Eun Bi Kang

Light Controllable Surface Coating for Effective Photothermal Killing of Bacteria

Although the electronic properties of conducting films have been widely explored in optoelectronic fields, the optical absorption abilities of surface-coated films for photothermal conversion have been relatively less explored in the production of antibacterial coatings. Here, we present catechol-conjugated poly(vinylpyrrolidone) sulfobetaine (PVPS) and polyaniline (PANI) tightly linked by ionic interaction (PVPS:PANI) as a novel photothermal antibacterial agent for surface coating, which can absorb broadband near-infrared (NIR) light. Taking advantage of the NIR light absorption, this coating film can release eminent photothermal heat for the rapid killing of surface bacteria. The NIR light triggers a sharp rise in photothermal heat, providing the rapid and effective killing of 99.9% of the Gram-positive and -negative bacteria tested within 3 min of NIR light exposure when used at the concentration of 1 mg/mL. Although considerable progress has been made in the design of antibacterial coatings, the user control of NIR-irradiated rapid photothermal destruction of surface bacteria holds increasing attention beyond the traditional boundaries of typical antibacterial surfaces.

Highly Efficient Visible Blue-Emitting Black Phosphorus Quantum Dot: Mussel-Inspired Surface Functionalization for Bioapplications

The preparation of blue-emitting black phosphorus quantum dots (BPQDs) is based on the liquid-phase exfoliation of bulk BP. We report the synthesis of soluble BPQDs showing a strong visible blue-light emission. Highly fluorescent (photoluminescence quantum yield of ≈5% with the maximum emission (λmax) at ≈437 nm) and dispersible BPQDs in various organic solvents are first prepared by simple ultrasonication of BP crystals in chloroform in the ambient atmosphere. Furthermore, simple mussel-inspired surface functionalization of BPQDs with catechol-grafted poly(ethylene glycol) in basic buffer afforded water-soluble blue-emitting BPQDs showing long-term fluorescence stability, very low cytotoxicity, and excellent fluorescence live cell imaging capability.

Performance of NIR-Mediated Antibacterial Continuous Flow Microreactors Prepared by Mussel-Inspired Immobilization of Cs0.33WO3 Photothermal Agents

An antibacterial continuous flow microreactor was successfully prepared by sequential mussel-inspired surface engineering of microchannels by using catechol-grafted poly(N-vinylpyrrolidone) and immobilization of near-infrared active Cs0.33WO3 nanoparticles inside the polydimethylsiloxane(PDMS)-based microreactors. Excellent phothothermal antibacterial acitivity over 99.9% was accomplished toward Gram-positive and -negative bacteria upon near-infrared irradiation during continuous operation up to 30 days. This was achieved without releasing Cs0.33WO3 nanoparticles from the surface of the microchannels, confirming the robust immobilization of photothermal agents through the mussel-inspired chemistry. The cleaning of used microreactors was easily attainable by simple acid treatment to release immobilized photothermal agents from the surface of the microchannels, enabling efficient recycling of used microreactors.

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 β-cyclodextrin (β-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 β-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 β-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.

Mechanochemical synthesis of fluorescent carbon dots from cellulose powders

A novel mechanochemical method was firstly developed to synthesize carbon nanodots (CNDs) or carbon nano-onions (CNOs) through high-pressure homogenization of cellulose powders as naturally abundant resource depending on the treatment times. While CNDs (less than 5 nm in size) showed spherical and amorphous morphology, CNOs (10-50 nm in size) presented polyhedral shape, and onion-like outer lattice structure, graphene-like interlattice spacing of 0.36 nm. CNOs showed blue emissions, moderate dispersibility in aqueous media, and high cell viability, which enables efficient fluorescence imaging of cellular media.

Synthesis of catechol-functionalized polymer–based crosslinked thermoresponsive hydrogels for tissue-adhesive material:

Injectable and temperature-sensitive hydrogels were synthesized for use as a tissue-adhesive material between dopamine end-capped Pluronic and CCDP-q-PDB (2-chloro-3′,4′-dihydroxyacetophenone-quaternized poly((dimethyl aminoethyl methacrylate)-co-(t-butylmethacrylate))). The mixture of dopamine end-capped Pluronic and CCDP-q-PDB exists in a viscous solution state at room temperature, but becomes a gel via in situ crosslinking at body temperature. The hydrogel structure was shown to be more stable than Pluronic F127 copolymers in aqueous solution. At a 14:8 wt% ratio of dopamine end-capped Pluronic to CCDP-q-PDB, the sol quickly transformed into a gel at body temperature and under physiological conditions (<10 s), showing excellent gel stability. To evaluate the tissue-adhesive properties, the temperature-sensitive crosslinked dopamine end-capped Pluronic CCDP-q-PDB hydrogels, which can be applied for drug delivery, tissue engineering, and for use as tissue adhesives, were tested using a universal testing machine.

Temperature-sensitive carbon dots derived from poly(N-isopropylacrylamide) for fluorescence on–off properties

Here, we report novel thermo-responsive fluorescent nanoparticles of carbonized poly(N-isopropylacrylamide) (PNIPAAm) through two pathways, partial carbonized PNIPAAm (F-PNIPAAm) and full carbonized PNIPAAm (FNP) acid treatment. The carbonized PNIPAAm generated different properties depending on acid treatment time to control the lower critical solution temperature (LCST) behaviors as a biosensor based on a fluorescence on–off system. Furthermore, the FNP–PNIPAAm also showed reversible capability based on fluorescence intensity, with a high fluorescence signal observed at room temperature (25 °C) but quenching at physiological temperature (37 °C). H-NMR, FT-IR, X-ray dispersion (XRD), and X-ray photoelectron spectroscopy (XPS) confirmed the associated chemical moieties of FNP–PNIPAAm and FNP. After confirming the cytotoxicity of the prepared material, we carried out in vitro bio-imaging studies using MDAMB, A-549, and MDCK cells by confocal laser-scanning microscopy. Therefore, we successfully established a convenient, rapid, and ecofriendly synthetic approach to the synthesis of FNPs based on PNIPAAm. These FNPs exhibited tunable luminescence properties, high aqueous stability, and low cytotoxicity, suggesting potential applications in bio-labeling, bio-imaging, and optoelectronics.