Although
organosilanes, especially 3-aminopropyltriethoxysilane
(APTES), are commonly used to functionalize oxide substrates for a
variety of applications ranging from molecular/biosensors and electronics
to protective layers, reliable and controlled deposition of these
molecules remains a major obstacle. In this study, we use surface
potential analyses to record and optimize the gas-phase deposition
of APTES self-assembled monolayers (SAMs) and to determine the resulting
change of the electrokinetic potential and charge at the solid–liquid
interface when the system is exposed to an electrolyte. Using a gas-phase
molecular layer deposition setup with an in situ molecule deposition
sensor, APTES is deposited at room temperature onto ozone-activated
SiO2. The resulting layers are characterized using various
techniques ranging from contact angle analysis, ellipsometry, fluorescence
microscopy, X-ray photoelectron spectroscopy, and electrokinetic analysis
to AFM. It turns out that adequate postdeposition treatment is crucial
to the formation of perfect molecular SAMs. We demonstrate how a thick
layer of APTES molecules is initially adsorbed at the surface; however,
the molecules do not bind to SiO2 and are removed if the
film is exposed to an electrolyte. Only if the film is kept in a gaseous
environment (preferable at low pressure) for a long enough time do
APTES molecules start to bind to the surface and form the SAM layer.
During this time, superfluous molecules are removed. The resulting
modification of the electrokinetic potential at the surface is analyzed
in detail for different states.
The interface between electronic
components and biological objects
plays a crucial role in the success of bioelectronic devices. Since
the electronics typically include different elements such as an insulating
substrate in combination with conducting electrodes, an important
issue of bioelectronics involves tailoring and optimizing the interface
for any envisioned applications. In this paper, we present a method
for functionalizing insulating substrates (SiO2) and metallic
electrodes (Pt) simultaneously with a stable monolayer of organic
molecules ((3-aminopropyl)triethoxysilane (APTES)). This monolayer
is characterized by high molecule density, long-term stability, and
positive surface net charge and most likely represents a self-assembled
monolayer (SAM). It facilitates the conversion of biounfriendly Pt
surfaces into biocompatible surfaces, which allows cell growth (neurons)
on both functionalized components, SiO2 and Pt, which is
comparable to that of reference samples coated with poly-L-lysine (PLL). Moreover, the functionalization greatly improves the
electronic cell–chip coupling, thereby enabling the recording
of action potential signals of several millivolts at APTES-functionalized
Pt electrodes.
Modifying the surfaces of oxides using self-assembled monolayers offers an exciting possibility to tailor their surface properties for various applications ranging from organic electronics to bioelectronics applications. The simultaneous use of different molecules in particular can extend this approach because the surface properties can be tuned via the ratio of the chosen molecules. This requires the composition and quality of the monolayers to be controlled on an organic level, that is, on the nanoscale. In this paper, we present a method of modifying the surface and surface properties of silicon oxide by growing self-assembled monolayers comprising various compositions of two different molecules, (3-aminopropyl)-triethoxysilane and (3-glycidyloxypropyl)-trimethoxysilane, by means of in situ controlled gas-phase deposition. The properties of the resulting mixed molecular monolayers (e.g., effective thickness, hydrophobicity, and surface potential) exhibit a perfect linear dependence on the composition of the molecular layer. Finally, coating the mixed layer with poly(l-lysine) proves that the density of proteins can be controlled by the composition as well. This indicates that the method might be an ideal way to optimize inorganic surfaces for bioelectronics applications.
We carry out an approach to dynamic manipulation of a nondiffracting cosine-Gauss plasmonic beam (CGPB) illuminated with an incident phase modulation within nanostructures by a spatial light modulator (SLM). By changing the hologram addressed on the SLM, dynamic control on the lobe width and the propagating direction of the CGPB is experimentally verified. Finally, we demonstrate an application example of this dynamic CGPB in routing optical signals to multichannel subwavelength wave guides through numerical simulation.
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