Hailiang Huang

Surface-enhanced Raman scattering effect of ordered gold nanoparticle array for rhodamine B with different morphologies

In this study, well-ordered gold nanoparticle array on silicon substrate was adopted as an active surface-enhanced Raman scattering substrate for detecting rhodamine B (RB), and the influence of RB morphologies on surface-enhanced Raman scattering (SERS) properties was discussed. The Au nanoparticle array was prepared by using patterned P4VP nanodomains of poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) diblock copolymer thin films as nanoreactors which is a simple and economical approach. The results show that Raman spectra of RB on the Au nanopaticle array have much stronger intensity than those on the bare silicon substrate by detecting same RB solution. It indicates that the prepared Au nanoparticle array on silicon substrate has a significant Raman enhancement for RB. Interestingly, the Raman intensity of RB from its ethanol solution is much stronger than that from its aqueous solution due to the special morphologies of RB formed in their ethanol solutions. This work provides an effective approach to prepare highly sensitive and stable surface-enhanced Raman scattering substrate.

Fluorescence enhancement of the conjugated polymer films based on well-ordered Au nanoparticle arrays

In this paper, well-ordered Au nanoparticle arrays on silicon substrates were employed as efficient metal-enhanced fluorescence (MEF) substrates for investigating the fluorescence properties of the conjugated polymer poly(3-hexylthiophene) (P3HT). The ordered Au nanoparticle arrays were fabricated by block copolymer self-assembly technology, and the particle sizes were controlled by adjusting the molar ratios of HAuCl4 precursor to vinyl pyridine units. The approach is economical and suitable to fabricate large-area MEF substrates. The results about fluorescence properties of P3HT showed that the fluorescence intensities of the P3HT films were improved on ordered Au nanoparticle arrays compared to those on bare silicon substrate and were significantly enhanced with the Au nanoparticle sizes increasing. The mechanism is based on localized surface plasmon resonances, coupling and propagating surface plasmons, and the emission enhancement mainly resulted from the increase of the excitation rate. This work provides a new way to prepare efficient MEF substrates for high-performance fluorescence-based devices.

Patterning of triblock copolymer film and its application for surface-enhanced Raman scattering

In this paper, microphase behavior of an ABC triblock copolymer, polystyrene-block-poly(2-vinylpyridine)-block-poly( ethylene oxide), namely PS-b-P2VP-b-PEO, was systematically studied during spin-coating and solvent vapor annealing based on various parameters, including the types of the solvent, spin speed and thickness. The morphological features and the microdomain location of the different blocks were characterized by atomic force microscope (AFM) and high resolution transmission electron microscopy (HRTEM). With increasing thickness, the order-order transition from nanopores array to the pattern of nanostripes was observed due to microdomain coarsening. These processes of pattern transformation were based on the selectivity of toluene for different blocks and on the contact time between solvent molecules and the three blocks. This work provides different templates for preparation of gold nanoparticle array on silicon wafer, which can be adopted as an active surface-enhanced Raman scattering (SERS) substrate for poly(3-hexylthiophene) (P3HT).

Fabrication of Ordered Nanopattern by using ABC Triblock Copolymer with Salt in Toluene

Ordered nanopatterns of triblock copolymer polystyrene-block-poly(2-vinylpyridine)-block- poly (ethylene oxide)(PS-b-P2VP-b-PEO) have been achieved by the addition of lithium chloride (LiCl). The morphological and structural evolution of PS-b-P2VP-b-PEO/LiCl thin films were systematically investigated by varying different experimental parameters, including the treatment for polymer solution after the addition of LiCl, the time scale of ultrasonic treatment and the molar ratio of Li+ ions to the total number of oxygen atoms (O) in PEO block and the nitrogen atoms (N) in P2VP block. When toluene was used as the solvent for LiCl, ordered nanopattern with cylinders or nanostripes could be obtained after spin-coating. The mechanism of nanopattern transformation was related to the loading of LiCl in different microdomains.

Gap-plasmon of Fe 3 O 4 @Ag core-shell nanostructures for highly enhanced fluorescence detection of Rhodamine B

A novel gap-plasmon of Fe3O4@Ag core-shell nanoparticles for surface enhanced fluorescence detection of Rhodamine B (RB) was developed. Fe3O4@Ag core-shell nanostructures with Ag shell and Fe3O4 core were synthetized by self-assembled method with the assistance of 3-mercaptopropyl trimethoxy silane (MPTS). To study the RB fluorescence enhanced by gap-plasmon, the fluorescence properties of RB on the substrates with different nanogap densities were systematically investigated, and the results showed that the fluorescence intensity of RB on Fe3O4@Ag core-shell NPs substrate was much stronger than that on bare glass substrate, and the fluorescence intensity was further improved by using multilayer Fe3O4@Ag core-shell NPs substrate which had higher nanogap density. Different from the mechanism that is based on the maximum overlap of the surface plasmon resonance (SPR) band and emission band, the mechanism of the fluorescence enhancement in our work is based on the localized surface plasmon (LSP) and the gap plasmon near-field coupling with the Fe3O4@Ag core-shell NPs. Besides, the detection limit obtained was as low as 1×10-7 mol/L, and the Fe3O4@Ag core-shell NPs substrate had high selectivity for RB fluorophores. It was demonstrated that the Fe3O4@Ag core-shell NPs substrate had activity, good stability, and selectivity for fluorescence detection of RB. And the detection of RB by the surface plasmon enhanced fluorescence was more convenient and rapid than the traditional detection methods in previous works.

Nanopattern Transformation of ABC Triblock Copolymer Thin Films Induced by Strong Solvent Selectivity and Annealing

Nanopattern transformation behaviors of polyisoprene-block-polystyrene-block-poly(2-vinylpyridine) (PI-b-PS-b-P2VP) asymmetric ABC triblock copolymer were investigated systematically with various control parameters, including different solvents for polymer solution and annealing conditions in this paper. Ordered nanopattern of PI-b-PS-b-P2VP with hexagonal cylinders could be obtained when PI-b-PS-b-P2VP toluene solution was spin-coated on silicon substrate followed by toluene vapor annealing process. When the film with hexagonal and cylindrical nanopattern was exposed to saturated toluene vapor, the order-order transition of cylindrical nanopattern to parallel nanopattern was observed due to the strong selectivity of toluene to PS and PI blocks. Furthermore, fingerprint nanopattern could also be obtained by solvent annealing in tetrahydrofuran vapor. The nanopattern transformation was due to different selectivity of solvents and incompatibilities of the three blocks of PI-b-PS-b-P2VP under various solvent annealing conditions.

Tunable Electromagnetic Enhancement of Gold Nanoparticle Arrays

In this paper, triblock copolymer polyisoprene-block-polystyrene-block-poly(2-vinylpyridine) (PI-b-PS-b-P2VP) micelles containing HAuCl4 were spin-coated on silicon wafers followed by calcination to form gold nanoparticle arrays. Subsequently the surface optical performances of poly(3-hexylthiophene) (P3HT)-coated Au nanoparticle arrays were investigated. The particle size and the interparticle distance of the gold nanoparticle arrays could be controlled by adjusting the molar ratio of HAuCl4 precursor to vinyl pyridine units in PI-b-PS-b-P2VP and the spin speed during spin-coating. The results demonstrated that Au nanoparticle arrays with large nanoparticle size were able to produce strong electromagnetic field enhancement. Furthermore, the ratio of average particle size to average interparticle distance increased with decreasing spin speed, resulting in strong electromagnetic field enhancement for metal-enhanced fluorescence (MEF) and surface-enhanced Raman scattering (SERS).