Chi-Jen Liu

Enhancement of cell radiation sensitivity by pegylated gold nanoparticles

Biocompatible Au nanoparticles with surfaces modified by PEG (polyethylene glycol) were developed in view of possible applications for the enhancement of radiotherapy. Such nanoparticles exhibit preferential deposition at tumor sites due to the enhanced permeation and retention (EPR) effect. Here, we systematically studied their effects on EMT-6 and CT26 cell survival rates during irradiation for a dose up to 10 Gy with a commercial biological irradiator (E(average) = 73 keV), a Cu-Kalpha(1) x-ray source (8.048 keV), a monochromatized synchrotron source (6.5 keV), a radio-oncology linear accelerator (6 MeV) and a proton source (3 MeV). The percentage of surviving cells after irradiation was found to decrease by approximately 2-45% in the presence of PEG-Au nanoparticles ([Au] = 400, 500 or 1000 microM). The cell survival rates decreased as a function of the dose for all sources and nanoparticle concentrations. These results could open the way to more effective cancer irradiation therapies by using nanoparticles with optimized surface treatment. Difficulties in applying MTT assays were also brought to light, showing that this approach is not suitable for radiobiology.

Optimizing the size and surface properties of polyethylene glycol (PEG)-gold nanoparticles by intense x-ray irradiation

The polyethylene glycol (PEG) modified gold nanoparticle complex was synthesized by a one-solution synchrotron x-ray irradiation method. The impact on the structure and morphology of the gold nanoparticles of process parameters such as the PEG molecular weight, the PEG/gold molar ratio and the x-ray dosage were investigated. The size of PEG modified gold particles was found to decrease with increasing PEG addition and x-ray dosage. With the capability to monitor the absorption spectra in situ during the fast synthesis process, this opens the way to accurate control of the size and distribution. PEG chains with an intermediate length (MW6000) were found optimal for size control and colloidal stability in biologically relevant media. Our x-ray synthesized PEG-gold nanoparticles could find interesting applications in nanoparticle-enhanced x-ray tumour imaging and therapy.

Enhancement of irradiation effects on cancer cells by cross-linked dextran-coated iron oxide (CLIO) nanoparticles

We investigated iron oxide nanoparticles with two different surface modifications, dextran coating and cross-linked dextran coating, showing that their different internalization affects their capability to enhance radiation damage to cancer cells. The internalization was monitored with an ultrahigh resolution transmission x-ray microscope (TXM), indicating that the differences in the particle surface charge play an essential role and dominate the particle-cell interaction. We found that dextran-coated iron oxide nanoparticles cannot be internalized by HeLa and EMT-6 cells without being functionalized with amino groups (the cross-linked dextran coating) that modify the surface potential from -18 mV to 13.4 mV. The amount of cross-linked dextran-coated iron oxide nanoparticles uptaken by cancer cells reached its maximum, 1.33 x 10(9) per HeLa cell, when the co-culture concentration was 40 microg Fe mL(-1) or more. Standard tests indicated that these internalized nanoparticles increased the damaging effects of x-ray irradiation, whereas they are by themselves biocompatible. These results could lead to interesting therapy applications; furthermore, iron oxide also produces high contrast for magnetic resonance imaging (MRI) in the diagnosis and therapy stages.

Ideally ordered 10 nm channel arrays grown by anodization of focused-ion-beam patterned aluminum

Arrays of ideally ordered alumina nanochannels with unprecedented ∼10nm pore size, 40–50 nm interpore spacing, and improved channel uniformity have been fabricated by anodizing an aluminum substrate with a guiding pattern on its surface. The pattern is an array of hexagonally close-packed concaves fabricated by focused ion beam direct sputtering; and its lattice constant is carefully matched to the conditions of the subsequent anodization process in order to achieve effective guiding in the growth of the nanochannels and therefore the ordering of an array.

Fabrication of an ordered nanoparticle array with a nanoaperture membrane used as a contact-mask

In this paper, we provide a useful technology to fabricate a long-range ordered nanoparticle array with a feature size under 30 nm. By adjusting the incident angle of Ar + beam milling on a U-shaped barrier layer of anodic alumina oxide, we can create a long-range ordered nanoaperture array with samples prepared by a focused-ion-beam-guided process. Compared to the naturally self-organized alumina nanochannels, the FIB-guided process has increased long-range ordering and uniformity of aperture size, and the aperture size can be varied by changing the grazing angle. The nanoaperture membrane can be used as a contact-mask and its undercut structure has another advantage for nanolithography. This technique could be extensively applied to the manufacturing of advanced nanodevices in large areas and as a catalyst to fabricate one-dimensional nanosized materials. (Some figures in this article are in colour only in the electronic version)

Enhanced growth of anodic alumina nanochannels on Ga-ion pre-irradiated aluminuma)

Exposure of an Al substrate to energetic Ga ions is found to result in enhanced growth rate of its nanochannels during a subsequent anodization process. Depending on the ion dose, the nanochannels in the pre-irradiated area exhibit different lengths. This interesting phenomenon is exploited by scanning a Ga focused ion beam over the desired area to facilitate the fabrication of arrays of anodic alumina nanochannels with custom-designed super-structure, which is based on the variation of channel length in different areas.

Anomalously Enhanced Raman Scattering From Longitudinal Optical Phonons On Ag‐Nanoparticle‐Covered GaN And ZnO

Received 20 August 2009; accepted 25 November 2009; published online 20 January 2010The authors report experimental studies of surface-enhanced Raman scattering SERS ofwurtzite-type GaN and ZnO crystalline samples covered with Ag-nanoparticles. The longitudinaloptical phonons consistently exhibit unusually intense Raman enhancement in comparison withother phonons. The anomaly is interpreted by a proposed model based on a resonant Ramanscattering process assisted by metal-induced gap states at the Ag/GaN and Ag/ZnO interfaces. Thisstudy suggests that SERS of lattice vibrations in inorganic semiconductors is sensitive to theirpropagation nature, providing a progressive perspective view on electron-mediated enhancedRaman scattering. ©

Uniformly enhanced Raman scattering on arrays of silver nanoparticles separated by 5 nm gaps

Different arrays of Ag-nanoparticles grown on anodic alumina nanochannels with precisely tunable gaps (5~25 nm) are exploited for surface-enhanced Raman spectroscopy (SERS). The enhancement becomes significant for gaps below 10 nm and turns dramatically large when gaps reach an unprecedented value of 5 nm. The results are quantitatively consistent with theories based on collectively coupled surface plasmon. Such nanofabricated substrates with consistently uniform and large dynamic range have many chemical/biological sensing applications.