Schiff Base Modified Paper Test Strips for Naked Eye Detection of Copper Ions in Mixed Aqueous Media

A multi responsive Schiff base sensor L with thiophenol moiety was synthesized by the single-step condensation method. The structural analysis of the sensor was proposed by
¹
H-NMR, UV- Visible absorption, HRMS and FT-IR spectroscopy. Sensor L exhibited an instant appearance of yellow color on the addition of copper ions. Since copper gave an intense color change, therefore detailed studies were performed for copper sensing w.r.t. designed sensor L. Selectivity and sensitivity of sensor concerning copper metal ions were established by performing various UV-Visible spectroscopic and colorimetric studies. The 1:1 binding framework of the L-Cu
²⁺
complex is confirmed by Job’s Plot and further supported by DFT studies. With the help of Benesi-Hildebrand equation, the detection limit and the association constants were found to be
$3.15 \times 10^{-6}$
M and
$1.16 \times 10^{4}$
M
⁻¹
, respectively. In addition, sensor L was transferred onto solid substrates including silica and paper strips for establishing its utility in the onsite detection of copper ions.