*3.4. Ag+ Detection in Tap Water and Lake Water Samples Using the M-DNA Sensor*

To examine the performance of the *M-DNA* sensor for Ag<sup>+</sup> detection in other water sources, we detected Ag+ in tap water samples and two different lake water samples. The local tap water and lake water samples were collected and boiled for 5 min to remove chlorine, and lake water samples were further filtered with a 0.22 μm membrane following the reported procedures in the literature [26]. The *M-DNA* sensor was prepared using the treated tap and lake water samples instead of laboratory DI water, and no Ag+ was detectable in these samples. We then added Ag<sup>+</sup> with known concentrations to the *M-DNA* sensor and recorded the fluorescence intensity. The Ag+ concentration was calculated using the calibration curve shown in Figure 4C. The recovery ranged from 93.3% to 98.5% in tap water samples and 96.7% to 107.8% in lake water samples (Table 1), revealing a good accuracy of the *M-DNA* sensor for Ag+ detection in environmental water sources.


**Table 1.** Ag+ detection in tap and lake waters using the *M-DNA* sensor.

<sup>a</sup> The standard deviations were obtained from three replicative experiments.
