Geunseok Jang

Highly Selective Cysteine Detection and Bioimaging in Zebrafish through Emission Color Change of Water-Soluble Conjugated Polymer-Based Assay Complex

A new concept for rapid, label-free cysteine sensing method is proposed via possible naked eye-detection of red-to-blue emission color change. Intermolecular exciton migration in conjugated polyelectrolyte-based assay complex is adopted to enhance selectivity and sensitivity for cysteine sensing by formation and dissociation of polymer-Hg(2+)-thymine assay complex in the absence and presence of cysteine, respectively. The assay complex shows red emission due to cooperative aggregation of conjugated polyelectrolyte, thymine, and Hg(2+). Upon exposure to cysteine, the assay complex dissociates into individual molecules showing transparent, blue-emitting solution, because cysteine extracts Hg(2+) from the assay complex via more favorable binding between cysteine and Hg(2+).

New Fluorescent Metal-Ion Detection Using a Paper-Based Sensor Strip Containing Tethered Rhodamine Carbon Nanodots

A strip of tethered rhodamine carbon nanodots (C-dots) was designed for selective detection of Al(3+) ion using a Förster resonance energy transfer (FRET)-based ratiometric sensing mechanism. The probe consisted of rhodamine B moieties immobilized on the surface of water-soluble C-dots. Upon exposure to Al(3+), the rhodamine moieties showed a much enhanced emission intensity via energy transfer from the C-dots under excitation at their absorption wavelength. The detection mechanism was related to the Al(3+)-induced ring-opening of rhodamine on C-dots through the chelation of the rhodamine 6G moiety with Al(3+), leading to a spectral overlap of the absorption of C-dots (donor) and the emission of ring-opened rhodamine (acceptor). In addition, a paper-based sensor strip containing the tethered rhodamine C-dots was prepared for practical, versatile applications of Al(3+) sensing. The paper-based sensor could detect Al(3+) over other metal ions efficiently, even from a mixture of metal ions, with increased emission intensity at long-wavelength emission via FRET. Sensing based on FRET of C-dots is color-tunable, can be recognized with a naked eye, and may provide a new platform for specific metal-ion sensing.

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.

Conjugated Polymer Dots-on-Electrospun Fibers as a Fluorescent Nanofibrous Sensor for Nerve Gas Stimulant

A novel chemical warfare agent sensor based on conjugated polymer dots (CPdots) immobilized on the surface of poly(vinyl alcohol) (PVA)-silica nanofibers was prepared with a dots-on-fibers (DoF) hybrid nanostructure via simple electrospinning and subsequent immobilization processes. We synthesized a polyquinoxaline (PQ)-based CP as a highly emissive sensing probe and employed PVA-silica as a host polymer for the elctrospun fibers. It was demonstrated that the CPdots and amine-functionalized electrospun PVA-silica nanofibers interacted via an electrostatic interaction, which was stable under prolonged mechanical force. Because the CPdots were located on the surface of the nanofibers, the highly emissive properties of the CPdots could be maintained and even enhanced, leading to a sensitive turn-off detection protocol for chemical warfare agents. The prepared fluorescent DoF hybrid was quenched in the presence of a chemical warfare agent simulant, due to the electron transfer between the quinoxaline group in the polymer and the organophosphorous simulant. The detection time was almost instantaneous, and a very low limit of detection was observed (∼1.25 × 10(-6) M) with selectivity over other organophosphorous compounds. The DoF hybrid nanomaterial can be developed as a rapid, practical, portable, and stable chemical warfare agent-detecting system and, moreover, can find further applications in other sensing systems simply by changing the probe dots immobilized on the surface of nanofibers.

Aggregation-deaggregation-triggered, tunable fluorescence of an assay ensemble composed of anionic conjugated polymer and polypeptides by enzymatic catalysis of trypsin.

We prepared a water-soluble conjugated polymer composed of electron-donating units and electron-accepting groups in the backbone. The polymer exhibits a short wavelength (blue) emission in aqueous solution and long wavelength (red) emission in the solid state, because of intermolecular energy transfer. Considering this, we develop a new approach for the sensitive detection of trypsin, which is known to control pancreatic exocrine function, using an ensemble system composed of the anionically charged conjugated polymer and cationically charged polypeptides (such as polylysine and polyarginine). The blue-emitting, water-soluble conjugated polymer becomes aggregated upon exposure to the polypeptides, leading to a red-emitting assay ensemble. The red-emitting assay ensemble becomes dissociated in the conjugated polymer and polypeptide fragments by selective degradation of trypsin, which then exhibits recovery of blue emission. This emission-tuning assay ensemble allows for detection of trypsin at nanomolar concentrations, which enables naked-eye detection. Importantly, this strategy can be employed for label-free, continuous assay for trypsin.

