Cellulose is one of the most abundant biopolymers, and its many properties make it suitable for application in numerous fields, such as sensor and biosensor fabrication. It is indeed biodegradable and renewable, nontoxic, biocompatible, and widely available at low cost (https://doi.org/10.3390/chemosensors10090352). In addition, cellulose boasts different structural arrangements such as Cellulose Nanocrystals (CNCs), which are among the most promising cellulose-derived nanomaterials for applications in biosensors. In fact, CNCs can be formulated into thin films to be used as support material for the immobilization of proteins (enzymes, antibodies, etc.) (https://doi.org/10.3390/chemosensors10090352, https://doi.org/10.1016/j.sbsr.2020.100368). In this work, we exploited antibody-functionalized CNCs to develop a microfluidic paper-based analytical device (µPAD) for the detection of myeloperoxidase blood levels, which have been shown to be altered in patients with Alzheimer's disease (AD) (https://doi.org/10.5539/gjhs.v6n5p87, https://doi.org/10.1111/j.1471-4159.2004.02527.x, https://doi.org/10.1016/j.arr.2020.101130). In particular, upon their covalent functionalization with anti-myeloperoxidase antibody, CNCs were deposited onto filter paper, thus providing a uniform and stable functionalized layer. Subsequently, employing the origami format, myeloperoxidase contained in the sample was captured by the immobilized antibody and then detected, exploiting its ability to catalyse the luminol/hydrogen peroxide chemiluminescence reaction. Emitted photons were detected by employing a portable highly sensitive charge-coupled device (CCD) camera and analyzed to obtain quantitative information. A limit of detection of 5.8 ng/mL was obtained, which enables clear distinction between healthy and AD patients’ myeloperoxidase blood levels (https://doi.org/10.3233/jad-131469). In addition, the selectivity of the system was evaluated by testing the possible interference of haemoglobin, which is also able to catalyse the chemiluminescence reaction. In the future, the same approach will be used for developing origami µPADs for detecting other AD biomarkers exploiting chemiluminescence sandwich immunoassays.

This research is supported by the PRIN2022 project 2022WN89PC “Biomimetic sensing platforms for the detection of Alzheimer's disease related biomarkers”.