Synthesis of Polyindole and Its Use with Graphite Extracted from Dry Batteries for the Fabrication of a Selective Electrode for Tropicamid

Conductive polymers have emerged as vital materials in the development of advanced electrochemical sensors, owing to their unique electrical properties and structural tunability. Among them, polyindole (PIN) has shown considerable promise, yet remains underexplored compared to its counterparts. In this study, polyindole was successfully synthesized via chemical oxidative polymerization using anhydrous ferric chloride under mild conditions. Comprehensive characterization was carried out using FT-IR, ¹H-NMR, and differential scanning calorimetry (DSC), alongside molecular weight determination via osmotic pressure, confirming the polymer’s structural integrity and thermal stability. To enhance its electrochemical performance, the synthesized PIN was incorporated into a composite with expanded graphite, which was chemically derived from recycled graphite extracted from spent dry cell batteries. This sustainable approach not only improved conductivity but also aligned with environmentally conscious material reuse. The resulting PIN/expanded graphite composite was fabricated into a sensing electrode for the electrochemical detection of tropicamide, a clinically significant anticholinergic drug. The sensor demonstrated a well-defined Nernstian response over a broad linear range (10⁻³–10⁻⁶ M), with a slope of –19.6 mV/decade and a rapid response time of approximately 50 seconds, underscoring its potential in pharmaceutical analysis and point-of- care diagnostics.