Su-Ji Jeon

Single-step and rapid growth of silver nanoshells as SERS-active nanostructures for label-free detection of pesticides.

We explored a single-step approach for the rapid growth of Ag nanoshells (Ag NSs) under mild conditions. Without predeposition of seed metals, a uniform and complete layer of Ag shells was rapidly formed on silica core particles within 2 min at 25 °C via single electron transfer from octylamine to Ag(+) ions. The size and thickness of the Ag NSs were effectively tuned by adjusting the concentration of silica nanoparticles (silica NPs) with optimal concentrations of AgNO3 and octylamine. This unusually rapid growth of Ag NSs was attributed to a significant increase in the reduction potential of the Ag(+) ions in ethylene glycol (EG) through the formation of an Ag/EG complex, which in turn led to their facile reduction by octylamine, even at room temperature. A substantial enhancement in the surface-enhanced Raman scattering (SERS) of the prepared Ag NSs was demonstrated. The Ag NSs were also utilized as SERS-active nanostructures for label-free detection of the pesticide thiram. The Ag NS-based SERS approach successfully detected thiram on apple peel down to the level of 38 ng/cm(2) in a label-free manner, which is very promising with respect to its potential use for the on-site detection of residual pesticides.

One-step synthesis of silver nanoshells with bumps for highly sensitive near-IR SERS nanoprobes

A seedless, one-step synthetic route to uniform bumpy silver nanoshells (AgNSs) as highly NIR sensitive SERS substrates is reported. These substrates can incorporate Raman label compounds and biocompatible polymers on their surface. AgNS based NIR-SERS probes are successfully applied to cell tracking in a live animal using a portable Raman system.

Optical Detection of Enzymatic Activity and Inhibitors on Non-Covalently Functionalized Fluorescent Graphene Oxide

It has been of great interest to measure the activity of acetylcholinesterase (AChE) and its inhibitor, as AChE is known to accelerate the aggregation of the amyloid beta peptides that underlie Alzheimers disease. Herein, we report the development of graphene oxide (GO) fluorescence-based biosensors for the detection of AChE activity and AChE inhibitors. To this end, GO was non-covalently functionalized with phenoxy-modified dextran (PhO-dex-GO) through hydrophobic interaction; the resulting GO showed excellent colloidal stability and intense fluorescence in various aqueous solutions as compared to pristine GO and the GO covalently functionalized with dextran. The fluorescence of PhO-dex-GO remarkably increased as AChE catalyzed the hydrolysis of acetylthiocholine (ATCh) to give thiocholine and acetic acid. It was found that the turn-on fluorescence response of PhO-dex-GO to AChE activity was induced by protonation of carboxyl groups on it from the product of the enzymatic hydrolysis reaction, acetic acid. On the basis of its turn-on fluorescence response, PhO-dex-GO was able to report kinetic and thermodynamic parameters involving a maximum velocity, a Michaelis constant, and an inhibition dissociation constant for AChE activity and inhibition. These parameters enable us to determine the activity of AChE and the efficiency of the inhibitor.

Structuring Pd Nanoparticles on 2H-WS2 Nanosheets Induces Excellent Photocatalytic Activity for Cross-Coupling Reactions under Visible Light

Effective photocatalysts and their surface engineering are essential for the efficient conversion of solar energy into chemical energy in photocatalyzed organic transformations. Herein, we report an effective approach for structuring Pd nanoparticles (NPs) on exfoliated 2H-WS2 nanosheets (WS2/PdNPs), resulting in hybrids with extraordinary photocatalytic activity in Suzuki reactions under visible light. Pd NPs of different sizes and densities, which can modulate the photocatalytic activity of the as-prepared WS2/PdNPs, were effectively structured on the basal plane of 2H-WS2 nanosheets via a sonic wave-assisted nucleation method without any reductants at room temperature. As the size of Pd NPs on WS2/PdNPs increased, their photocatalytic activity in Suzuki reactions at room temperature increased substantially. In addition, it was found that protic organic solvents play a crucial role in activating WS2/PdNPs catalysts in photocatalyzed Suzuki reactions, although these solvents are generally considered much less effective than polar aprotic ones in the conventional Suzuki reactions promoted by heterogeneous Pd catalysts. A mechanistic investigation suggested that photogenerated holes are transferred to protic organic solvents, whereas photogenerated electrons are transferred to Pd NPs. This transfer makes the Pd NPs electron-rich and accelerates the rate-determining step, i.e., the oxidative addition of aryl halides under visible light. WS2/PdNPs showed the highest turnover frequency (1244 h-1) for photocatalyzed Suzuki reactions among previously reported photocatalysts.

