Nowadays interdigitated electrode (IDE) based sensors have stimulated increasing interest in the application of biosensor field. A large number of finger electrodes as comb structure gain high sensitivity through electrical measurements. In this research study, we have demonstrated a novel mechanism as biocontrollable variable resistor through solid state conducting Polymer Bridge to detect single-stranded E. coliO157:H7 DNA. The gap of AuIDE sensor on Si substrate was used to create DNA biosensor. Functionalization steps of the AuIDE to create biosensor was based on silanization by APTES, immobilization of E.coliO157:H7 synthetic probe singlestranded DNA (ssDNA), blocking with tween-20. The well fabricated AuIDE biosensor was physically characterized by using scanning electron microscope (SEM) and high power microscope (HPM). Molecular assembly of the functionalized biosensor was analyzed structurally using Energy-dispersive Xray spectroscopy (EDX) and electrically using current–voltage measurements (I-V). The selectivity of the biosensor was identified electrically using complementary, noncomplementary and single base mismatch ssDNA targets. Blocking step with tween-20 was important to detect target specifically. The obtained variations in current indicate the varied concentrations of E. coli targets and it is confirmed that biosensor is suitable to detect different concentrations in the range from 10 fM to 10 µM.

E.coli O157:H7 is one of the harmful foodborne pathogenic disease causing bacterium which leads many illnesses and even deaths each year. IDT or IDE (Interdigitated Electrode) based biosensors usually use electrochemical behavior through impedometric detection. In this paper we describe a novel mechanism for E.coli O157:H7 ssDNA target detection via electrical behavior through E.coli O157:H7 probe and (3-Aminopropyl)triethoxysilane (APTES) functionalized Au IDE biosensor. Tween-20 was used as blocking the nonspecific binding on non-immobilized area of the E.coli ssDNA probes. Au IDE was fabricated on the Si substrate using CMOS and conventional photolithographic process. Fabricated Au IDE was physically characterized by using high power microscope (HPM) and scanning electron microscope (SEM). IDE electrode edges were characterized using 3D nano profiler. The E.coli O157:H7 ssDNA probes were used as the receptor to capture the specific target ssDNA and Au IDE was used as the transducer. I-V characteristics were performed for each functionalization step as bare Au IDE, silanization and immobilization. Well functionalized biosensor was hybridized with complementary, non-complementary and single base mismatch ssDNA to confirm the specificity. Sensitivity measurements were done using different concentrations of complementary ssDNA targets from 1fM to 10 µM. The sensitivity and limit of detection (LOD) of the biosensor are 14.3 mAM−1 and 0.8 fM respectively. It was confirmed that Au IDE biosensor shown here is capable to detect specific and low concentrated E.coli O157:H7 ssDNA targets successfully.

A new type of tag antenna, which is made by placing four identical planar inverted-L antennas (PILAs) in rotational symmetry constellation, is proposed for designing a miniature on-metal tag antenna. It shows good omnidirectional characteristics in the azimuth plane. In the design, the directive radiation beams of the respective PILAs are tactfully combined to form a stable omnidirectional pattern. The proposed tag is compact with a small size of 40 mm × 40 mm × 1.6 mm (0.122 λ × 0.122 λ × 0.005 λ). Here, all the PILAs are inductively excited by a circular loop, which also introduces additional reactance for improving the impedance matching. The proposed tag antenna is able to achieve a stable read distance of 5.9 m on metal in the azimuth plane when it is tested using equivalent isotropic radiated power of 4 W. The operating frequency of the tag is stable and it is not affected much by changes in the backing metal.

A UHF RFID wristband tag is designed using a planar inverted-F antenna (PIFA). With the use of the folding technique and the PP-2 soft foam substrate, the tag can be made compact, light-weight, and flexible for electronic package. The tag's footprint is only 900 mm2 with almost 100% power transmission. From simulation, the wristband tag has a theoretical read range of 8.3 m at 923 MHz when placed on a rectangular phantom. With a 3.28 W EIRP, it is also experimentally demonstrated that the wristband tag can be read from 5.1 m when it is tested on minced meat.

A miniature folded patch with a dimension of 40 mm × 40 mm × 1.6 mm (0.1156λ × 0.1156λ × 0.0046λ at 867 MHz) is proposed for designing a passive metal-mountable tag. It consists of a square patch which is equally separated into two rectangular patches. Since the patch resonator usually has high resonant frequency, multiple tuning mechanisms are always needed to bring down the frequency so that it can be used for designing a tag antenna in the UHF band. In the proposed design, each patch is incorporated with a C-shaped slot and three thin inductive stubs for performing different levels of frequency tunings. An equivalent circuit has been built for estimating the input impedance of the antenna. Reasonable agreement is found between the measured, modeled, and simulation results. The proposed tag antenna is readable from 5 m with an EIRP of 3.28 W when placed on a 20 cm x 20 cm metal plate.

A compact folded dipole antenna that consists of two C-shaped arms, which are placed in the antipodal constellation, is proposed for designing a metal-mountable miniature tag antenna in the UHF band. Here, each of the dipole arms is composed of four unequal line segments for reducing the current crowding effect and for improving the tag's performance. Two inductive shorting stubs are introduced for tuning the tag's resonant frequency. The proposed tag antenna is made using a flexible substrate and it is electrically small, having a circuit size of 50 mm × 30 mm × 1.6 mm (0.153λ × 0.092λ × 0.005λ). It has been found that conjugate match can be easily obtained by adjusting the dimensions of the C-shaped arms and the inductive shorting stubs. When mounted on metal, the proposed tag antenna is able to achieve a maximum read distance of 9.1 m at the equivalent isotropic radiated power of 4 W. The proposed tag antenna is found to be platform insensitive and it can read beyond 7 m when placed on dielectric objects.

A semiflexible E-shaped folded patch with a compact footprint of 30 mm × 30 mm x 3 mm (0.091λ × 0.091λ × 0.0091λ at 912 MHz) is proposed for designing a miniature ultrahigh frequency tag for on-metal applications. The proposed tag antenna is simple in structure, and it has eight design parameters to achieve different levels of tuning. By changing the parameters, coarse and fine tunings can be easily performed to vary the tag's resonant frequency. In spite of its compactness, the proposed tag antenna is able to provide sufficient resistance and inductive reactance to enable conjugate match with the chip. Due to conjugate match, the proposed tag antenna has achieved a power transmission coefficient of ~1 and a maximum read distance of 14.5 m (with 4 W equivalent isotropic radiated power) on metal even it is electrically small. It has a radiation efficiency of 53%

A planar inverted-S antenna (PISA) is proposed for designing a compact ultrahigh frequency (UHF) radio frequency identification (RFID) tag for on-metal applications. For the first time, a U-shaped arm is embedded into the middle layer of the tag structure for effectively miniaturizing the footprint. Here, a serpentine patch is tactfully placed on top of the U-shaped arm to achieve a higher level of miniaturization. A compact UHF tag (25 mm × 25 mm × 3.2 mm), with a good power transmission coefficient of 99.7% and a long read distance of greater than 11 m, has been successfully demonstrated. It is also shown that our tag size can be further reduced to 15 mm × 15 mm × 3.2 mm by simply adjusting the geometrical parameters, without sacrificing the power transmission coefficient much. With reference to a 4 W EIRP reader output power, the proposed tag antenna can be read from 11.9 m. For the tag with a footprint of 15 mm × 15 mm, the read range is estimated to be at least 7 m.