D. M. Bubb

The deposition, structure, pattern deposition, and activity of biomaterial thin-films by matrix-assisted pulsed-laser evaporation (MAPLE) and MAPLE direct write

Two techniques, Matrix-Assisted Pulsed-Laser Evaporation (MAPLE) and MAPLE Direct Write (MDW) were developed to deposit biomaterial thin-films. MAPLE involves dissolving or suspending the biomaterial in a volatile solvent, freezing the mixture to create a solid target, and using a low fluence pulsed laser to evaporate the target for deposition of the solute inside a vacuum system. Using simple shadow masks, i.e. lines, dots and arrays, pattern features with length scales as small as 20 μm can be deposited using multiple materials on different types of substrates. MDW uses pulsed laser to directly transfer material from a ribbon to a substrate. Patterns with a spatial resolution of ∼10 μm can be written directly. Biomaterials ranging from polyethylene glycol to eukaryotic cells, i.e. Chinese hamster ovaries, were deposited with no measurable damage to their structures or genotype. Deposits of immobilized horseradish peroxidase, an enzyme, in the form of a polymer composite with a protective coating, i.e. polyurethane, retained their enzymatic functions. A dopamine electrochemical sensor was fabricated by MDW using a natural tissues/graphite composite. These examples and the unique features of MAPLE and MDW for biosensor fabrication have been discussed.

Laser transfer of biomaterials: Matrix-assisted pulsed laser evaporation (MAPLE) and MAPLE Direct Write

Two techniques for transferring biomaterial using a pulsed laser beam were developed: matrix-assisted pulsed laser evaporation (MAPLE) and MAPLE direct write (MDW). MAPLE is a large-area vacuum based technique suitable for coatings, i.e., antibiofouling, and MDW is a localized deposition technique capable of fast prototyping of devices, i.e., protein or tissue arrays. Both techniques have demonstrated the capability of transferring large (mol wt>100 kDa) molecules in different forms, e.g., liquid and gel, and preserving their functions. They can deposit patterned films with spatial accuracy and resolution of tens of μm and layering on a variety of substrate materials and geometries. MDW can dispense volumes less than 100 pl, transfer solid tissues, fabricate a complete device, and is computed aided design/computer aided manufacturing compatible. They are noncontact techniques and can be integrated with other sterile processes. These attributes are substantiated by films and arrays of biomaterials, e.g., polymers, enzymes, proteins, eucaryotic cells, and tissue, and a dopamine sensor. These examples, the instrumentation, basic mechanisms, a comparison with other techniques, and future developments are discussed.

The effect of the matrix on film properties in matrix-assisted pulsed laser evaporation

Thin films of polyethylene glycol of average molecular weight 1400 amu have been deposited by matrix-assisted pulsed laser evaporation (MAPLE). The deposition was carried out in vacuum (∼10−6 Torr) with an ArF (λ=193 nm) laser at a fluence of 220–230 mJ/cm2. Films were deposited on NaCl plates and glass microscope slides. Both deionized water (H2O) and chloroform (CHCl3) were used as matrices. The physiochemical properties of the films are compared via Fourier transform infrared spectroscopy, and electrospray ionization mass spectrometry. The results show that the matrix used during MAPLE can greatly affect the chemical structure and molecular weight distribution of the deposited film. The infrared absorption spectrum shows evidence for C–Cl bond formation when CHCl3 is used as a matrix, while there is little evidence in the IR data for photochemical modification when H2O is used as a matrix. Time-of-flight analysis was performed using a quadrupole mass spectrometer to monitor evaporation of a frozen CHCl...

Laser-based processing of polymer nanocomposites for chemical sensing applications

Pulsed laser deposition (PLD) has been used to fabricate polymer/carbon nanocomposite thin films for use in chemical sensors (chemiresistors). Ethylene vinyl acetate copolymer (EVA) films (undoped and 20% carbon by weight) were deposited using an ArF excimer laser (193 nm) at fluences between 150 and 300 mJ/cm2. The structure and morphology of the deposited films were characterized using Fourier transform infrared spectroscopy (FTIR), Raman scattering, and transmission and scanning electron microscopy (TEM). An analysis of the FTIR spectra indicates that a film deposited using an undoped EVA target is primarily polyethylene, suggesting that the acetate group is photochemically or photothermally removed from the starting material. Gas phase measurements of the laser-evaporated material using a quadrupole time of flight mass spectrometer confirm the production of the acetyl radical on the target surface. Analysis of TEM of films deposited using C-doped targets shows that the carbon black particles (initiall...

Infrared-to-visible upconversion in thin films of LaEr(MoO4)3

LaEr(MoO4)3 thin films have been grown by pulsed laser deposition. The films were characterized by x-ray diffraction, Rutherford backscattering, and fluorescence measurements. The results show that the deposited films were epitaxial with their c axis oriented along the surface normal. Films illuminated with 980 nm laser light show visible emission spectra. This visible emission arises as a result of the Er 4f−4f transitions and their lifetimes. Such so-called “upconverting phosphors” are important to the development of new chemical and biological sensing applications.

Resonant infrared pulsed-laser deposition of a sorbent chemoselective polymer

Fluoropolyol, a sorbent chemoselective polymer, has been deposited as a thin film by resonant infrared pulsed laser deposition using a free electron laser operating at 2.90 μm, a wavelength resonant with the hydroxl stretch. A comparison of the infrared absorbance of the deposited film and starting material shows no evidence of chemical decomposition in the film. Gel permeation chromatography shows that the film and starting material have nearly the same molar mass. The results are particularly applicable to the fabrication of chemical and biological sensors. The concept of resonant pulsed laser deposition using intrinsic vibrational modes may have wide applicability for organic materials.

Time-of-flight study of the ionic and neutral particles produced by pulsed-laser ablation of frozen glycerol

The emitted particles from pulsed-laser ablation (PLA), λ=193 nm and fluence=88–400 mJ/cm2, of frozen glycerol was examined using time-of-flight mass spectrometry. The data are analyzed using supersonic molecular-beam theory and the result is interpreted using a thermal/fluid-dynamic model. Both intact and fragmented glycerol are emitted in the PLA process at all fluences and their concentration ratio is fluence dependent. Fragmentation occurs predominantly at one of the C–C bonds forming CH2–OH (31 amu) and HO–CH2–CH–OH (61 amu). CH3 is produced at the target which requires the protonation of a CH2 fragment. At fluences higher than 250 mJ/cm2, ions are detected. These ions have very high velocity, >2000 m/s, and their intensity increases with fluences. PLA is thus not suitable for glycerol transfer under these conditions due to fragmentation. The data show that particle emission proceeds as a simple thermal vaporization process at fluences <200 mJ/cm2. Higher fluences will yield a Knudsen layer (KL), whi...