  Lead (Pb2+) toxification in society is one of the most concerning public
health crisis that remains unaddressed. The exposure to Pb2+ poisoning leads to
a multitude of enduring health issues, even at the part-per-billion scale
(ppb). Yet, public action dwarfs its impact. Pb2+ poisoning is estimated to
account for 1 million deaths per year globally, which is in addition to its
chronic impact on children. With their ring-shaped cavities, crown ethers are
uniquely capable of selectively binding to specific ions. In this work, for the
first time, the synergistic integration of highly-scalable silicon photonics,
with crown ether amine conjugation via Fischer esterification in an
environmentally-friendly fashion is demonstrated. This realises a photonic
platform that enables the in-situ, highly-selective and quantitative detection
of various ions. The development dispels the existing notion that Fischer
esterification is restricted to organic compounds, laying the ground for
subsequent amine conjugation for various crown ethers. In this work, the
platform is engineered for Pb2+ detection, demonstrating a large dynamic
detection range of 1 - 262000 ppb with high selectivity against a wide range of
relevant ions. These results indicate the potential for the pervasive
implementation of the technology to safeguard against ubiquitous lead poisoning
in our society.
