<p>The industrial use of indium has increased significantly in recent years, raising concerns about its release into the environment during production, recycling, and waste disposal processes. Indium and its compounds may accumulate in environmental compartments and have been associated with adverse effects on aquatic organisms as well as potential human health risks, including pulmonary toxicity following occupational exposure. Therefore, the development of rapid, cost-effective, selective, and in situ analytical methods for indium determination is of considerable importance. In this study, a potentiometric In³⁺–selective sensor was fabricated and its analytical performance was evaluated. The developed sensor exhibited good selectivity toward In³⁺ ions over various potentially interfering ions, a Nernstian sensitivity of 20.2 ± 0.82 mV/decade, a wide linear working range of 1.0 × 10^− 2–1.0 × 10^− 6 M, a low detection limit of 4.71 × 10^− 7 M, and a fast response time of 8&#xa0;s. In addition, the sensor worked effectively over a broad pH range (5.0–10.0) and demonstrated satisfactory repeatability. The sensor was successfully employed as an indicator electrode in the potentiometric titration of In³⁺ ions with ethylenediaminetetraacetic acid (EDTA). Furthermore, its applicability was verified through the analysis of environmental water samples, yielding satisfactory recovery values and demonstrating the potential of the proposed sensor for practical indium(III) determination in environmental samples.</p>