  As a key precursor for nitrogenous compounds and fertilizer, ammonia affects
our lives in numerous ways. Rapid and sensitive detection of ammonia is
essential, both in environmental monitoring and in process control for
industrial production. Here we report a novel and nonperturbative method that
allows rapid detection of ammonia at detection levels of only a few thousand
molecules, based on the non-contact, all-optical detection of surface-enhanced
Raman signals. We show that this simple and affordable approach enables ammonia
probing at selected regions of interest with high spatial resolution, making in
situ and operando observations possible.

Applied Physics;Chemical Physics