Remote Surfaces Research Articles

Direct monitoring of antigen-antibody interactions by spectral interferometry

Spectral interferometry as a tool for on-line monitoring of immunoreactions is described. The setup consists of a light source, a thin transparent light interference layer as the sensing interface and a diode array spectrometer. Optical coupling is achieved by means of a bifurcated fiber optics. The basic principle is the measurement of the reflection spectra perpendicular to the sensing film. Incident light is partially reflected at the adjacent and remote surfaces of this film. The reflected partial beams show interference resulting in an interference spectrum. Deposition of a layer of protein at the interface during an immunoreaction changes the reflected spectrum. If the refractive indices of film and protein layer are matched, the change in the interference spectrum can be calculated as an increase in the thickness of the film. The reaction of rabbit-IgG with anti-rabbit-IgG on polystyrene shows high specificity. All steps of the test protocol can be clearly identified by changes in layer thickness. Quantitative evaluation of concentration dependency shows a linear correlation between antibody concentrations and initial rate of thickness increase. Investigated concentrations range from 0.5–25 μg/ml. Data can be calculated from a time interval of 100 s incubation time, indicating the capability of this rapid label-free system.

Nondestructive ultrasonic transducer

An extendable probe that permits nondestructive ultrasonic inspection of a workpiece for flaws is disclosed which provides information indicative of flaw presence and location. The probe includes a pair of waveguides capable of elastic wave transmission. A first waveguide is excited to produce elastic waves which travel along the waveguide to an end of the waveguide in elastic wave transmitting contact with the surface of the workpiece under inspection. A second waveguide is maintained in contact with the workpiece a selected distance from the first waveguide and a sensor is disposed on the second waveguide for reception of elastic waves. In the absence of workpiece defects intermediate the contact points of the first and second waveguides, elastic waves are transmitted from the first waveguide to the second waveguide through the workpiece to the sensor and an output signal representative of transmitted elastic waves is produced by the sensor. The presence of a crack or flaw in the workpiece between or proximate to respective ends of the waveguides is apparent as a variation in the amplitude of the sensor output signal. Inspection of relatively inaccessible remote surfaces is facilitated with the probe which is thin and extendable. The distance from the sensors to a workpiece flaw is determinable from travel time of elastic waves in the waveguides and the workpiece. Detection of flaws of varied orientation in the workpiece is achieved by pivotable orientation of the waveguide ends with respect to the workpiece.