Debra Wawro

Optical fiber endface biosensor based on resonances in dielectric waveguide gratings

A new fiber optic sensor integrating dielectric diffraction gratings and thin films on optical fiber endfaces is prosed for biomedical sensing applications. This device utilizes a resonant dielectric waveguide grating structure fabricated on an optical fiber endface to probe reactions occurring in a sensing layer deposited on its surface. The operation of this sensor is based upon a fundamental resonance effect that occurs in waveguide gratings. An incident broad- spectrum signal is guided within an optical fiber and is filtered to reflect or transmit a desired spectral band by the diffractive thin film structure on its endface. Slight changes in one or more parameters of the waveguide grating, such as refractive index or thickness, can result in a responsive shift of the reflected or transmitted spectral peak that can be detected with spectroscopic instruments. This new sensor concept combines improved sensitivity and accuracy with attractive features found separately in currently available fiber optic sensors, such as large dynamic range, small sensing proximity, real time operation, and remote sensing. Diffractive elements of this type consisting of a photoresist grating on a Si3N4 waveguide have been fabricated on multimode optical fiber endfaces with 100 micrometers cores. Preliminary experimental tests using a tunable Ti:sapphire laser indicate notches of 18 percent in the transmission spectrum of the fiber endface guided-mode resonance devices. A theoretical analysis of the device performance capabilities is presented and applied to evaluate the feasibility and potential advantages of this bioprobe.

Bacterial biofilm formation on a human cochlear implant.

Objective: To report the characteristics of a bacterial biofilm from the surface of a cochlear implant. Background: Bacterial biofilm formation on implanted devices causes intractable infections and device extrusions necessitating device removal, with loss of function. More information is needed about biofilm characteristics and interactions with the implant surface before better treatments can be designed. Study Design: A retrospective case review was combined with a descriptive histological study of the surface of an otologic device. Methods: The receiver/stimulator device removed from a cochlear implant patient because of intractable infection and partial device extrusion was fixed and processed for microscopic examination. Its surface and the material present on its surface were analyzed using light and electron microscopy, focusing on surface texture, cell types, and bacteria species and extracellular polymeric substances present within the biofilm. Results: Stereomicroscopic examination revealed extracellular polymeric substances, pinkish yellow in color, with spheres of uniform size scattered throughout, indicative of a biofilm containing Staphylococcus aureus. Biofilm density was greatest in depressions on the surface of the implant. Cross-sectional analysis revealed bacteria interspersed with polymorphonuclear leukocytes. Scanning electron microscopic examination demonstrated an amorphous layer of extracellular polymeric substances containing small filaments, bacteria, and inflammatory cells. Only Staphylococcus aureus was detected. Conclusion: Cochlear implant material can provide a surface for bacterial biofilm formation. Impressions can provide an environment conducive to biofilm establishment and growth, ultimately necessitating device removal, with loss of implant function. Biofilm characterization should aid in design of cochlear implant devices less susceptible to biofilm formation.

Guided-mode resonance effects in thin-film diffractive optics and their applications

High-efficiency resonance coupling effects in zero-order diffractive multilayer structures have applications in fields such as optical filtering and laser technology. These resonance effects arise on phase matching of an incident laser beam to a leaky waveguide mode. Then, in theory, complete energy exchange between the input wave and a reflected wave can take place within narrow ranges in wavelength, angle of incidence, index of refraction, or layer thickness. This paper addresses theoretical modeling, experimental realization, and applications of this so-called guided-mode resonance (GMR) effect. In particular, the achievable GMR-filter efficiencies, spectral linewidths, sideband levels, and polarization characteristics are treated with a plane-wave model and a Gaussian-beam model. Resonance bandpass filters operating in reflection and transmission are shown to exhibit high efficiencies and extended low sidebands. Genetic algorithms are applied to solve inverse resonance-filter design problems. Applications including GMR laser mirrors, electro-optic modulators, and resonant Brewster filters are presented. Experimental results are shown to agree well with theoretical calculations.

