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theses

Psychological stress in our daily life affects many biomarkers, such as cortisol. Monitoring cortisol might permit real-time evaluation of psychological stress. To address this need, we propose a low-cost, portable device for cortisol detection by integrating cortisol antibodies with GO(graphene oxide) on a conductive paper substrate. Current paper-based electronics and biosensors mainly use paper as a passive substrate to transport fluid. This effort is attempting to leverage the multiscale, porous architecture of cellulosic fibers to tune their electrochemical properties. Tuning the morphology of paper and adding smart functionalization with electroactive materials will lead to a substrate that has a high surface-to-volume ratio between the conductive fibers and fluid entrapped in the open pores. In this work, we prepared a nanoporous conductive paper to further our understanding of cellulose-based matrices containing conductive polymer and graphene oxide (GO). For this study, the four types of fabricated paper included softwood, 50% softwood: 50% nanofibrillated cellulose, nanofibrillated cellulose, and Whatman paper. For the preparation of the conductive paper, we developed a scalable process of functionalizing conductive paper substrates via drop-casting of PEDOT:PSS (poly(3,4-ethylene dioxythiophene) polystyrene sulfonate). PEDOT:PSS- coated Whatman paper showed the largest conductivity at 0.51S/cm, the conductivity of PEDOT:PSS-coated NFC paper is 0.42S/cm. Unlike conductivity, CP (specific capacitance) and CSC (charge storage capacity) depend on the total content of PEDOT:PSS inside the paper cellulose matrix. The CSC and Cp of NFC paper-based electrodes are about 4 times higher than Whatman paper-based electrodes. In order to bind anti-cortisol antibody on paper electrodes, we attached GO to the detect pad, and modified it with EDC (1-Ethyl-3-(3- dimethylaminopropyl)carbodiimide)-NHS (N-Hydroxysuccinimide). Then, we tested our working electrodes in PBS (phosphate-buffered saline solution) spiked with cortisol. When we used GO-EDC-NHS modified biosensor as working electrode and in cortisol-PBS solution, the anti-cortisol antibodies on paper electrodes can bind with cortisol antigens in PBS. While the concentration of cortisol phosphate buffer saline solution increases, the biosensor shows changes in the imaginary part of the impedance and phase angle. To model the reaction between cortisol and anti-cortisol, we use ZsimpWin software to fit the EIS (Electrochemical Impedance Spectroscopy) and Bode plot to tailor the reaction circuit. This paper-based nano biosensor enables the detection of cortisol and paves the way toward economically and flexible paper-based biosensors by using techniques such as dip coating. Scientifically understanding how the nanoscale porosity of paper affects electrochemical performance has the potential to enable scalable applications in health monitoring.

http://dissertations.umi.com/gsnb.rutgers:12134

M.S.

Includes bibliographical references

doi:10.7282/t3-e8zx-1798

The author owns the copyright to this work.