A 96-well wax printed Prussian Blue paper for the visual determination of cholinesterase activity in human serum

In the last decades, there is a growing search for analytical strategies to ensure clinical analysis without the need of laboratory set-up and skilled personnel. Indeed, user-friendly and low-cost devices are highly valued in the era of sustainability for their capability to be applied in low-resource contexts, such as developing countries. To address this issue, herein we report a 96-well paper-based and laboratory setup-free optical platform for the detection of butyrylcholinesterase enzyme (BChE) activity in human serum. We used chromatographic paper to realize a novel analytical tool exploiting its porous structure for reagentless synthesize Prussian Blue Nanoparticles (the sensing element), as well to load all the reagents required for the measurement. The principle of BChE activity detection relies on the reaction between the enzymatic product thiocholine and Prussian Blue, giving the Prussian White with subsequently Prussian Blue's fading, detected by a common office scanner supported by ImageJ software. Using this novel paper-based optical platform, BChE activity was linearly detected in the 2-15 U/mL range with a detection limit down to 0.8 U/mL. The accuracy was successfully demonstrated by recovery study with spiked serum and by comparing the data with the gold standard method.