Enzymatic Polymer Brush Interfaces for Electrochemical Sensing in Biofluids

Electrochemical sensors enable specific and sensitive detection of biological markers. However, most small molecule analytes are not electroactive. Therefore, enzymes are widely used for selective breakdown of the markers into electro-active species. However, it has proven difficult to design a sensor interface where any enzyme can be controllably immobilized in high amounts with preserved activity. In addition, most interfaces cease to function in biofluids due to "fouling" of the sensor surface. Here we present a generic strategy employting polymer brushes for enzymatic electrochemical sensing which resolves these issues. Generic conjugation chemistry is used to covalently bind large amounts of enzymes (>1 μg/cm²). Remarkably, despite this enzyme load, the (∼200 nm thick) brushes remain highly hydrated and practically invisible by electrochemical methods: Small molecules freely access the underlying electrode and the charge transfer resistance increment is exceptionally low (<10 Ω). The enzymatic polymer brush interfaces enable specific detection of the biomarkers glucose and glutamate by simple chronoamperometry. Furthermore, by sequential immobilization of several enzymes, cascade reactions can be performed, as illustrated by detection of acetylcholine. Finally, the sensor interface still functions in cerebrospinal fluid (10× diluted, unfiltered). In conclusion, polymer brushes provide extended possibilities for enzymatic catalysis and electrochemical sensing.