Polyadenine-based fluorescent probe for high-selective determination of copper ion in freshwater

ABSTRACT

In this work, a polyadenine-based fluorescent probe (pAFP) was designed for highly selective determination of Cu²⁺ in various freshwater sources. The pAFP contained a fluorescent group carboxyfluorescein (FAM) and a guanine-cytosine-guanine-cytosine (GCGC) sequence which was linked to the ends of a polyadenine strand. The complexation between polyadenine strand and Cu²⁺ induced the transition of polyadenine strand from a loose random coil to a compact structure, resulting in the proximity of the GCGC to the FAM and subsequent fluorescent quench of the FAM. Our work identified the polyadenine strand as a novel recognization element for Cu²⁺, which displayed high selectivity and appropriate affinity (10⁴ ~ 10⁵ M⁻¹) to Cu²⁺, with a stoichiometric ratio of 1:1. Based on it, the pAFP provided a dynamic range from 80 nM to 20 µM for the determination of Cu²⁺and a detection limit of 62 nM, meeting the requirements of the World Health Organization (WHO) and Environmental Protection Agency (EPA). The analysis of Cu²⁺-spiked real samples from lentic (Yudai Lake) and a lotic freshwater system (Xiangjiang River) revealed the high accuracy of the method, evidencing the application of this proposed sensor towards wide-field freshwater detection. Compared to other reported fluorescent probes, our pAFP displays a much simpler composition and structure. Meanwhile, in the actual procedure, our method only requires a simple pretreatment of the water sample by a 0.22 μm syringe filter, and the whole test procedure can be completed within 10 min. Such a convenient, low-cost and time-saving method for the determination of Cu²⁺will greatly facilitates the on-site and real-time monitoring of Cu²⁺ in different freshwater sources and subsequent water quality control.

KEYWORDS:

• Polyadenine strand
• fluorescent probe
• copper ion
• freshwater

Author contributions

# J.C. and B.S. contributed equally to this work. The manuscript was written through the contributions of all authors. All authors have approved the final version of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was financially supported by the National Natural Science Foundation of China [21573290], The Open Research Fund of State Key Laboratory of Physical Chemistry of Solid Surface, Xiamen [201814], The State Key Laboratory of Fine Chemicals, Dalian University of Technology [KF1910], and the Hunan Provincial Science and Technology Plan Project, China [No. 2019TP1001].