Capacitive Lateral Flow Test for Sub-fM Analysis of Serum HER-2/ <i>neu</i> Using a Magnetic Cellulase-Linked Aptamer Sandwich Strategy

Lateral flow assays (LFAs) for noninvasive liquid biopsy analysis of blood-circulating cancer biomarkers are a low-cost and easy-to-use point-of-care (POC) option for cancer diagnosis and treatment monitoring. Yet, commercial LFAs are often insufficiently specific or sensitive and suffer from ELISA's drawbacks of high-cost reagents. Here, we have developed an electrochemical lateral flow test (e-LFT) for serum HER-2/<i>neu</i>. In HER2-positive cancers, liquid biopsy techniques are particularly valuable because they enable continuous monitoring of the HER-2/<i>neu</i> status throughout HER-2/<i>neu</i>-targeted therapy. The indicator-free e-LFT uses the cellulase-linked aptamer sandwich strategy and reads the capacitive changes (changes in the electric-double-layer charging) induced by cellulase digesting nitrocellulose-covered screen-printed electrodes. The e-LFT detects 0.1 fM HER-2/<i>neu</i> in 150 μL of 10% human serum in 5 min, with sensitivity 16.13 μC fM^-1 and a linear logarithmic concentration range from 0.1 fM to 10 pM HER-2/<i>neu</i>. Interference from 10% serum (∼20% of the signal produced by 0.1 fM HER-2/<i>neu</i>) was mitigated by the corresponding response correction. The e-LFT demonstrates advantageous POC testing features, including high analytical accuracy, rapid real-world sample analysis, and low cost, being 60 times faster and 300 times cheaper than optical ELISA. It surpasses current LFTs, making it a promising POC diagnostic tool for rapid and accurate liquid biopsy analysis of HER-2/<i>neu</i>.