Algae-paper integrated sensor for bisphenol determination in zebrafish embryos

Contaminant level assessment in in-vivo models and their environments remains an open issue that still needs smart solutions. Most of the analytical methods work as off-site analysis performed via instrumental techniques, while there is a lack of rapid strategies for real-time monitoring. Herein, self-contained Algae-paper sensors, produced using a sustainable approach, are proposed to determine Bisphenol A (BPA) bioconcentration in zebrafish embryos (Z-EBs) and to monitor the levels in culture medium. Paper sensors were manufactured in series using a stencil printing approach and equipped with a by-product-derived nanomaterial (biochar) prepared in water via liquid-phase exfoliation, avoiding organic solvents. The best sensor paper-substrate and conductive-ink/biochar combination was studied. Algae paper, derived from seaweed biomass wastes, was able to support stencil printing and biochar with nano-fibrillar morphology, enabling the achievement of the required analytical performance. Algae sensors' exploitability was demonstrated for Z-EBs exposed to different levels of BPA. The sensors accurately traced the BPA level variation in Z-EBs culture medium along the 96 h of the in vivo study (Relative Error - 14/+12 %) by simple immersion and measurement. Bioaccumulated BPA assessment in exposed Z-EBs was achieved via in-matrix calibration (Limit of Detection = 58 nM/13 μg L^-1), with reproducible data (RSD ≤ 8.8 %, n = 3) and quantitative recoveries (94-118 %), endorsing the sensor reliability. Algae sensors are useful in discriminating sublethal BPA levels characterized by different developmental delays of Z-EBs. A sustainable sensor, produced following a circular economy route, was developed, demonstrating, for the first time, the exploitability of portable electrochemical devices for BPA determination for in vivo studies. The Algae-paper sensor allows both real-time monitoring of BPA levels during exposure studies and evaluation of bioaccumulation in Z-EBs at the end of the exposure period.