Waveguide-grating couplers for illumination of photonic antennas

To obtain uniform illumination of photonic reconfigurable antennas, a waveguide grating with a nonuniform grating profile may be used. Theoretical studies using approximate models indicate that the grating profile should have a hyperbolic spatial variation along the length of the coupler. This yields a spatially varying diffraction efficiency that compensates for the loss of light as it is diffracted out of the waveguide. Utilizing a holographic interferometer with a computer controlled shutter in one arm, gratings with appropriate spatial profile variation have been recorded in photoresist and transferred to produce photopolymer waveguide gratings. These planar couplers are integrated with optical fiber bundles for input light delivery. The grating periods are chosen to produce orthogonally propagating output waves. A dielectric mirror arrangement is used to reflect the parasitic diffracted order back onto the antenna element. The best devices obtained to date exhibit output uniformity of plus or minus 6% over a coupler length of 20 mm with total efficiency exceeding 50%.

Photonic Sensor System for Screening Serum Biomarker Proteins in Ovarian Cancer

Ovarian cancer is among the most deadly types of cancers among women, with about 21,990 new cases diagnosed every year in the United States (American Cancer Society, 2011). About 15,460 of these women will die from ovarian cancer. If diagnosed while the cancer is still localized, survival rates of at least 5 years are likely. Unfortunately, less than 20% of cases are found at an early stage due to the absence of reproducible and definitive diagnostic tools. Because ovarian cancers occur deep in the pelvis, there are often few symptoms until the cancer is at an advanced stage. Furthermore, many of the symptoms of ovarian cancer (such as back pain, fatigue, and abdominal bloat) are common and difficult to distinguish from those not caused by cancer. Because of this lack of symptom specificity, most ovarian cancers are substantially advanced at the time of diagnosis. Staging of the cancer is critically important in order to determine the most effective treatment modality. Currently there are no routine clinical diagnostic assays using urinalysis or seranalysis for early screening or staging of ovarian cancer. However, there are several research studies (Bignotti et al., 2007; and Liotta et al., 2005) that identify potential biomarker indicators that can be used for this purpose. When a woman is suspected of having ovarian cancer, medical diagnostics typically include an ultrasound of the abdomen and pelvis as well as a blood test that includes measurement of the CA-125 protein levels (American Cancer Society, 2011). CA 125 is a protein biomarker found in greater concentration in tumor cells than in other cells of the body. However, since CA-125 levels can be elevated due to other benign causes, it is primarily used to monitor women with a known cancer of the ovary to determine treatment efficacy. Measurement of CA-125 levels is not accepted as a sufficient test for an early screening indicator in ovarian cancer. Thus, improved methods are needed to provide a specific and early screen for this deadly disease.

Optical nanotechnology enables rapid label-free diagnostics for cancer biomarker screening

A high-accuracy biosensor system has been developed to provide rapid detection of biomarker proteins as indicators of ovarian cancer. This photonic detection system is based upon guided-mode resonance sensor technology. The buildup of the attaching biolayer can be monitored directly, without use of chemical tags, by following the corresponding resonance shift with a spectrometer or detector array. Additionally, these high-resolution sensors employ multiple resonance peaks at identical physical location on the sensor surface. Each of these resonance peaks responds uniquely to the detection event, thereby enriching the data set available for quantification. The peaks result from individual, polarization-dependent resonant leaky modes that are the foundation of this technology. Examples are presented for detection of ovarian cancer biomarkers (fibronectin and apoliprotein A-1) in serum and cell culture supernatant, with detection sensitivities to ~20 ng/ml. Minimal nonspecific binding was measured in cell media and serum backgrounds. We also present an example dual-polarization resonance response with corresponding backfitting results that illustrate the capability to distinguish between changes at the sensor surface due to biolayer adhesion and those due to sample background changes.