& Luminescence | Hot Paper | A Highly Sensitive Bimodal Detection of Amine Vapours Based on Aggregation Induced Emission of 1,2-Dihydroquinoxaline Derivatives Parvej Alam + , [a, b] Nelson L. C. Leung + , [a, b] Huifang Su, [a, b] Zijie Qiu, [a, b] Ryan T. K. Kwok, [a, b] Jacky W. Y. Lam, [a, b] and Ben Zhong Tang* [a, b, c] Abstract: 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-con- suming and requires expensive analytical instrumentation. A much simpler and more cost-effective method for monitor- ing food fermentation is to detect biogenic amines generat- ed as a by-product during food decomposition. In this work, a series of 1,2-dihydroquinoxaline derivatives (DQs) with ag- gregation-induced emission (AIE) characteristics were syn- thesised 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 bi- modal 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 ef- fective technique to monitor food safety. Introduction Over USD 220 billion worth of meat and seafood was shipped all over the world in 2016. [1] Because of this, food safety and human health are fundamentally important issues. Much re- search has been done to ensure that the transported food re- mains fresh and unspoiled, [2] and many methods have been designed to monitor the safety of food products. [3] For exam- ple, time-temperature indicators (TTI) [4] have been developed to show whether raw food materials have been exposed to elevated temperatures for an extended duration of time. Indeed, even the FDA has adopted guidelines for the use of TTIs in US seafood products to ensure food safety. [5] However, maintaining a chilled temperature only slows down the enzy- matic processes of food spoilage. In fact, biogenic amine species, such as putrescine and cadaverine, produced by mi- crobes, have been found in rainbow trout stored at 0 8C by the second day. [6] Biogenic amines have gained recognition as good indicators of food freshness because they are products of microbial fermentation. [7] In the process of food spoilage, microbes break down amino acids through deaminisation to generate ammonia and decarboxylation to generate biogenic amines such as cadaverine, putrescine, spermidine, spermine and others (Scheme 1). Biogenic amines not only signal the freshness of the food, but also have adverse impact on human health and physiological functions. [8] In fact, putrescine, cadav- erine, spermidine and spermine can react with nitrites to gen- erate nitrosamines, a known carcinogen, in processes such as meat curing. [9] [a] Dr. P. Alam, + N. L. C. Leung, + Dr. H. Su, Z. Qiu, Dr. R. T. K. Kwok, Dr. J. W. Y. Lam, Prof. B. Z. Tang HKUST Shenzhen Research Institute No. 9 Yuexing 1st Rd, South Area, Hi-tech Park Nanshan, Shenzhen 518057 (P. R. China) E-mail : tangbenz@ust.hk [b] Dr. P. Alam, + N. L. C. Leung, + Dr. H. Su, Z. Qiu, Dr. R. T. K. Kwok, Dr. J. W. Y. Lam, Prof. B. Z. Tang Department of Chemistry, Division of Biomedical Engineering Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction Institute for Advanced Study Institute of Molecular Functional Materials and State Key Laboratory of Molecular Neuroscience The Hong Kong University of Science and Technology Clear Water Bay, Kowloon, Hong Kong (P. R. China) [c] Prof. B. Z. Tang Guangdong Innovative Research Team SCUT-HKUST Joint Research Laboratory State Key Laboratory of Luminescent Materials and Devices South China University of Technology Guangzhou 510640 (P. R. China) [ + ] P.A. and N.L.C.L. contributed equally to this work. Supporting information, including NMR spectra, mass spectra, absorption and emission spectra, AIE PL curves, absorption and emission spectra changes after protonation of DQ2, Job plot of DQ2, PL reversibility of H + DQ2, calculated average intensity plot after exposure to ammonia vapour, photograph of H + DQ2 filter paper strip sealed with salmon sample at room temperature and 2 8C, and photographs H + DQ2 filter paper strip sealed with white-leg shrimp, and the ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/ chem.201703253. Chem. Eur. J. 2017, 23, 14911 – 14917  2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 14911 Full Paper DOI: 10.1002/chem.201703253