Sing Hai Tang

In vitro cancer cell imaging and therapy using transferrin-conjugated gold nanoparticles

Gold nanoparticles were conjugated with transferrin molecules for targeting, imaging and therapy of breast cancer cells (Hs578T, ATCC). Results show that, the transferrin-transferrin receptor-mediated cellular uptake of gold nanoparticles is six times of that in the absence of this interaction. As a consequence, the laser power effective for photothermal therapy of the cancer cells was reduced to values of two orders of magnitude lower. To demonstrate the efficiency of the conjugated gold nanoparticles in selectively targeting cancer cells, the cellular uptake of the gold nanoparticles by noncancerous cells (3T3, ATCC) was also investigated. The cellular uptake by the normal cells is only one fourth of that by the cancerous cells indicating that the transferrin-transferrin receptor interaction plays an important role in controlling the cellular uptake of the gold nanoparticles.

Controlled growth of single-walled carbon nanotubes by catalytic decomposition of CH4 over Mo/Co/MgO catalysts

It was found that the addition of molybdenum to Co/MgO catalysts could remarkably increase the yield and also improve the quality of single-walled carbon nanotubes (SWNTs) from catalytic decomposition of methane. The generation rate of SWNTs was raised at least 10 times and the formation of amorphous carbon was suppressed. But there is an optimum content of Mo and Co, beyond which multi-walled carbon nanotubes (MWNTs) were formed. In other words, the relative amount of SWNTs and MWNTs could be controlled by the composition of catalysts. The obtained SWNTs showed a very high BET surface area. The promotion role of molybdenum was discussed.

Excitonic nonlinear absorption in CdS nanocrystals studied using Z-scan technique

Irradiance dependence of excitonic nonlinear absorption in cadmium sulfide (CdS) nanocrystals has been studied by using Z-scan method with nanosecond laser pulses. The wavelength dependence of nonlinear absorption has also been measured near the excitonic transition of 1S(e)–1S3/2(h). We observe the saturable absorption, which can be described by a third-order and a fifth-order nonlinear process for both 3.0-nm-sized and 2.3-nm-sized CdS nanocrystals. The experimental results show that the excitonic nonlinear absorption of CdS nanocrystals is greatly enhanced with decreasing particle size. A two-level model is utilized to explain both irradiance and wavelength dependence of the excitonic nonlinearity.

Two-dimensional structures of ferroelectric domain inversion in LiNbO3 by direct electron beam lithography

We report on the fabrication of domain-reversed structures in LiNbO3 by means of direct electron beam lithography at room temperature without any static bias. The LiNbO3 crystals were chemically etched after exposure of the electron beam, and then the patterns of domain inversion were characterized by atomic force microscopy (AFM). In our experiment, an interesting phenomenon occurred when the electron beam wrote a one-dimensional grating on the negative c face: a two-dimensional (2D) dotted array was observed on the positive c face, which is significant for its potential to produce 2D and three-dimensional photonic crystals. Furthermore, we also obtained 2D ferroelectric domain inversion in the whole LiNbO3 crystal by writing the 2D square pattern on the negative c face. Such a structure may be utilized to fabricate 2D nonlinear photonic crystal. AFM demonstrates that a 2D domain-reversed structure has been achieved not only on the negative c face of the crystal, but also across the whole thickness of th...

Controlled surface-plasmon coupling in SiO2-coated gold nanochains for tunable nonlinear optical properties

Linear chains of SiO2-coated Au nanoparticles, exhibiting large third-order nonlinearity at multiple wavelengths ranging from visible to near infrared, were successfully synthesized and self-assembled on glass substrates using a reduction of HAuCl4 and chemical surfactant modification. The optical absorption spectra peaking at 530, 620, 715, 830, and 1100nm wavelengths were measured to the transverse and longitudinal surface plasmon resonance modes of 2, 3, 4, and 5 Au particles, respectively. Greatly enhanced third-order nonlinear optical responses have been observed at multiple wavelengths.

