Conductive polymer-based electrochemical aptasensor for sensitive detection of cylindrospermopsin in water resources

Increasing environmental pollution and climate change intensify the occurrence of harmful cyanobacterial blooms. These blooms release cyanotoxins, such as cylindrospermopsin (CYN), a hepatotoxic compound that threatens freshwater ecosystems, ecological stability, and human health. Addressing this challenge requires effective monitoring strategies aligned with the United Nations Sustainable Development Goal 6 (Clean Water and Sanitation). In this study, pencil graphite electrode (PGE) and conductive polymer based electrochemical aptasensor systems were developed for the selective and sensitive detection of CYN in both laboratory (deionized water) and environmental (lake water) samples. The proposed sensors provide low-cost, rapid, and reliable analytical platforms for environmental monitoring and sustainable water management. Poly(3,4-ethylenedioxythiophene) (PEDOT), and polypyrrole (PPy) were electropolymerized onto PGEs to enhance conductivity and provide effective CYN-specific aptamer (cynApt) immobilization. The surface morphologies and elemental compositions of bare PGE, PGE/PEDOT, and PGE/PPy were characterized by scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX), while their electrochemical properties were systematically evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Functional groups formed after polymer deposition and subsequent aptamer immobilization were analyzed using Fourier transform infrared (FT-IR) spectroscopy. The first system, PGE/PEDOT/cynApt, achieved detection limits of 0.23 ± 0.005 ng mL^-1 (0.55 ± 0.013 nM) and 0.27 ± 0.008 ng mL^-1 (0.65 ± 0.018 nM) for CYN in deionized and lake water, respectively, using CV. The second system, PGE/PPy/cynApt, exhibited superior performance, reaching detection limits of 0.18 ± 0.005 ng mL^-1 (0.43 ± 0.012 nM) in deionized water and 0.24 ± 0.009 ng mL^-1 (0.58 ± 0.022 nM) in lake water, respectively, using EIS. Conductive polymer modifications, with PEDOT and PPy, significantly enhanced the analytical response. Both platforms exhibited high selectivity toward CYN over other environmentally relevant cyanobacterial toxins, including okadaic acid (OA), saxitoxin (STX), and anatoxin-a (ATX-a), which are known to co-occur with CYN in freshwater blooms. In addition, the developed aptasensors retained their functional performance over a 7-day storage period, indicating suitable stability for practical use. This practical approach for the early detection of CYN in aquatic environments contributes to the prevention of water-related health risks and supports sustainable agricultural practices.