Development of a novel fluorimetric sensor based on polypyrrole doped with 4-(methylsulfonyl)-2-nitrobenzoic acid (MSNBA) for sensitive detection of copper (Cu²⁺)

In this study, we successfully electrochemically synthesized a polypyrrole film doped with 4-methylsulfonyl-2nitrobenzoic acid (MSNBA) within an aqueous medium containing 0.01 M MSNBA, 0.003 M NaOH, and 0.01 M pyrrole. Our investigation encompassed a thorough exploration of both electrochemical and spectroscopic properties, confirming the effective incorporation of MSNBA as a dopant within the electroactive PPy chain. The morphological characterization of the film was undertaken using scanning electron microscopy (SEM). The optical properties, particularly UV-visible absorption, and fluorescence spectroscopy, were scrutinized in a dilute DMF solution. The UV-visible absorption spectra revealed a broad absorption band centered around 292 nm, attributed to the pi ->pi* 1B - 1La/1Lb transitions of the oligo-benzenes in the film. In parallel, fluorescence spectra exhibited remarkable consistency between the solid state and solution, featuring an excitation peak at 345 nm (346 nm in solution) and an emission peak around 401 nm (403 nm in solution). Exploring the impact of copper (II) ions on absorption and fluorescence spectra unveiled a notable quenching effect along two distinct linearity domains. Various mathematical treatments, including the Stern-Volmer equation (R1 = 0.98, Ksv1 = 5.104 and R2 = 0.99, Ksv2 = 1.54.106), the Perrin equation, and the polynomial equation, were applied to elucidate the nature of this fluorescence quenching. Our findings indicated that the fluorescence extinction, as a function of Cu2+ ion concentration, aligns well with the polynomial equation, signifying a combination of dynamic and static quenching (Io/I = 1.08(+/- 0.04) + 1.46(+/- 0.44)105[Q]- 1.15(+/- 0.75)1010 [Q]2). Moreover, we explored the potential application of this method for the determination of Cu2+. Calibration graphs demonstrated excellent linearity between fluorescence intensity and Cu2+ concentration in the range of 0-5.4 mu M. Notably, the detection limit of 1.2 mu M surpassed the LOD for Cu2+ (20 mu M) in drinking water set by the EPA, suggesting the viability of this approach for sensitive detection in environmental monitoring.