Fahmida S. Tulip

An Inductive Link-Based Wireless Power Transfer System for Biomedical Applications

A wireless power transfer system using an inductive link has been demonstrated for implantable sensor applications. The system is composed of two primary blocks: an inductive power transfer unit and a backward data communication unit. The inductive link performs two functions: coupling the required power from a wireless power supply system enabling battery-less, long-term implant operation and providing a backward data transmission path. The backward data communication unit transmits the data to an outside reader using FSK modulation scheme via the inductive link. To demonstrate the operation of the inductive link, a board-level design has been implemented with high link efficiency. Test results from a fabricated sensor system, composed of a hybrid implementation of custom-integrated circuits and board-level discrete components, are presented demonstrating power transmission of 125 mW with a 12.5% power link transmission efficiency. Simultaneous backward data communication involving a digital pulse rate of up to 10 kbps was also observed.

A Mediator Free Amperometric Bienzymatic Glucose Biosensor Using Vertically Aligned Carbon Nanofibers (VACNFs)

A biosensor is proposed for selective and sensitive detection of glucose. This electrochemical amperometric bienzymatic glucose biosensor is constructed by co-immobilization of horseradish peroxidase and glucose oxidase on vertically aligned carbon nanofibers (VACNFs). An enzyme wiring technique is used to plug the enzymes with the metal electrode using VACNFs, which facilitates an effective way to transfer electrons from the electrode to the electrochemical reaction centers. Direct electron transfer of horseradish peroxidase at the VACNF electrode is observed. Mediator or membrane free operation of this biosensor can potentially result in the application of these sensors in environmental monitoring, healthcare, as well as in varieties of scientific experiments. Experimental results indicate that the proposed biosensor can detect very low level of glucose (as low as 0.4 μM). Operational characteristics of the bienzymatic biosensor in terms of detection limit, sensitivity, and selectivity are also examined.

Integrated MOSFET-Embedded-Cantilever-Based Biosensor Characteristic for Detection of Anthrax Simulant

In this work, MOSFET-embedded cantilevers are configured as microbial sensors for detection of anthrax simulants, Bacillus thuringiensis. Anthrax simulants attached to the chemically treated gold-coated cantilever cause changes in the MOSFET drain current due to the bending of the cantilever which indicates the detection of anthrax simulant. Electrical properties of the anthrax simulant are also responsible for the change in the drain current. The test results suggest a detection range of 10 μL of stimulant test solution (a suspension population of 1.3 × 107 colony-forming units/mL diluted in 40% ethanol and 60% deionized water) with a linear response of 31 μA/μL.

Vertically Aligned Carbon Nanofiber based Biosensor Platform for Glucose Sensor

Vertically aligned carbon nanofibers (VACNFs) have recently become an important tool for biosensor design. Carbon nanofibers (CNF) have excellent conductive and structural properties with many irregularities and defect sites in addition to exposed carboxyl groups throughout their surfaces. These properties allow a better immobilization matrix compared to carbon nanotubes and offer better resolution when compared with the FET-based biosensors. VACNFs can be deterministically grown on silicon substrates allowing optimization of the structures for various biosensor applications. Two VACNF electrode architectures have been employed in this study and a comparison of their performances has been made in terms of sensitivity, sensing limitations, dynamic range, and response time. The usage of VACNF platform as a glucose sensor has been verified in this study by selecting an optimum architecture based on the VACNF forest density.

A robust VACNF platform for electrochemical biosensor

Vertically aligned carbon nanofiber (VACNF) is a promising electrode structure for electrochemical biosensor platform. In this paper, we address the mechanical stability and reusability issues of VACNF arrays. We demonstrate that improvement in mechanical stability requires special attention to surface treatment. We show that a thin SU8 layer on nanofiber forest forms a flexible passive layer at the base of the array and that wet etching works best to remove the passive layer from the VACNF tips. The optimum time for wet etching was found to be 2-3 minutes. We show that SU8 treated VACNF arrays have improved signal-to-noise response compared to the untreated bare VACNF arrays.

