Abstract
Detection of the Cu2+ ions is crucial because of its environmental and biological implications. The fluorescent-based organic sensors are not suitable for Cu2+ detection due to their short penetration depth caused by the UV/visible excitation source. Therefore, we have demonstrated a highly sensitive and selective near-infrared (NIR) excitable poly(acrylic acid) (PAA) coated upconversion nanoparticles (UCNPs) based sensor for Cu2+ detection. We construct the PAA modified Na(Yb, Nd)F4@Na(Yb, Gd)F4:Tm@NaGdF4 core-shell-shell structured UCNPs based sensor via a co-precipitation route. The upconversion emission intensity of the PAA-UCNPs decreases linearly with the increase in the Cu2+ concentration from 0.125 to 3.125 μM due to the copper carboxylate complex formation between Cu2+ and PAA-UCNPs. The calculated detection limit of the PAA-UCNPs based sensor is 0.1 μM. The PAA-UCNPs based sensor is very sensitive and selective toward detecting the Cu2+ ions, even when the Cu2+ co-exist with other metal ions. The EDTA addition has significantly reversed the upconversion emission quenching by forming the EDTA-Cu2+ complex based on their greater affinity toward the Cu2+. Therefore, the PAA-UCNPs based sensor can be a promising candidate for Cu2+ detection because of their higher sensitivity and selectivity under 980 nm NIR excitation.
Highlights
To detect the trace elements, both essential (Cr, Co, Cu, Fe, Li, Mg, Mn, Ni, Se, and Zn) and non-essentials (P and S), developing highly selective and sensitive sensors is a crucial, useful and challenging task in the fields of medical, environment, and biology (Helal et al, 2011)
Post OA removal, the upconversion nanoparticles (UCNPs) are further functionalized by the poly(acrylic acid) (PAA) and the Fourier transform infrared (FT-IR) spectrum of the PAA-capped UCNPs is presented in Figure 1B, which clearly shows the characteristics doublet at 1,560 and 1,636 cm−1 assigned to asymmetric stretching vibrations of CO, and CO2 groups of PAA ligand, respectively (Liu et al, 2013; Feng et al, 2015; Kong et al, 2017)
We conclude that the capping of the PAA group onto the surface of the UCNPs is successful
Summary
To detect the trace elements, both essential (Cr, Co, Cu, Fe, Li, Mg, Mn, Ni, Se, and Zn) and non-essentials (P and S), developing highly selective and sensitive sensors is a crucial, useful and challenging task in the fields of medical, environment, and biology (Helal et al, 2011). Preparation of PAA Capped UCNPs (Kong et al., 2017) Typically, 30 mg of poly acrylic acid (PAA) was added to the deionized water (9 mL) with NaOH (0.1 M in deionized water) to adjust the pH at 8 under robust stirring at room temperature, followed by the addition of uncapped UCNPs (1 mL) dropwise, and the mixture was stirred for another 2 h This solution was mixed with DEG (10 mL) and heated at 105◦C for 1 h under stirring for water evaporation. For upconversion emission spectra of the selective experiment with 980 nm laser excitation, 40 μL PAA-UCNPs dispersion (0.025 M) was added to a 4 mL bottle, the metal ion solution (5 × 10−6 M or 5 × 10−4 M, respectively), was added by means of a micro-pipette and diluted to 4 mL. N where δ is the standard deviation of the blank solution, S is the slope of the calibration curve, xi is the average value from the calculation, x is the measured data point, and N is the number of readings employed for obtaining average
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