Synthesis of triphenylamine-containing conjugated polyelectrolyte and fabrication of fluorescence color-changeable, paper-based sensor strips for biothiol detection

A new water-soluble conjugated polyelectrolyte containing triphenylamine groups with aldehyde pendants was synthesized, which featured distinctly different emission colors according to its states, in aqueous solution and in the solid. Paper-based strips containing the polymer were prepared by simple immersion of filter paper in the polyelectrolyte solution for practical and efficient detection of biothiols including cysteine and homocysteine. The presence of aldehyde groups enables us to demonstrate noticeable fluorescence emission color changes (green-to-blue) because of the alterations in electron push–pull structure in the polymer via a reaction between the aldehyde group of the polymer and the aminothiol moiety in biothiol compounds. The presence of an aldehyde group and a sulfonate side chain was found to be indispensable for the cysteine reaction site and for a hydrophilic environment allowing the easy approach of cysteine, respectively, resulting in a simple and easy detection protocol for biothiol compounds.

Simultaneous detection and removal of radioisotopes with modified alginate beads containing an azo-based probe using RGB coordinates.

We prepared alginate beads that were modified with an azo-based probe molecule to monitor simultaneously the removal (by alginate) and probing (by the azo-probe molecule) of radioisotopes such as cobalt, strontium, and cesium ions. As an azo-probe molecule, Basic Orange 2 (BO2) was immobilized to the alginate bead. The BO2 in aqueous solution exhibited a slight red shift in absorption with a change in color from orange to dark orange upon addition of cobalt and strontium ions. In contrast, the color of BO2 did not change upon exposure to cesium ions. Thus, the covalently embedded BO2 in alginate beads could adsorb cobalt and strontium ions resulting in recognizable color change of the beads, which was induced by the formation of a complex between BO2 and metal ions. The color changes of the beads in the presence of metal ions were determined quantitatively using RGB color coordinate values. In addition to effectively removing metal ions, the colorimetric coordinate method provides a convenient and simple sensing technique for naked-eye metal ion detection.

Fluorescence sensing of glucose using glucose oxidase incorporated into a fluorophore-containing PNIPAM hydrogel

We present a new composite material composed of pH sensitive fluorescent dyes in a poly(N-isopropylacrylamide)-based hydrogel and incorporating glucose oxidase (GOx), which provides a platform for fluorescence sensing of glucose in the clinically relevant range of 100 μM to 100 mM in aqueous solution. Fluorescein and rhodamine B dyes are well known for their dramatic pH-responsive changes in fluorescence emission color, in which they were introduced to the hydrogel as comonomers. As D-glucose was oxidized to D-glucono-δ-lactone producing hydrogen peroxide and a proton through the enzymatic action of GOx, the generated proton affects the fluorescence of the composite hydrogel. The composite hydrogel exhibited high selectivity to glucose over other sugars and metal ions. The combined role of a soft hydrogel and oxidase highlights the potential of the new composite material design for selective detection of glucose in aqueous solution.

Conjugated polymer-hybridized silica nanoparticle as a fluorescent sensor for cysteine

The detection of important biological thiols such as cysteine (Cys) is highly relevant to a variety of fundamental physiological processes in organisms. A conjugated polymer with pendant aldehyde group, which was used for reactive site for Cys, was synthesized via Suzuki coupling polymerization and the polymer was immobilized on the surface of amine-functionalized silica nanoparticles. The conjugated polymer-modified silica nanoparticles could be dispersed in alcoholic media, exhibiting various emission colors according to the alcoholic media, presumably due to the various polarity of the alcohols used. The organic–inorganic hybrid showed changes in emission color upon exposure to Cys with high selectivity over other amino acids, because of the specific reaction of aldehyde in the polymer and aminothiol group in Cys.

Fabrication, biofunctionalization, and simultaneous multicolor emission of hybrid “dots-on-spheres” structures for specific targeted imaging of cancer cells

We report a simple technique for the fabrication of dots-on-spheres (DoS) structures in which conjugated polymer dots (CPdots) are immobilized on the surface of silica spheres via charged interaction. Red-, green-, and blue-emissive conjugated polymers were synthesized and employed to validate the feasibility of an approach to develop a DoS system with emission across the visible range. The robust binding of CPdots to silica particles provides a buffer resistance and good stability to photoirradiation and mechanical agitation. Further bioconjugation of the DoS system is achieved by the introduction of polyarginine and neu antibody that is specific for the HER2 receptor, leading to their successful application to targeted imaging of SKBR-3 breast cancer cells overexpressing HER2. Moreover, DoS with simultaneous multicolor emissions of red, green, and blue can be easily synthesized and used to demonstrate the versatility of this strategy for multicolor cellular imaging based upon a single excitation source. We believe that this hybrid DoS strategy and the easy fabrication of organic polymer nanoparticles with silica substrates will facilitate their effective integration of organic and inorganic materials into versatile applications.