Development of a label-free, impedance-based biosensor to identify harmful effects of pesticides on insect cells

Insects are a major part of the planet's ecosystem and their vital role as pollinators for agriculture is undisputed. Alongside factors as climate change or loss of habitats, rising use of pesticides emerges as a key threat to insect populations. For fighting this man-made problem, development of an easy, fast, sensitive, and non-invasive biosensor for determining pesticide toxicity may help to ban harmful substances and formulations. Here, a biosensor based on Sf21 (Spodoptera frugiperda) insect cells as sensors and electric cell-substrate impedance sensing (ECIS) as physical transducer is described. Sf21 cell suspensions and well-defined pesticide solutions were mixed immediately before seeding on planar gold-film electrodes. The capacitance at 20 kHz was recorded as a function of time as a measurand for cell adhesion providing dose–response profiles of pesticide impact. For future in-field applications, decoupling of the cell culture routines from the actual cytotoxicity assay is mandatory. Thus, suspensions of Sf21 cells were cryopreserved at –80°C in the wells of multielectrode arrays and thawed anytime for conducting the assays. Five pesticides were tested for their concentration-dependent cytotoxicity expressed as EC₅₀ values by ECIS and validated using the well-established WST-1 cell viability assay. Results were found to be in good agreement. Our studies revealed cytotoxic effects of some pesticides sold for home usage far below the recommended concentration and were found to be more toxic than formulations sold for agricultural industry only.