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A survey of biophysical and biomedical applications of free-electron lasers (FELs) is presented. FELs are pulsed light sources, collectively operating from the microwave through the x-ray range. This accelerator-based technology spans gaps in wavelength, pulse structure, and optical power left by conventional sources. FELs are continuously tunable and can produce high-average and high-peak power. Collectively, FEL pulses range from quasicontinuous to subpicosecond, in some cases with complex superpulse structures. Any given FEL, however, has a more restricted set of operational parameters. FELs with high-peak and high-average power are enabling biophysical and biomedical investigations of infrared tissue ablation. A midinfrared FEL has been upgraded to meet the standards of a medical laser and is serving as a surgical tool in ophthalmology and human neurosurgery. The ultrashort pulses produced by infrared or ultraviolet FELs are useful for biophysical investigations, both one-color time-resolved spectroscopy and when coupled with other light sources, for two-color time-resolved spectroscopy. FELs are being used to drive soft ionization processes in mass spectrometry. Certain FELs have high repetition rates that are beneficial for some biophysical and biomedical applications, but confound research for other applications. Infrared FELs have been used as sources for inverse Compton scattering to produce a pulsed, tunable, monochromatic x-ray source for medical imaging and structural biology. FEL research and FEL applications research have allowed the specification of spin-off technologies. On the horizon is the next generation of FELs, which is aimed at producing ultrashort, tunable x rays by self-amplified spontaneous emission with potential applications in biology.

We present a continuous-flow microfluidic device that enables cell by cell separation of cells selectively tagged with magnetic nanoparticles. The cells flow over an array of microfabricated magnetic stripes, which create a series of high magnetic field gradients that trap the magnetically labeled cells and alter their flow direction. The process was observed in real time using a low power microscope. The device has been demonstrated by the separation of leukocytes from whole human blood.

The present invention relates to a device for interfacing nanofluidic and microfluidic components suitable for use in performing high throughput macromolecular analysis. Diffraction gradient lithography (DGL) is used to form a gradient interface between a microfluidic area and a nanofluidic area. The gradient interface area reduces the local entropic barrier to nanochannels formed in the nanofluidic area. In one embodiment, the gradient interface area is formed of lateral spatial gradient structures for narrowing the cross section of a value from the micron to the nanometer length scale. In another embodiment, the gradient interface area is formed of a vertical sloped gradient structure. Additionally, the gradient structure can provide both a lateral and vertical gradient.

We made uniform arrays of nanometer scale structures using nanoimprint lithography over large areas (100 mm wafers). The nanofluidic channels were further narrowed and sealed by techniques that are based on nonuniform deposition. The resulting sealed channels have a cross section as small as 10 nm by 50 nm, of great importance for confining biological molecules into ultrasmall spaces. These techniques can be valuable fabrication tools for Nanoelectromechanical Systems and Micro/Nano Total Analysis Systems.

We describe a microfluidic device for on-chip chemical processing, such as staining, and subsequent washing of cells. The paper introduces “separator walls” to increase the on-chip incubation time and to improve the quality of washing. Cells of interest are concentrated into a treatment stream of chemical reagents at the first separator wall for extended on-chip incubation without causing excess contamination at the output due to diffusion of the unreacted treatment chemicals, and then are directed to the washing stream before final collections. The second separator wall further reduces the output contamination from diffusion to the washing stream. With this approach, we demonstrate on-chip leukocyte staining with Rhodamine 6G and washing. The results suggest that other conventional biological and analytical processes could be replaced by the proposed device.

This is a theoretical paper which examines at a game theoretical perspective the dynamics of cooperators and cheater cells under metabolic stress conditions and high spatial heterogeneity. Although the ultimate aim of this work is to understand the dynamics of cancer tumor evolution under stress, we use a simple bacterial model to gain fundamental insights into the progression of resistance to drugs under high competition and stress conditions.

Separation of blood cells by native susceptibility and by the selective attachment of magnetic beads has recently been demonstrated on microfluidic devices. We discuss the basic principles of how forces are generated via the magnetic susceptibility of an object and how microfluidics can be combined with micron-scale magnetic field gradients to greatly enhance in principle the fractionating power of magnetic fields. We discuss our efforts and those of others to build practical microfluidic devices for the magnetic separation of blood cells. We also discuss our attempts to integrate magnetic separation with other microfluidic features for developing handheld medical diagnostic tools.

Protoheme rebinding of carbon monoxide after photodissociation has been observed at temperatures from 5 to 340 K for times from 2 μs to 1 ks. Below 80 K, binding is nonexponential in time and CO‐concentration independent, above 230 K exponential and the rate is CO‐concentration proportional. A model is proposed in which the carbon monoxide, moving from the solvent to the binding site at the ferrous heme iron, encounters two successive barriers. The outer is formed by the solvent, the inner is a property of the heme and probably connected to the motion of the iron from the spin‐2 deoxy to the spin‐0 carbon monoxide state. The temperature dependence of the two processes yields all activation enthalpies and entropies for the two barriers. The nonexponential rebinding observed at low temperatures implies that the inner barrier possesses distributed activation enthalpy and entropy. The enthalpy spectrum and the entropy spread are determined. The spectrum demonstrates that heme exists in many different conformational states. At low temperatures, these states are frozen; above about 230 K, rapid conformational relaxation renders rebinding exponential. Below 15 K, quantum‐mechanical molecular tunneling dominates. The tunneling rate yields the width of the innermost barrier. Earlier experiments on carbon monoxide binding to myoglobin had provided evidence for four barriers. The present results imply that the innermost barrier in myoglobin is caused by the heme, the outermost by the solvent, and the two intermediate ones by the globin.

Brownian dynamics is used to simulate the decay anisotropy of short linear DNA fragments modeled as a string of beads. The model is sufficiently general to allow for static bends, anisotropic bending, and elastic constants for bending and twisting which can vary along the chain. In limiting cases, simulations are found to be in excellent agreement with analytic theory down to a correlation length of at least 500 A. This model is then used to analyze the 0–2.5 μs triplet depletion anisotropy decay of a 209 base pair sea urchin DNA fragment. It is concluded that the conventional worm‐like chain model, in which bending is isotropic and/or there are no static bends along the chain, is unable to account for the experimental results unless a correlation length of 1000 A is assumed. A worm‐like chain with anisotropic bending requires a similar but slightly larger correlation length.

The electron exchange kinetics between plastocyanin and iron hexacyanide has been studied by laser temperature jump. A general kinetic scheme assuming weak binding of the iron hexacyanide to a distant (10 A) site has been used to extract intrinsic exchange rates of 68±20 s−1 for Cu(2+) to Cu(1+) reduction, and 200±100 s−1 for the reverse reaction. These intrinsic rates have been compared to simple nonadiabatic tunneling theories and found to be in reasonable agreement.

Many transient phenomena extend over more than two orders of magnitude in time. Such processes are most efficiently observed with systems that possess logarithmic time bases. A digital analyzer is described that records smoothly and in one sweep transient processes over more than eight orders of magnitude in time. A typical sweep covers the time range from 2 μsec to 5 min.

We have used a simple dye laser driven by a Q‐switched Nd:YAG laser as an amplifier for subnanosecond pulses from a nitrogen laser driven dye laser. Energy gains of up to 150 are observed, with final pulse energies of 200 μJ at 650 nm.