g-Dah Chen

Photoacoustic Imaging of Multiple Targets Using Gold Nanorods

Photoacoustic (PA) imaging has been used mainly for anatomical and functional imaging. Although functionalized nanoparticles also have been developed for PA molecular imaging, only single targeting has been demonstrated. In this study, PA imaging of multiple targets using gold nanorods is demonstrated experimentally using HER2 and CXCR4 as target molecules. The two corresponding monoclonal antibodies were conjugated to two types of gold nanorod with different aspect ratios. Gold nanorods with mean aspect ratios of 5.9 and 3.7 exhibited peak optical absorptions at 1000 and 785 nm, respectively. Appropriate selection of laser irradiation wavelength enhances PA signals by 7-12 dB and allows signals from gold nanorods corresponding to specific bindings to be distinguished. This approach potentially allows the expression levels of different oncogenes of cancer cells to be revealed simultaneously.

Photoacoustic flow measurements by use of laser-induced shape transitions of gold nanorods.

A quantitative technique for flow measurements based on a wash-in analysis is proposed. The technique makes use of the shape dependence of the optical absorption of gold nanorods and the transitions in their shape induced by pulsed laser irradiation. The photon-induced shape transition of gold nanorods involves mainly a rod-to-sphere conversion and a shift in the peak optical absorption wavelength. The application of a series of laser pulses will induce shape changes in gold nanorods as they flow through a region of interest, with quantitative flow information being derived from the photoacoustic signals from the irradiated gold nanorods measured as a function of time. To demonstrate the feasibility of the technique, a Nd:YAG laser operating at 1064 nm was used for irradiation and a 1 MHz ultrasonic transducer was used for acoustic detection. The flow velocity ranged from 0.35 to 2.83 mm/s. Excellent agreement between the measured velocities and the actual velocities was demonstrated, with a linear regression correlation coefficient of 0.93. This study is a pioneer work on wash-in flow estimation in photoacoustic imaging.

Multiple targeting in photoacoustic imaging using bioconjugated gold nanorods

Cancer cells presented altered surface molecules to encourage their growth and metastasis. Expression of oncogeneic surface molecules also play important roles in the prediction of clinical outcome and treatment response of anti-cancer drugs. It is thus conceivable that imaging of cancer lesions while simultaneously obtaining their pathogenic information at molecular level of as many oncogenic proteins as possible is of great clinical significance. Gold nanoparticles have been used as a contrast agent for photoacoustic imaging. In addition, gold nanoparticles can be bioconjugated to probe certain molecular processes. An intriguing property of gold nanoparticles is its ability to tailor its optical properties. For example, size effects on the surface plasmon absorption of spherical gold nanoparticles have shown that the peak optical absorption red-shifts with the increasing particle size. In addition, the optical absorption spectrum of cylindrical gold nanoparticles (i.e., gold nanorods) exhibits a strong absorption band that is directly related to the aspect ratio. With these unique characteristics, selective targeting can be achieved in photoacoustic molecular imaging. Specifically, gold nanorods with different aspect ratios can be bioconjugated to different antibodies. Multiple targeting and simultaneous detection can then be achieved by using laser irradiation at the respective peak optical absorption wavelength. In this study, photoacoustic multiple targeting using gold nanorods is experimentally demonstrated. We have chosen Her2 and CXCR4 as our primary target molecule as Her2 expression is associated with growth characteristics and sensitivity to Herceptin chemotherapy. On the other hand, CXCR4 expression predict the organ-specific metastatic potential of the cancer cells for clinical intervention in advance. Monoclonal antibody (mAb) against Her2/neu was conjugated to nanorods with several different aspect ratios. The agarose gel is suitable for photoacoustic signal acquisition. A wavelength tunable Ti-Sapphire laser was used for laser irradiation and a 1 MHz ultrasound transducer was used for acoustic detection. The optical wavelength of the laser was tuned between 800 nm and 940 nm, corresponding to gold nanorods of an aspect ratio ranging from 3.7 to 5.9. The results clearly show the potential of photoacoustic molecular imaging with multiple targeting in revealing different oncogene expression levels of the cancer cells.

An overview of the insertion device development at SRRC

Abstract Five high performance insertion devices, namely W20, U10, U5, U9 and EPU5.6, have been constructed and installed in the storage ring of the Synchrotron Radiation Research Center (SRRC). Among them, the 2-m-long conventional undulator U10 and the 4-m-long elliptically polarized undulator EPU5.6 were designed and built in-house. These two devices have achieved high magnetic field quality and high spectral performance. To facilitate hard-X-ray experiments, the project of building a superconducting wavelength shifter (SWLS) and a superconducting multi-pole wiggler (SMPW) is ongoing. These two superconducting insertion devices were designed to be cryogen-free.

Successful Operation of the 500 MHz SRF Module at TLS

A project to replace two existing room-temperature radio frequency (RF) cavities by one CESR-III 500 MHz superconducting radio frequency (SRF) module was initiated for the Taiwan Light Source (TLS) synchrotron ring in 1999. The goals are to double the photon flux of the synchrotron light by doubling the electron beam current and to increase the stability of the electron beam by taking the advantage of the ultra-weak high-order modes (HOM) of the SRF cavity. The SRF module has been routinely operated since February 2005. The NSRRC users have benefited from a very high photon flux stability (Δ I0/I0∼ 0.05%) that had never been achieved previously. Here, we report the initial operational experience of the SRF system.

Commissioning and Operations Results of the Industry-Produced CESR-Type SRF Cryomodules

Upon signing a technology transfer agreement with Cornell University, ACCEL began producing turn-key 500 MHz superconducting cavity systems. Five such cryomodules have been delivered and commissioned to date. Four of them are installed in accelerators for operation (two in CESR and one each in Canadian Light Source and Taiwan Light Source) and one serves as an off-line spare at CLS. One more cryomodule is scheduled for testing in early 2005. It will be a spare unit for TLS. Three cryomodules for DIAMOND Light Source are being fabricated at ACCEL. The commissioning results and operational experience with the cryomodules in CESR, CLS and TLS are presented.

Recent developments of the Synchrotron Light source at NSRRC

1) The storage ring operation energy was raised to 1.5 GeV, the maximum value limited by dipole magnets, to improve electron beam lifetime and to extend its spectrum to higher energies in 1996. 2) Five permanent-magnet insertion devices have been constructed and installed, as listed in Table I, by the end of 1999 to provide synchrotron radiation with higher brightness and energies. In 2003, the U10 undulator was removed and loaned to ANKA, Germany. 3) The booster energy was increased from 1.3 to 1.5 GeV. With this accomplishment, the facility can perform full energy injection and reduces the transient behavior between shifts, opening the possibility of top-up injection mode. 4) The stability of electron beam has been improved. With the raise of electron beam position monitors (EBPM) resolution to better than 1μm, the reduction of both air and cooling water temperature fluctuations to less than ±0.1 , and the °C implementation of the global feedback system, the beam orbit stability of ~ 1μm with a drift of ~ 5μm in a single shift is routinely achievable now.