Hee-Jo Lee

Biosensing using split-ring resonators at microwave regime

A split-ring resonator (SRR) array is experimentally demonstrated for a biosensing device at microwave frequencies. Each SRR in the array is excited by a time-varying H-field component through a microstrip transmission line in which microwaves propagate in the quasitransverse electromagnetic mode. It is found that the resonant frequency changes due to the binding of biotin and streptavidin onto the surface of the SRRs. The observed change values represent around ΔfB=120MHz and ΔfB-S=40MHz, respectively. Finally, the SRR-based biosensing device suggests a few improvements for increasing sensitivity and describes its possible application.

DNA sensing using split-ring resonator alone at microwave regime

In this paper, the feasibility of utilization of a single element double split-ring resonator as a biosensing device has been demonstrated. The compact resonator has been excited by time-varying magnetic fields generated from the 50 Ω microstrip transmission line. In this work, DNA hybridization is recognized with shift in S21 resonant frequency. When thiol-linked single stranded-DNA is immobilized onto a gold (Au) surface and is then coupled with complementary-DNA, the frequency changes by Δfss-DNA=20 MHz and Δfhybridization=60 MHz, respectively. Thus, it is clear that the resonator can be utilized as a DNA sensing element in the microwave regime.

A symmetric metamaterial element-based RF biosensor for rapid and label-free detection

A symmetric metamaterial element-based RF biosensing scheme is experimentally demonstrated by detecting biomolecular binding between a prostate-specific antigen (PSA) and its antibody. The metamaterial element in a high-impedance microstrip line shows an intrinsic S21 resonance having a Q-factor of 55. The frequency shift with PSA concentration, i.e., 100 ng/ml, 10 ng/ml, and 1 ng/ml, is observed and the changes are Δf ≈ 20 MHz, 10 MHz, and 5 MHz, respectively. The proposed biosensor offers advantages of label-free detection, a simple and direct scheme, and cost-efficient fabrication.

Intrinsic characteristics of transmission line of graphenes at microwave frequencies

In this paper, we have quantitatively evaluated the effective surface conductivity of chemical vapor deposition-grown graphene through a full-wave electromagnetic method and also investigated the intrinsic characteristics of the transmission line (TL) of the graphene at frequency ranging from 0.5 to 40 GHz. According to the simulated data based on the measured S-parameters, the effective conductivity of single- and multi-layer graphene (MLG) was about 4.3 × 106 S/m and 1.2 × 106 S/m, respectively. Furthermore, we confirm that multi-layer graphene is more suitable for use in transmission lines compared to single-layer graphene in the observed frequency region.

Asymmetric split-ring resonator-based biosensor for detection of label-free stress biomarkers

In this paper, an asymmetric split-ring resonator, metamaterial element, is presented as a biosensing transducer for detection of highly sensitive and label-free stress biomarkers. In particular, the two biomarkers, cortisol and α-amylase, are used for evaluating the sensitivity of the proposed biosensor. In case of cortisol detection, the competitive reaction between cortisol-bovine serum albumin and free cortisol is employed, while alpha-amylase is directly detected by its antigen-antibody reaction. From the experimental results, we find that the limit of detection and sensitivity of the proposed sensing device are about 1 ng/ml and 1.155 MHz/ng ml−1, respectively.

Recent research trends of radio-frequency biosensors for biomolecular detection.

This article reviews radio-frequency (RF) biosensors based on passive and/or active devices and circuits. In particular, we focus on RF biosensors designed for detection of various biomolecules such as biotin-streptavidin, DNA hybridization, IgG, and glucose. The performance of these biosensors has been enhanced by the introduction of various sensing schemes with diverse nanomaterials (e.g., carbon nanotubes, graphene oxide, magnetic and gold nanoparticles, etc.). In addition, the RF biosensing platforms that can be associated with an RF active system are discussed. Finally, the challenges of RF biosensors are presented and suggestions are made for their future direction and prospects.

Noncontact Proximity Vital Sign Sensor Based on PLL for Sensitivity Enhancement

In this paper, a noncontact proximity vital sign sensor, using a phase locked loop (PLL) incorporated with voltage controlled oscillator (VCO) built-in planar type circular resonator, is proposed to enhance sensitivity in severe environments. The planar type circular resonator acts as a series feedback element of the VCO as well as a near-field receiving antenna. The frequency deviation of the VCO related to the body proximity effect ranges from 0.07 MHz/mm to 1.8 MHz/mm (6.8 mV/mm to 205 mV/mm in sensitivity) up to a distance of 50 mm, while the amount of VCO drift is about 21 MHz in the condition of 60 °C temperature range and discrete component tolerance of ±5%. Total frequency variation occurs in the capture range of the PLL which is 60 MHz. Thus, its loop control voltage converts the amount of frequency deviation into a difference of direct current (DC) voltage, which is utilized to extract vital signs regardless of the ambient temperature. The experimental results reveal that the proposed sensor placed 50 mm away from a subject can reliably detect respiration and heartbeat signals without the ambiguity of harmonic signals caused by respiration signal at an operating frequency of 2.4 GHz.

Radio-frequency characteristics of graphene oxide

We confirm graphene oxide, a two-dimensional carbon structure at the nanoscale level can be a strong candidate for high-efficient interconnector in radio-frequency range. In this paper, we investigate high frequency characteristics of graphene oxide in range of 0.5–40 GHz. Radio-frequency transmission properties were extracted as S-parameters to determine the intrinsic ac transmission of graphene sheets, such as the impedance variation dependence on frequency. The impedance and resistance of graphene sheets drastically decrease as frequency increases. This result confirms graphene oxide has high potential for transmitting signals at gigahertz ranges.

An RF Circuit Model for Interdigital Capacitors-Based Carbon Nanotube Biosensors

We present improved RF circuit modeling of a biosensing element based on a single-walled carbon nanotube combined interdigital capacitors at microwave frequencies. From the resultant circuit, the lumped element values for biomolecular binding are accurately obtained. It is thereby found that the completed RF circuit model shows excellent agreement with measured results. This implies that the electrical properties of a specific biomolecular binding system can be quantitatively analyzed if an optimal RF circuit model is constructed. Finally, we suggest that the suggested methodology can be used to analyze other biomolecular sensing methods.

DNA sensing based on single element planar double split-ring resonator

In this paper, a feasibility of using double split ring resonator (DSRR) having negative permeability as a biosensor has been demonstrated. The compact DSRR has been excited by a microstrip transmission line, and the DNA hybridization in which single-stranded deoxyribonucleic acid (ss-DNA) is coupled with a complementary deoxyribonucleic acid (c-DNA), it is recognized with change in S21 resonant frequency. When ss-DNA is immobilized onto gold (Au) surface and then is coupled with c-DNA, the resonant frequency has been changed by Δƒss-DNA=20 MHz and Δƒhybridization=60 MHz for two cases. It is clear that DSRR can be utilized as a DNA sensing element at microwave regime.