  We propose an on-chip mid-infrared (MIR) photonic spectroscopy platform for
aerosol characterization to obtain highly discriminatory information on the
chemistry of aerosol particles. Sensing of aerosols is crucial for various
environmental, climactic, warfare threat detection, and pulmonary healthcare
applications. Further, there are a number of unintended situations for
potential exposure to bioaerosols such as viruses, bacteria, and fungi. For
instance, the current pandemic scenario of COVID-19 occurring across the world.
Currently, chemical characterization of aerosols is performed using FTIR
spectroscopy yielding chemical fingerprinting because most of the vibrational
and rotational transitions of chemical molecules fall in the MIR range; and
Raman spectroscopy. Both techniques use free space bench-top geometries. Here,
we propose miniaturized on-chip MIR photonics-based aerosol spectroscopy
consisting of a broadband spiral-waveguide sensor that significantly enhances
particle-light interaction to improve sensitivity. The spiral waveguides are
made of a chalcogenide glass material (Ge23Sb7S70) which shows a broad
transparency over IR range. We demonstrate the sensing of N-methyl
aniline-based aerosol particles with the device. We anticipate that the sensor
will readily complement existing photonic resonator-based particle sizing and
counting techniques to develop a unified framework for on-chip integrated
photonic aerosol spectroscopy.
