A Highly Sensitive Bimodal Detection of Amine Vapours Based on Aggregation Induced Emission of 1,2-Dihydroquinoxaline Derivatives. 
The detection of food spoilage is a major concern in food safety as large amounts of food are transported globally.  Direct analysis of food samples is often time-consuming and requires expensive analytical instrumentation.  A much simpler and more cost-effective method for monitoring food fermentation is to detect biogenic amines generated as a by-product during food decomposition.  In this work, a series of 1,2-dihydroquinoxaline derivatives (DQs) with aggregation-induced emission (AIE) characteristics were synthesised and their protonated forms, that is, H+ DQs, can be utilised for the sensitive detection of biogenic amines.  For example, upon exposure to amine vapours, deprotonation occurs that converts the red-coloured, non-emissive H+ DQ2 back to its yellow-coloured, fluorescent parent form.  The bimodal absorption and emission changes endow the system with high sensitivity, capable of detecting ammonia vapour at a concentration of as low as 690 ppb.  Taking advantage of this, H+ DQ2 was successfully applied for the detection of food spoilage and was established as a robust and cost effective technique to monitor food safety.