Institute of Intelligent Machines, Chinese Academy of Sciences , Hefei, Anhui 230031, China.
Department of Chemistry, University of Science and Technology of China , Hefei, Anhui 230026, China.
ACS Appl Mater Interfaces. 2017 Jun 7;9(22):18897-18903. doi: 10.1021/acsami.7b05827. Epub 2017 May 26.
Classical pH test papers are widely used to measure the acid-base degree of media in a qualitative or semiquantitative manner. However, the extension of portable and inexpensive methods to a wide range of analytes so as to eliminate the tediousness of instrumental assays remains unsuccessful. Here, we report a novel kind of dual-colored carbon dot (CD) ratiometric fluorescent test paper for the semiquantitative assay of copper ions (Cu) by a dose-sensitive color evolution. The preparation of the test paper is based on the following two interesting findings: on the one hand, residual p-phenylenediamine at the surface of as-synthesized red CDs (r-CDs) efficiently binds Cu ions to produce a strong visible absorption that overlaps the emission of blue CDs (b-CDs); on the other hand, the Cu ions render the adsorption of small b-CDs onto the surface of larger r-CDs through their dual-coordinating interactions with the surface ligands of both r-CDs and b-CDs. These two mechanisms lead to a specific spectral energy transfer to quench the fluorescence of b-CDs with a sensitive detection limit of 8.82 nM Cu, whereas the red fluorescence of r-CDs is unaffected as a stable internal standard. Ratiometric fluorescent test papers have been prepared using a mixture of r-CDs and b-CDs (1:7) as ink by jetprinting on a piece of paper. With the addition of Cu ions, the blue test paper produces a consecutive wide-colored evolution from blue to orange-red, with a dose-discerning ability as low as 25 nM.
经典的 pH 试纸广泛用于定性或半定量地测量介质的酸碱程度。然而，将便携式和廉价的方法扩展到广泛的分析物范围，以消除仪器分析的繁琐性，仍然没有成功。在这里，我们报告了一种新型的双色碳点（CD）比率荧光试纸，用于通过剂量敏感的颜色演变对半定量测定铜离子（Cu）。试纸的制备基于以下两个有趣的发现：一方面，合成的红色 CD（r-CDs）表面的残留对苯二胺有效地与 Cu 离子结合，产生强烈的可见吸收，与蓝色 CD（b-CDs）的发射重叠；另一方面，Cu 离子通过与 r-CDs 和 b-CDs 的表面配体的双重配位相互作用，使较小的 b-CDs 吸附到较大的 r-CDs 表面上。这两种机制导致特定的光谱能量转移，猝灭 b-CDs 的荧光，检测限低至 8.82 nM Cu，而 r-CDs 的红色荧光不受影响，作为稳定的内标。通过喷墨打印在一张纸上，使用 r-CDs 和 b-CDs（1:7）混合物作为墨水制备比率荧光试纸。随着 Cu 离子的加入，蓝色试纸从蓝色连续产生宽范围的颜色演变到橙红色，剂量辨别能力低至 25 nM。
