The detection of copper ion (Cu²⁺) has become a long-term and arduous task in the field of environmental monitoring and human health. Current methods based on branched polyethylenimine (BPEI) for the detection of Cu²⁺ more or less suffer from being time-consuming and having a high cost or complex surface modifications. Herein, an ultra-facile and rapid colorimetric method was explored to detect Cu²⁺ in 100% aqueous solution by a direct format using only BPEI. Cu²⁺ could be captured by BPEI and form BPEI–Cu²⁺ complexes, which resulted in a color change from colorless to blue within 5 s, associated with the strong absorption peak at 278 nm. The lower the molecular weight and the concentration of BPEI are, the lower the detection limit is. When the molecular weight and the concentration of BPEI were 600 and 21.5 mg L⁻¹, respectively, the detection limit was calculated to be 1.21 μM, and the linear range was 2 μM to 50 μM. Besides, BPEI also had an excellent selectivity toward Cu²⁺. This ultra-facile, rapid and inexpensive method offers great potential for various applications in biomedicine, environmental protection, food safety and so on.

中文翻译：

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用支链聚乙烯亚胺在100％水溶液中 进行铜^2+的超简便快速比色检测†

铜离子（Cu ²⁺）的检测已经成为环境监测和人类健康领域中的长期且艰巨的任务。用于检测Cu ^2+的基于支链聚乙烯亚胺（BPEI）的当前方法或多或少地耗时且具有高成本或复杂的表面修饰。在本文中，探索了一种超简便，快速的比色法，仅使用BPEI，即可通过直接形式检测100％水溶液中的Cu ²⁺。BPEI可以捕获Cu ²⁺并形成BPEI–Cu ²⁺配合物，导致在5 s内颜色从无色变为蓝色，这与278 nm处的强吸收峰有关。分子量和BPEI浓度越低，检测限越低。当BPEI的分子量和浓度分别为600和21.5 mg L ^-1时，计算的检出限为1.21μM，线性范围为2μM至50μM。此外，BPEI对Cu ^2+的选择性也极好。这种超简便，快速且廉价的方法为生物医学，环境保护，食品安全等方面的各种应用提供了巨大的潜力。