Turn on fluorescent detection for Cd²⁺ based on surfactant controlled squaraine aggregation

Area of Science:

• Analytical Chemistry
• Materials Science
• Environmental Science

Background:

• Heavy metal contamination, particularly from cadmium (Cd2+), poses significant environmental and health risks.
• Development of selective and sensitive fluorescent chemosensors is crucial for detecting heavy metal ions in aqueous environments.
• Squaraine dyes offer unique photophysical properties suitable for sensor applications.

Purpose of the Study:

• To synthesize and characterize a novel thymine-squaraine based fluorescent chemosensor (SQ).
• To investigate the sensor's selectivity and sensitivity towards various heavy metal ions in aqueous media.
• To explore the application of the SQ sensor for detecting Cd2+ in real-world samples like wastewater.

Main Methods:

• Amide coupling reaction to synthesize the thymine-squaraine fluorophore.
• UV-vis and fluorescent spectrometry for detection and selectivity studies.
• Job's plot, Benesi-Hilderbrand analysis, ESI-MS, NMR, and DFT calculations for mechanism elucidation.
• Application testing in wastewater samples.

Main Results:

• The developed SQ sensor exhibited high selectivity for Cd2+ over other tested metal ions.
• A turn-on fluorescence signal was observed in the presence of Cd2+, enhanced by the cationic surfactant CTAB.
• The binding stoichiometry was determined as 1:1 with a binding constant of 2.03 × 10^3 M^-1.
• DFT calculations supported the proposed coordination mechanism involving carbonyl oxygen and the amide CO group.

Conclusions:

• The thymine-squaraine based fluorescent chemosensor (SQ) demonstrates excellent selectivity and sensitivity for Cd2+ detection.
• The sensor's performance is influenced by surfactants, leading to deaggregation and enhanced fluorescence.
• The study provides a robust method for Cd2+ detection applicable to environmental monitoring, including wastewater analysis.