Developing A Microfluidic-Based System To Quantify Cell Capture Efficiency

Micro-fabrication technology has substantial potential for identifying molecular markers expressed on the surfaces of tissue cells and viruses. It has been found in several conceptual prototypes that cells with such markers are able to be captured by their antibodies immobilized on microchannel substrates and unbound cells are flushed out by a driven flow. The feasibility and reliability of such a microfluidic-based assay, however, remains to be further tested. In the current work, we developed a microfluidic-based system consisting of a microfluidic chip, an image grabbing unit, data acquisition and analysis software, as well as a supporting base. Specific binding of CD59-expressed or BSA-coupled human red blood cells (RBCs) to anti-CD59 or anti-BSA antibody-immobilized chip surfaces was quantified by capture efficiency and by the fraction of bound cells. Impacts of respective flow rate, cell concentration, antibody concentration and site density were tested systematically. The measured data indicated that the assay was robust. The robustness was further confirmed by capture efficiencies measured from an independent ELISA-based cell binding assay. These results demonstrated that the system developed provided a new platform to effectively quantify cellular surface markers effectively, which promoted the potential applications in both biological studies and clinical diagnoses.

Influence of Contact Angle and Tube Size on Capillary-Driven Flow Under Microgravity

The influence of contact angle and tube radius on the capillary-driven flow for circular cylindrical tubes is studied systematically by microgravity experiments using the drop tower. Experimental results show that the velocity of the capillary flow decreases monotonically with an increase in the contact angle. However, the time-evolution of the velocity of the capillary flow is different for different sized tubes. At the beginning of the microgravity period, the capillary flow in a thinner tube moves faster than that in a thicker tube, and then the latter overtakes the former. Therefore, there is an intersection between the curves of meniscus velocity vs microgravity time for two differently sized tubes. In addition, for two given sized tubes this intersection is delayed when the contact angle increases. The experimental results are analyzed theoretically and also supported by numerical computations.

Electron dynamics and harmonics emission spectra due to electron oscillation driven by intense laser pulses

The dynamics and harmonics emission spectra due to electron oscillation driven by intense laser pulses have been investigated considering a single electron model. The spectral and angular distributions of the harmonics radiation are numerically analyzed and demonstrate significantly different characteristics from those of the low-intensity field case. Higher-order harmonic radiation is possible for a sufficiently intense driving laser pulse. A complex shifting and broadening structure of the spectrum is observed and analyzed for different polarization. For a realistic pulsed photon beam, the spectrum of the radiation is redshifted for backward radiation and blueshifted for forward radiation, and spectral broadening is noticed. This is due to the changes in the longitudinal velocity of the electron during the laser pulse. These effects are much more pronounced at higher laser intensities giving rise to even higher-order harmonics that eventually leads to a continuous spectrum. Numerical simulations have further shown that broadening of the high harmonic radiation can be limited by increasing the laser pulse width. The complex shifting and broadening of the spectra can be employed to characterize the ultrashort and ultraintense laser pulses and to study the ultrafast dynamics of the electrons. (c) 2006 American Institute of Physics.

Energetic protons emitted from coulomb explosion dynamics of large-sized hydrogen clusters driven by an ultrashort intense laser pulse

Protons with very high kinetic energy of about 10keV and the saturation effect of proton energy for laser intensity have been observed in the interaction of an ultrashort intense laser pulse with large-sized hydrogen clusters. Including the cluster-size distribution as well as the laser-intensity distribution on the focus spot, the theoretical calculations based on a simplified Coulomb explosion model have been compared with our experimental measurements, which are in good agreement with each other.

Electron quantum path tuning and isolated attosecond pulse emission driven by a waveform-controlled multi-cycle laser field

We investigate high-order harmonic emission and isolated attosecond pulse (IAP) generation in atoms driven by a two-colour multi-cycle laser field consisting of an 800 nm pulse and an infrared laser pulse at an arbitrary wavelength. With moderate laser intensity, an IAP of similar to 220 as can be generated in helium atoms by using two-colour laser pulses of 35 fs/800 nm and 46 fs/1150 nm. The discussion based on the three-step semiclassical model, and time-frequency analysis shows a clear picture of the high-order harmonic generation in the waveform-controlled laser field which is of benefit to the generation of XUV IAP and attosecond electron pulses. When the propagation effect is included, the duration of the IAP can be shorter than 200 as, when the driving laser pulses are focused 1 mm before the gas medium with a length between 1.5 mm and 2 mm.

IBM PC Data Acquisition and Processing Software Evaluation

Commercially available software packages for IBM PC-compatibles are evaluated to use for data acquisition and processing work. Moss Landing Marine Laboratories (MLML) acquired computers since 1978 to use on shipboard data acquisition (Le. CTD, radiometric, etc.) and data processing. First Hewlett-Packard desktops were used then a transition to the DEC VAXstations, with software developed mostly by the author and others at MLML (Broenkow and Reaves, 1993; Feinholz and Broenkow, 1993; Broenkow et al, 1993). IBM PC were at first very slow and limited in available software, so they were not used in the early days. Improved technology such as higher speed microprocessors and a wide range of commercially available software made use of PC more reasonable today. MLML is making a transition towards using the PC for data acquisition and processing. Advantages are portability and available outside support.

Laser-driven coherent betatron oscillation in a laser-wakefield cavity

The origin of beam disparity in emittance and betatron oscillation orbits, in and out of the polarization plane of the drive laser of laser-plasma accelerators, is explained in terms of betatron oscillations driven by the laser field. As trapped electrons accelerate, they move forward and interact with the laser pulse. For the bubble regime, a simple model is presented to describe this interaction in terms of a harmonic oscillator with a driving force from the laser and a restoring force from the plasma wake field. The resulting beam oscillations in the polarization plane, with period approximately the wavelength of the driving laser, increase emittance in that plane and cause microbunching of the beam. These effects are observed directly in 3D particle-in-cell simulations.

Laser-driven inertial ion focusing

A Hohlraum-like configuration is proposed for realizing a simple compact source for neutrons. A laser pulse enters a tiny thin-shelled hollow-sphere target through a small opening and is self-consistently trapped in the cavity. The electrons in the inner shell-wall region are expelled by the light pressure. The resulting space-charge field compresses the local ions into a thin layer that becomes strongly heated. An inward expansion of ions into the shell cavity then occurs, resulting in the formation at the cavity center of a hot spot of ions at high density and temperature, similar to that in inertial electrostatic confinement.

Electron self-injection and acceleration driven by a tightly focused intense laser beam in an underdense plasma

A scheme for electron self-injection in the laser wakefield acceleration is proposed. In this scheme, the transverse wave breaking of the wakefield and the tightly focused geometry of the laser beam play important roles. A large number of the background electrons are self-injected into the acceleration phase of the wakefield during the defocusing of the tightly focused laser beam as it propagates through an underdense plasma. Particle-in-cell simulations performed using a 2D3V code have shown generation of a collimated electron bunch with a total number of 1.4 x 109 and energies up to 8 MeV. (C) 2005 American Institute of Physics.