We review recent advances in laser cell surgery, and investigate the working mechanisms of femtosecond laser nanoprocessing in biomaterials with oscillator pulses of 80-MHz repetition rate and with amplified pulses of 1-kHz repetition rate. Plasma formation in water, the evolution of the temperature distribution, thermoelastic stress generation, and stress-induced bubble formation are numerically simulated for NA=1.3, and the outcome is compared to experimental results. Mechanisms and the spatial resolution of femtosecond laser surgery are then compared to the features of continuous-wave (cw) microbeams. We find that free electrons are produced in a fairly large irradiance range below the optical breakdown threshold, with a deterministic relationship between free-electron density and irradiance. This provides a large ‘tuning range’ for the creation of spatially extremely confined chemical, thermal, and mechanical effects via free-electron generation. Dissection at 80-MHz repetition rate is performed in the low-density plasma regime at pulse energies well below the optical breakdown threshold and only slightly higher than used for nonlinear imaging. It is mediated by free-electron-induced chemical decomposition (bond breaking) in conjunction with multiphoton-induced chemistry, and hardly related to heating or thermoelastic stresses. When the energy is raised, accumulative heating occurs and long-lasting bubbles are produced by tissue dissociation into volatile fragments, which is usually unwanted. By contrast, dissection at 1-kHz repetition rate is performed using more than 10-fold larger pulse energies and relies on thermoelastically induced formation of minute transient cavities with lifetimes <100 ns. Both modes of femtosecond laser nanoprocessing can achieve a 2–3 fold better precision than cell surgery using cw irradiation, and enable manipulation at arbitrary locations.

Mechanisms of femtosecond laser nanosurgery of cells and tissues

Chemical Science Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352; Department of Chemistry, ShelbyHall, University of Alabama, Box 870336, Tuscaloosa, Alabama 35487-0336; Notre Dame Radiation Laboratory, University of Notre Dame,Notre Dame, Indiana 46556; Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 0520-8107; Argonne NationalLaboratory, 9700 South Cass Avenue, Argonne, Illinois 60439; Department of Computer Science and Department of Physics, 2710 University Drive,Washington State University, Richland, Washington 99352-1671; Lawrence Berkeley National Laboratory, 1 Cyclotron Road Mailstop 1-0472,Berkeley, California 94720; Department of Chemistry and Biochemistry, University of Texas at Austin, 1 University Station A5300,Austin, Texas 78712; Office of Basic Energy Sciences, U.S. Department of Energy, SC-141/Germantown Building, 1000 Independence Avenue,S.W., Washington, D.C. 20585-1290; Department of Physics and Engineering Physics, Stevens Institute of Technology, Castle Point on Hudson,Hoboken, New Jersey 07030; Department of Chemistry, Johns Hopkins University, 34th and Charles Streets, Baltimore, Maryland 21218;Department of Chemistry, University of Southern California, Los Angeles, California 90089-1062; Department of Chemistry, The Ohio StateUniversity, 100 West 18th Avenue, Columbus, Ohio 43210-1185; Department of Chemistry, Columbia University, Box 3107, Havemeyer Hall,New York, New York 10027; Department of Chemistry, University of Pittsburgh, Parkman Avenue and University Drive,Pittsburgh, Pennsylvania 15260; Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000; Department of Physics andAstronomy, Rutgers, The State University of New Jersey, 136 Frelinghuysen Road, Piscataway, New Jersey 08854-8019; Department of Chemistry,516 Rowland Hall, University of California, Irvine, Irvine, California 92697-2025; Stanford Synchrotron Radiation Laboratory, Stanford LinearAccelerator Center, 2575 Sand Hill Road, Mail Stop 69, Menlo Park, California 94025; School of Chemistry and Biochemistry, Georgia Institute ofTechnology, 770 State Street, Atlanta, Georgia 30332-0400; Geology Department, University of California, Davis, One Shields Avenue,Davis, California 95616-8605; Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue,Cambridge, Massachusetts 02139-4307; Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084Received July 23, 2004

http://casey.brown.edu/chemistry/research/LSWang/publications/194.pdf

Role of water in electron-initiated processes and radical chemistry: issues and scientific advances.

The damage induced by the impact of low energy electrons (LEE) on 
biomolecules is reviewed from a radiobiological perspective with emphasis on 
transient anion formation. The major type of experiments, which measure the 
yields of fragments produced as a function of incident electron energy 
(0.1-30 eV), are briefly described. Theoretical advances are also 
summarized. Several examples are presented from the results of recent 
experiments performed in the gas-phase and on biomolecular films bombarded 
with LEE under ultra-high vacuum conditions. These include the results 
obtained from DNA films and those obtained from the fragmentation of 
elementary components of the DNA molecule (i.e., the bases, sugar and 
phosphate group analogs and oligonucleotides) and of proteins (e.g. amino 
acids). By comparing the results from different experiments and theory, it 
is possible to determine fundamental mechanisms that are involved in the 
dissociation of the biomolecules and the production of single- and 
double-strand breaks in DNA. Below 15 eV, electron resonances (i.e., the 
formation of transient anions) play a dominant role in the fragmentation of 
all biomolecules investigated. These transient anions fragment molecules by 
decaying into dissociative electronically excited states or by dissociating 
into a stable anion and a neutral radical. These fragments can initiate 
further reactions within large biomolecules or with nearby molecules and 
thus cause more complex chemical damage. Dissociation of a transient anion 
within DNA may occur by direct electron attachment at the location of 
dissociation or by electron transfer from another subunit. Damage to DNA is 
dependent on the molecular environment, topology, type of counter ion, 
sequence context and chemical modifications.

