Tuning of Surface Charge of Functionalized Poly(Carboxybetaine) Brushes Can Significantly Improve Label‐Free Biosensing in Complex Media

Poly(carboxybetaine) brushes are excellent antifouling platforms allowing facile functionalization with biorecognition elements via carbodiimide/N-hydroxysuccinimide (EDC/NHS) chemistry. However, residual active NHS esters and the loss of zwitterionic balance after the conjugation may impair initially excellent antifouling properties. This problem has so far been addressed either by using spontaneous hydrolysis or deactivation of residual NHS esters by the reaction with a small amino compound bearing hydroxyl or carboxyl groups. In contrast to this approach, and instead of using a single deactivator, here the use of tailored mixtures of deactivating agents containing carboxyl groups and sulfo or sulfate groups with permanent negative charge that allow to tune surface charge balance is investigated. The approach is applied to poly(carboxybetaine acrylamide) (pCBAA) and copolymer of carboxybetaine methacrylamide with N-(2-hydroxypropyl) methacrylamide [p(CBMAA-co-HPMAA)]. The fouling from undiluted blood plasma or crude minced meat is suppressed by one order of magnitude compared to commonly used deactivation protocols, while the label-free surface plasmon resonance detection of E.coli O157:H7 in crude minced meat shows the limit of detection improved by two orders of magnitude (3.2 x 10(3) CFU mL(-1) in a direct detection assay format). The reported approach may be applied to other zwitterionic platforms which suffer from impaired antifouling properties after the platform modifications.