Pop-Up Paper-Based Biosensor for a Dual-Mode Lung Cancer ctDNA Assay Based on Novel CoB Nanosheets with Dual-Enzyme Activities and a Portable Smartphone/Barometer for Readout

Timely monitoring of circulating tumor DNA (ctDNA) in serum is meaningful for personalized diagnosis and treatment for lung cancer. Cheap and efficient point-of-care testing (POCT) has emerged as a promising method, especially in a low-resource setting. Herein, (i) a 3D pop-up paper-based POCT device was designed and manufactured via a cheap method; it was used for saving time and efficiently building a biosensor; (ii) a novel cobalt boride nanosheet (CoB NS) nanozyme with abundant groups was used for POCT dual-mode signal transduction and then a portable smartphone/pressure meter to readout; (iii) a user-friendly smartphone app was fabricated for achieving more convenient POCT. Detailly, the dual-mode signal generated was based on the CoB NS with peroxidase activity to catalyze a chromogenic agent to develop color and with catalase activity to catalyze decomposition of H₂O₂ to O₂. Density functional theory (DFT) and experimental results showed a good catalysis performance of the CoB NS via studying its five possible catalytic pathways, in which the metal Co is the catalytic active site center that acts as the electron donor and promotes electron transfer between the CoB NS and the adsorbed substrates. Benefiting from that, the proposed method showed good analytical ability in detecting ctDNA. Besides, its accuracy was valued by comparing it with the standard qPCR method to detect real samples from tumor cells and tumor-bearing mice, which showed a consistent result and potential practical applicability of the proposed method for POCT ctDNA. In general, this work not only provided a dual-mode POCT platform that could also be applied for other analytes but also first revealed the nanozyme properties of the CoB NS and inspired its new application from electrocatalysis, energy, etc. to biomedicine.