DaBin Yim

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.

Monodisperse Microshell Structured Gelatin Microparticles for Temporary Chemoembolization

Embolization is a nonsurgical, minimally invasive procedure that deliberately blocks a blood vessel. Although several embolic particles have been commercialized, their much wider applications have been hampered owing mainly to particle size variation and uncontrollable degradation kinetics. Herein we introduce a microfluidic approach to fabricate highly monodisperse gelatin microparticles (GMPs) with a microshell structure. For this purpose, we fabricate uniform gelatin emulsion precursors using a microfluidic technique and consecutively cross-link them by inbound diffusion of glutaraldehyde from the oil continuous phase to the suspending gelatin precursor droplets. A model micromechanic study, carried out in an artificial blood vessel, demonstrates that the extraordinary degradation kinetics of the GMPs, which stems from the microshell structure, enables controlled rupturing while exhibiting drug release under temporary chemoembolic conditions.

β-Lactoglobulin Peptide Fragments Conjugated with Caffeic Acid Displaying Dual Activities for Tyrosinase Inhibition and Antioxidant Effect

The regulation of tyrosinase activity and reactive oxygen species is of great importance for the prevention of dermatological disorders in the fields of medicine and cosmetics. Herein, we report a strategy based on solid-phase peptide chemistry for the synthesis of β-lactoglobulin peptide fragment/caffeic acid (CA) conjugates (CA-Peps) with dual activities of tyrosinase inhibition and antioxidation. The purity of the prepared conjugates, CA-MHIR, CA-HIRL, and CA-HIR, significantly increased to 99%, as acetonide-protected CA was employed in solid-phase coupling reactions on Rink amide resins. The tyrosinase inhibitory activities of all CA-Pep derivatives were higher than the activity of kojic acid, and CA-MHIR exhibited the highest tyrosinase inhibition activity (IC50 = 47.9 μM). Moreover, CA-Pep derivatives displayed significantly enhanced antioxidant activities in the peroxidation of linoleic acid as compared to the pristine peptide fragments. All CA-Pep derivatives showed no cytotoxicity against B16-F1 melanoma cells.

Fluorescent 2D WS2 Nanosheets Bearing Chemical Affinity Elements for the Recognition of Glycated Hemoglobin

It is required to exfoliate and functionalize 2D transition metal dichalcogenides (TMDs) in an aqueous solution for biological and medical applications. Herein, the approach for the simultaneous exfoliation and functionalization of 2D WS2 nanosheets using boronic acid-modified poly(vinyl alcohol) (B-PVA) in an aqueous solution is reported, and the B-PVA-functionalized WS2 nanosheets (B-PVA-WS2 ) are exploited as a fluorescent biosensor for the detection of glycated hemoglobin, HbA1c. The synthetic B-PVA polymer facilitates the exfoliation and functionalization of WS2 nanosheets from the bulk counterpart in the aqueous solution via a pulsed sonication process, resulting in fluorescent B-PVA-WS2 nanohybrids with a specific recognition of HbA1c. The fluorescence of the B-PVA-WS2 is quenched in the presence of HbA1c, whereas PVA-functionalized WS2 (PVA-WS2 ), not bearing boronic acid as a recognition moiety, shows no fluorescence changes upon the addition of the target. The B-PVA-WS2 is able to selectively detect HbA1c at the concentration as low as 3.3 × 10-8 m based on its specific fluorescence quenching.