Khandaker A. Al Mamun

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 CMOS potentiostatic glucose monitoring system for VACNF amperometric biosensors

In this paper we show a stable glucose monitoring system for vertically aligned carbon nanofiber based biosensors. The system is comprised of a modified grounded working electrode potentiostat using a common gate transimpedance amplifier and a current starved voltage controlled oscillator. The system provides a low power solution for portable applications and facilitates wireless data transfer. The system is implemented in a commercially available 0.18μm 6 metal 1 poly standard CMOS process. The potentiostat consumes 72.4μW of power from a 1.8V supply, and the system occupies 0.0457mm2 of chip area.

A SPICE model for perimeter-gated single photon avalanche diode

In this work a comprehensive SPICE model is demonstrated for perimeter-gated single photon avalanche diodes (PGSPAD) fabricated in commercial 0.5 μm CMOS process. This model simulates the trigger of an avalanche event of PGSPAD due to photon absorption, along with the quenching behavior. It also simulates the I-V characteristic, where the breakdown voltage can be modulated with applied gate voltage. The modeling parameters are experimentally extracted from fabricated PGSPADs. This model simulates both the static and dynamic behaviors of the device. Simulated results are validated with experimental data to demonstrate the accuracy of the model.

A Glucose Biosensor Using CMOS Potentiostat and Vertically Aligned Carbon Nanofibers

This paper reports a linear, low power, and compact CMOS based potentiostat for vertically aligned carbon nanofibers (VACNF) based amperometric glucose sensors. The CMOS based potentiostat consists of a single-ended potential control unit, a low noise common gate difference-differential pair transimpedance amplifier and a low power VCO. The potentiostat current measuring unit can detect electrochemical current ranging from 500 nA to 7 μA from the VACNF working electrodes with high degree of linearity. This current corresponds to a range of glucose, which depends on the fiber forest density. The potentiostat consumes 71.7 μW of power from a 1.8 V supply and occupies 0.017 mm2 of chip area realized in a 0.18 μm standard CMOS process.

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.

Cell impedance sensing system based on vertically aligned carbon nanofibers

We demonstrate an electric cell substrate impedance sensing system (ECIS) based on vertically aligned carbon nanofibers (VACNF). The nanofibers having an average length of 4.45 μm are deterministically fabricated on transparent quartz substrates and are examined using SEM. Bovine aortic smooth muscle cells cultured on the VACNF ECIS system over a 10 hour period show a change in measured impedance over time.

A low power integrated bowel sound measurement system

Bowel signal monitoring finds numerous applications in medical and pathological fields. A portable bowel sound monitoring system requires front end amplifiers, data converters, signal processors and power efficient operation. In this paper, a low power integrated bowel sound monitoring system has been proposed and implemented. The system consists of a tunable charge amplifier, a feature extraction block, a bowel sound detection unit and a bowel sound occurrence rate count block. The system is implemented in a standard 6 metal 1 poly 180nm CMOS process. The developed integrated system consumes 52μW of power from a 1V supply.

A low-power low-noise transimpedance amplifier for an integrated biosensing platform

In this paper, we design a low power, low noise transimpedance amplifier for ultra-low biosignal amplification. The proposed transimpedance amplifier is implemented in a standard 6 metal, 1 poly 0.18μm CMOS process. The amplifier is capable of producing 215MΩ transimpedance gain, 0.615MHz bandwidth; 910fA/√Hz input referred noise at 100Hz while consuming only 139μW DC power.

A 10.6μm × 10.6μm CMOS SPAD with integrated readout

Single photon avalanche diodes (SPAD) are sensitive optical sensing tools. Incoming photons trigger avalanche events resulting in large device currents. In this paper, we show experimental results for a 10.6 μm × 10.6 μm perimeter gated SPAD with integrated readout circuitry in 0.5 μm 2 poly, 3 metal standard CMOS process. The dark count rate demonstrates a functional relationship with the gate and the excess bias voltage. A compact readout topology is used which takes advantage of the Miller effect to reduce the readout area footprint, thus increasing the pixel fill factor.

In tegration of carbon nanostructures on CMOS for lab-on-a-chip sensing

We review the challenges and suggest future directions of carbon nanostructure CMOS integration for lab-on-a-chip systems. Power and area requirements of standard benchtop sensor instrumentation limits their use in portable applications. We have been developing carbon based nanostructures and low power analog readouts to enable sensitive and highly efficient sensor measurement in a single measurement platform. Specifically, we review integration methods for carbon nanofibers and nanospikes with sensor readouts on a CMOS platform. These lab-on-chip systems offer high throughput, require low operating power and allow complete system implementation in portable and implantable devices.