<p>A chemosensor (CNS) built on a naphthalene fluorophore was developed, featuring a disulfide-bridged dimer structure. The probe CNS was completely characterized by the usual spectral analysis methods like ¹H NMR, ¹³C NMR, and HR-MS. The CNS probe selectively detects Cu²⁺ ions and subsequently recognizes the amino acid tryptophan in a semi-aqueous medium of DMF:H₂O solution. The detection of Cu²⁺ ions occur via three distinct mechanisms: suppression of the photoinduced electron-transfer process (PET), arrested rotation of diuryl groups leading to conformational change, and a blue-shifted fluorescence enhancement through intramolecular charge-transfer (ICT). With a 1:1 complexation ratio and a detection limit of 2.14 x 10⁻⁴ M, the CNS probe has been successfully applied in various practical scenarios, including real water sample analysis, glyphosate detection, smartphone-based color detection, and Cu²⁺ ion testing using a cotton-swab method.</p> Graphical Abstract <p>Disulfide-bridged dimer based sensor CNS is synthesized for the detection of Cu²⁺ ions and subsequently recognizes the amino acid tryptophan in a semi-aqueous medium of DMF:H₂O solution followed by various application studies including real water sample analysis, glyphosate detection, smartphone-based color detection, and Cu²⁺ ion testing using a cotton-swab method</p> <p></p>