A reagent-free paper-based sensor embedded in a 3D printing device for cholinesterase activity measurement in serum

tHerein, we report a first example of a rapid and easy to use paper-based printed sensor embedded ina 3D printing device to measure the butyrylcholinesterase activity in serum samples. The innovativedevice relies on a paper-based sensor fabricated using wax printing and screen-printing technologies,combined with a printed holder made by stereolithography using 3D printing technology. To measure thebutyrylcholinesterase activity, butyrylthiocholine was used as enzymatic substrate and the by-productthiocholine was detected with a paper-based electrochemical sensor modified with a Carbon Black andPrussian Blue nanocomposite. The presence of this nanocomposite allowed to perform the butyryl-cholinesterase activity measurement at low applied potential (+300 mV vs. Ag/AgCl pseudoreference),since it is able to electrocatalyse the thiocholine oxidation, overcoming the fouling problem occurring ata bare electrode. To obtain a “reagent free” sensor, butyrylthiocholine was loaded on the filter paper for areliable stand-alone measurement, requiring only the sample addition. This device, after the calibrationwith standard solutions, was tested in serum samples, achieving a linear range up to 12 UI/mL and adetection limit of 0.5 IU/mL. To evaluate the accuracy of the device, recovery studies were performed inserum samples, demonstrating the suitability as a point of care for screening analysis of BChE activitymeasurement, taking into account that the normal value range is comprised between 5.9 and 13.2 IU/mL.