Molecularly imprinted polymer on cotton materials as substrates for smartphone-based image and distance-based analysis of Cu(II) in water samples

 Cotton fabric was used as a substrate for smartphone-based image analysis of Cu(II) in drinking water. To enhance its selective and specific binding sites on the cotton surface, a molecularly imprinted polymer (MIP) was introduced using color complexes of 4-(2-pyridylazo)resorcinol–Cu(II) (PAR–Cu(II)) as the template molecule, 3-aminopropyltriethoxysilane (APTES) as the functional monomer, tetraethoxysilane (TEOS) as the crosslinker and NH₃ as the catalyst. After achieving optimum conditions, the obtained CF MIP/PAR–Cu(II) presented a red color, which was changed to yellow upon the removal of Cu(II) with 1.5 M HCl. After using CF-MIP/PAR to detect Cu(II), the red, green and blue intensities of the images captured using a smartphone were analyzed using the ImageJ program. For the calibration curve plotted between Dgreen intensity and Cu concentration, the linear range was 0.10–1.0 mg L⁻¹ with the best correlation coefficient (R²) of 0.999. The limit of detection (LOD) and the limit of quantification (LOQ) were found to be 0.038 and 0.11 mg L⁻¹, respectively. To obtain a distance-based device, MIP-modified cotton thread (CT-MIP/PAR) with a four-channel design was used as an alternative device. The distance of red color development was measured after using CT-MIP/PAR to detect Cu(II). The linear range was 0.50–3.0 mg L⁻¹ with an R² of 0.997. The LOD and LOQ were 0.18 and 0.56 mg L⁻¹, respectively. The proposed methods provide simple, portable and inexpensive devices with high accuracy and precision for the detection of Cu(II) in drinking water.