Paper-based colorimetric chemosensor for highly sensitive and selective detection of Cd²⁺ in water and food samples

In this research, a new colorimetric chemosensor, (E)-2-methyl-5-(naphthalen-1-yldiazenyl)quinolin-8-ol (NAAMQ), utilizing naphthylamine-quinolinol was developed. The NAAMQ structure was verified through CHN, ¹H NMR, FT-IR, and ¹³C NMR analyses. The sensor's detection capability was assessed using visual techniques and UV-Vis absorption spectroscopy. The NAAMQ chemosensor exhibited a notable and vivid color transition from light yellow to dark purple when exposed to cadmium(II) ions (Cd²⁺). Moreover, two bathochromic shifts of about 22 and 137 nm were observed in the UV-Vis spectra, attributed to the formation of the NAAMQ-Cd²⁺ complex. Additionally, the binding constant and stoichiometric ratio for NAAMQ-Cd²⁺ were determined to be 2.90 × 10⁴ M^-1 and 1 : 1, respectively. The NAAMQ chemosensor demonstrated a linear response range to Cd²⁺ ions from 0.02 to 25 µM, with a limit of detection (LOD) of 26.19 nM (2.94 µg L^-1). The NAAMQ can be dissociated from the NAAMQ-Cd²⁺ complex using EDTA and the sensor can be reused up to 6 times for Cd²⁺ ion detection. Additionally, NAAMQ-based test strips were successfully developed and utilized to detect Cd²⁺ ions without the need for complex instrumentation. In addition, the NAAMQ chemosensor was used to detect and measure Cd²⁺ cations in various foodstuffs and water samples.