Bulk and Surface Acoustic Wave Sensor Arrays for Multi-Analyte Detection: A Review

Bulk acoustic wave (BAW) and surface acoustic wave (SAW) sensor devices have successfully been used in a wide variety of gas sensing, liquid sensing, and biosensing applications. Devices include BAW sensors using thickness shear modes and SAW sensors using Rayleigh waves or horizontally polarized shear waves (HPSWs). Analyte specificity and selectivity of the sensors are determined by the sensor coatings. If a group of analytes is to be detected or if only selective coatings (i.e., coatings responding to more than one analyte) are available, the use of multi-sensor arrays is advantageous, as the evaluation of the resulting signal patterns allows qualitative and quantitative characterization of the sample. Virtual sensor arrays utilize only one sensor but combine itwith enhanced signal evaluation methods or preceding sample separation, which results in similar results as obtained with multi-sensor arrays. Both array types have shown to be promising with regard to system integration and low costs. This review discusses principles and design considerations for acoustic multi-sensor and virtual sensor arrays and outlines the use of these arrays in multi-analyte detection applications, focusing mainly on developments of the past decade

Bulk and Surface Acoustic Wave Biosensors for Milk Analysis

Milk and dairy products are common foods and, therefore, are subject to regular controls. Such controls cover both the identification and quantification of specific components and the determination of physical parameters. Components include the usual milk ingredients, mainly carbohydrates, proteins, and fat, and any impurities that may be present. The latter range from small molecules, such as drug residues, to large molecules, e.g., protein-based toxins, to pathogenic microorganisms. Physical parameters of interest include viscosity as an indicator of milk gelation. Bulk and surface acoustic wave sensors, such as quartz crystal microbalance (QCM) and surface acoustic wave (SAW) devices, can principally be used for both types of analysis, with the actual application mainly depending on the device coating and the test format. This review summarizes the achievements of acoustic sensor devices used for milk analysis applications, including the determination of physical liquid parameters and the detection of low- and high-molecular-weight analytes and microorganisms. It is shown how the various requirements resulting from the respective analytes and the complex sample matrix are addressed, and to what extent the analytical demands, e.g., with regard to legal limits, are met

Microfluidic Impedance Biosensor Chips Using Sensing Layers Based on DNA-Based Self-Assembled Monolayers for Label-Free Detection of Proteins

A microfluidic chip for electrochemical impedance spectroscopy (EIS) is presented as bio-sensor for label-free detection of proteins by using the example of cardiac troponin I. Troponin I is one of the most specific diagnostic serum biomarkers for myocardial infarction. The microfluidic impedance biosensor chip presented here consists of a microscope glass slide serving as base plate, sputtered electrodes, and a polydimethylsiloxane (PDMS) microchannel. Electrode functionalization protocols were developed considering a possible charge transfer through the sensing layer, in addition to analyte-specific binding by corresponding antibodies and reduction of nonspecific protein adsorption to prevent false-positive signals. Reagents tested for self-assembled monolayers (SAMs) on gold electrodes included thiolated hydrocarbons and thiolated oligonucleotides, where SAMs based on the latter showed a better performance. The corresponding antibody was covalently coupled on the SAM using carbodiimide chemistry. Sampling and measurement took only a few minutes. Application of a human serum albumin (HSA) sample, 1000 ng/mL, led to negligible impedance changes, while application of a troponin I sample, 1 ng/mL, led to a significant shift in the Nyquist plot. The results are promising regarding specific detection of clinically relevant concentrations of biomarkers, such as cardiac markers, with the newly developed microfluidic impedance biosensor chip

Microfluidic Impedance Biosensor Chip with DNA-Based Self-Assembled Monolayers for Label-Free Detection of Cardiac Biomarker Troponin I

A microfluidic chip for electrochemical impedance spectroscopy (EIS) is presented as biosensor for the detection of cardiac troponin I (cTnI), which is one of the most specific diagnostic serum biomarkers for myocardial infarction. Impedimetric biosensors enable the detection of a variety of analytes, including small molecules, proteins, and cells. As analyte detection is direct and label-free, they allow fast detection of biomarkers, which is essential in the diagnosis of cardiac infarctions to promote a positive outcome. The EIS chip presented here consists of a microscope glass slide serving as base plate, sputtered electrodes, and a polydimethylsiloxane (PDMS) microchannel. The electrode design mainly consists of a working electrode and a counter electrode made of gold. A silver reference electrode can be included, if required. Protocols for electrode functionalization were developed considering a low initial impedance in addition to analyte-specific binding by corresponding antibodies and reduction of non-specific protein adsorption to prevent false-positive signals. Reagents tested for self-assembled monolayers (SAM) on gold electrodes included hydrocarbons with thiol groups and thiolated oligonucleotides. The optimized coating used thiolated single-strand DNA (ssDNA) and 1,4-benzenedithiol on the working electrode and 1,4-benzenedithiol on the counter electrode. After hybridization with corresponding ssDNA carrying an amino group, the reaction with glutaric anhydride led to carboxyl groups, on which anti-cTnI antibody was covalently coupled using carbodiimide chemistry. The PDMS microchannel was bonded on the glass slide with the functionalized electrodes, and the completed EIS chip was connected to the readout system. Sampling with human serum albumin (HSA), 1000 ng/mL, led to negligible signal changes, while sampling with cTnI, 1 ng/mL, led to a significant signal shift in the Nyquist plot. Sampling and measurement took only a few minutes. The results were promising regarding a future cost-effective biosensor array chip for the rapid detection of clinically relevant biomarkers in real samples

Polynomial Structure of the (Open) Topological String Partition Function

In this paper we show that the polynomial structure of the topological string partition function found by Yamaguchi and Yau for the quintic holds for an arbitrary Calabi-Yau manifold with any number of moduli. Furthermore, we generalize these results to the open topological string partition function as discussed recently by Walcher and reproduce his results for the real quintic.Comment: 15 page

Polymer Structures on Surface Acoustic Wave Biosensors

The influence of surface structuring on surface acoustic wave (SAW) biosensor signals has been investigated. Polymer structures on the sensor surfaces were applied by lithography or by self-assembling of polystyrene microparticles. In first experiments, structured and unstructured sensors led to similar results in a model affinity assay using streptavidin and biotinylated protein. On the other hand, structuring had a strong effect on SAW sensor signals obtained by protein adsorption on parylene C coated sensors. Depending on the protein, both decreased (albumin, streptavidin) and increased (fibrinogen) signals were observed with structured SAW sensors. Particularly the latter could contribute to facilitated blood analysis in the future

Extended Supersymmetries and the Dirac Operator

We consider supersymmetric quantum mechanical systems in arbitrary dimensions on curved spaces with nontrivial gauge fields. The square of the Dirac operator serves as Hamiltonian. We derive a relation between the number of supercharges that exist and restrictions on the geometry of the underlying spaces as well as the admissible gauge field configurations. From the superalgebra with two or more real supercharges we infer the existence of integrability conditions and obtain a corresponding superpotential. This potential can be used to deform the supercharges and to determine zero modes of the Dirac operator. The general results are applied to the Kahler spaces CP^n.Comment: 22 pages, no figure