/pdf/low-energy-electron-driven-damage-in-biomolecules-5cn6qjrfa5.pdf

Low energy electron-driven damage in biomolecules

Collisions of 0--4 eV electrons with thin DNA films are shown to produce single strand breaks. The yield is sharply structured as a function of electron energy and indicates the involvement of ${\ensuremath{\pi}}^{*}$ shape resonances in the bond breaking process. The cross sections are comparable in magnitude to those observed in other compounds in the gas phase in which ${\ensuremath{\pi}}^{*}$ electrons are transferred through the molecule to break a remote bond. The results therefore support aspects of a theoretical study by Barrios et al. [J. Phys. B 106, 7991 (2002)] indicating that such a mechanism could produce strand breaks in DNA.

/pdf/dna-strand-breaks-induced-by-0-4-ev-electrons-the-role-of-1ngkm1xm4r.pdf

DNA strand breaks induced by 0-4 eV electrons: the role of shape resonances.

Nonthermal secondary electrons with initial kinetic energies below 100 eV are an abundant transient species created in irradiated cells and thermalize within picoseconds through successive multiple energy loss events. Here we show that below 15 eV such low-energy electrons induce single (SSB) and double (DSB) strand breaks in plasmid DNA exclusively via formation and decay of molecular resonances involving DNA components (base, sugar, hydration water, etc.). Furthermore, the strand break quantum yields (per incident electron) due to resonances occur with intensities similar to those that appear between 25 and 100 eV electron energy, where nonresonant mechanisms related to excitation/ionizations/dissociations are shown to dominate the yields, although with some contribution from multiple scattering electron energy loss events. We also present the first measurements of the electron energy dependence of multiple double strand breaks (MDSB) induced in DNA by electrons with energies below 100 eV. Unlike the SSB and DSB yields, which remain relatively constant above 25 eV, the MDSB yields show a strong monotonic increase above 30 eV, however with intensities at least 1 order of magnitude smaller than the combined SSB and DSB yields. The observation of MDSB above 30 eV is attributed to strand break clusters (nano-tracks) involving multiple successive interactions of one single electron at sites that are distant in primary sequence along the DNA double strand, but are in close contact; such regions exist in supercoiled DNA (as well as cellular DNA) where the double helix crosses itself or is in close proximity to another part of the same DNA molecule.

Single, double, and multiple double strand breaks induced in DNA by 3-100 eV electrons.

Boudaiffa, B., Cloutier, P., Hunting, D., Huels, M. A. and Sanche, L. Cross Sections for Low-Energy (10 – 50 eV) Electron Damage to DNA. Radiat. Res. 157, 227 – 234 (2002). We report direct measurements of the formation of single-, double- and multiple strand breaks in pure plasmid DNA as a function of exposure to 10 – 50 eV electrons. The effective cross sections to produce these different types of DNA strand breaks were determined and were found to range from approximately 10−17 to 3  × 10−15 cm2. The total effective cross section and the effective range for destruction of supercoiled DNA extend from 3.4 to 4.4  × 10−15 cm2 and 12 to 14 nm, respectively, over the range 10 – 50 eV. The variation of the effective cross sections with electron energy is discussed in terms of the electron's inelastic mean free path, penetration depth, and dissociation mechanisms, including resonant electron capture; the latter is found to dominate the effective cross sections for single- and double-strand breaks at ...

Cross sections for low-energy (10-50 eV) electron damage to DNA.

Thymidine was exposed to low-energy electrons (LEE) as a thin solid film under a high vacuum. Nonvolatile radiation products, remaining on the irradiated surface, were analyzed by HPLC/UV and GC/MS...

Glycosidic bond cleavage of thymidine by low-energy electrons.

Cecchini, S., Girouard, S., Huels, M. A., Sanche, L. and Hunting, D. J. Single-Strand-Specific Radiosensitization of DNA by Bromodeoxyuridine. Radiat. Res. 162, 604–615 (2004). The effects of bromodeoxyuridine (BrdUrd) substitution for thymidine on γ-ray-induced strand breakage were determined in single- and double-stranded oligonucleotides and double-stranded oligonucleotides containing a mismatched bubble region. BrdUrd does not sensitize complementary double-stranded DNA to γ-ray-induced strand breakage, but it greatly sensitizes single-stranded DNA. However, when the BrdUrd is present in a single-stranded bubble of a double-stranded oligonucleotide, the non-base-paired nucleotides adjacent to the BrdUrd as well as several unpaired sites on the opposite unsubstituted strand are strongly sensitized. The radiosensitization properties of BrdUrd result primarily from the electrophilic nature of the bromine, making it a good leaving group and leading to the irreversible formation of the uridine-yl ...

Darel Hunting

Papers

Single, double, and multiple double strand breaks induced in DNA by 3-100 eV electrons.

Cross sections for low-energy (10-50 eV) electron damage to DNA.

Glycosidic bond cleavage of thymidine by low-energy electrons.

Single-Strand-Specific Radiosensitization of DNA by Bromodeoxyuridine