Jerri A. Tribble

Bacteria identification of otitis media with fluorescence spectroscopy.

We have investigated the fluorescence profiles of four common pathogens: S. pneumoniae, S. aureus, M. catarrhalis, and H. influenzae. The steady‐state auto fluorescence spectra of bacteria are measured as a function of the incident light from 200 to 700 nm. The spectra for each bacterium are combined into a fluorescence profile or fluorescence finger print. Each bacterium produces a unique in vitro fluorescence profile when measured in a saline suspension. The profiles are reproducible. Suspensions of a bacterial strain, where the identification is not known, can be correctly matched to a small library of previously measured fluorescence profiles using a linear least‐squares fitting algorithm. In addition, we have measured the fluorescence and absorption spectrum of the tympanic membrane removed from a chinchilla. The optical properties of the tympanic membrane and the least‐squares identification process form precept for a non‐invasive, fluorescence based bacterial diagnosis technique to be used in otitis media.

Noninvasive optical diagnosis of bacteria causing otitis media

Currently, the identification of the bacteria responsible for acute otitis media requires a painful invasive procedure: tympanocentesis. To develop a rapid and noninvasive technique for bacterial diagnosis, the fluorescence profiles of four common pathogens and the optical characteristics of the tympanic membrane have been investigated. Each bacterium produces a unique in vitro fluorescence profile when measured in a saline suspension. Also, spectrally resolved transmission measurements from the chinchilla tympanic membrane demonstrate an optical window that will transmit sufficient light for in vivo measurement of the fluorescence profiles. Thus, we have established the precept for a fluorescence‐based bacterial diagnosis technique to be used in otitis media. This paper presents the theory, optical data, and a discussion of the device engineering involved in the technique.

Biomedical applications of free-electron lasers

Tunable, pulsed radiation sources in the ultraviolet, visible, and infrared wavelength ranges offer novel opportunities for investigating laser-induced biomedical effects. Free-electron lasers (FELs) deliver continuously tunable, pulsed radiation in the infrared, providing the capability to selectively target radiation into the vibrational modes of water or other biopolymers. Experimental techniques for measuring the absorption spectra of biological samples are described. These spectra indicate wavelengths that potentially serve as the basis for laser-induced biomedical effects. Some practical considerations for infrared, visible, and UV spectroscopy of biological samples are summarized, and the connection between biomedical research and more fundamental investigations of vibrational energy transfer are emphasized.

Free-electron laser as the ideal stress-wave generator

Laser-induced thermal-elastic stress waves are of importance both in therapeutic applications and in potential morbidity associated with laser surgical procedures. Recent experiments have shown that drug cytotoxicity can be enhanced with stress waves and that direct cell injury correlates with the stress gradient (stress rate of change). To systematically investigate the biological effects of stress waves, it is essential to vary individually the parameters of the stress wave. The Free Electron Laser (FEL) is the ideal laser for generating controllable stress waves. A unipolar stress wave can be characterized by its rise time, duration, peak pressure, and decay time. For short laser pulses, the rise time and decay time are dependent upon the absorption depth of the tissue and can be varied by changing the wavelength of the FEL. The duration of the stress wave can be changed by selecting a different number of micropulses from the FEL macropulse with Pockels cell. The peak pressure can be altered by varying the laser intensity. Results on water have confirmed that the individual parameters of the stress wave can be varied independently.

Two years of free-electron laser applications research in biological physics

The Vanderbilt free-electron laser has been operational for several years. This extended collaboration has been investigating outstanding problems in biological physics and medical physics with several research goals in mind. Our most fundamental goal is to improve the understanding of intermolecular and intramolecular vibrational energy transfer mechanisms in biopolymers. Our approach is to pursue both experimental and theoretical research addressing vibrational energy transfer in biological physics. The remaining goals can be summarized as the application of our fundamental advancements in polymer physics to molecular biology and to clinical and surgical medicine.

Partitioning-of-energy model for laser ablation of tissue

A theoretical model is presented to account for the experimental observation that infrared tissue ablation is optimized by the use of wavelengths near the amide II band of proteins. The model recognizes the partitioned absorption of IR photons between protein and water due to overlapping spectral features along with the dynamics of biopolymers, the loss of mechanical integrity in proteins, and the explosive role played by the vaporization of water. The theoretical foundation for this model can be found in previous accounts of thermal confinement, multicomponent models, and selective photothermolysis.

Applications of free-electron lasers to measurements of energy transfer in biopolymers and materials

Free-electron lasers (FELs) provide tunable, pulsed radiation in the infrared. Using the FEL as a pump beam, we are investigating the mechanisms for energy transfer between localized vibrational modes and between vibrational modes and lattice or phonon modes. Either a laser-Raman system or a Fourier transform infrared (FTIR) spectrometer will serve as the probe beam, with the attribute of placing the burden of detection on two conventional spectroscopic techniques that circumvent the limited response of infrared detectors. More specifically, the Raman effect inelastically shifts an exciting laser line, typically a visible frequency, by the energy of the vibrational mode; however, the shifted Raman lines also lie in the visible, allowing for detection with highly efficient visible detectors. With regards to FTIR spectroscopy, the multiplex advantage yields a distinct benefit for infrared detector response. Our group is investigating intramolecular and intermolecular energy transfer processes in both biopolymers and more traditional materials. For example, alkali halides contain a number of defect types that effectively transfer energy in an intermolecular process. Similarly, the functioning of biopolymers depends on efficient intramolecular energy transfer. Understanding these mechanisms will enhance our ability to modify biopolymers and materials with applications to biology, medecine, and materials science.