Torbjörn G.I. Ling

MEMS devices with voltage driven flexible elements

An array of nanometric dimensions consisting of two or more arms, positioned side by side, wherein the arms are of such nanometric dimensions that the beams can be moved or deformed towards or away from one another by means of a low voltage applied between the beams, whereby to produce a desired optical, electronic or mechanical effect. At nanometer scale dimensions structures previously treated as rigid become flexible, and this flexibility can be engineered since it is a direct consequence of material and dimensions. Since the electrostatic force between the two arms is inversely proportional to the square of the distance, a very considerable force will be developed with a low voltage of the order of 1-5 volts, which is sufficient to deflect the elements towards or away from one another. As preferred, the bulk of the element may comprise an insulating material, and an upper conductive layer is applied on the upper surface, where the element is formed by a nanolithography method such as nanoimprint lithography (NIL). Alternatively the elements may be formed completely of conductive material, where the elements are formed by a CMOS metalization process.

Nanoimprint- and UV-lithography: Mix&Match process for fabrication of interdigitated nanobiosensors

A complete nanobiosensor structure consisting of a 200 @mm x 200 @mm area containing 100 nm sized interdigitated nanoelectrodes with varied interelectrode distances has been fabricated using nanoimprint lithography (NIL) in combination with UV-lithography. The complete structure has been characterized with admittance spectroscopy. In the paper are discussed the needs and key issues for nanosensors and the capability offered by using NIL for fabrication of such sensors.

Partition affinity ligand assay (pala). A new approach to binding assays

A two-phase partitioning technique was used to separate free from bound labelled ligand in a binding assay. Efficient separation was accomplished by modifying one of the reactants in such a way that it partitions preferentially to one of the two phases. The biospecific interactions between the lectin concanavalin A and various carbohydrates and glycoproteins were investigated in this model study.

Fabrication and characterization of a nanosensor for admittance spectroscopy of biomolecules

We have fabricated nanometer‐sized interdigitated electrode patterns using electron beam lithography and liftoff techniques. The aim of the investigation was to find out whether the dimensions (i.e., the electrode separations) of the pattern would affect the admittance signal of the biomolecules in between the electrodes. Since the admittance signal scales with the geometrical factor A/d, where A is the electrode area and d is the separation, we chose to keep A/d constant when changing the electrode separation in order to eliminate this trivial effect on the admittance signal. An interdigitated electrode structure having an interelectrode spacing in the nanometer regime makes it possible to reach high nonstationary as well as stationary electric field strengths while having a low applied voltage level. Hence, electrode reactions will be as small as possible, while a high signal to noise ratio is obtained. We have been able to experimentally study the response of the impedance behavior to high electric fie...

Immunological quantitation of bacterial cells using a partition affinity ligand assay: A model study on the quantitation of streptococci B

Abstract A new immunoassay for bacterial cells is described. Aqueous two-phase systems were used to separate the different reactants after binding, the principle being that in the direct assay free and bound reactants shall be recovered from different phases. In the competitive binding assay the bacteria are present in two forms—one native (to be quantified) and one modified (in fixed amount)—so that after binding and separation the complexes are recovered from different phases. 125 I-Labeled antibodies were used in the competitive assay and enzyme-labeled antibodies in the direct binding assay. In the system studied here streptococci were quantified. The direct enzyme immunoassay was more sensitive than the competitive radioimmunoassay. The smallest number of cells that could be quantified was 2500. Total time for one assay was 40–120 min.

Development and characterization of silane antisticking layers on nickel-based stamps designed for nanoimprint lithography

In this study we will report on the development of a process to establish antisticking layers on nickel-based stamps, which are used in several industrial applications of nanoimprint lithography or related methods. The fluorinated alkyl silane films have been deposited onto different Ni-based stamp surfaces in order to minimize the adhesion tendency at the stamp/polymer interface. Film thickness, chemical composition, purity, and binding mechanisms of the silane groups to different stamp surface materials have been determined by photoelectron spectroscopy (XPS). In the case of electroplated nickel stamps—where low imprint qualities are observed—multilayer thick films cover the stamp surfaces, consisting of polymerized, cross-linked alkyl silanes, which are poorly bound to the surface. In order to overcome these restrictions a 100 A thick polycrystalline titanium layer has been established in a sandwich position between the nickel substrate and the silane film. Here, silane film thicknesses in the monomolecular region together with evidences for strong covalent linkage between the silane groups and the oxidized Ti surface can be concluded from the XPS results, leading to film properties and imprint qualities, which are comparable to those formerly observed for silicon stamps.

Application of partition affinity ligand assay (PALA) in a quick test for quantitation of staphylococcus aureus bacterial cells

A novel immunochemical method for the quantitation of bacterial cells is described. The method, which is based on separation of bound from free reactants in aqueous two-phase systems has been studied both as direct and competitive binding assays, with a system consisting of intact cells of Staphylococcus aureus and human immunoglobulin G molecules. To achieve high resolution, one of the reactants was modified so that the two reactants, the bacterial cells and the immunoglobulin molecules, occurred in different phases of the phase system. When binding takes place, the partition of one of the reactants is changed. The degree of change is then correlated to the amount of reactant present. Using this method, cell numbers in the region 10(5)-10(7) can be quantified. An assay takes 40-90 min.

FLow-injection binding assays: a way to increase the speed in binding analyses

A flow-injection analysis system was equipped with a small column containing immobilized concanavalin A. Pulses containing glucosides or glycoproteins were passed over the column, the lectin bound the carbohydrates. By using horseradish peroxidase as a labeled carbohydrate and letting it compete with other glucosides or mannosides a competitive binding assay for the latter was set up. When the enzyme activity had been evaluated, the column was rinsed and reconditioned, allowing a new assay to be run. To speed up the assay, substrates for the enzyme marker, peroxidase, were present in the perfusing buffer. A computerized evaluation of the absorbance peak allowed the time of the assay cycle to be reduced to 70 s. The sensitivity of this binding assay was fully comparable with those reported for other systems using the same reactants.

Partition Affinity Ligand Assay (PALA): Applications in the Analysis of Haptens, Macromolecules, and Cells

Publisher Summary The partition affinity ligand assay (PALA) method is normally used as a nonequilibrium method, that is, the binding reaction involved does not have to reach equilibrium. A requirement for a binding assay in aqueous two-phase systems is that the reactants in the binding reaction must have markedly different partition coefficients. The PALA principle includes incubation of the reaction mixture and subsequent separation with an added phase system, both steps being carried out in a single test tube. No separate washing steps and centrifugations are needed. In a direct binding assay, the binding between two different molecules is utilized to quantify one of them. Sufficiently concentrated aqueous solutions of some water-soluble polymers, forming phase systems, can be used for selective distribution of macromolecules. Such phase systems have a top phase rich in one of the polymers and a bottom phase rich in the other. Compared to the phase systems generally used in chemistry, that is, those containing organic solvents, such water-rich systems have been shown to be better for separating biological material.

Immunoassays in aqueous two-phase systems

Aqueous two-phase systems provide a novel and convenient method for separating bound from free fractions in a binding assay. The ease of automation of this type of procedure makes it particularly attractive for separations based on immobilized ligands or binders or on adsorbents.