Probing Sequence-Dependent Orientation in VOC Binding Peptides During IPA Exposure Using Near-Edge X-Ray Absorption Fine Structure Spectroscopy

Human psychological stress and fatigue levels can be monitored in real-time through performance-related biomarkers such as volatile organic compounds (VOCs) present in the exhaled breath using peptide-based graphene field effect transistors (GFETs). Ultimately, the biotic/abiotic interface is responsible for VOC recognition and subsequent sensor. During VOC exposure, perturbations to the biotic/abiotic interface results in changes to the electronic structure of the graphene, triggering a measurable electronic response. Aromatic residues in the peptides are considered the strongest driving force for noncovalent peptide functionalization of the graphene surfaces. As such, π−π interactions are predicted to play an essential role in sensor performance and thus provide an opportunity for directed sequence design for sensor optimization.<br/>In this work, we determined the overall orientation on various 7-mer VOC binding peptides with different aromatic content on the graphene surface using near-edge X-Ray absorption fine structure (NEXAFS) spectroscopy. Two set of peptides were studied, the first set of sequences was generated via AI and MD simulations for optimal IPA binding. The second set of peptides were modifications of the first set, where key aromatic binding residues were substituted with non-binding functionalities. Peptide orientation was determined on functionalized graphene surfaces before and after dosing with IPA within the NEXAFS chamber to monitor perturbations to peptide morphology under simulated sensors conditions. Overall, clear differences in orientation were determined with NEXAFS, showcasing clear sequence dependence on peptide surface morphology and their interactions with IPA during dosing. This understanding can assist with knowledge-driven development of new sequences for device optimization, which can be further extended beyond VOC GFETs and into various fields of biosensing.