Visible-Light-Driven Asymmetric TiO2-Based Photocatalytic Micromotor Hybridized with a Conjugated Polyelectrolyte and Glucose Oxidase.

We fabricated a TiO2-based micromotor that was asymmetrically decorated with a water-soluble conjugated polymer (WSP) on one hemisphere and glucose oxidase (GOx) on the opposite hemisphere. The WSP, which had photocatalytic activity for H2O2 decomposition, enabled motion of the micromotor under visible light. The GOx on the other hemisphere of the micromotor decomposed glucose to produce H2O2 and enabled motion of the micromotor without light irradiation. In addition, WSP and GOx were attached to TiO2 by chemical bonds, providing stability during use. As a result, the micromotor could move by self-generating H2O2 for its own fuel by consuming glucose even without photoirradiation. The micromotor could move faster than without visible light irradiation through the synergistic decomposition of glucose and H2O2 under visible light by the diffusiophoretic mechanism with a speed of 7.49 µm/s.

Emission Tuning with Size-Controllable Polymer Dots from a Single Conjugated Polymer.

Two conjugated polymers (CPs) with various compositions of phenylene and benzoselenadiazoben (BSD) are synthesized to have a special emitting property; different fluorescence colors in solution and in the solid states, allowing the resulting conjugated polymer dots (Pdots) to emit different fluorescence colors upon their size variation. The photophysical property of such different-sized Pdots is investigated using fluorescence spectra and fluorescence lifetimes. A decrease in the fluorescence lifetime of Pdots is observed with an increase in the size of Pdots, caused by quantitative change in energy transfer from phenylene (energy donor) to the BSD unit (energy acceptor). The results provide that any CP can be used for the fabrication of Pdots with size-tunable emission, as long as the CP shows different emissions according to its phases. Such emission of Pdots can even be observed when in the solid solution in polymer matrix, which emits different fluorescence colors depending on the size of embedded Pdots in the polymer matrix.

Full-Color Emissive Poly(Ethylene Oxide) Electrospun Nanofibers Containing a Single Hyperbranched Conjugated Polymer for Large-Scale, Flexible Light-Emitting Sheets.

White-light-emitting protocols based on organic materials have received much attention in the academic and industrial fields because of their potential applications in full-color displays and back-lighting units for liquid crystal displays. Here, the attempt is made to fabricate white-light-emitting, electrospun poly(ethylene oxide) (PEO) sheets containing controlled concentrations of a single light-emitting material composed of a type of hyperbranched conjugated polymer (HCP). The HCPs used here have the unique property of exhibiting a variety of fluorescence colors in the electrospun matrix that is caused by the different distances between HCP chains depending on their concentrations, leading to different degrees of intermolecular energy transfer. Therefore, the emission colors of the PEO sheets can be easily manipulated by simply varying the HCP concentrations in the PEO matrix. The resulting method for fabricating nanofibers comprising light-emitting materials in the polymer matrix has great potential for easy fabrication of cost-effective, flexible light-emitting system.

Functionalized, Fluorescent, Conjugated Polymer Nanospheres for Protein Targeting via Förster Resonance Energy Transfer.

We report the preparation of fluorescent nanospheres based on conjugated polymers, which enables a facile fluorescence color tuning. The fluorescent nanospheres have aldehyde groups on the surface that enable the introduction of a protein ligand, biotin. The intrinsic fluorescence of the nanospheres allows detection of a dye-labeled target protein, streptavidin, via Förster resonance energy transfer. The controlled biofunctionalization of conjugated polymer-based fluorescent nanospheres represents a novel approach with high applicability to sensing of biological molecules.

Green synthesis and antimicrobial activity of silver chloride nanoparticles stabilized with chitosan oligomer.

