Role of Different Receptor-Surface Binding Modes in the Morphological and Electrochemical Properties of Peptide-Nucleic-Acid-Based Sensing Platforms

Abstract

Label-free detection of charged biomolecules, such as DNA, has experienced an increase in research activity in recent years, mainly to obviate the need for elaborate and expensive pretreatments for labeling target biomolecules. A promising label-free approach is based on the detection of changes in the electrical surface potential on biofunctionalized silicon field-effect devices. These devices require a reliable and selective immobilization of charged biomolecules on the device surface. In this work, self-assembled monolayers of phosphonic acids are used to prepare organic interfaces with a high density of peptide nucleic acid (PNA) bioreceptors, which are a synthetic analogue to DNA, covalently bound either in a multidentate (∥PNA) or monodentate (⊥PNA) fashion to the underlying silicon native oxide surface. The impact of the PNA bioreceptor orientation on the sensing platform’s surface properties is characterized in detail by water contact angle measurements, atomic force microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. Our results suggest that the multidentate binding of the bioreceptor via attachment groups at the γ-points along the PNA backbone leads to the formation of an extended, protruding, and netlike three-dimensional metastructure. Typical “mesh” sizes are on the order of 8 ± 2.5 nm in diameter, with no preferential spatial orientation relative to the underlying surface. Contrarily, the monodentate binding provides a spatially more oriented metastructure comprising cylindrical features, of a typical size of 62 ± 23 × 12 ± 2 nm2. Additional cyclic voltammetry measurements in a redox buffer solution containing a small and highly mobile Ru-based complex reveal strikingly different insulating properties (ion diffusion kinetics) of these two PNA systems. Investigation by electrochemical impedance spectroscopy confirms that the binding mode has a significant impact on the electrochemical properties of the functional PNA layers represented by detectable changes of the conductance and capacitance of the underlying silicon substrate in the range of 30–50% depending on the surface organization of the bioreceptors in different bias potential regimes.

Effect of Counterion Binding to Swelling of Polyelectrolyte Brushes

“…Charged interfaces are ubiquitous in aqueous systems, ranging from water–oil emulsion , to cell membranes, and they are playing key roles in determining properties and functionalities in numerous applications and processes, such as food industry, − oil drilling, , pharmaceutical products, biology, and so forth. Tremendous research efforts have been made to study charged interfaces, not only because of the huge demands for achieving outstanding and novel performance and functionalities but also in order to gain basic understandings about the underlining mechanism and the governing factors.…”

Annealing‐Free Ohmic Contacts to n‐Type GaN via Hydrogen Plasma‐Assisted Atomic Layer Deposition of Sub‐Nanometer AlOx

“…An instrumental broadening of 1.2 eV was determined by fitting the Au 4f core level spectrum of a freshly evaporated Au calibration sample. [55] Surface Photovoltage Characterization: SPV measurements were performed using an in-house built CPD setup equipped with a commercial Kelvin probe and controller (Kelvin Probe S and Kelvin Control 07, Besocke Delta Phi GmbH). A collimated light-emitting diode (𝜆 = 340 nm, ML340L4, Thorlabs) was used for illumination at an intensity of ≈35 mW cm −2 .…”

“…An instrumental broadening of 1.2 eV was determined by fitting the Au 4f core level spectrum of a freshly evaporated Au calibration sample. [ 55 ]…”

Modular Assembly of Vibrationally and Electronically Coupled Rhenium Bipyridine Carbonyl Complexes on Silicon

“…The intensity was further normalized over the total number of counts, integrated over all the relevant element peaks. A detailed description of the XPS data processing can be found elsewhere (25).…”