Increase In Impedance Magnitude Research Articles

An Impedance Aptasensor with Microfluidic Chips for Specific Detection of H5N1 Avian Influenza Virus.

In this research a DNA aptamer, which was selected through SELEX (systematic evolution of ligands by exponential enrichment) to be specific against the H5N1 subtype of the avian influenza virus (AIV), was used as an alternative reagent to monoclonal antibodies in an impedance biosensor utilizing a microfluidics flow cell and an interdigitated microelectrode for the specific detection of H5N1 AIV. The gold surface of the interdigitated microelectrode embedded in a microfluidics flow cell was modified using streptavidin. The biotinylated aptamer against H5N1 was then immobilized on the electrode surface using biotin–streptavidin binding. The target virus was captured on the microelectrode surface, causing an increase in impedance magnitude. The aptasensor had a detection time of 30 min with a detection limit of 0.0128 hemagglutinin units (HAU). Scanning electron microscopy confirmed the binding of the target virus onto the electrode surface. The DNA aptamer was specific to H5N1 and had no cross-reaction to other subtypes of AIV (e.g., H1N1, H2N2, H7N2). The newly developed aptasensor offers a portable, rapid, low-cost alternative to current methods with the same sensitivity and specificity.

Frequency dependent and surface characterization of DNA immobilization and hybridization

The hybridization of oligomeric DNA was investigated using the frequency dependent techniques of quartz crystal microbalance (QCM) and electrochemical impedance spectroscopy (EIS). Synthetic 5′-amine-terminated single stranded oligonucleotides (ssDNA) were immobilized on the surface of the oxidized platinum driving electrodes of AT-cut quartz QCM crystals using 3-glycidoxypropyl-trimethoxysilane. Similar ssDNA coupling was accomplished on the exposed glass surface between the metallic digits of microlithographically fabricated interdigitated microsensor electrodes (IMEs). Confirmation of this covalent coupling surface chemistry was achieved using Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR). Substantial changes in resonant frequency values (0.012% decrease) and electrochemical impedance values (both real and imaginary components) (35.4 and 42.1% increase in impedance magnitude at 1.0 Hz in buffer and deionized water, respectively) were observed resulting from hybridization of the attached ssDNA upon exposure to its complement under appropriate hybridization conditions. Non-complementary (random) oligomer sequence demonstrated a modest change in resonant frequency and a non-detectable change in impedance. Microarray glass slide surfaces modified with 3-glycidoxypropyltrimethoxysilane (GPS), shown to be advantageous in the design and use of microarrays of amine-terminated ssDNA, is confirmed to arise from direct covalent coupling of the DNA to the surface with little non-specific adsorption. The possibility to detect the binding state of DNA in the vicinity of an electrode, without a direct connection between the measurement electrode and the DNA is hereby reported. The potential for development of label-free, low-density DNA microarrays is demonstrated and is being pursued.

Electrical impedance in the subicular area of rats during paradoxical sleep

A four-electrode method of chronically measuring impedance of less than 1 mm 3 parts of brain in unrestrained rats is described. The method is usually good from about 1.5 to 3,000 cycle/sec for the absolute value of phase angle, and relative changes in magnitude of impedance can be measured from about 1.5 to 10,000 cycle/sec. Testing current of 2 × 10 −8 amp is used, which produces a signal of about 20 μv. Stability for hours and days is sometimes, but not always, achieved. In the subicular area, there is invariably an increase in magnitude of impedance of up to 25% during paradoxical sleep. In the same animal, this increase is the same during all episodes of paradoxical sleep lasting longer than 1 min, and is the same at 32 to 10,000 cycle/sec. The phase angle at 100 to 1,000 cycle/sec becomes 1 or 2 deg more negative during paradoxical sleep. There are no changes or very small changes in Ammon's horn and the fascia dentata. Because these data are fairly complete, the mechanisms which might possibly be responsible for these impedance changes can be stated specifically in semiquantitative form. Among several possibilities, a single one cannot be chosen on the basis of these impedance data alone, but from other considerations, a decreased size of interstitial space seems by far the most likely.