Ji Ha Lee

Functionalized magnetic nanoparticles as chemosensors and adsorbents for toxic metal ions in environmental and biological fields

Functionalized magnetic nanoparticles, composed of both inorganic and organic components, have recently been examined as promising platforms for detection and separation applications. This unique class of nanomaterials can retain not only beneficial features of both the inorganic and organic components, but can also provide the ability to systematically tune the properties of the hybrid materials through the combination of appropriate functional components. This tutorial review focuses on the recent development of functionalized magnetic nanoparticles for use in biological and environmental applications, in which these chromogenic and fluorogenic chemosensors can selectively detect and separate specific toxic metal ions.

Bisindole anchored mesoporous silica nanoparticles for cyanide sensing in aqueous media

For CN(-) recognition, a series of bisindolyl compounds 1-3 were prepared, and their chromodosimetric color changes toward anions were investigated. Nucleophilic addition of the cyanide ion to the meso position of the bisindolyl group gave rise to breaking of the double bond conjugation, thereby inducing spectroscopic changes in the compound. Mesoporous silica nanoparticles 3 also gave color changes from deep orange to yellow in response to the cyanide ion.

Supramolecular gels with high strength by tuning of calix[4]arene-derived networks

Supramolecular gels comprised of low-molecular-weight gelators are generally regarded as mechanically weak and unable to support formation of free-standing structures, hence, their practical use with applied loads has been limited. Here, we reveal a technique for in situ generation of high tensile strength supramolecular hydrogels derived from low-molecular-weight gelators. By controlling the concentration of hydrochloric acid during hydrazone formation between calix-[4]arene-based gelator precursors, we tune the mechanical and ductile properties of the resulting gel. Organogels formed without hydrochloric acid exhibit impressive tensile strengths, higher than 40 MPa, which is the strongest among self-assembled gels. Hydrogels, prepared by solvent exchange of organogels in water, show 7,000- to 10,000-fold enhanced mechanical properties because of further hydrazone formation. This method of molding also allows the gels to retain shape after processing, and furthermore, we find organogels when prepared as gel electrolytes for lithium battery applications to have good ionic conductivity.

Fluorescent Composite Hydrogels of Metal–Organic Frameworks and Functionalized Graphene Oxide

GO MOFs! Azobenzoic acid functionalized graphene (A-GO) can act as a structure-directing template that influences hydrogel formation together with metal-organic frameworks (MOFs). Zn(2+) MOFs of pyridine derivatives work as framework linkers between the A-GO sheets (MOF-A-GO, see figure). MOF-A-GO exhibits a strong fluorescence enhancement upon gel formation. In addition, MOF-A-GO selectively recognizes trinitrotoluene.

A tetrazole-based metallogel induced with Ag+ ion and its silver nanoparticle in catalysis

A tetrazole-based ligand forms a supramolecular metallogel in the presence of Ag+ in aqueous solution at basic condition. The silver-induced metallogel has been characterized by SEM, TEM, XRD and rheometry. The metallogel exhibits a fiber structure. Upon standing, silver nanoparticles grow in the gel. TEM confirmed that the particles are exclusively formed in the gel fibers. The size of the silver nanoparticles formed on the gel fibers is dependent to the concentration of silver during gel formation. The silver nanoparticles show a face-centered cubic crystalline structure. The silver nanoparticles can effectively catalyze reduction of 4-nitrophenol by sodium borohydride in aqueous solution. The formation of Ag+-induced metallogels does not strongly depend on anions. According to DFT calculations, two silver cations are coordinated to nitrogen at the tetrazole moiety. The other silver cation is coordinated to the nitrogen of the pyridine and coordinated to the oxygen of the amide moiety. Furthermore, the rheological properties of the Ag+-tetrazole-based metallogel were strongly dependent on the concentration of AgClO4.