Nanocrystalline silver (Ag) and Ag containing nanostructure synthesized using various methods have been studied for their antimicrobial, wound healing, and anti-inflammatory efficacy. Among these, crystalline silver chloride (AgCl) nanostructures exhibit desirable properties for biological and biomedical applications. However, most of them are synthesized using hazardous agents and organic solvents, which has been limited for application in the biological field. A simple and environmentally friendly method was demonstrated for AgCl nanoparticles stabilized with chitosan oligomer (CHI-AgCl NPs) as both a resource of Cl ions and stabilizing agent with expectations of synergistic effects. The CHI-AgCl NPs stabilized by the chitosan oligomer had spherical morphology with a mean diameter of 42 ± 15 nm. Ag ions precipitated as AgCl in presence of Cl ions, which remained in the protonated amine group after HCl hydrolysis of the chitosan. Moreover, much of the amine and hydroxyl group bound to the AgCl NPs for growth and stabilization. These nanoparticles were characterized via various spectroscopic techniques, including UV-Vis spectrophotometry, X-ray photoelectron spectrometry, X-ray diffractometry, and transmission electron microscopy.

Silica-Based Platform Decorated with Conjugated Polymer Dots and Prussian Blue for Improved Photodynamic Cancer Therapy.

To advance cancer treatment, we have developed a novel composite material consisting of conjugated polymer dots (CPDs) and Prussian blue (PB) particles, which were immobilized on, and encapsulated within, silica particles, respectively. The CPDs functioned as both a photosensitizer and a photodynamic agent, and the PB acted as a photothermal agent. The silica platform provided a biocompatible matrix that brought the two components into close proximity. Under laser irradiation, the fluorescence from the CPDs in the composite material enabled cell imaging and was subsequently converted to thermal energy by PB. This efficient energy transfer was accomplished because of the spectral overlap between the emission of donor CPDs and the absorbance of acceptor PB. The increase in local temperature in the cells resulted in a significant increase in the amount of reactive oxygen species (ROS) generated by CPDs, in which their independent use did not produce sufficient ROS for cancer cell treatment. To assess the impact of the enhanced ROS generation by the composite material, we conducted experiments using cancer cells under 532 nm laser irradiation. The results showed that with the increase in local temperature, the generated ROS increased by 30% compared with the control, which did not contain PB. When the silica-based composite material was positioned at the periphery of the tumor for 120 h, it led to a much slower tumor growth than other materials tested. By using a CPD-based photodynamic therapy platform, a new simplified approach to designing and preparing cancer treatments could be achieved, which included photothermal PB-assisted enhanced ROS generation using a single laser. This advancement opens up an exciting new opportunity for effective cancer treatment.

Fabrication of nanofibrous PbO2 electrode embedded with Pt for decomposition of organic chelating agents.

A new fabrication method of nanofibrous metal oxide electrode comprising Pt nanofiber (Pt-NF) covered with PbO2 on a Ti substrate was proposed. Pt-NF was obtained by performing sputtering deposition of Pt on the surface of electrospun poly(vinyl alcohol) (PVA) nanofiber on a Ti substrate, in which PVA was then removed by calcination (Ti/Pt-NF). Subsequently, by introducing PbO2 to the Ti/Pt-NF using the electrodeposition method, a nanofibrous Ti/Pt-NF/PbO2 electrode was finally obtained. Because the Ti substrate was covered by nanofibrous Pt, it had no environmental exposure and thus, was not oxidized during calcination. The crystal structure of the PbO2 mainly consisted of ß-form rather than α-form; the ß-form was suitable for electrochemical decomposition and remained stable even after 20 h of use. The nanofibrous Ti/Pt-NF/PbO2 electrodes showed 10% lower anode potential, 1.6 times higher current density at water decomposition potential, lower electrical resistance in the ion charge transfer resistance, and 2.27 times higher electrochemically active surface area than those of a planar-type Ti/Pt/PbO2 electrode, and demonstrated excellent electrochemical performance. As a result, compared with the planar electrode, the Ti/Pt-NF/PbO2 electrode showed more effective electrochemical decomposition toward nitrilotriacetic acid (80%) and ethylenediaminetetraacetic acid (83%), which are commonly used as chelating agents in nuclear decontamination.

Cobalt ion-mediated cysteine detection with a hyperbranched conjugated polyelectrolyte as a new sensing platform.

A highly efficient colorimetric and fluorescence turn-off probe for the sensitive and selective detection of the biologically important amino acid, cysteine (Cys), is demonstrated using a newly synthesized water-soluble hyperbranched polymer (HP) containing sulfonic acid groups. The detection mechanism involves two steps: (i) the slight quenching of HP in the presence of Co(2+) in advance; and (ii) the gradual quenching of the HP-Co(2+) complex according to the concentration of Cys due to the absorption screening effect of the formation of the Cys-Co(2+) complex, which prevents HP from absorbing excitation energy.

