Pop-Up Paper-Based\nBiosensor for a Dual-Mode Lung\nCancer ctDNA Assay Based on Novel CoB Nanosheets with Dual-Enzyme\nActivities and a Portable Smartphone/Barometer for Readout

Timely monitoring of circulating tumor DNA (ctDNA) in\nserum is\nmeaningful for personalized diagnosis and treatment for lung cancer.\nCheap and efficient point-of-care testing (POCT) has emerged as a\npromising method, especially in a low-resource setting. Herein, (i)\na\n3D pop-up paper-based POCT device was designed and manufactured via\na cheap method; it was used for saving time and efficiently building\na biosensor; (ii) a novel cobalt boride nanosheet (CoB NS) nanozyme\nwith abundant groups was used for POCT dual-mode signal transduction\nand then a portable smartphone/pressure meter to readout; (iii) a\nuser-friendly smartphone app was fabricated for achieving more convenient\nPOCT. Detailly, the dual-mode signal generated was based on the CoB\nNS with peroxidase activity to catalyze a chromogenic agent to develop\ncolor and with catalase activity to catalyze decomposition of H<sub>2</sub>O<sub>2</sub> to O<sub>2</sub>. Density functional theory\n(DFT) and experimental results showed a good catalysis performance\nof the CoB NS via studying its five possible catalytic pathways, in\nwhich the metal Co is the catalytic active site center that acts as\nthe electron donor and promotes electron transfer between the CoB\nNS and the adsorbed substrates. Benefiting from that, the proposed\nmethod showed good analytical ability in detecting ctDNA. Besides,\nits accuracy was valued by comparing it with the standard qPCR method\nto detect real samples from tumor cells and tumor-bearing mice, which\nshowed a consistent result and potential practical applicability of\nthe proposed method for POCT ctDNA. In general, this work not only\nprovided a dual-mode POCT platform that could also be applied for\nother analytes but also first revealed the nanozyme properties of\nthe CoB NS and inspired its new application from electrocatalysis,\nenergy, etc. to biomedicine.