Surface treatments and functional layer placement: Enhancing repeatability of electronic nose measurements

Electronic nose applications require a functional layer (binder) to activate the sensing and detection of the target analytes. However, challenges in selectivity and cross-sensitivity have been observed due to unspecific binding on nonfunctionalized sensor surfaces. Besides that, non-uniform response signals have been observed for different sensory units and attributed to non-uniform functionalization. This article explores a technique to control functional layer immobilization and passivation of the sensor surface by modifying the sensor surface properties and the binder-surface interactions. The study is demonstrated for a piezoelectrically driven microcantilever sensor sensing 1,5-diaminopentane (cadaverine), a volatile organic compound (VOC) proven meat and fish freshness marker. The findings demonstrate that surface pretreatment with hydrofluoric acid buffer before applying the analyte binder significantly enhances functional layer adhesion within the functionalization region on the microcantilever surface and hinders unspecific binding. Importantly, this process remains repeatable, allowing for efficient upscaling in sensor unit production. Furthermore, the microcantilever configuration adopted herein plays a role in binder positioning due to structural barriers on the sensor surface. The combination of binder position control and analyte adsorption exclusivity has practical implications, ultimately enhancing the repeatability of electronic noses across various applications.