Ultrasensitive miniaturized optical sensor for trace cyanide detection via supramolecular solvent microextraction of cyano-dithizone adduct

The ultrasensitive detection of cyanide ions (CN⁻) at sub-trace levels in aqueous environments has emerged as an imperative analytical challenge, driven by its lethality for ecological systems and public health. The implementation of wavelength-dependent spectrochemical methodologies based on chromogenic adduct formation for CN⁻ quantification in aqueous media remains intrinsically challenging, owing to intrinsic self-absorbance, spectral convolution, and diffuse background scattering that collectively compromise analytical resolution and selectivity. In this study, a novel, eco-compatible, and analytically robust sample pretreatment protocol was devised for the ultra-trace extraction of CN⁻ ions from aqueous matrices, based on supramolecular solvent-based dispersive liquid–liquid microextraction (SM-DLLME) strategy, prior to miniaturized UV–visible spectrophotometric quantification. The supramolecular phase, comprising self-assembled reverse micelles of 1-octanol dispersed in tetrahydrofuran (THF), was spontaneously generated upon injection of the binary solvent mixture into CN⁻-containing aqueous solutions buffered at pH 10. Subsequent ultrasonic irradiation facilitated rapid micellization and dispersion, enabling the efficient partitioning of the hydrophobic neutral brownish-orange cyano-dithizone adduct [CN(H₂Dz)₂], centrifuged and extracted into the supramolecular phase. The chromogenic adduct was quantitatively assessed for CN⁻ ions at λ_max = 470 nm, with linearity across the concentration range 0.05–0.3 μg/mL (R² = 0.999). The acquired detection and quantification limits were 1.03 × 10⁻² and 4.01 × 10⁻² μg/mL, respectively. The sensor was implemented in spiked real water samples and yielded outstanding recoveries (100.3 ± 2.4 % to 101.8 ± 1.7 %), validated via the Student's t-test (t_exp = 1.5 < t_tab = 2.78, n = 5, P = 0.05). Furthermore, the chemical equilibrium, stoichiometric configuration, and thermodynamic parameters governing formation of the [CN(H₂Dz)₂] adduct were systematically elucidated and assigned. The assay can assist as a talented substitute for CN⁻ detection in food, biogenic amines and food freshness. Incorporation of dithizone as a functional complexing agent markedly enhanced the sensing performance and selectivity of the established SM-DLLME system and thus enhanced the analytical scope for ultra-trace detection of CN⁻ ions in complex aqueous matrices. The proposed sample prep avoids the use of toxic organic solvents or complex nanomaterials, providing a direct and effective strategy for monitoring and quality control of CN⁻ ions in environmental water.