compounds. Exhaled breath is one of the most accessible and zero-invasive samples to monitor human health and performance. For example, recent studies have demonstrated that analyzing the exhaled breath is practical for fast-diagnosing of COVID-19. [1,2] Volatile organic compounds (VOCs) [3][4][5][6] in the exhaled breath serve as performance-related biomarkers providing rich information on human physiological/physical statuses [7][8][9][10][11] such as psychological stress and fatigue level. A miniaturized sensor is key to building a wearable sensing suite with the capability to monitor human breath. Conventional VOC detection tools are either bulky or non-selective. For example, gas chromatography-mass spectrometry (GC-MS) is accepted as a gold standard for measuring breath VOCs. [12][13][14] However, GC-MS is bulky due to its heating and vacuum systems and requires a long operation time due to the VOC sampling and separation process. Photo-ionized detectors (PIDs) are another commercial off-the-shelf, portable VOC sensors commonly applied to gas sensing. [15,16] These sensors (VOC-TRAQ, MOCON, Inc., Minneapolis, MN, USA) range their dimensions Carbon nanotube (CNT) chemiresistors have emerged as miniaturized platforms for wearable volatile organic compound (VOC) sensors. As a promising biorecognition element (BRE), a short peptide can functionalize CNT to be sensitive and selective to target VOCs. However, unveiling the VOCoptimized peptide-CNT pair for gas-phase sensing remains unclear. Here, a novel multimodal molecular toolset for designing, building, and probing suitable BRE-CNT sensors using machine learning, molecular dynamics, and near-edge X-ray absorption fine structure spectroscopy is presented. This computational and experimental suite predicts the peptide conformation on the CNT surface and probes how the peptide-CNT interfaces affect the VOC sensing. Then, peptide-functionalized CNT chemiresistors are tested against various VOCs to confirm the efficacy of the toolkit. The results show that the vertically oriented peptide on the CNT surface hinders VOC access to the peptide-CNT interface, resulting in a significantly lower sensor signal than the CNT chemiresistor with the horizontally oriented peptide. The interactive computational and experimental results strongly indicate that a peptide conformation plays an important role in VOC sensing sensitivity.