Graduation Year

2014

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Chemical Engineering

Major Professor

Ashok Kumar

Co-Major Professor

Venkat Bhethanabotla

Keywords

biosensors, diamond, iron oxide grafted, nanocomposite, polyaniline

Abstract

This dissertation presents the synthesis and application of nanodiamond based materials for electrochemical biosensors. In this research work, nanodiamond particles have been used to prepare doped and undoped nanocrystalline diamond films, and conducting polymer composites for enhanced biosensing. The performance of the synthetized materials towards sensing applications was evaluated against glucose amperometric biosensing. Besides, cholesterol biosensing was attempted to prove the capabilities of the platform as a generic biosensing substrate.

Biosensors have been proved to provide reliable detection and quantification of biological compounds. The detection of biological markers plays a key factor in the diagnosis of many diseases and, even more importantly, represents a major aspect in the survival rate for many patients. Among all of the biosensors types, electrochemical biosensors have demonstrated the best reliability to cost ratio. Amperometric biosensors, for example, have been used for decades as point of care sensing method to monitor different conditions such as glucose. Despite the amount the research presented, the sensitivity, selectivity, stability, low cost and robustness are always driving forces to develop new platforms for biosensor devices.

In the first phase of this dissertation, we synthesized undoped and nitrogen doped nanocrystalline diamond films. The synthetic material was thoroughly studied using different material characterization techniques and taken through a chemical functionalization process. The functionalization process produced a hydrogen rich surface suitable for enzymatic attachment. Glucose oxidase was covalently attached to the functionalized surface to form the biosensing structure. The response of the biosensor was finally recorded following voltammetry and amperometric techniques under steady state and dynamic conditions. The experimental results demonstrated that conductivity induced by the doping process enhanced the sensitivity of the sensing structure with respect to the undoped substrate. Also, the functionalization procedure showed strong bonding to avoid enzyme leaching during the measurements.

Later, in the second phase of this dissertation, the nanodiamond particles were used as filler for conducting polymer composites. The objective for developing these composite materials was to overcome the high resistivity observed for nanocrystalline films. The experimental results demonstrated that the inclusion of nanodiamond particles increased the sensitivity of the overall structure towards the quantification of glucose with respect to the nanocrystalline films and the bare polymer. Besides, the experiment showed a noticeable enhancement in the signal-to-noise ratio and the mechanical stability of the sensing platform due to the nanodiamond addition. The best structures from the previous experiments were further grafted with iron oxide nanoparticles to attempt signal amplification. Initial experiments with nanodiamond based composited showed similar current for low glucose concentrations for two different active electrochemical sensing areas. This observation indicates that more area is still available to transport signal and to enhance even further the sensing action. Oxidation of iron oxide nanoparticles after initial enzymatic decomposition of glucose has been proved to provide higher current for the same glucose concentration; thus, creating amplification effect for the signal. Finally, the toxicity of the nanomaterial synthesized during this dissertation was evaluated in mammalian cells. The advances in biosensing techniques indicate the potential application of amperometric platform for continuous implantable devices; hence, the toxicity of the materials becomes a key aspect of the platform design.

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