Fluorometric detection of lectin with water-soluble hyperbranched conjugated polymer using mannose mediation.

A water-soluble hyperbranched polymer containing boronic acid groups at the ends of the polymer, which are capable of binding to diol-containing mannose, was syntheized. The hyperbranched polymer was prepared by a palladium-catalyzed Suzuki cross-coupling reaction using the tribromo monomer for the hyperbranched type structure. The water-soluble hyperbranched polymer (HP) exhibited enhanced fluorescence intensity upon exposure to lectin in the presence of mannose compared to other proteins, such as lysozyme and cytochrome c, because mannose plays a key role in binding both lectin and HP resulting in selective sensing toward lectin.

Cesium ion adsorption and desorption on electrospun mesoporous silica nanofibers immobilized with Prussian blue.

To fabricate an efficient Cs ion adsorbent and prevent unexpected loss of Prussian blue (PB) colloidal particles during use, PB was immobilized on the surface of electrospun mesoporous silica nanofibers (MSFs) via a newly developed method of double exposure to Fe (III) ions. To introduce PB on MSFs, the MSFs were functionalized with ethylenediamine moiety to bind to Fe (III) ions, which would firmly anchor PB. MSFs were pretreated with Fe (III) ions and exposed to K4 [Fe(II) (CN)6] to form PB. We found that this process did not provide a sufficient PB amount on the MSFs. To increase the PB amount, after initial PB formation, the MSFs were treated with Fe (III) ions again so that the unreacted K4 [Fe(II) (CN)6] remaining on the MSFs could become PB. An investigation of the adsorption isotherms and kinetics of the nanofibrous adsorbent indicated that monolayer chemisorption had occurred. The maximum Cs ion adsorption capacity using the method of double exposure to Fe (III) ions was determined to be 14.66 mg/g, which was higher by a factor of 2.24 than the case that was not prepared by this method. Cs ions were selectively adsorbed over other cations and could be removed in both acidic and basic conditions, presumably because of the robust MSFs.

Fabrication of a porous polyacrylonitrile nanofiber adsorbent for removing radioactive 60Co.

A Co2+ adsorbent was prepared using electrospun porous polyacrylonitrile (PAN) nanofibers, featuring easy recovery for reuse compared with a nanoparticle-based adsorbent. As an efficient ligand for Co2+, ethylenediaminetetraacetic acid (EDTA) was introduced on the surface of porous PAN nanofibers with the aid of a branched polyethyleneimine (PEI) linker to obtain an adsorbent with carboxylic acid groups. On the adsorbent surface, the carboxylic acid and amine groups from EDTA could adsorb Co2+ via ion exchange and chelation, and amine groups from PEI that remained after EDTA functionalization played a role in coordinating Co2+. The amine and carboxylic acid groups were simultaneously involved in the adsorption on the surface, making it possible to remove Co2+ over a wide pH range. An investigation of the adsorption isotherms and kinetics of the nanofibrous adsorbent indicated that monolayer chemisorption was achieved with a maximum Co2+ adsorption capacity of 8.32 mg/g. In addition, radioactive 60Co was efficiently removed by the adsorbent with a removal extent of more than 98%. Considering the easy separation from Co2+ solution and regeneration of the nanofibrous adsorbent and its availability in a wide pH range, the adsorbent has great advantages in practical applications.

Simultaneous detection and removal of mercury ions in aqueous solution with fluorescent conjugated polymer-based sensor ensemble.

A water-soluble, sulfur-containing fluorescent conjugated polymer exhibits a visible fluorescence color change for detection of mercury in the presence of thymine. A new concept provides the design of a sensor ensemble using a simple combination method. This strategy avoids the need for complicated design and synthesis of a recognition group, eliminating the tedious synthetic efforts for the preparation of a sensor material.

Fluorescence Modulation of Conjugated Polymer Nanoparticles Embedded in Poly(N-Isopropylacrylamide) Hydrogel.

