Nanocellulose / Nanocarbon Composites for Direct Electrochemical Detection of Small Molecules

Nanocellulosic materials are rapidly developing into highly versatile and sustainable alternatives for synthetic polymers in several high value applications. They are of particular interest in various sensor architectures due to their unique properties such as high strength, large surface area with potential for functionalization, hygroscopicity and film forming tendency. Further, their ability to disperse carbon nanomaterials in stable aqueous suspensions has resulted in an increased interest towards the development of nanocellulose / nanocarbon electrochemical platforms for detection of various drugs and biomolecules in the recent years. However, this field is still in its infancy, and there is an evident need to understand the role of different nanocellulosic materials in tailoring the electroanalytical performance of the resultant nanocellulose / nanocarbon composites. In this thesis, we have used nanocellulosic materials with different geometries and functionalizations, to develop composite electrode architectures with commercial multiwalled carbon nanotubes (MWCNT). The physical and chemical nature of the nanocellulosic materials, MWCNT, and their composites, are studied using several surface and bulk characterization methods and are correlated to the electrochemical performances of the composites evaluated using both outer and inner sphere redox molecules. We have shown that both cellulose nanocrystals (CNC) and cellulose nanofibrils (CNF) having different surface functionalizations, can be used to develop highly stable, robust electrochemical platforms with MWCNT, without compromising the electrochemical activity of the MWCNT. The nanocellulose geometry is clearly demonstrated to have a significant effect upon the composite morphology, where the highly functionalized CNFs result in open architectures with more exposed MWCNT surface, and CNCs result in denser architectures with the CNC packed closely around the MWCNT. Correspondingly, the CNF-based composites exhibit higher electrochemically active surface area, increased electrostatic effects and stronger redox currents for all measured analytes. The nature and degree of nanocellulose functionalization is shown to have a significant effect on the extent of electrostatic effects in the composite, offering a promising route towards tailoring the ionics electivity. Finally, we demonstrate that all the nanocellulose / MWCNT composites proposed in this work are capable of achieving significantly higher sensitivity and selectivity towards a cationic inner sphere redox molecule such as dopamine, compared to current commercial standard MWCNT electrodes.