Applications of Lithium Niobate acoustic plate mode devices as sensors for liquids

The operation principles of acoustic wave sensors for liquids are summarized and results are reported on the use of ZX-LiNbO3 acoustic plate mode (APM) devices as detectors for dilute electrolyte and metal ion solutions. The APM is a slow shear wave having a relatively strong acousto-ionic interaction, and thus allows to measure the liquid electrical properties by the perturbation of the wave propagation characteristics. To utilize the APM device as a selective chemical sensor for liquids, the surface is derivatized in order to covalently couple a chemical selective film onto it. For the development of a selective sensor, the surface cleaning and derivatization of the LiNbO3 surface proved to be a major obstacle. We will summarize our recent results on the derivatization of LiNbO3 with alkylaminosilanes. To understand the relationship between the state of the oxide substrate surface and the homogeneity and structural aspects of aminosilane monolayers further, model experiments with different aminosilanes on a Si(100) surface covered with a native oxide layer are described

Proteinnachweis mit akustischen Sensoren

Die hohe Spezifität von Antigen/Antikörper‐Wechselwirkungen ist in den vergangenen Jahrzehnten intensiv genutzt worden, um präzise Nachweismethoden für Makromoleküle zu entwickeln. Hauptziel hierbei war der Nachweis von Krankheitserregern sowie infektionsspezifischer und Stoffwechsel‐bestimmender Proteine. Trotz ihrer hohen Empfindlichkeit besitzen diese Analysetechniken einige Nachteile. So sind sie in der Regel zeitintensive Mehrschrittverfahren, die für eine direkte Beobachtung von Prozeßabläufen nicht geeignet sind, und sie erfordern den Einsatz von Markierungsstoffen. Ein neuer Forschungszweig beschäftigt sich daher mit der Entwicklung alternativer Nachweistechniken, die — bei hoher Empfindlichkeit und Selektivität — eine on‐line Detektion unmarkierter Moleküle ermöglichen. Bisher gewonnene Ergebnisse zeigen, daß akustische Sensoren einen vielversprechenden Ansatz zur Realisierung eines derartigen Konzeptes bieten

In situ detection of cells and biochemical reactions by optical diffraction

The combination of mesoscopic surface patterning and Fourier diffraction optics represents a new sensor concept for (bio)chemical applications. Antibodies have been covalently linked to microstructures formed by μCP and provide the basis for the in situ detection of cells, which serve as scattering elements for the incident laser beam

Analyse des Salzgehaltes von Lösungen mit Ultraschall

Akustische Sensoren für den Nachweis geladener Teilchen in Flüssigkeiten zeichnen sich durch sehr kleine Abmessungen aus. Sie registrieren den Einflu0 der Ionen auf die Fortpflanzungsgeschwindigkeit von Schallwellen

Experimental determination of mass sensitivity of APM sensors by CVD thin films

Acoustic wave devices have been used as gravimetrical sensors in both gas and liquid environments. In case of corrosive analytes the use of acoustic plate modes (APMs) has proved to be a promising concept as sensor electrodes and analyte are strictly separated. While mass sensitivity of quartz microbalances and surface acoustic waves has been studied in detail both theoretically and experimentally, there are only few data on the mass sensitivity of APMs. In order to overcome this lack of information we determined the mass sensitivity of APMs on ZX-LiNbO 3 using a chemical vapour deposition (CVD) method. Results are reported on the frequency dependence of mass sensitivity and the effects of metallization thickness and applied constant strain. The obtained data are compared to liquid-phase measurement

Multifrequency evaluation of different immunosorbents on acoustic plate mode sensors

Previous studies of acoustic plate modes on ZX-LiNbO3 have indicated that practical mass-sensitive immunosensors can be implemented by using devices with higher frequencies of operation and/or by improving techniques for the immobilization of antibodies. However, it is also known from these studies that the viscoelastic properties of aminosilane films, used for the covalent immobilization of antibodies on the crystal surface, cannot be ignored in the sensor response. In the present work, in an attempt to study the effect of viscoelasticity of the binding film, three different films with different viscoelasticity and binding capacities, an aminosilane, a dextran, and a poly-(etherurethane)-based immunosorbent (XP-5), were prepared on the sensor surface for the immobilization of antibodies. Immunochemical reactions were monitored by the acoustic plate mode sensor at three different frequencies, thus allowing the direct observation of the frequency dependence of mass sensitivity with different films. Depending on the type of immunosorbent, the sensitivity at the third harmonic was enhanced by a factor of 2-5 with respect to the fundamental response. A third acoustic mode at a closely spaced frequency to the third harmonic yielded lower sensitivity values, which indicates that sensitivity depends not only on the frequency of device operation but also on particle displacement amplitude and components of the selected wave. Since antigen binding capacities of the different immunosorbents were determined independently by a modified ELISA test, sensor responses can also be correlated to the immunosorbent structure, and hence the viscoelastic properties. A dual delay line configuration was used which compensates for second-order effects such as temperature variations and nonspecific adsorption

Polymer Induced Swelling of Solid Supported Lipid Membranes

In this paper, we study the interaction of charged polymers with solid supported 1,2 dimyristoyl sn glycero 3 phosphocholine DMPC membranes by in situ neutron reflectivity. We observe an enormous swelling of the oligolamellar lipid bilayer stacks after incubation in solutions of poly allylamine hydrochloride PAH in D2O. The positively charged polyelectrolyte molecules interact with the lipid bilayers and induce a drastic increase in their d spacing by a factor of 4. Temperature, time, and pH influence the swollen interfacial lipid linings. From our study, we conclude that electrostatic interactions introduced by the adsorbed PAH are the main cause for the drastic swelling of the lipid coatings. The DMPC membrane stacks do not detach from their solid support at T gt; Tm. Steric interactions, also introduced by the PAH molecules, are held responsible for the stabilizing effect. We believe that this novel system offers great potential for fundamental studies of biomembrane properties, keeping the membrane s natural fluidity and freedom, decoupled from a solid support at physiological condition