A series of conjugated polymers (CPs) emitting red, green, and blue (RGB) fluorescence were synthesized via the Suzuki coupling polymerization. Polymer dots (Pdots) were fabricated by the reprecipitation method from corresponding CPs, in which the Pdot surface was functionalized to have an allyl moiety. The CP backbones were based on the phenylene group, causing the Pdots to show identical ultraviolet-visible absorption at 350 nm, indicating that the same excitation wavelength could be used. The Pdots were covalently embedded in poly(N-isopropylacrylamide) (PNIPAM) hydrogel for further use as a thermoresponsive moiety in the polymer hydrogel. The polymer hydrogel with RGB emission colors could provide thermally reversible fluorescence changes. The size of the hydrogel varied with temperature change because of the PNIPAM's shrinking and swelling. The swollen and contracted conformations of the Pdot-embedded PNIPAM enabled on-and-off fluorescence, respectively. Fluorescence modulation with 20 to 80% of the hydrogel was possible via thermoreversibility. The fluorescent hydrogel could be a new fluorescence-tuning hybrid material that changes with temperature.

Sulfur-encapsulated zeolite micromotors for the selective removal of cesium from high-salt water with accelerated cleanup times.

Bubble-propelled sulfur-encapsulated NaX zeolite (S-NaX) micromotors were developed for the selective removal of cesium from high-salt conditions with accelerated cleanup times. NaX was first modified with sulfur to provide additional Lewis acid-base interactions with Cs+ for enhanced Cs+ selectivity, and then Pt was half-deposited on S-NaX for bubble propulsion via the catalytic decomposition of H2O2. The average velocity of the resulting S-NaX/Pt micromotors in 5 wt% H2O2 is 39.7 ± 17.1 µm/s, which is higher than that of a previously reported Cs adsorbent micromotor (35.4 µm/s). The Cs+ ion-exchange kinetics of the S-NaX micromotor is 1.32 times higher than that of the NaX micromotor in a 5 wt% H2O2 solution where the molar ratio of Na+ to Cs+ is 200, even though the sulfur in the S-NaX micromotor causes an adverse effect on the propulsion speed due to the sulfur poisoning effect. Moreover, the S-NaX micromotor in simulated groundwater also exhibited excellent Cs+ removal performance with distribution coefficient (Kd) values at least 3.2 times higher than those of the nonpropelled S-NaX and NaX micromotor, demonstrating the great potential for the treatment of radioactive Cs+-contaminated water.

Controlled light emission in spin-assisted layer-by-layer assemblies with fluorophores.

We report controlled light emissions from spin-assisted layer-by-layer (LbL) thin films containing a donor-acceptor pair of fluorescent dyes. Based on their spectral overlap, we selected rhodamine 123 (R123) and rhodamine B (RB) as the donor and acceptor, respectively. For the construction of multilayered thin films, a complex of each dye and poly(sodium 4-sulfonate) (PSS-R123 and PSS-RB) was prepared and then alternately spin coated with poly(allyamine hydrochloride) (PAH). LbL assemblies were fabricated with a sequence of [PAH/PSS-RB]/([PAH/PSS])n/[PAH/PSS-R123]. Since the distance between R123 and RB was precisely adjusted by the number of bilayers (n) of [PAH/PSS] between them, we were able to tune the light emission from the thin film by controlling the efficiency of the energy transfer.

Aldehyde-functionalized, water-soluble poly(para-phenylene): synthesis and streptavidin assay using FRET.

We have attempted to synthesize water-soluble poly(para-phenylene) derivative, poly{[2,5-bis(3-sulfonatobutoxy)-1,4-phenylene sodium salt]-alt-(1,4-phenylene)} (PPP-SO3). Aldehyde groups, versatile functional intermediate groups for immobilization of biomolecules, were introduced at both ends of PPP-SO3 chain to produce PPP-SO3-CHO. PPP-SO3-CHO showed good solubility in aqueous solution and blue emission color, which was expected as an energy donor in FRET mechanism. Biotin was attached to the polymer end groups via imine linkage to use as a ligand for streptavidin immobilization. The biotin coupled with polymer chain enables the polymer to bind with FITC-streptavidin leading to energy transfer from the blue-emitting polymer to green-emitting FITC via FRET.

