Perchlorate, with its strong oxidizing properties and high stability, is one of the most important energy-containing materials widely used in solid propellants, military production, aerospace equipment, fireworks and other fields. According to the U.S. Explosives Data Center, perchlorate/chlorate as a raw material directly or indirectly involved in 63.4% of the total number of explosive cases worldwide. Therefore, it is of great practical importance to carry out highly sensitive and accurate field detection of trace perchlorate solids to ensure national public safety. The explosives sensing detection team at the Xinjiang Institute of Physical and Chemical Technology, Chinese Academy of Sciences has long been dedicated to the research of trace hazardous chemical detection methods, and has developed a series of new solutions in the principles and device design for highly sensitive, rapid and identification detection of hazardous explosives, especially uncontrolled explosives (Adv. Mater. 2020, 32, 1907043, Adv. Sci. 2020, 2002991, Angew. Chem. Int. Ed. 2022, DOI: 10.1002/anie.202203358, etc.). Recently, we have made progress in the field visualization detection of perchlorate, and proposed a new strategy of ultra-sensitive colorimetric-fluorescence dual-mode visualization sensing based on the synergistic modulation of self-assembled complex probes and hydrogel coupling, which successfully realized the field dual-mode visualization detection of ultra-trace perchlorate.

The team took the triclopyr platinum(II) auxiliary ligand as the entry point, combined with quantum chemical calculations, and systematically investigated the effects of different auxiliary ligands on the spectral energy and luminescence stability of the MMLCT state due to Pt-Pt metal interaction of triclopyr platinum(II) self-assembly products in aqueous solution, and elucidated the general laws of auxiliary ligands regulating the luminescence properties of perchlorate induced aggregation products. It was found that the self-assembled products of perchlorate-induced aggregation of platinum(II) tripyridine had the lowest energy and most stable MMLCT absorption/emission spectra when isothiocyanate was the auxiliary ligand, while the highest MMLCT intensity of the self-assembled products occurred when bromine was the auxiliary ligand. Therefore, in combination with the counter-anion modulation, a colorimetric-fluorescent bimodal visualization probe with good water solubility of the triclopyr platinum(II) complex perchlorate was obtained, and highly sensitive, highly specific, rapid, bimodal visualization sensing of perchlorate was achieved.

On this basis, the team proposed an enhancement strategy for the local enhancement of the luminescence signal of the sensing material using the coupling effect between the hydrogel reaction medium and the probe. By coupling this Pt(II) complex probe to a PVA hydrogel with a homogeneous network structure, the interaction of the self-assembled generated micron-scale one-dimensional fibrous aggregates with the hydrogel network achieves complete anchoring of the luminescence products and direct observation of the colorimetric-fluorescence bimodal sensing signal of 0.75 μm (0.73 fg) perchlorate single particles, and the detection limit of perchlorate in air The detection limit of suspended particles was as low as 0.02 fg.

The proposed strategy of fine tuning of auxiliary ligands to enhance the bimodal visual sensing performance of self-assembled anion probes can not only provide guidance for the design of anion probes with specific bimodal optical response signals, but also develop an ultra-sensitive olfactory sensing method based on the direct observation of single particle response signals, which can be used as a reference for sensing other ultra-trace difficult-to-volatile chemicals. In addition, the explosives sensing detection team took this research as the core, and jointly published one regional local standard (DB 65/T 4451-2021 "Visual Chemical Colorimetric Method for Detection of Chlorate and Perchlorate") with Xinjiang Public Security Department, which provides the operational specification for perchlorate inspection and identification for related industries.

The research results were published in Journal of Materials Chemistry A (back cover of the journal) and Sensors and Actuators B: Chemical, respectively, with PhD student Zhen Su as the first author and Dou Xincun and Yushu Li as co-corresponding authors. The theoretical calculations were done in collaboration with Prof. Kun Li of Taiyuan University of Science and Technology. The research work was supported by the National Natural Science Foundation of China, the Chinese Academy of Sciences, and the regional projects.

Translated with www.DeepL.com/Translator (free version)