Novel Pb(ii) coordination frameworks: synthesis, crystal structures and unusual third-order nonlinear optical propertiesElectronic supplementary information (ESI) available: crystal packing diagram of complex 2. See http://www.rsc.org/suppdata/jm/b3/b315682f/

Three novel Pb(II) coordination complexes, [Pb(dimb)(DMF)(NO3)2]n1, [Pb(dimb)(SCN)2]n2 [dimb = 1,3-bis(imidazol-1-ylmethyl)-benzene], {[Pb(bimb)1.5(NO3)2](DMF)}n3 [bimb = 4,4′-bis(imidazol-1-methyl)-biphenyl], were synthesized and characterized by X-ray crystallography. Complex 1 exhibits a one-dimensional (1D) zigzag chain structure, which has two crystallographically independent Pb(II) atom centers. Complex 2 possesses a two-dimensional (2D) corrugated network, which contains 24-membered M2L2 metallocyclic rings. Complex 3 has a 1D infinite non-interpenetrated molecular ladder, which has very large cavities with dimensions of 17.89 × 20.34 A, and DMF molecules fill the channel formed by adjacent two ladders. The third-order nonlinear optical (NLO) properties of the three complexes were measured by a Z-scan technique in DMF solution. All three complexes possess weak absorption and strong refraction. Their third-order NLO refractive coefficients, n2, are −5.96 × 10−19 m2 W−1 for 1, −8.34 × 10−19 m2 W−1 for 2, and −7.15 × 10−19 m2 W−1 for 3. It is notable that two Pb(II) complexes 1 and 3 with 1D structure show strong self-defocusing behavior, which are different from the reported 1D coordination complexes containing d10 metal ions; also, complex 2 is the first 2D coordination compound that possesses strong self-defocusing behavior. The χ(3) values of complexes 1, 2 and 3 were calculated to be 4.46 × 10−13, 6.25 × 10−13 and 5.42 × 10−13 esu, respectively.

Observation of resonant energy transfer in Au:CdS nanocomposite

Au:CdS nanocomposite film was investigated using femtosecond pump–probe measurement at 800 nm. Time dependence of transmittance shows a two-photon absorption followed by a saturable absorption and recovery process, which clearly demonstrates that resonant energy transfer between CdS and Au nanocomposite systems occur with excitation at 800 nm. In addition, enhancement of the two-photon absorption coefficient in Au:CdS nanocomposite with a factor of more than 6 was observed compared to that of bulk CdS.

Size and dielectric dependence of the third-order nonlinear optical response of Au nanocrystals embedded in matrices

The third-order nonlinear optical response of Au nanocrystals embedded in BaTiO(3) and ZrO(2) matrices was investigated through the off-resonance femtosecond optical Kerr effect. Compared with pristine films, the nonlinearity of composite films shows an enhancement that depends on the sizes of Au particles and the refractive index of the matrices. We performed a calculation based on Lorenz-Mie scattering theory to explain the experimental results. Additionally, the nonlinearity was optimized by determination of the values of the particle size and the refractive index of the matrix.

Stress effect on Raman spectra of Ce-doped BaTiO3 films

Ce-doped BaTiO3 (BTO:Ce) thin films prepared on MgO (100) substrates by pulsed laser deposition (PLD) at oxygen pressure of 1.2×10-3 and 17 Pa have been studied by micro-Raman spectroscopy, x-ray diffraction (XRD) and atomic force microscopy (AFM). The film deposited at lower oxygen pressure has a larger lattice parameter in the direction normal to the substrate surface, and the film has smaller grains and a smoother surface. The polarized Raman peaks of both as-deposited films show blue shifts and linewidth broadening in comparison to those of the BaTiO3 single crystal. The blue shifts are attributed to tensile stresses in the films. Our results indicate that the grain size increases and the tensile stress relaxes with annealing. We have shown that quantum confinement and oxygen vacancies are not the dominant factors for the observed Raman spectral changes.

Size-dependent excited state properties of CdS nanocrystals

Abstract CdS nanocrystals of different particle sizes dispersed in ZrO2 films were fabricated by sol–gel and dipping method. The size dependent excited state optical properties were systematically investigated by photoluminescence, time-resolved photoluminescence and Raman spectroscopy. The experimental results show that the relaxation of the excited state is composed of two processes. The fast component that arises from band edge emission shows a weak dependence on particle size, while the slow component, which is attributed to the shallow defect level emission, exhibits strong dependence on particle sizes.