Self-assembly of supramolecualr metallogelator containing 2-(2'-hydroxyphenyl) benzoxazole/Zn(II) chelate.

A low molar mass organogelator 1 containing 2-(2'-hydroxyphenyl)benzoxazole (HPB) unit with long alkyl chain was synthesized by the reaction with HPB and octyl isocyanate in THF at room temperature. A new chelate-based organogelator 1-Zn(II) was prepared with the reaction of 1 and zinc(II) acetate in methanol and dichloromethane at mild condition. The gelation ability of organogelator was tested by heating-cooling method in various organic solvents, and the opaque gel was formed from DMF. Well-developed self-assembled structure of organogel was confirmed with field emission-scanning electron microscope (FE-SEM) and transmission electron microscope (TEM), and the optical properties of organogel upon aggregation were monitored by UV-Vis and fluorescence spectroscopy, 1-Zn(II) was self-assembled to the sheet-like structure with the thickness of fully extended length of molecules.

Synthesis and electrostatic nano-assembly of water-soluble polybenzothiadiazole derivatives with long-wavelength emission in the solid states.

We have synthesized APBT and APTBT containing benzothiadiazole units by Suzuki cross-coupling reaction with good yield. The polymers showed blue emission colors in aqueous solutions, while long wavelength shift was observed in the solid state due to facilitated exciton migration. APBT and APTBT are water-soluble and highly-fluorescent conjugated polymers with negatively charged sulfonate side chains and thus they can be electrostatically assembled with oppositely charged polyelectrolyte such as cationic polymer, poly(dimethyldiallylammonium chloride) (PDAC) via layer-by-layer (LbL) deposition technique on a glass slide. According to the increased the number of bilayer, we found that the assembled film exhibited larger enhancement of the long wavelength emission relative to the blue emission, due to the increased excition migration.

Synthesis of poly(N-isopropylacrylamide) polymer crosslinked with an AIE-active azonaphthol for thermoreversible fluorescence.

A fluorescent polymer was synthesized using N-isopropylacrylamide (NIPAM) crosslinked with a divinylazonaphthol monomer via radical emulsion polymerization. Because the crosslinked polymer contained an aggregation-induced emissive (AIE) azonaphthol-based crosslinker, a thermoreversible sol-gel transformation and gelation-induced reversible fluorescence alteration were successfully attained in an aqueous medium. Like typical PNIPAM, the size and transmittance of the polymer dramatically decreased near the lower critical solution temperature (LCST, 36 °C). Such gelation facilitated aggregation of the polymer chains, resulting in the close contact between azonaphthol groups producing fluorescence. The crosslinked polymer exhibited changes in dual properties: one is related to PNIPAM structural alteration, which corresponds to conventional swelling/shrinkage behavior; and the other is involved in the reversible fluorescence change in response to the swelling/shrinkage. Because the major backbone of the polymer was composed of NIPAM with an LCST at 36 °C, the resultant polymer is expected to have potential applications in biologically related fields.

Size-dependent fluorescence of conjugated polymer dots and correlation with the fluorescence in solution and in the solid phase of the polymer.

Three conjugated polymers (CPs) were synthesized to obtain CPs with the same backbone but with different compositions of repeat units (phenylene and benzoselenadiazole (BSD)). The dominant composition of phenylene units and a smaller amount of BSD in the CP backbone enabled the CPs to emit different fluorescence colors according to their condition (solution or solid), which was caused by the difference in intermolecular electron transfer between CP backbones. Inspired by this, we fabricated polymer dots (Pdots) with various sizes using the CPs to control the number of CP chains within a spherical Pdot. This implied that smaller Pdots, where the chance of intermolecular electron transfer would be at a minimum, would accommodate fewer polymer chains than larger ones. The minimum chance for intermolecular electron transfer resulted in a short-wavelength emission, which was the identical emission color encountered in liquid CP solution. A more frequent intermolecular electron transfer was expected in larger Pdots, exhibiting long-wavelength emission, which was the same as observed in solid CPs. White-light-emitting Pdots that showed Commission Internationale de 1'Eclairage (CIE) coordinates of (0.34, 0.31) were fabricated simply by controlling the Pdot size.