Real-time monitoring of microbial activity using hydrogel-hybridized carbon nanotube transistors

We demonstrate a unique system mainly composed of a carbon nanotube field-effect transistor (CNT-FET) integrated with malt extract agar (MEA) hydrogel for the real-time monitoring of microbial growth and activity. Consumption of nutrients and production of metabolites by microbial cells such as fungi or yeast results in the change of chemical properties of the hydrogel matrix, and this chemical change is detected by the underlying CNT-FET underneath the MEA hydrogel. In this study, we were able to distinguish the different growth phases (lag phase, log phase and stationary phase) of microbial organisms from the conductance measurement of the MEA-hybridized CNT-FET. Two fungal species (Aspergillus niger, Aspergillus versicolor), and one yeast species (Saccharomyces cerevisiae) were tested. The CNT-FET signals showed peculiar signal patterns according to the microbial species, enabling the classification of microbial species in terms of CNT-FET signal patterns. The CNT-FET signals were compared with pH change of the MEA hydrogel matrix, and the CNT-FET signal followed the microorganism activity more closely than the pH signal. We expect that this platform can serve as a suitable substitute of currently time-consuming, high-cost, and laborious microbial monitoring procedure and expedite the development of improved simultaneous monitoring of various fungal and/or bacterial organisms.