A Novel Donor-Acceptor Fluorescent Sensor for Zn2+ with High Selectivity and its Application in Test Paper

The new role of dipyrromethene chemosensor for absorbance-ratiometic and fluorescence "turn-on" sensing Zn2+ ions in water-organic solutions and real water samples

This study presents a dipyrromethene-based sensitive and selective probe for Zn2+ ions detection in aqueous and water-organic media. The probe demonstrates absorbance-ratiometric and "off-on" fluorescent sensing for Zn2+ in a DMSO/H2O (9:1, v/v) mixture. The 3,3',4,4',5,5'-hexamethyl-2,2'-dipyrromethene (HL), similar to its analogs, exhibits weak fluorescence (with a quantum yield of less than 0.001). However, upon the presence of Zn2+ ions in the sensor HL solution, there is a remarkable increase (up to 200-fold) in fluorescence intensity due to the formation of a stable intramolecular chelate complex [ZnL2]. This complex formation induces a significant hyperchromic effect and a red shift (57 nm) in the characteristic absorption bands. The sensing mechanism of the probe towards Zn2+ ions was thoroughly investigated through absorbance and fluorescent titrations, molar ratio plots, 1H NMR, and DFT/TDDFT studies. The fluorescence response exhibited a strong linear relationship with Zn2+ concentration within the range of 0 to 5.7 × 10-6 mol/L. The detection limit (LOD) and limit of quantitation (LoQ) for Zn2+ were determined as 2 × 10-8 mol/L and 6.6 × 10-8 mol/L, respectively. Moreover, the probe demonstrated high selectivity for Zn2+ ions over other metal ions (Na+, Mg2+, Al3+, Cr3+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Pd2+, Cd2+, Hg2+, Pb2+). Test systems in the form of test-strips and cotton-pads were developed based on the dipyrromethene sensor for rapid "naked-eye" detection of zinc ions in water. The sensor was successfully applied for detecting Zn2+ ions in real water samples.

A Fluorescent Probe Based on the Hydrazone Schiff Base for the Detection of Zn2+ and its Application on Test Strips

A novel fluorescent probe SHK for Zn²⁺ detection was designed based on the hydrazone Schiff base, successfully synthesized by Suzuki coupling and condensation reactions. The probe SHK in DMSO/H₂O showed extremely weak fluorescence. However, the solution exhibited an intensive yellow-green emission with the introduction of Zn²⁺. In contrast, negligible fluorescence change was observed when other metal ions were added, suggesting a high selectivity of SHK for Zn²⁺ detection. The Job's Plot analysis revealed that a 1:1 stoichiometric adduct SHK-Zn²⁺ formed during the Zn²⁺ sensing. The binding constant of the complex was determined to be 184 M^- 1, and the detection limit for Zn²⁺ was calculated to be 112 µM. Moreover, the probe SHK achieved selective fluorescence sensing for Zn²⁺ on test strips, which guaranteed its practical application prospect.