Electrochemically controlled patterning for biosensor arrays.

Identifier:  TDX:326

Handle: https://hdl.handle.net/20.500.11797/TDX326

Authors:  Dondapati, Srujan Kumar

Abstract:
There is an increasing demand of multianalyte sensing devices having potential applications in biomedical, biotechnological, industrial and environmental fields. A good spatial control during biomolecule deposition step is strictly necessary; each biomolecule has to be precisely deposited on the surface of the relevant sensor (eg., an amperometric transducer), avoiding mixing that can compromise the biosensor specificity. The aim of this thesis is to develop different patterning methods for the selective immobilization of biomolecules. The first method is selective electrodeposition of biofunctionalized Au nanoparticles for biosensor arrays. This is an electrochemically controlled patterning method where the Au nanoparticles modified by the enzymes initially and later the enzyme modified Au nanoparticles were electrodeposited selectively on the electrode surface. As a part of this methodology, initially biofunctionalized Au nanoparticles were prepared using three different approcahes. One is Au-thiol dative bonding, the second is direct adsorption and finally electrostatic layerby- layer approach. Different biomolecules like horse radish peroxidase(HRP), glucose oxidase (GOX), bovine serum albumin(BSA), and finally fluorescence labelled oilgonucleotide thiols were used to attch to the Au nanoparticles. Biofunctionalized Au nanoparticles were characterized by different techniques like zeta sizer, UV-Vis spectroscopy, transmission electron microscopy (TEM). UV-Vis spectroscopy showed the successfull modification of Au nanoparticles with a characterstic surface plasmon peak related to the stability. By using zeta sizer, layer-by-layer modification of the Au nanoparticles with redox polymer and enzymes were characterized successfully. Changes of the Au nanoparticles modified with BSA was characterised at different pH s by using the zeta sizer. After the preparation of biofunctionalized particles, some fundamental studies were done with electrodeposition of Au nanoparticles modified with medically important BSA, redox polymer to see how different parameters like potential, time of deposition, interelectrode distance, counter electrode sized, pH, effect the electrodeposition. As a part of these fundamental studies Au colloids modified with HRP and GOX were deposited for studying the electrocalaytic behaviour of the enzymes on the Au nanoparticles after electrodeposition. Later this methodology was applied for creating biosensor arrays by using two different approaches. In the first approach, GOX and HRP functionalized redox polymer modified Au nanoparticles were electrodeposited successfully on an interdigitated electrode (IDE) array with complete absence of non-specific response. In the second approach the particles were modified with an extra redox polymer layer and proved that there is complete absence of nonspecific response after electrodeposition. Moreover, this patterning methodology is generic and can be used for production of different biochips. The second method is another electrochemically controlled patterning method where the electrodes were immobilized with self assembled monolayers with electroactive functionalities which can be tunable with potentials. In this methodology, electroactive self-assembled monolayer contains an active ligand aldehyde which can be readily conjugated to the primary amine group of the biomolecule is protected in the form of acetal. Later when a active potential was applied to the underlying electrode surface, the acetal functionality is deprotected to reveal the aldehyde functionality which was further conjugated to the biomolecule. Two enzymes GOX, HRP were used as model proteins to prove the versatility of this technique. Amperometric as well as real time measurements proved the selective applicability of this technique for creation of biosensor arrays. The third methodology is also an electrochemically controlled patterning methodology where the special advantage of the electrochemically-controlled immobilization of the 4,4-bipyridyl was taken as base for the creation of biosensor arrays. In this methodology, carboxylic acid functionalised 4,4, bipyridyl molecules were synthesized and characterized by electrochemistry. Later the biomolecules were conjugated to these special molecules for the creation of sensor arrays. Proof of selectivity was shown using colourimetrically with minimal non-specific response. Finally in the fourth method which is based on the photolithography technique, two different oxidases GOX & SOX were patterned along with redox polymer selectively on an IDE array using the lift off process with complete absence of cross-talk. As a part of this methodology, different immobilization methods were optimized initially for checking the best optimisation strategy. Later different reagents were tried to optimise the best reagent that prevents the non-specific adsorption. Later this optimised system was applied on the pholithographically created IDE array. Sarcosine and glucose sensors responded selectively to their substrates with complete absence of cross talk. This thesis is structured in 7 chapters. Chapter 1 establishes to basics of the biosensor arrays, electrochemically controlled patterning methods, other selectively patterned methods, photolithography and summary of this thesis. Chapter 2 describes about the gold colloid synthesis, modification with the biomolecules, stability studies. Chapter 3 decribes fundamental studies of the electrodeposition of the functionalised Au nanoparticles on the electrode surface. Chapter 4 describes the application of the electrodeposition of the protein functionalised Au nanoparticles for the creation of biosensor arrays. Chapter 5 describes the selective immobilization of biomolecules through electrochemical deprotection of electroactive self-assembled monolayers. Chapter 6 describes the synthesis, characterization and selective immobilization of HRP functionalized 4,4-bipyridyl derivatives. Chapter 7 describes the selective microscale protein patterning of two oxidases on an IDE array through photolithography. Finally chapter 8 summarizes the conclusions and the future work.