Direct Diagnosis of Chalkbrood Disease by Smelling Infected Honey Bee Larvae via Bioelectronic Noses with a Single-Carbon-Atomic Resolution

Honey bees who play environmentally crucial roles have suffered from various fungal diseases. Despite efforts to sustain healthy colonies from such diseases, conventional methods often rely on visual inspections, delaying diagnoses. In this study, a bioelectronic nose mimicking the honey bee olfactory system is developed for the direct diagnosis of chalkbrood by smelling infected honey bee larvae. Here, specific olfactory receptors of Apis mellifera (AmOrs) recognizing phenethyl acetate, a chalkbrood odorant, were selected through investigating a library of AmOrs. Among candidate receptors, Apis mellifera olfactory receptor 13a (AmOr13a) was, for the first time, identified to exhibit the highest specificity to phenethyl acetate. To build a bioelectronic nose, a carbon nanotube field-effect transistor (CNT-FET) was hybridized with nanovesicles containing AmOr13a. Our device could be utilized for the real-time detection of phenethyl acetate down to 1 fM and 31.6 ppb in aqueous and gaseous environments, respectively. Moreover, it could discriminate similar floral odorants with a single-carbon-atomic resolution. Notably, this device allowed us to diagnose chalkbrood infection directly from honey bee larvae. In this respect, our bioelectronic nose can be a powerful tool as on-site assessment platforms and thus provide broad opportunities for basic studies on insect olfactory systems and applications in agricultural industries.