Abstract
On-site determination of trace copper ions in natural waters is of great significance to environmental monitoring, and how to develop accurate and specific point-of-care test methods is one critical issue. In the study, a paper-based analytical device (PAD) being modified with a new truncated DNAzyme (CLICK-T, which was derived from a reported DNAzyme-CLICK-17) was developed for Cu ions detection. The detection mechanism was based on Cu(II)-catalyzed azide-alkyne cycloaddition (Cu(II)AAC) reaction. It can directly conduct on-site analysis of Cu(II) ions based on fluorescent signals detected using a mobile phone. In the assay, the CLICK-T was firstly modified on the PADs. Then, water samples containing Cu ions mixed with 3-azido-7-hydroxycoumarin and 3-butyn-1-ol were instantly dripped on PADs and incubated for 20 min. Finally, the PADs were excited at 365 nm and emitted fluorescence which could be analyzed on site using smart phones. The Cu(II) concentration could be quantified through RGB analysis with the aid of iPhone APP software. The limit of detection is 0.1 µM by the naked eye due to the fact that CLICK-T exhibited a good catalytic effect on Cu(II)AAC. The Cu(II) concentration could also be directly detected without using reductant, such as ascorbic acid, which is prone to be oxidized in air. This simplifies the PDA detection process improves its efficiency. The PAD is convenient for the on-site analysis of Cu ions in natural waters.
Highlights
Copper is an essential trace element in living organisms, an excess amount of copper accumulated in the body would be a threat to human health [1]
The paper-based analytical device (PAD) is convenient for the on-site analysis of Cu ions in natural waters
Cu(II)AAC between 3-butyn-1-ol (BOL) and 3-azide-7-hydroxycoumarin (AHC), which was catalyzed by CLICK-T DNAzyme on detection disks of PADs (Figure 1)
Summary
Copper is an essential trace element in living organisms, an excess amount of copper accumulated in the body would be a threat to human health [1]. Cu by using azide-tagged AuNPs and 1,4-diethynylbenzene (DEB) to form [1,2,3]-triazolelinked aggregates with LOD of 0.5 μM [12] Many of these colorimetric methods are difficult to monitor copper concentration lower than 1 μM by the naked eye; they could not meet the demands of on-field detection of trace Cu ions in natural waters [13]. Liu et al [15] has selected one kind of DNAzyme named CLICK-17, a long single-stranded DNA with 76 bases (76-nt), which could catalyze Cu(II) for Cu(II)AAC without using the reductive reagent This meant Cu(II) could be directly determined without being reduced into Cu+ [7]. Naked eye and quantified by the smartphone; (B) The fluorescent light development mechanism
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