title: Highly sensitive spectroscopic detection of heme-protein submonolayer films by channel integrated optical waveguide.
abstract: A highly sensitive technique based on optical absorption using a single-mode, channel integrated optical waveguide is described for broad spectral band detection and analysis of heme-containing protein films at a glass/water interface. Fabrication steps and device characteristics of optical waveguides suitable for operation in the wavelength range of 400 - 650 nm are described. Experimental results reported here show a limit of detection smaller than 100 pg/cm(2) for a submonolayer of ferricytochrome c by probing the Soret transition band with a 406-nm semiconductor diode laser propagating in a single-mode, ion-exchanged channel waveguide. By taking advantage of the exceptionally low limit of detection, we examined the adsorption isotherm of cytochrome c on a glass surface with unprecedented detail. Unlike other surface-specific techniques (e.g. SPR, integrated optic Mach-Zehnder interferometer) that probe local refractive-index changes and therefore are very susceptible to temperature fluctuations, the integrated optical waveguide absorption technique probes molecular-specific transition bands and is expected to be less vulnerable to environmental perturbations.
authors.forename: Ismail E
authors.initials: IE
authors.lastname: Araci
authors.forename: Sergio B
authors.initials: SB
authors.lastname: Mendes
authors.forename: Nasuhi
authors.initials: N
authors.lastname: Yurt
authors.forename: Seppo
authors.initials: S
authors.lastname: Honkanen
authors.forename: N
authors.initials: N
authors.lastname: Peyghambarian