Performance of a highly sensitive optical waveguide Mach-Zehnder interferometer immunosensor

We describe a highly sensitive sensor which uses the evanescent field of a reusable planar optical waveguide as the sensing element. The waveguide used is optimized to obtain a steep dependence of the propagation velocity on the refractive-index profile near the surface. The adsorption of a layer of proteins thus results in a phase change, which is measured interferometrically using a Mach-Zehnder interferometer set-up. The stability of the interferometer is such that phase changes = (1 × 10-2)2pi per hour can be measured. Immunoreactions have been monitored down to concentrations of 5 × 10-11 M of a 40 kDa protein

Development of an optical waveguide interferometric immunosensor

A Mach-Zehnder interferometer is presented, which uses the evanescent field of a planar optical waveguide as the sensing element. Changes in the refractive index profile occurring in the immediate vicinity of the waveguide surface cause the propagation velocity of the light passing through it to change. This is measured interferometrically. Adsorption processes of antibodies onto the waveguide surface as well as immunoreactions have been monitored. Concentrations of 2.5 × 10¿8 M (1 × 10-3 mg/ml) of the antigen HCG (molecular weight = 39 600) have been measured so far

Refractive index and layer thickness of an adsorbing protein as reporters of monolayer formation

A method is presented for a separate real-time determination of refractive index and layer thickness of an adsorbing thin layer. The changing angular deflections of TE and TM modes in a dedicated planar waveguide structure are measured. A resolution of 0.01 in the refractive index and 0.5 nm in the average thickness is obtained. The method is illustrated with experimental results on the binding of an antibody to the substrate, both in a physisorption and in an immunoreaction. In the latter, results are consistent with an end-on binding of the antibody to the surface

Temperature dependence of Raman vibrational bandwidths in poly(rA) and rAMP

Isotropic and anisotropic spontaneous Raman spectra were obtained from solutions of poly(ra) and rAMP in buffer. The temperature dependence of these spectra was measured to elucidate the influence of macromolecular dynamics and solvent dynamics on the bandwidths of base vibrations in the single stranded polynucleotide poly(rA). The temperature dependence of a bandwidth depends upon the particular vibration under study. The bands can for the larger part be described by Lorentz functions. When fitted by Voigt functions, maximally 10% of each bandprofile of the adenine base vibrations can be attributed to a Gaussian component. The second moment has been determined from the spectra for the 725 cm¿1 band. From the second moment and the bandwidth, we were able to deduce that the vibrational oscillator is in the fast modulation limit. The determined timescale (perturbation correlation time 0.13 ps) eliminate perturbations connected to long range diffusion like concentration fluctuations (timescale in the order of 10 ps). The spectra were analyzed by an extensive curve fitting procedure providing accurate bandparameters (position, width and integrated intensity). The 725 cm¿1 band of adenine has a bandwidth which is dependent upon the degree of polymerization. In RAMP it is 17.6 cm¿1, in stacked (i.e. low temperature 5°C) poly(rA) it is 11.5 cm¿1. The bandwidth of the adenine vibration at 1336 cm¿1 cm¿1 has a temperature dependence which is similar to the intensity changes of the Raman and the absorption hypochromic effect as a function of temperature. The melting transition can therefore be followed by the changes in bandwidth of suitable vibrations

An improved optical method for surface plasmon resonance experiments

In this paper an inexpensive optical device is described, which is capable of measuring the optical reflectance at different angles, while keeping the laser spot stationary at one point of the surface. This is accomplished by applying cylindrical optics. Its use is demonstrated in a surface plasmon resonance (SPR) sensor. A coil-operated vibrating mirror is used to obtain an angle scan of about 4 degrees. The angle of minimum reflectance can be detected with an accuracy of approximately 2 × 10−3 degrees. Despite the use of simple optical components, disturbance of laser beam parallelism is no more than 0.02 degrees. Displacement of the laser spot at the surface during the angle scan is kept within 0.2 mm. The device eliminates disturbances due to surface irregularities in measurements.\u

Accretion disks in Algols: progenitors and evolution

There are only a few Algols with measured accretion disk parameters. These measurements provide additional constraints for tracing the origin of individual systems, narrowing down the initial parameter space. We investigate the origin and evolution of 6 Algol systems with accretion disks to find the initial parameters and evolutionary constraints for them. With a modified binary evolution code, series of close binary evolution are calculated to obtain the best match for observed individual systems. Initial parameters for 6 Algol systems with accretion disks were determined matching both the present system parameters and the observed disk characteristics. When RLOF starts during core hydrogen burning of the donor, the disk lifetime was found to be short. The disk luminosity is comparable to the luminosity of the gainer during a large fraction of the disk lifetime.Comment: 8 pages, 6 figures , accepted by A&

The cytodisk: A cytometer based upon a new principle of cell alignment

A new method is described for one-dimensional alignment of small particles such as biological cells. A drop of the particle suspension is spread out on a flat disk or plate equipped with V-shaped grooves such as are present on a gramophone disk. After drying, the particles are located on the bottom of the grooves and are thus aligned in a one-dimensional array. The new alignment procedure is demonstrated with a suspension of fluorescent polystyrene micropheres (diameter 3.8 µm) and a suspension of the unicellular algae chlorella vulgaris (diameter about 3 µm). It appears that the alignment of cells and spheres is very good. \ud When using microspheres, more than 95% of the particles in the grooves are located within ±2 µm of the centre line of the groove. Based upon this cell-alignment principle, a new cytometer, named the cytodisk, is proposed. The proposed system has a number of advantages over the flow cytometer, among which is the unique ability of relocating a previously measured cell for further measurement or visual examination. \ud A prototype of a cytodisk, developed for initial test measurements, was built in our laboratory. The apparatus, constructed from a record player and ordinary long-playing records, uses a simple mechanical tracking system and a single optical fiber for fluorescence excitation and detection. With this apparatus it is demonstrated that a cytodisk can indeed perform quite well: A histogram of fluorescing microspheres could be measured with a coefficient of variation of 4.1%. The performance of this prototype is limited by the quality of the mechanical tracking system and the optical system used. It is expected that considerable improvements may be obtained by using a more sophisticated optical detection system such as the tracking system in use in optical disk players

Raman anemometry, a method for component-selective velocity measurements of particles in a flow

An anemometer for the measurement of the velocity of particles of different substances in a flow, separate and apart from that of the flow itself, is described. The substances are distinguished by Raman scattering. The velocity is obtained by relating the autocorrelated scattering signal to the known laser beam profile