Tryptamine psychoactive substances, such as α-Methyltryptamine (AMT), is a kind of monoamine alkaloids with an indole ring structure, the rapid, highly sensitive and specific identification of trace AMT is of great significance for social stability, people’s safety and family harmony. However, the specific fluorescent detection of α-Methyltryptamine (AMT) presents a great challenge because similar amine groups and benzene rings exist in a variety of amines. Prof. DOU Xincun from Xinjiang Technical Institute of Physics and Chemistry of Chinese Academy of Sciences proposed a novel molecular probe design strategy, which aims to improve the Schiff base reactivity between the recognition site and the primary amine-containing analytes by regulating the electron-withdrawing ability of the π conjugate bridge, thereby realizing high sensitivity and selectivity recognition for AMT. This work was published in Analytical Chemistry. 

In this work, the results demonstrated that the precise modulation of the electron-withdrawing strength of the π-conjugate bridge is of great significance to regulate the electrophilicity of the aldehyde in the Schiff base-based fluorescence probe, which in turn facilitates its reactivity with amine-containing analytes. Three TCF-based Schiff base-based fluorescence probes were prepared using aldehyde as the recognition site of α-Methyltryptamine, benzene, benzothiadiazole and 2,5-dibromobenzene with different electron-withdrawing abilities as the π-conjugated bridges. Among them, the aldehyde in BrFS-TCF has the largest electrostatic potential, which is more prone to take place the Schiff base reaction, making it the most ideal probe molecule for the detection of AMT. It should be noted that not only a fluorescent detection limit of 13 nM, a colorimetric detection limit of 132 nM, and a response of less than 0.1 s were obtained, but also the distinguishment of other primary amines can be achieved by combining with the convolutional neural network algorithm. Moreover, the probe design has been shown to be reliable for detecting trace amounts of AMT solutions in artificial saliva and solid residues. It is expected that the present probe design and regulation strategy would not only provide a new idea for the specific, identification and discrimination of primary amine-containing drugs, but also promote the development of trace hazards and illicit drugs detection methodologies.

This work was supported by the National Natural Science Foundation of China, the Youth Innovation Promotion Association of the Chinese Academy of Sciences, the Tianshan Talents Plan, and the Key Research and Development Program of Xinjiang. 

Figure: Schematic illustration of the designed strategy of the TCF-based Schiff base probe and the modulation of the electron-withdrawing strength of π-conjugate bridge.