Beyond Simple Cartoons: Challenges in Characterizing Electrochemical Biosensor Interfaces

Abstract

Design and development of surface-based biosensors is challenging given the multidisciplinary nature of this enterprise, which is certainly the case for electrochemical biosensors. Self-assembly approaches are used to modify the surface with capture probes along with electrochemical methods for detection. Complex surface structures are created to improve the probe-target interaction. These multicomponent surface structures are usually idealized in schematic representations. Many rely on the analytical performance of the sensor surface as an indication of the quality of the surface modification strategy. While directly linked to the eventual device, arguments for pursuing a more extensive characterization of the molecular environments at the surface are presented as a path to understanding how to make electrochemical sensors that are more robust, reliable with improved sensitivity. This is a complex task that is most often accomplished using methods that only report the average characteristics of the surface. Less often applied are methods that are sensitive to the probe (or adsorbate) present in nonideal configurations (e.g., aggregates, clusters, nonspecifically adsorbed). Though these structures may compose a small fraction of the overall modified surface, they have an uncertain impact on sensor performance and reliability. Addressing this issue requires application of imaging methods over a variety of length scales (e.g., optical microscopy and/or scanning probe microscopy) that provide valuable insight into the diversity of surface structures and molecular environments present at the sensing interface. Furthermore, using in situ analytical methods, while complex, can be more relevant to the sensing environment. Reliable measurements of the nature and extent of these features are required to assess the impact of these nonideal configurations on the sensing process. The development and use of methods that can characterize complex surface based biosensors is arguably required, highlighting the need for a multidisciplinary approach toward the preparation and analysis of the biosensor surface. In many ways, representing the surface without reliance on overly simplified cartoons will highlight these important considerations for improving sensor characteristics.

Square Wave Voltcoulommetry Analysis of the Influence of the Electrostatic Environment on the Electrochemical Functionality of Redox Monolayers

“…A first approach to achieve a more accurate description of the electrochemical behaviour of modified interfaces with confined electroactive molecules is to consider the existence of intermolecular or supramolecular interactions, which can be, in general, of repulsive or attractive nature . Repulsive interactions may be the result of the appearance of coulombic long range repulsions due to an inefficient electrostatic screening of the redox probes when they have a net charge ,,. On the other hand, attractive interactions could be related with Van der Waals (i. e., odd‐even) or π‐π interactions ,,,.…”

Single Molecule Profiling of Molecular Recognition at a Model Electrochemical Biosensor

“…Molecular recognition is influenced by the interactions between the probe and the biointerface, which consists of neighboring probe molecules and captured biomarkers (target molecules), the passivating layer, the solid substrate (planar 3 or nanostructured surfaces [4][5], and the solution. [6][7] An outstanding challenge is that the influences of the biointerface are complex and difficult to predict, hampering the effort to form biosensors with predictable performance. Extensive studies have explored the effects of probe design, 8 probe surface density, [9][10][11][12] surface chemistry, [13][14] and surface morphology.…”

“…The heterogeneous local density of probe molecules was thought to have difficult-to-predict influences on the accessibility of target molecules to the probe molecules (crowding interactions). 9,[16][17] Numerous studies provided indirect evidence that the impacts of the poorly controlled, often heterogeneous spatial organization of probe molecules 18 may be profound: they may not only limit detection sensitivity 4,16 but also be the root cause of the large device-to-device signal variabilities 6,[19][20][21][22] of many of these surface-based sensors devices. Immobilization procedures that enhance probe dispersion 18 were found to improve reproducibility in target binding.…”

Recent Lipid Membrane-Based Biosensing Platforms

“…Competitive transduction technologies and systems should become smaller and portable without compromising resolution and accuracy. Further, in situ imaging analysis should become available for mapping the transducer surface in order to measure the concentration and distribution of bioelements on the bilayer [96].…”