaluronic acid in the fluorescence "on" mode, followed by the attachment of manganese oxide (MnO2) nanosheets for fluorescence quenching (fluorescence "off"). We hypothesized that the fluorescence intensity of paclitaxel (PTX)-MnO2/FCN would suddenly increase (fluorescence "on") in the presence of a high level of glutathione (GSH) in cancer cells, owing to the reduction of MnO2 to Mn2+ and cleavage of the disulfide bond. Consequently, PTX would be released from the FCN system. Consistent with this hypothesis, the designed system recovered FCN fluorescence and triggered drug release through the cleavage of the disulfide bond by GSH. Moreover, PTX-MnO2/FCN demonstrated stable fluorescence intensity after GSH treatment, serving as a potential biosensor. PTX-MnO2/FCN exhibited excellent biocompatibility with normal cells and selectively targeted tumor cells, highlighting the therapeutic capabilities of this system. The developed PTX-MnO2/FCN structure may serve as a smart drug delivery system with diagnostic and therapeutic properties, good selectivity, and compatibility, and with excellent potential for biomedical applications.

Photothermal-modulated reversible volume transition of wireless hydrogels embedded with redox-responsive carbon dots.

The reversible volume transition of redox-responsive hydrogels by near-infrared (NIR) irradiation has recently attracted significant attention as a novel therapy matrix for tracking and treating cancer via stimuli-responsive fluorescence on/off with controllable volume transition via a wireless sensing system. Herein, a NIR-induced redox-sensitive hydrogel was synthesized by blending a hydrogel with IR825-loaded carbon dots (CD) to achieve enhanced mobility of nanoparticles inside a gel network, and reversible volume phase transitions remotely controlled by a smartphone application via the induction of different redox environments. The presence of CD-IR825 in the thermosensitive poly(N-isopropylacrylamide) hydrogel network imparted fluorescence, electronic and photothermal properties to the hydrogels, which resulted in volume shrinkage behavior of the hydrogel upon exposure to NIR laser irradiation due to the redox-sensitive CDs. Under the NIR on/off cycles, the photothermal temperature, fluorescence, and porous structure were reversed after turning off the NIR laser. The hydrogel responsiveness under GSH and NIR light was studied using a wireless device based on the changes in the resistance graph on a smartphone application, generating a fast and simple method for the investigation of hydrogel properties. The in vitro cell viabilities of the MDA-MB cancer cells incubated with the composite hydrogel in the presence of external GSH exhibited a higher photothermal temperature, and the cancer cells were effectively killed after the NIR irradiation. Therefore, the NIR-induced redox-responsive nanocomposite hydrogel prepared herein has potential for use in cancer treatment and will enable the study of nanoparticle motion in hydrogel networks under multiple stimuli via a wireless device using a faster and more convenient method.

High performance of electrochemical and fluorescent probe by interaction of cell and bacteria with pH-sensitive polymer dots coated surfaces.

Using pH-switchable fluorescent polymer dots (PD) by means of fluorescent, colorimetric, and electrochemical signals generated from surfaces coated with PD of zwitterionic structure provided a fast and easy method to assess their performance in mammalian cell and bacterial interactions. The PD-coated surfaces showed high sensitivity over a broad range of pH levels by switching reversibly zwitterionic states, which led to an excellent cellular resistance effect by inhibiting the attachment of nearly 95% of mammalian cells. Similarly, they exhibited a strong interaction with the negatively charged surfaces of bacteria, as observed in the fluorescence ON/OFF system. In addition, PD were employed to detect the attachment of mammalian and bacterial cells: we deposited PD on a screen-printed carbon electrode for cyclic voltammetry analysis. Notably, the presence of cells remarkably interfered with the current flow between the PD and the screen-printed carbon electrode surface by causing an impressive decline in both reduction-oxidation signals, implying the high sensitivity of the PD-coated surfaces to cells and bacteria in different pH environments. Therefore, as smart materials with high sensitivity, biocompatibility, selectivity, and accuracy, PD-coated surfaces represent a promising approach to visualizing and controlling biological cell attachment, thereby helping to avoid contamination in biomedical applications.

