A novel “off-on” fluorescence probe based on the discarded cigarette butts-based carbon quantum dots and silver nanoparticles for iodide ions detection

Discarded cigarette butts, a form of waste often left behind, pose a serious environmental threat. Therefore, recycling these cigarette butts is essential for reducing environmental pollution and supporting a circular economy. This study presents, for the first time, a novel approach to producing nicotine-based carbon quantum dots (NIC-CQDs) from discarded cigarette butts. These NIC-CQDs, combined with silver nanoparticles (AgNPs), were used to construct a novel “off-on” fluorescent probe for the highly sensitive detection of iodide ions (I⁻). Experimental results demonstrated that the obtained NIC-CQDs exhibited stable and intense blue luminescence, with a maximum emission wavelength (λ_em) of 472 nm and a maximum excitation wavelength (λ_ex) of 366 nm. Through the inner filter effect (IFE), AgNPs effectively quench the fluorescence of NIC-CQDs, while the presence of trace amounts of I⁻ reverses this quenching phenomenon. Based on this phenomenon, a novel off-on fluorescent probe (NIC-CQDs-AgNPs) was designed to detect trace I⁻ in aqueous solution using the obtained NIC-CQDs and AgNPs. Under optimal conditions, the NIC-CQDs-AgNPs probe demonstrated a linear detection range for I⁻ from 0.1 to 90 μM (R² = 0.993) with a detection limit as low as 32 nM. The probe was successfully utilized for monitoring I⁻ in real water samples with recoveries of 94.28–104.28 % (RSD <4.81 %), which indicated that the fluorescent probe has enormous application potential to detect trace I⁻ in environmental water samples.