Jeong-Yong Choi

Silanization of Ag-Deposited Magnetite Particles: An Efficient Route to Fabricate Magnetic Nanoparticle-Based Raman Barcode Materials

Silica-coated Ag nanostructures usable as magnetic nanoparticle-based Raman barcode materials were developed. Initially, 283 nm sized spherical magnetite particles composed of 13 nm sized superparamagnetic Fe(3)O(4) nanoparticles were synthesized, and silver deposition was conducted using butylamine as the reductant of AgNO(3) in ethanol. The Ag-deposited Fe(3)O(4) (Fe(3)O(4)@Ag) particles are found to be efficient surface-enhanced Raman scattering (SERS) substrates with the enhancement factor at 632.8 nm excitation to be about 3 x 10(6). After SERS markers such as benzenethiol, 4-mercaptotoluene, 4-aminobenzenethiol, and 4-nitrobenzenethiol were adsorbed onto the silver surface, poly(allylamine hydrochloride) (PAH) was coated onto them using the layer-by-layer deposition method such that a subsequent base-catalyzed silanization could readily form a 60 nm thick silica shell around the PAH layer by a biomimetic process. The cross-linked silica shells effectively prevented the SERS-marker molecules from being liberated from the surface of the Fe(3)O(4)@Ag particles. Although the gram magnetization decreased nearly to one-half of the initial value because of coating with silver and silica, the remaining magnetization was nonetheless strong enough for the silica-coated Fe(3)O(4)@Ag particles to be used as barcode materials operating via SERS.

Silver-coated dye-embedded silica beads: a core material of dual tagging sensors based on fluorescence and Raman scattering.

We have developed a new type of dual-tag sensor for immunoassays, operating via both fluorescence and surface-enhanced Raman scattering (SERS). A one-shot fluorescence image over the whole specimen allows us to save considerable time because any unnecessary time-consuming SERS measurements can be avoided from the signature of the fluorescence. Dye-embedded silica beads are prepared initially, and then SERS-active silver is coated onto them via a very simple electroless-plating method. The Raman markers are subsequently assembled onto the Ag-coated silica beads, after which they are stabilized by silanization via a biomimetic process in which a poly(allylamine hydrochloride) layer formed on the Raman markers by a layer-by-layer deposition method acting as a scaffold for guiding silicification. In the final stage, specific antibodies are attached to the silica surface in order to detect target antigens. The fluorescence signal of the embedded dye can be used as a fast readout system of molecular recognition, whereas the SERS signals are subsequently used as the signature of specific molecular interactions. In this way, the antibody-grafted particles were found to recognize antigens down to 1 × 10(-10) g mL(-1) solely by the SERS peaks of the Raman markers.

pH effect on surface potential of polyelectrolytes-capped gold nanoparticles probed by surface-enhanced Raman scattering.

Nanoparticles are commonly stabilized through the adsorption of acidic/basic polyelectrolytes around the surface of the particle. One example of these nanoparticles is poly(ethylenimine) (PEI)-capped Au nanoparticles. In this work, we have examined by means of surface-enhanced Raman scattering (SERS) of 2,6-dimethylphenylisocyanide (2,6-DMPI) how much the surface potential of Au nanoparticles is affected by the solution pH through the mediation of the protonation and deprotonation of PEI in contact with Au nanoparticles. In fact, the surface-potential-dependent isocyanide (NC) stretching peak of 2,6-DMPI has shifted sharply around pH 8.5, close to the pK(a) value of the primary amine of PEI. When a negatively charged poly(acrylic acid) (PAA) was deposited onto the PEI, the peak shift of the NC stretching band took place around pH 6.5, close to the average pK(a) value of PEI and PAA. When additional PEI was deposited on PAA, the peak shift of the NC stretching band occurred once again around pH 8.5, indicative of the stronger interaction of upper two polyelectrolyte layers. These data clearly illustrate the usefulness of SERS in the elucidation of a delicate interaction of cationic and anionic polyelectrolytes, especially in layer-by-layer deposition.

Effect of organic vapors and potential-dependent Raman scattering of 2,6-dimethylphenylisocyanide on platinum nanoaggregates

The surface-enhanced Raman scattering characteristics of 2,6-dimethylphenylisocyanide (2,6-DMPI) on Pt nanoaggregates, in ambient and electrochemical environments and in the presence of organic vapors, were examined and compared with those on Au nanoaggregates. Due to the exclusive adsorption via the isocyanide group, the NC stretching band was very susceptible to the measurement conditions although the ring associated bands showed negligible peak shifts. In ambient conditions, the peak shift of the NC stretching vibration on Pt (29 cm(-1)) was one half of that on Au (61 cm(-1)), suggesting that the electron donation capability of the isocyanide group to Au was greater than that to Pt. In the electrochemical environment, the NC stretching peak varied linearly with slopes of ∼42 and ∼36 cm(-1) V(-1) on Pt and Au, respectively. On the other hand, the NC stretching bands of 2,6-DMPI on Pt red-shifted by as much as 15 and 41 cm(-1), in the presence of acetone and ammonia, respectively, corresponding to the lowering of the surface potential of Pt nanoaggregates from +0.2 to -0.2 and -0.8 V, respectively. On Au nanoaggregates, however, acetone appeared to increase the surface potential of Au from +0.2 to +0.3 V, although ammonia decreased the surface potential from +0.2 to -0.4 V. Acetone must then act as an electron donor when interacting with Pt while it serves as an electron acceptor when interacting with Au, in agreement with an ab initio quantum mechanical calculation.

Silver Nanostructures Applicable As Core Materials Of SERS‐Based Molecular Sensors And Barcodes

We have developed a simple electroless plating method used to prepare silver‐deposited silica or magnetic beads and also succeeded in coating them further with silica layers, without affecting the surface‐enhanced Raman scattering (SERS) spectral features of marker molecules assembled on the silver nanostructures. The Ag‐deposited dye‐embedded silica beads can then be used as a dual‐tag sensor, operating via both fluorescence and SERS, for immunoassays and the Ag‐deposited Fe3O4‐embedded silica beads can be used as Raman barcode materials, possessing also strong enough magnetic moments.