Fluorescent optical sensor for Fe3+ detection using Syzygium aromaticum derived carbon quantum dots embedded in corn starch biopolymeric film.

Excessive Fe3+ contamination in aquatic environments poses significant risks to water quality and ecosystem health, necessitating the development of rapid, low-cost, and sustainable detection platforms. A sustainable solid-state fluorescent sensor was evaluated for Fe3+ detection using carbon quantum dots (CQDs) derived from Syzygium aromaticum embedded within a corn starch biopolymeric film. The clove-derived CQDs, synthesized via a green hydrothermal route, exhibited quasi-spherical morphology with an average particle size of 3.02 nm, excitation-dependent blue fluorescence with a maximum emission at 440 nm under 350 nm excitation, a fluorescence quantum yield of 9.46%, and a high negative zeta potential (-45 mV), indicating excellent colloidal stability. Incorporation of CQDs into the starch matrix significantly enhanced film performance, increasing tensile strength from 21.21 to 27.26 MPa and reducing water vapor permeability from 7.27 to 6.63 × 10-10 g m-1 s-1 Pa-1, while simultaneously increasing surface wettability (contact angle decreased from 72° to 62°), indicating enhanced surface polarity without compromising barrier properties. The CS-CQDs film exhibited strong and selective fluorescence quenching toward Fe3+, with F/F₀ decreasing to ~0.10 at 1 ppm, a Stern-Volmer constant of 3.678 ± 0.256 ppm-1, and excellent linearity (R2 = 0.9887). The detection limit was calculated as 0.163 ppm, below both World Health Organization (0.3 ppm) and Indonesian drinking water standards (0.2 ppm). Accurate Fe3+ quantification in tap and underground water was achieved with recoveries of 94.8-104.0% and RSD values below 1%. This low-cost platform enables portable, real-time water quality monitoring, supporting SDG 6, 14, and 15.