Surface Functionalization of Platinum Electrodes with APTES for Bioelectronic Applications

Abstract

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.

Mechanical and Electronic Cell–Chip Interaction of APTES-Functionalized Neuroelectronic Interfaces

“…The discussion is based on the knowledge that our gas-phase-based MLD yields monolayers of chemically bound APTES not only on SiO 2 but also on Pt surfaces, an electrode material suitable for neuroelectronic interfaces. 19 We will start with the analysis of the impact of the molecules on the electrode−electrolyte impedance (see Figure 1c). Electronic Characterization of the Electrode−Electrolyte Interface.…”

“…For example, surface potential measurements, which determine the electrokinetic potential at the shear plane between the OHL and the mobile layer, indicate that the APTES SAMs have a significant impact on the shear plane and its potential. 19 The total impedance of a metallic electrode in an electrolyte is typically described by the Randles circuit 21 (see Figure 2a). It consists of the electrolyte resistor R el connected in series with the impedance Z formed by the double-layer capacitor C dl parallel to the charge-transfer resistor R ct .…”

“…Figure 5 provides a comparison of the characteristic impedance parameters of the Pt electrodes with and without APTES coating. The data are obtained from sets (4 each) of rectangular electrodes (size 200 to 20 000 μm 2 ; see Methods) which were first cleaned (physically and via ozone; see Methods) for the first impedance analysis and then coated with an APTES SAM 19 (see Methods) for the second run of impedance experiments. The resulting spectra are analyzed via the modified Randle model (see schematic in Figure 5a) and the characteristic parameters are then used to evaluate the average and error values of n-values, R ct , and C eff .…”

“…For example, the use of an amino functional group leads to an increase of the surface potential, which makes the surface more attractive for neural cells. 17,18 In a previous work 19 we demonstrated that the amino silane 3aminopropyltriethoxysilan (APTES) can form SAMs on SiO 2 as well as on Pt surfaces. Furthermore, we showed that the electronic signal transfer of multielectrode arrays (MEA) can be vastly improved by functionalization with APTES (see action potentials (AP) in Figure 1a,b).…”

Atomic/Molecular Layer Deposition for Designer's Functional Metal–Organic Materials

“…New organic components have also been developed for the purely organic MLD processes; the MLD material library already includes, besides the initially introduced polyimides [ 15,17–22,137–143 ] and polyamides, [ 15,23–28,144–149 ] many other polymers: polyurea, [ 29,30,37,38,51,150–164 ] polythiourea, [ 52 ] polyurethane, [ 165,166 ] polyazomethine, [ 167–172 ] poly(3,4‐ethylenedioxy‐thiophene), [ 173–177 ] polyimide–polyamide, [ 141 ] poly(ethylene terephthalate) (PET), [ 50,178–180 ] and others. [ 31,32,39–44,176,181–200 ] In recent years, the organic precursor library has been rapidly expanding. We have collected in Table 1 the organic precursors so far used in ALD/MLD processes, together with the heating temperatures employed for their evaporation in the corresponding process conditions; [ …”