Label free detection of human MIG using AlGaN/GaN high electron mobility transistor

The paper demonstrates a novel way of detecting Monokine induced by interferon gamma (MIG) in physiological condition (150mM phosphate buffer solution) using a two terminal device. To provide specific MIG detection capability, anti-MIG IgG molecular affinity interface receptors were formed on a short self-assembled monolayer (SAM) on a floating gold sensing gate of a biochemically modified AlGaN/GaN high electron mobility transistor (HEMT) device. Floating gate configuration used for biomolecule detection eliminates the need of external gate voltage and represents purely the effect of biomolecules immobilization and binding events on the gate surface.

GaN-AlGaN high electron mobility transistors for multiple biomolecule detection such as photosystem I and human MIG

This paper demonstrates a novel way of using a single type of high electron mobility transistor (HEMT) device for detecting two kinds of biomolecules (Photosystem I and recombinant human monokine induced by interferon gamma, MIG). MIG was successfully detected in 150 mM concentration of phosphate buffer solution (PBS). Floating gate configuration used for biomolecule detection eliminates the need of external gate voltage and represents purely the effect of biomolecules immobilization and binding events on the gate surface.

Modeling of AlGaN/GaN HEMT based stress sensors

GaN based devices show great potential for high power, high frequency and extreme-environment applications. Due to spontaneous and piezoelectric polarization properties, these devices are also suitable for pressure monitoring or detection of biomolecules causing surface stress. Therefore, GaN based monolithic sensor system can be applied for the detection of biomolecules or pressure imaging for biomedical applications, sensor data processing and transmission of the sensor data even in extreme environmental conditions. This paper investigates the analytical performance of GaN high electron mobility transistor (HEMT) device for the induced strain due to external pressure and surface stress. Analytical expressions for the conductance-stress behavior of the sensor have been developed. The change in two-dimensional electron gas density at the heterointerface of AlGaN/GaN layers resulting from the change in polarizations causes change in the output current of the device. The effects of both the tensile and the compressive strains due to the external force have been studied. This model can be effectively applied to the measurement of target force and to the detection of polar or nonpolar biomolecules.

Direct Label-Free Electrical Immunodetection of Transplant Rejection Protein Biomarker in Physiological Buffer Using Floating Gate AlGaN/GaN High Electron Mobility Transistors

Monokine induced by interferon gamma (MIG/CXCL9) is used as an immune biomarker for early monitoring of transplant or allograft rejection. This paper demonstrates a direct electrical, label-free detection method of recombinant human MIG with anti-MIG IgG molecules in physiologically relevant buffer environment. The sensor platform used is a biologically modified GaN-based high electron mobility transistor (HEMT) device. Biomolecular recognition capability was provided by using high affinity anti-MIG monoclonal antibody to form molecular affinity interface receptors on short N-hydroxysuccinimide-ester functionalized disulphide (DSP) self-assembled monolayers (SAMs) on the gold sensing gate of the HEMT device. A floating gate configuration has been adopted to eliminate the influences of external gate voltage. Preliminary test results with the proposed chemically treated GaN HEMT biosensor show that MIG can be detected for a wide range of concentration varying from 5 ng/mL to 500 ng/mL.

Detection of Transplant Rejection Chemokine Protein Biomarker in Physiological Salt Concentration

Monokine induced by interferon gamma (MIG) is an important biomarker for early monitoring of transplant rejection. This letter presents a novel technique for detecting human MIG by using immunologically-modified field effect transistors. Detection of MIG with anti-MIG antibody in high concentration phosphate buffer saline solution was achieved for the first time. To provide specific MIG detection capability, anti-MIG IgG molecular affinity interface receptors were formed on a short self-assembled monolayer on a floating gold sensing gate of a biochemically modified AlGaN/GaN high electron mobility transistor device.