Arsen Babajanyan

Microwave dielectric resonator biosensor for aqueous glucose solution

We report a near-field microwave biosensor based on a dielectric resonator to detect glucose concentration. A microwave biosensor with a high Q dielectric resonator allows observation of the small variation of the glucose concentration by measuring the shift of the resonance frequency and the microwave reflection coefficient S(11). We observed the concentration of glucose with a detectable resolution up to 5 mgml at an operating frequency of about f=1.68 GHz. The change in the glucose concentration is directly related to the change in the reflection coefficient due to the electromagnetic interaction between the dielectric resonator and the glucose solution.

Sodium chloride sensing by using a near-field microwave microprobe

The authors observed the NaCl concentration of solutions using a near-field microwave microprobe (NFMM). Instead of the usual technique, they take advantage of the noncontact evaluation capabilities of a NFMM. A NFMM with a high Q dielectric resonator allows observation of small variations of the permittivity due to changes in the NaCl concentration. By measuring the reflection coefficient S11, they could observe the concentration of NaCl. The measured signal-to-noise was about 53dB and the minimum detectible signal was about 0.005dB∕(mg∕ml). In order to determine the probe selectivity, they measured a mixture solution of NaCl and glucose.

Noninvasive in vitro measurement of pig-blood D-glucose by using a microwave cavity sensor

We have developed an electromagnetic microwave cavity sensor based on the resonant frequency shift for real time measurement of the glycemia in pig blood. We could determine the concentration of d-glucose in pig blood in the range of 150-550mg/dl at the resonance frequency near 4.75GHz with a bandwidth of 300MHz. The change in the d-glucose concentration in blood brings microwave reflection coefficient S(11) changes of about 6.26dB and resonance frequency shifts of about 11.25MHz due to the electromagnetic interaction between the cavity resonator and the blood filled plastic tube inserted into the cavity. This proposed system provides a unique approach for real time noninvasive and contactless glucose monitoring.

Investigation of space charge at pentacene/metal interfaces by a near-field scanning microwave microprobe

Space charge properties at the interface of pentacene thin films on gold (Au) and aluminum (Al) surfaces were investigated by using a near-field scanning microwave microprobe. The space charge was observed by measuring the microwave reflection coefficient S11 and compared with the result of a Kelvin-probe method. The obtained ΔS11 of the pentacene thin films on Al increased as the pentacene film thickness increased due to the accumulation of negative space charges. Using the pentacene field effect transistor with a Au source, hole injection from the Au electrode into pentacene with varying drain source biasing was imaged by near-field scanning microwave microprobe.

Direct imaging of photoconductivity of solar cells by using a near-field scanning microwave microprobe

A near-field scanning microwave microprobe (NSMM) technique has been used to investigate the photovoltaic effect in solar cells. As the photoconductivity of the n-type silicon layer in the solar cells was varied due to the incident light intensities and the wavelength, we could directly observe the photoconductivity changes inside the solar cells by measuring the change of reflection coefficient S11 of the NSMM at an operating frequency near 4.1 GHz. We also directly imaged the photoconductivity changes by NSMM. Photoconductivity in solar cells is determined from the visualized microwave reflection coefficient changes at the interfaces with high sensitivity.

Non-invasive in vitro sensing of d-glucose in pig blood

We have developed an electromagnetic resonant spiral sensor and have measured the glycemia in pig blood and the concentration of D-glucose in aqueous solution by using a real-time electromagnetic interaction phenomenon between the microwave sensor and the liquid. We could determine the concentration of glucose with a minimal resolution of 5 mg/dl in the 100-600 mg/dl concentration range at operating frequencies of about 7.65 GHz (for the glucose aqueous solution) and 7.77 GHz (for the pig blood sample). The change in the glucose concentration brings the changes of the microwave reflection coefficient due to the electromagnetic interaction between the resonator and the glucose solution. The in vitro results show the measured signal-to-noise ratio of about 34 dB, and the minimum detectible signal level of about 0.022 dB/(mg/dl). Our proposed system provides a unique approach for non-invasive and non-contact glucose monitoring, and it may serve as a bloodless glucometer.

A three-dimensional finite element model of near-field scanning microwave microscopy

A three-dimensional finite element model of an experimental near-field scanning microwave microscope (NSMM) has been developed and compared to experiment on non conducting samples. The microwave reflection coefficient S11 is calculated as a function of frequency with no adjustable parameters. There is qualitative agreement with experiment in that the resonant frequency can show a sizable increase with sample dielectric constant; a result that is not obtained with a two-dimensional model. The most realistic model shows a semi-quantitative agreement with experiment. The effect of different sample thicknesses and varying tip sample distances is investigated numerically and shown to effect NSMM performance in a way consistent with experiment. Visualization of the electric field indicates that the field is primarily determined by the shape of the coupling hooks.

Magneto-optical visualization by Bi:YIG thin films prepared at low temperatures

A device for the imaging of magnetic fields and domain structures based on the Faraday effect has been developed using garnet thin films prepared by the metal-organic decomposition method as indicators. The sensitivity was improved by using high concentration bismuth substituted yttrium iron garnet thin films with in-plane magnetic anisotropy. Low temperature synthesis of the films (BixY3−xFe5O12; x = 2) on glass substrates of thickness about 0.8 μm is described and the Faraday rotation angle is measured to be about −11°/μm.

Label-free DNA microarray bioassays using a near-field scanning microwavemicroscope

A near-field scanning microwave microscope (NSMM) is used to readout and visualize homemade 10-mer oligonucleotide microarrays and an Agilent 60-mer DNA microarray as a realistic test of NSMM applicability to multiplexed sequence analysis. Sensitive characterization of DNA coverage and high resolution mapping of DNA spots in the microarray were realized by measuring the change of microwave reflection coefficient (S₁₁) at about 4 GHz operating frequency. Hybridization between target (free) and capture (immobilized) sequences leads to changes in the microwave reflection coefficient, which were measured by the NSMM. These changes are caused by hybridization-induced modification of the dielectric permittivity profile of the DNA film. The dynamic range based on analysis of the 10-mer microarrays is over 3 orders of magnitude with the detection limit estimated below 0.01 strands/μm². The NSMM method should be readily capable of detecting target coverages down to 98% of probe coverage. We also directly image the patterned DNA microarray by NSMM with a 2 μm resolution. The complementary optical image of the DNA microarray visualized by using a relative fluorescent intensity metric agrees well with the NSMM results.

Investigation of photoconductivity of silicon solar cells by a near-field scanning microwave microscope.

The photovoltaic effect in silicon solar cells were investigated by using a near-field scanning microwave microscope (NSMM) technique by measuring the microwave reflection coefficient at an operating frequency near 4GHz. As the photoconductivity in the solar cells was varied due to the incident light intensities and the wavelength, we could observe the photoconductivity changes at heterojunction interfaces inside the solar cells by measuring the change of reflection coefficient S(11) of the NSMM. By measuring the change of reflection coefficient, we also directly imaged the photoconductivity changes at heterojunction interfaces inside the solar cells.