Commercial reagents-based six-mode sensor: One-step detection of iodide ions without enzymes or nanomaterials

Multi-signal sensors possess immense potential for point-of-care testing, yet their widespread adoption is hindered by reliance on complex nanomaterial synthesis or fragile enzymatic systems. Herein, we propose a "six-in-one" multi-mode sensor for rapid iodide ion (I^-) detection, leveraging only three commercially available reagents: chloroplatinic acid (H₂PtCl₆), hexadecyl trimethylammonium bromide (CTAB), and 3,3',5,5'-tetramethylbenzidine (TMB). The core innovation lies in a dynamic "on-off-on" oxidation triggered by target I^- ions as follows: H₂PtCl₆ with strong oxidative capacity directly oxidizes TMB to its two-electron product (TMB²⁺) ("On" State). CTAB coordinates with H₂PtCl₆ thereby blocking its surface and completely inhibiting TMB oxidation ("Off" State). I^- selectively displaces CTAB via competitive coordination, partially restoring H₂PtCl₆'s oxidation activity to generate the one-electron product (TMBox) ("Reactivation" State). Remarkably, the resulting TMBox exhibits six distinct signal outputs including visual and fluorescent color, absorbance, fluorescence, temperature, and electrical current. Compared to conventional single- or dual-mode methods, our six-mode approach improves reliability of detection results. This "magic cube" signals enables dual-mode qualitative analysis and four-mode quantitative detection, achieving a nanomolar-level detection limit for I^- detection. Critically, multi-mode sensor operates via one-step mixing without requiring nanomaterials, enzymes, or specialized equipment. We further demonstrate its utility in detecting I^- in biological (urine, serum), food (iodized salt) and environmental (Yellow River water, tap water) samples with recovery rates of 96.3 %-110.0 %. Statistical analysis demonstrated excellent reproducibility with relative standard deviations <3.1 % across repeated measurements. This work redefines the paradigm of multi-mode sensing, offering a cost-effective, field-deployable solution for environmental monitoring and clinical diagnostics.