Hyoung Kun Park

Self-assembly of poly(ethylenimine)-capped Au nanoparticles at a toluene-water interface for efficient surface-enhanced raman scattering.

Branched poly(ethylenimine) (PEI)-capped Au nanoparticles are prepared at room temperature using PEI as the reductant of hydrogen tetrachloroaurate (HAuCl4). The size of Au nanoparticles, ranging from 10 to 70 nm, is readily controlled by varying the relative amount of PEI used initially versus HAuCl4. The PEI-capped Au nanoparticles are further demonstrated to be assembled into a large area of 2-D aggregates at a toluene-water interface either by heating the mixture or by adding benzenethiol to the toluene phase at room temperature. Both films are quite homogeneous, but Au nanoparticles appear to be more closely packed in the film assembled via the mediation of benzenethiol. The optical property of the PEI-capped Au films is controlled by the amount of benzenethiol added to the toluene phase. The obtained large area of PEI-capped Au film exhibits strong SERS activity of benzenethiol and also exhibits a very intense SERS spectrum of 4-nitrobenzenethiol via a place-exchange reaction that takes place between benzenethiol and 4-nitrobenzenethiol. Because the proposed method is cost-effective and is suitable for the mass production of diverse Au films irrespective of the shapes of the underlying substrates, it is expected to play a significant role in the development of optical nanotechnology especially for surface plasmon-based analytical devices.

A Facile Deposition of Silver onto the Inner Surface of a Glass Capillary Tube for Micro-Surface-Enhanced Raman Scattering Measurements

Silver can be deposited very efficiently onto glass substrates using only ethanolic solutions of AgNO3 and butylamine. This paper reports that the inner surface of a glass capillary can also be coated evenly with silver by shaking it after soaking in ethanolic solutions of AgNO3 and butylamine; the silver deposited outside the capillary can be easily wiped off with cotton wool before drying. The grain size of the silver deposited onto the inner surface can be readily controlled within the range from 20 to 100 nm by varying the relative molar ratio of butylamine and AgNO3 used as reactants. Due to its nanoaggregated structure, the Ag coated capillary is a very efficient surface-enhanced Raman scattering (SERS) active substrate, particularly usable in the microanalysis of chemicals; the detection limit of adenine is as low as 1.0 × 10−7 M based on a signal-to-noise (S/N) ratio of 3. Since the proposed method is cost-effective and is suitable for the mass production of Ag coated capillaries, we fully expect it to play a significant role in the development of SERS based microchip analyzers and even in the fabrication of Ag coated hollow glass waveguides.

Controlled growth of calcium carbonate by poly(ethylenimine) at the air/water interface

Two metastable calcium carbonate polymorphs, hemispherical vaterite and needle-like aragonite, are selectively formed at the air/water interface by the mediation of poly(ethyleneimine)(with molecular weights of 25000 and 2000, respectively) dissolved in supersaturated calcium bicarbonate solution.

New Strategy for Ready Application of Surface-Enhanced Resonance Raman Scattering/Surface-Enhanced Raman Scattering to Chemical Analysis of Organic Films on Dielectric Substrates

Dropping of appropriately concentrated AgNO3 and NaBH4 solutions, as well as laser-ablated Ag sols, onto organic molecules results in the formation of aggregated Ag nanoparticles that can induce surface-enhanced Raman scattering (SERS) for the molecules. The addition of flocculating agents such as alkali halides can further increase the Raman signals. We demonstrate in this work that Raman spectra can be obtained even for 0.01 monolayers of R6G on Si simply by spreading silver nanoparticles and/or fabricating Ag nanoparticles and nanoaggregates at the gaps and vacant sites of R6G molecules. The application prospect of the present methodology is extremely high, not only because of its simplicity but also because of the fact that the observation of vibrational spectra is one of the most incisive methods for understanding the chemical and physical phenomena on a variety of surfaces.