  We propose that a photonic array of resonant circular dielectric waveguides
with subwavelength grating can be designed as a robust and sensitive
topological chemical sensor. The device can detect trace amounts of a given
chemical species through photonic edge modes that are impervious to most
sources of disorder. We perform a simulation in the mid-infrared that accounts
for the absorption loss introduced by chemical molecules in contact with a
strongly coupled photonic lattice of resonators. Due to the topological nature
of the device, its chemical sensitivity scales linearly with the system size
and can reach parts-per-billion range at the millimeter scale. Our findings
suggest that topological chemical sensors could empower the development of
novel on-chip integrated photonic sensing technologies.
