Abstract
Continuous monitoring of soil health is important in precision agriculture. Microbial activities can be an indicator for soil health, where the metabolism of the soil microbiota associated with plants plays a crucial role in plant development. These plant-associated microbiomes can also influence other traits such as disease resistance, growth, flowering, and abiotic stress tolerance. Activities of these microbial colonies affect all aspects of plant life because of their symbiotic relationship. Therefore, a thriving microbiota is directly related to soil health. By detecting and analyzing the variations of emitted volatile metabolites, it is possible to monitor the activities of the microbiota. These data can provide a deeper understanding of the relationship between activities of microbial communities and plant health. However, presently available low-cost, in situ sensors used in agriculture only detect a limited number of physical parameters such as moisture, pH, electrical conductivity, temperature, etc. Here we demonstrate microcantilever based photothermal spectroscopic sensors for detecting vapor phase analytes related to microbial activities such as CO2, methane, etc. Photothermal spectroscopy combines the temperature sensitivity of a bi-material cantilever with the selectivity of mid-infrared spectroscopy. Nanomechanical photothermal spectroscopy has sensitivity in the ppb range, fast response time, and requires no chemical coating for selectivity. Since the mid-infrared spectroscopy is free from overtones, it is extremely selective even in the presence of interfering compounds. Multiple IR peaks are monitored and analyzed using pattern recognition techniques for uniquely identifying the analyte molecules in vapor phase in the presence of interfering chemical compounds.