Rapid identification of different plastics for recycling is very important in overcoming the plastic waste challenge our society is facing today. An ideal plastic detector should be able to discern different plastics at the molecular level in a standoff fashion where the detector does not come in contact with the target plastic. We have demonstrated a standoff technique for the rapid identification of plastics based on their mid-IR absorption spectra. Since mid-IR region is free of overtones, this region is known as molecular finger print regime This technique is based on a variation of photoacoustic spectroscopy (PAS), where the light from a tunable infrared source, a quantum cascade laser (QCL), is scattered/reflected off the target plastic object. The returning scattered light is collected and made to create acoustic waves on a microfabricated cantilever sensor. Our experimental results show that the cantilever response, resonance frequency, amplitude, and bending, changes with infrared absorption characteristics of the target. A plot of cantilever response as a function of illuminating wavelength mimic the infrared absorption peaks of the plastics material producing a mechanical spectrum. The generated spectrum obtained for different plastics is then compared with that conventional spectrum for polymer identification.

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.