Surface Patterning and Nanowire Biosensor Construction: Soft Lithographic Templated Protein Assembly, Organic Monolayer Laser Patterning and Nanowire Biosensor Design

This thesis describes the preparation and characterization of three systems where
surfaces of solid matter are interfaced with organic and biomolecular
components, with the aim of creating (I) Patterned surfaces and (II) Functional
nanowire sensor platforms for bionanotechnological applications.
In part I - “Surface Patterning” - glass and gold surfaces serve as spatially
encoded immobilization supports for patterning of recombinant proteins and
organic monolayers. First, we combine micro-contact printing with a reactive
SNAP-tag protein to establish a general platform for templated protein assembly
on e.g. glass surfaces, providing parallel patterning via gentle and oriented
protein immobilization. Such protein patterns are useful for miniaturized
bioassays of protein function. Second, in a very different approach, we use a
highly focused laser beam to locally desorb alkanethiols from a self assembled
monolayer on gold, a technique useful for creating diverse monolayer patterns in
a direct-write fashion. Addition of a second alkanethiol forms a topologically
ultra flat but chemically patterned surface, which by inspection with scanning
electron microscopy and atomic force microscopy revealed submicron feature
sizes, varying linearly in size with laser power and irradiation time.
In Part II - “Nanoscale Biosensors” - Indium Arsenide (InAs) nanowires (NW)
incorporated in field effect transistor (FET) devices provide a sensitive platform
for detection of charged analyte species binding to the NW surface. A central
limitation to this biosensor principle is the screening of analyte charge by mobile
ions in electrolytes with physiological ionic strength. To overcome this problem,
we propose to use as capture agents proteins which undergo large
conformational changes. Using structure based protein charge prediction, we
show how ligand induced changes in conformation of two model proteins, both
being ligand binding domains from glutamate receptors, can lead to changes in
electrostatic potential predicted to be sufficient for NW sensing. Finally we, demonstrate how InAs nanowires can be biofunctionalized, integrated in FETs,
and used to detect charged species, as shown for H+ ions for pH sensing.