Label-free DNA microarray bioassays using a near-field scanning microwave microscope.

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.

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.

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.

Detection of DNA-hybridization using a near-field scanning microwave microscope.

A near-field scanning microwave microscope (NSMM) is used to detect sequence-specific hybridization between surface-immobilized and free DNA single strands. Hybridization between target (free) and capture (immobilized) sequences leads to changes in the reflection coefficient (S11) which are measured by the NSMM. These changes are caused by hybridization-induced modification of the dielectric constant profile of the DNA film. NSMM instrumentation does not require labeling of target sequences with fluorophores or other tagging groups. The physical basis of reflection coefficient changes underpinning the NSMM approach is discussed.

Visualization of magnetic domains by near-field scanning microwave microscope.

A near-field scanning microwave microscope (NSMM) system was used for the investigation of magnetic properties of a hard disk (HD) under an external magnetic field. To demonstrate local microwave characterization of magnetic domains by NSMM, we scanned the HD surface by measuring the microwave reflection coefficient S(11) of the NSMM at an operating frequency near 4.4GHz. The NSMM offers a reliable means for quantitative measurement of magnetic domains with high spatial resolution and sensitivity.

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.

Characterization of magnetic materials using a scanning microwave microprobe.

We investigated the electromagnetic properties of metals of iron, nickel, cobalt, aluminum, gold, copper, silver, and permalloy thin films on SiO2 substrates using a near-field microwave microprobe. The electromagnetic properties of metal sheets were estimated by measuring the microwave reflection coefficient S(11) and compared with the theoretical values. We observed the hysteresis behavior of permalloy thin films on SiO2 substrates using a near-field scanning microwave microprobes (NSMM) system. Experimental results are in good agreement with the theoretical model of transmission theory. In order to better characterize the electromagnetic properties of metals and magnetic metals instead of the usual method, we take advantage of the noncontact microprobing evaluation capabilities using a near-field microwave.

Characterization of Alq3 thin films by a near-field microwave microprobe.

We observed tris-8-hydroxyquinoline aluminum (Alq3) thin films dependence on substrate heating temperatures by using a near-field microwave microprobe (NFMM) and by optical absorption at wavelengths between 200 and 900 nm. The changes of absorption intensity at different substrate heating temperatures are correlated to the changes in the sheet resistance of Alq3 thin films.

Investigation of CdS thin films by a near-field microwave microprobe.

Cadmium sulphide (CdS) thin films with different microstructures and morphologies were measured by using a near-field microwave microprobe (NFMM). The NFMM system was coupled to a dielectric resonator with a distance regulation system at an operating frequency f=4.1 GHz. The changes in dielectric permittivity of CdS thin films due to different annealing temperatures were investigated by measuring the reflection coefficient S(11). CdS thin films with different microstructures and morphology were characterized by X-ray diffraction, atomic force microscopy and NFMM.