This paper describes the creation of a point-of-care (POC) biosensor for 4-hydroxytamoxifen (4-HT), a tamoxifen metabolite used in breast cancer treatment. The sensor repurposes a conventional glucometer by encoding the 4-HT signal within the electrical signal generated from glucose oxidation. This is achieved through protein engineering, specifically by inserting the ligand-binding domain of estrogen receptor-alpha into glucose dehydrogenase. A library of protein insertion variants was screened, revealing crucial roles of secondary and quaternary protein structures in signal propagation. An electrochemical algorithm decodes the 4-HT signal from glucose, and the sensor is made self-powered using glucose oxidation and further amplified using an organic electrochemical transistor (OECT), achieving milliampere-level signals. This interdisciplinary approach combines protein engineering, electrochemical sensing, and electrical engineering to create a low-cost, user-friendly biosensor.

Rong Cai, Chiagoziem Ngwadom, Ravindra Saxena, Jayashree Soman, Chase Bruggeman, David P. Hickey, Rafael Verduzco, Caroline M. Ajo-Franklin