2H-WS2 Quantum Dots Produced by Modulating the Dimension and Phase of 1T-Nanosheets for Antibody-Free Optical Sensing of Neurotransmitters

Modulating the dimensions and phases of transition metal dichalcogenides is of great interest to enhance their intrinsic properties or to create new physicochemical properties. Herein, we report an effective approach to synthesize 2H-WS2 quantum dots (QDs) via the dimension and phase engineering of 1T-WS2 nanosheets. The solvothermal reaction of chemically exfoliated 1T-WS2 nanosheets in N-methyl-2-pyrrolidone (NMP) under an N2 atmosphere induced their chopping and phase transition at lower temperature to produce 2H-WS2 QDs with a high quantum yield (5.5 ± 0.3%). Interestingly, this chopping and phase transition process showed strong dependency on solvent; WS2 QDs were not produced in other solvents such as 1,4-dioxane and dimethyl sulfoxide. Mechanistic investigations suggested that NMP radicals played a crucial role in the effective production of 2H-WS2 QDs from 1T-WS2 nanosheets. WS2 QDs were successfully applied for the selective, sensitive, and rapid detection of dopamine in human serum (4 min, as low as 23.8 nM). The intense fluorescence of WS2 QDs was selectively quenched upon the addition of dopamine and Au3+ ions due to fluorescence resonance energy transfer between WS2 QDs and the quickly formed Au nanoparticles. This new sensing principle enabled us to discriminate dopamine from dopamine-derivative neurotransmitters including epinephrine and norepinephrine, as well as other interference compounds.

Oxygen-mediated formation of MoSx-doped hollow carbon dots for visible light-driven photocatalysis

It is of great interest to modulate the photocatalytic activity of nanomaterials by varying their composition at the atomic scale and their nanostructure. Herein, we demonstrate a bottom-up approach for the synthesis of MoSx-doped hollow carbon dots (MoSHCDs) as a photocatalyst for the visible light-driven aerobic oxidative coupling of amines. The molecular oxygen-assisted solvothermal reaction of a MoS2 nanosheets/N-methyl-2-pyrrolidone dispersion provided MoSHCDs with a unique hollow interior of 6–7 nm as well as with doping of a large portion of pyridinic N atoms and MoSx. As compared to typical carbon dots not bearing hollow structures, the as-prepared MoSHCDs exhibited excellent photocatalytic activity in the oxidative coupling reactions of various amines under visible light irradiation at 25 °C. Mechanistic investigations suggested that doping with pyridinic N atoms and MoSx was responsible for the significantly improved photocatalytic activity of MoSHCDs in photocatalysis. The reaction mechanism of the oxidative coupling reactions of amines that were effectively promoted by MoSHCDs under visible light irradiation was also fully examined.

Quantum dot-assembled nanoparticles with polydiacetylene supramolecule toward label-free, multiplexed optical detection.

Quantum dot (QD)-assembled silica nanoparticles bearing a polydiacetylene (PDA) supramolecule on their surface (SiO(2)@QDs@PDA NPs) were developed for label-free and multiplexed detection of biological molecules. Two types of QD-assembled silica NPs (SiO(2)@QDs NPs) were prepared and coated with the PDA supramolecule via photo-induced polymerization of 10,12-pentacosadiynoic acid. One of the SiO(2)@QDs NPs was embedded with blue-QDs, and the other was embedded with green-QDs for encoding. The resulting SiO(2)@QDs@PDA NPs showed discrete QD photoluminescence for encoding as well as PDA fluorescence for sensing a target without interference or overlap. Under heating stress of the SiO(2)@QDs@PDA NPs, the color of the PDA changed from blue to red, which allowed us to observe the fluorescence emitted from red PDA. The mixture of two different SiO(2)@QDs@PDA NPs, SiO(2)@QDs@blue-PDA NPs not emitting the fluorescence of PDA and SiO(2)@QDs@red-PDA NPs where stress was brought onto turn on the PDA fluorescence, was effectively imaged and readily distinguished via fluorescence microscopy, indicating their potential for label-free and multiplexed detection of target molecules.

Effect of alpha-resorcylic acid–l-phenylalanine amide on collagen synthesis and matrix metalloproteinase expression in fibroblasts

Regulation of collagen synthesis and matrix metalloproteinases (MMPs) expression levels has been an important issue in medicinal, pharmaceutical and cosmetic industries. Herein, α-Resorcylic acid-phenylalanine amide (α-RA-F) was prepared and its biological activities were observed. We found that α-RA-F boosted collagen synthesis and reduced MMPs expression levels in human fibroblasts without cytotoxicity.

2D transition metal dichalcogenides with glucan multivalency for antibody-free pathogen recognition

The ability to control the dimensions and properties of nanomaterials is fundamental to the creation of new functions and improvement of their performances in the applications of interest. Herein, we report a strategy based on glucan multivalent interactions for the simultaneous exfoliation and functionalization of two-dimensional transition metal dichalcogenides (TMDs) in an aqueous solution. The multivalent hydrogen bonding of dextran with bulk TMDs (WS2, WSe2, and MoSe2) in liquid exfoliation effectively produces TMD monolayers with binding multivalency for pathogenic bacteria. Density functional theory simulation reveals that the multivalent hydrogen bonding between dextran and TMD monolayers is very strong and thermodynamically favored (ΔEb = −0.52 eV). The resulting dextran/TMD hybrids (dex-TMDs) exhibit a stronger affinity (Kd = 11 nM) to Escherichia coli O157:H7 (E. coli) than E. coli-specific antibodies and aptamers. The dex-TMDs can effectively detect a single copy of E. coli based on their Raman signal.The detection of pathogenic microorganisms is key consideration for safety across a wide range of fields. Here, the authors report on the simultaneous exfoliation and functionalisation of transition metal dichalcogenides with dextran for antibody-free detection of pathogenic Escherichia coli.