Photoluminescence-tunable fluorescent carbon dots-deposited silver nanoparticle for detection and killing of bacteria.

Innovative methods to detect and kill pathogenic bacteria have a pivotal role in the eradication of infectious diseases and the prevention of the growth of antibiotic-resistant bacteria. The combination of fluorescent carbon dots (FCDs) with silver nanoparticles (AgNPs) is an effective material for synergic detection and antimicrobial activity determination. However, the fluorescence quenching of the FCDs owing to an interaction with AgNP is a major limitation. In this study, we designed a system to utilize poly(vinylpyrrolidone) (PVP) and catechol chemistry (PVP@Ag:FCD) in order to avoid the fluorescence quenching of the FCD-AgNP combination due to Forster Resonance Energy Transfer (FRET). PVP@Ag:FCD exhibited bright fluorescence, which can be used for bacterial detection, through the promotion of electrostatic binding with the negatively-charged bacterial surface and generation of fluorescence quenching due to aggregation-induced quenching. Furthermore, the presence of silver nanoparticles in PVP@Ag:FCD produced an excellent bacteria killing efficiency against E. coli and S. aureus, even at low concentrations (0.1 mg/mL). In contaminated river water, the PVP@Ag:FCD system showed a simple, highly sensitive, and effective performance for both the detection and eradication of bacteria. Therefore, this system offers an auspicious method for the future detection and killing of bacteria.

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.

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.

pH-switchable bacteria detection using zwitterionic fluorescent polymer.

A zwitterionic fluorescent polymer with high sensitivity to pH changes was constructed for the detection and imaging of both gram-positive and gram-negative pathogenic bacteria. A detection probe using the zwitterionic fluorescent polymer was synthesized with single boron dipyrromethane (BODIPY) as a hydrophobic dye and bromoethane as a cationic group for bacteria binding with conjugated poly(sulfobetaine methacrylate) (BOD/BE-PSM). The zwitterionic fluorescent polymer bound to bacteria through ionic complexes between anionic groups on the bacterial surface and cationic BOD/BE-PSM groups after 1h incubation. This finding demonstrated that the fluorescence on/off system operated via changes in the hydrophilic and hydrophobic nature of the zwitterionic fluorescent polymer, depending on the pH (6.0, 7.4, or 9.0), at a fixed 1mg/mL polymer concentration. The system showed good stability with a limit of detection of 1mg/mL. Quenching caused by interactions with the hydrophobic BODIPY dye was also observed, enabling bacteria detection, as shown by fluorescence spectroscopy and confocal microscopy images. Our results indicated that the zwitterionic fluorescent polymer could be used to detect bacteria over a wide range of pH values.

Rapid fluorometric bacteria detection assay and photothermal effect by fluorescent polymer of coated surfaces and aqueous state.

A fluorescent dye and a photothermal agent were grafted onto a cationic polymer for rapid and simple bacteria detection in liquid and solid phase based fluorescence on/off. The integrated poly(vinylpyrrolidone) (PVP) backbone with catechol and bromoethane moieties possesses unique optical properties due to the presence of boron dipyrromethane (BODIPY) and near infared NIR-responsive IR825 (F-PVP). The cationic segments showed distinct fluorescence quenching patterns after interaction with gram-positive and gram-negative bacteria via polyion complex interactions. Fluorescence quenching depended on direct interaction of the bacterial cell membrane, as confirmed using SEM and confocal imaging. The detection limit was 1mg/mL for the liquid-phase assay and the minimal detectable concentration of bacteria using the solid-phase assay was 106CFU/mL. After bacterial detection in contaminated area, our system can directly kill bacteria via the photothermal conversion ability of the IR825 substituent using NIR exposure by polymer solution and limited in coated PP. Finally, the proposed biosensor is capable as potential material for detection of bacteria in simple liquid and solid phase assay.