Publication date: 17th July 2025
Cyanobacterial blooms that produce taste/odor metabolites (e.g., 2-MIB, geosmin) and toxins threaten drinking-water safety, yet conventional monitoring (nutrient analysis, physicochemical proxies, chlorophyll-a) lacks direct, real-time detection. Here, we present two complementary in-situ sensing platforms for rapid detection and quantification of phytoplankton presence and growth:
1) Ultra-Sensitive Bioelectronic Monitoring. We employ polyurethane (PU) foams dip-coated with PEDOT:PSS to create 199 cm² macroelectrodes that maximize double-layer capacitance and signal-to-noise sensitivity. We show that cohorts of Oscillatoria sp. exhibit synchronized electrical excitability. The collective cell activity is stress-dependent and produces large, coherent signals that scale linearly with electrode area - suggesting possible correlation with biomass and productivity. Electrochemical Impedance Spectroscopy (EIS) further resolves biofilm development and cell-density changes. Coordinated signaling emerges as intercellular Ca²⁺ waves, validated by fluorescent probes and suppressed by gadolinium chloride, suggesting a Ca²⁺-mediated paracrine mechanism potentially linked to 2-MIB or geosmin production.
2) Microcapillary Photometric Sensing. We use melt-extruded fluorinated ethylene propylene (FEP) strips coated with poly(vinyl alcohol) as hydrophilic “dip-stick” microcapillaries. These require no media exchange or aeration for months, and, when inoculated with Parachlorella kessleri, achieve a specific growth rate of μ = 0.37 d⁻¹ - matching a sparged Erlenmeyer and >3 times higher than an unsparged control. Their optical transparency permits non-invasive, single-cell imaging of morphology and cell-cycle events, benchmarked against high-resolution flow cytometry.
Together, these multimodal biohybrid platforms provide direct, in-situ readouts of microbial physiology, EPS formation, and metabolite risk factors - paving the way for scalable, proactive water-quality management and novel biocompatible sensing interfaces.
Paulo R.F. Rocha acknowledges the support and funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 947897).
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