A BODIPY-functionalized bimetallic probe for sensitive and selective color-fluorometric chemosensing of Hg2+

A new BODIPY dye conjugate has demonstrated selective quenching by mercury over other metal ions. Coupling of this probe to Au-Fe(3)O(4) nanoparticles as well as platinum electrodes offered sensitive systems for suspension and surface based sensing, respectively.

Instant visual detection of picogram levels of trinitrotoluene by using luminescent metal-organic framework gel-coated filter paper.

There is an ongoing need for explosive detection strategies to uncover threats to human security including illegal transport and terrorist activities. The widespread military use of the explosive trinitrotoluene (TNT) for landmines poses another particular threat to human health in the form of contamination of the surrounding environment and groundwater. The detection of explosives, particularly at low picogram levels, by using a molecular sensor is seen as an important challenge. Herein, we report on the use of a fluorescent metal-organic framework hydrogel that exhibits a higher detection capability for TNT in the gel state compared with that in the solution state. A portable sensor prepared from filter paper coated by the hydrogel was able to detect TNT at the picogram level with a detection limit of 1.82 ppt (parts per trillon). Our results present a simple and new means to provide selective detection of TNT on a surface or in aqueous solution, as afforded by the unique molecular packing through the metal-organic framework structure in the gel formation and the associated photophysical properties. Furthermore, the rheological properties of the MOF-based gel were similar to those of a typical hydrogel.

The selective immobilization of curcumin onto the internal surface of mesoporous hollow silica particles by covalent bonding and its controlled release

Mesoporous-type spherical hollow silica nanoparticles were prepared by using a self-assembled alanine-based amphiphile as a template and then were functionalized with curcumin molecules attached to the internal surface of the nanostructure by covalent bonding. The curcumin-immobilized mesoporous hollow silica nanoparticle (C-MHSP) was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), BET isotherms, FT-IR, Solid 13C CP/MAS NMR and powder-XRD. SEM and TEM images revealed spherical structures (100–150 nm outer diameter) containing 90–140 nm hollow cavities with a worm-like structure. The N2 adsorption–desorption isotherms obtained at 77 K showed a typical type IV isotherm with 4.7 nm of pore size and 448.66 m2 g−1 of surface area, respectively. Approximately 35% of the curcumin was selectively immobilized onto the internal surfaces of the mesoporous hollow silica particles by covalent bonds. The curcumin attached onto the internal surface of C-MHSP was efficiently released into the aqueous phase over 120 min at pH 10, indicating that the curcumin that was attached to the inside of the silica particle was effectively hydrolyzed by strong base. Our work provides a method by which the surface of the porous silica can be functionalized in a well-defined manner.

Fluorescence enhancement of a tetrazole-based pyridine coordination polymer hydrogel

Hydrogelation of a pyridine derivative (1) possessing tetrazole moieties as end groups, without long alkyl chain groups, results in the formation of a Mg(NO3)2 coordination polymer gel. The polymer exhibits a strong fluorescence enhancement upon gel formation. 1 can also be gelated with a variety of magnesium anions such as SO42−, NO3−, Cl−, Br− and I−, indicating that the coordination polymer gel formation of 1 does not strongly depend on anions. The SEM and AFM images of Mg2+ coordination polymer gel 1 display a fibrillar network several micrometres long, with widths in the range of 60–70 nm and thicknesses of about 3 nm. In addition, photophysical studies show that the hydrogel exhibits a typical π–π* transition and gives rise to high fluorescence behavior. The coordination polymer hydrogel exhibits viscoelastic behavior as evidenced from the rheological studies.

Fluorescent hydrogels formed by CH–π and π–π interactions as the main driving forces: an approach toward understanding the relationship between fluorescence and structure

Amide-linked tripyridine derivatives 1, with a para-substituent, and 2, with a meta-substituent, were gelated in water or water-DMSO. The gelation capabilities of 1 and 2 were attributed to the cooperative effects of mainly CH-π and π-π stacking or strong intermolecular hydrogen bonding interactions between the amide groups. The fluorescence properties of gels 1 and 2 were dependent on the binding strength of the π-π stacking.