Real-time monitoring of airborne cat allergen using a QCM-based immunosensor

The purpose of this study was to demonstrate the potential of real-time monitoring of airborne cat allergen powder using quartz crystal microbalance (QCM) technology. Monoclonal antibodies of cat allergen (Fel d 1) were immobilized onto a gold-coated quartz crystal using a cysteamine self-assembled monolayer (SAM). The QCM responses exhibited negative frequency shifts characteristic of mass uptake onto the sensor surface when exposed to airborne cat allergen powder. The cat allergen powder was 0.01 wt% Fel d 1; therefore, antigen–antibody binding occurred despite potential interference from dust particles. The absolute frequency shift increased linearly (log–log, R2 = 0.968) over the immunosensor working range, from 5.2 ng/L to 1.6 × 105 ng/L. Selectivity of the immunosensor between the cat allergen and a test dust was confirmed using SEM images and antibody affinity was confirmed by challenging an Escherichia coli antibody-coated crystal with airborne cat allergen. Positive frequency shifts were observed with the QCM for both negative controls. The research demonstrates that immunosensors based on QCM technology may become a viable alternative to conventional methods of real-time monitoring of bioaerosols.