Nitrogen-Doped Carbon Quantum Dot Nanoparticle Fluorescent Probes for Quantification of Ni(II) in Environmental Water Samples Collected using an Unmanned Aerial Vehicle

In this work, an innovative and low-cost method was developed to quantify Ni(II) ions in environmental water samples based on fluorescence digital images from quantum dots using a smartphone as a detector. The method is based on the fluorescence quenching of nitrogen-doped carbon dots (N,C-QDs) when nickel reacts with dimethylglyoxime. The fluorescence emission from nanoparticles is captured by a smartphone coupled to a portable UV-LED chamber. An analytical curve was developed to detect Ni(II), and a concentration range from 10.9 to 275.0 μg L^–1 with detection and quantification limits of 2.7 and 8.3 μg L^–1, respectively. Thus, the method attempted the recommended values of Ni(II) according to agencies such USEPA (100 μg L^–1), WHO (70 μg L^–1), EFSA (20 μg L^–1), and CONAMA (25 μg L^–1) for fresh waters. Moreover, to evaluate the accuracy and precision of the proposed method, a reference method based on inductively coupled plasma-optical emission spectrometry was used for comparison purposes. The results obtained by both methods showed no differences at a 95% confidence level (n = 3) when employing the F-test and T-test statistical methods. Furthermore, the fluorescence digital image-based (FDIB) method was highly selective for Ni(II) ions with an interference response lower than 5.0%, and it presented a good recovery from 93.6 to 109.0%. Moreover, aiming to develop a high-level automation method for environmental monitoring, an adapted unmanned aerial vehicle (UAV) controlled by a smartphone via Wi-Fi, equipped with a micropump and a miniaturized solenoid valve powered by a solar energy system, was developed. This innovation reduced collection time, allowed access to hard-to-reach locations, and reduced sampling costs by using renewable energy, thus being environmentally friendly. This new analytical method using N,C-QDs-FDIB-UAV proposed for monitoring Ni(II) in environmental water samples offers numerous advantages, such as high sensitivity, selectivity supplied by nanoparticle probe together the portability, low cost, autonomous, and an eco-friendly methodology obtained from the UAV system.