Thy-AuNP-AgNP Hybrid Systems for Colorimetric Determination of Copper (II) Ions Using UV-Vis Spectroscopy and Smartphone-Based Detection

Abstract

A colorimetric probe based on a hybrid sensing system of gold nanoparticles (AuNPs), silver nanoparticles (AgNPs), and thymine (Thy) was developed for easy and rapid detection of copper (II) ions (Cu2+) in solution. The underlying principle of this probe was the Cu2+-triggered aggregation of the nanoparticle components. Color change of the sensing solution (from red to purple) was clearly observed with naked eyes. The experimental parameters, including pH and concentration of tris buffer, thymine concentration and AgNP dilution ratios, were investigated and optimized. Once optimized, the limits of detection were found to be 1, 0.09 and 0.03 ppm for naked eyes, smartphone application and UV-vis spectrophotometer, respectively. Furthermore, determination of Cu2+ was accomplished within 15 min under ambient conditions. For quantitative analysis, the linearity of detection was observed through ranges of 0.09−0.5 and 0.03−0.5 ppm using smartphone application and UV-vis spectrophotometer, respectively, conforming to the World Health Organization guideline for detection of copper at concentrations < 2 ppm in water. This developed hybrid colorimetric probe exhibited preferential selectivity toward Cu2+, even when assessed in the presence of other metal ions (Al3+, Ca2+, Pb2+, Mn2+, Mg2+, Zn2+, Fe3+, Ni2+, Co2+, Hg2+ and Cd2+). The developed procedure was also successfully applied to quantification of Cu2+ in real water samples. The recovery and relative standard deviation (RSD) values from real water sample analysis were in the ranges of 70.14−103.59 and 3.21−17.63%, respectively. Our findings demonstrated a successful development and implementation of the Thy-AuNP-AgNP hybrid sensing system for rapid, simple and portable Cu2+ detection in water samples using a spectrophotometer or a smartphone-based device.

Keywords: colorimetric probe; copper (II) ion detection; gold nanoparticles; silver nanoparticles; smartphone; thymine.

Figure 1

Schematic representation of the principle of colorimetric detection of Cu²⁺ based on a Thy-AuNP-AgNP hybrid system in the (A) absence or (B) presence of Cu²⁺.

Figure 2

(i) The absorption spectra, (ii) the digital photographs and (iii) the TEM micrographs of the Thy-AuNP-AgNP solutions in the absence (A) and the presence (B) of Cu²⁺. Scale bars in the TEM micrographs are 100 nm.

Figure 3

The plots of ΔA_r values against (A) pH of tris buffer (pH 3−8), (B) concentration of tris buffer (0, 0.01, 0.1, and 1 M), (C) concentration of thymine (0.0625, 0.125, 0.25, and 0.5 M), and (D) dilution ratio of AgNPs:DW (undilute, 1:2, 1:5, and 1:10).

Figure 4

(A) Photographs of the Thy-AuNP-AgNP sensing solutions with various Cu²⁺ concentrations (0.00, 0.01, 0.05, 0.10, 0.25, 0.50, 1.00, 2.50, 5.00, 7.50 and 10.00 ppm) and (B) the corresponding absorption spectra.

Figure 5

(A) The plot of ΔA_r against the Cu²⁺ concentration in the range of 0–10 ppm. Each experiment was performed in triplicate. The linear regression line for Cu²⁺ concentration in the range of 0.03–0.5 ppm is indicated with a red line. The logarithmic regression line for Cu²⁺ concentration in the range of 0.5–10 ppm is indicated with a black line. Insets (B,C) are the expanded view of the linear and logarithmic regression lines, respectively. The linear and logarithmic equations along with the corresponding correlation coefficients are indicated in (A).

Figure 6

(A) The plot of Δ(B/R)_r against Cu²⁺ concentrations in the range of 0–10 ppm. The linear regression line for Cu²⁺ concentrations in the range of 0.09–0.5 ppm is indicated with a red line. The logarithmic regression line for Cu²⁺ concentrations in the range of 0.5–10 ppm is indicated with a black line. Insets (B,C) are expanded views of the linear and logarithmic regression lines, respectively. The linear and logarithmic equations along with the corresponding correlation coefficients are indicated in (A).

Figure 7

(A) Color changes and (B) absorption peak ratios at 600 nm and 520 nm, i.e., A₆₀₀ /A₅₂₀, of the hybrid sensing solutions in the presence of 1 ppm of the tested metal ions.

Figure 8

(A) Color changes and (B) the absorption peak ratios at 600 nm and 520 nm, i.e., A₆₀₀ /A₅₂₀, of solutions containing 1 ppm Cu²⁺ ion and 1 ppm of the indicated interference metal ions, as well as a solution mixing 1 ppm of these eleven interference metal ions (mixture).