New copolymer brushes for label-free affinity biosensors

Brushes of poly(HPMA-co-CBMAA) copolymer with an adjustable content of functional carboxybetaine (CBMAA) monomer units were grafted from surface of SPR chips using surface initiated atom transfer radical polymerization (SI ATRP). Compared to brushes of of poly(carboxybetaine) (polyCBAA), which so far have provided the best antifouling biorecognition layers, the new brushes were more resistant to undiluted human blood plasma, milk, and crude food extracts, particularly after the covalent attachment of bioreceptors. The incorporation of a selected number of functional CBMAA units in poly(hydroxypropyl methacrylamide) (poly(HPMA)) allowed us to reach ultralow fouling properties better than that of polyCBAA. A typical food-born pathogen bacteria, E.coli OI57:H7, was detected in crude extracts of hamburger and lettuce using SPR biosensor coated by biorecognition layers composed of poly(HPMA-co-CBMAA) brushes with covalently attached anti-E.coli antibodies. The SPR biosensor with attached surface antigen of hepatitis B virus HBsAg was used to detect the presence of anti-HBsAg antibodies as biomarkers of hepatitis B infection in standard clinical samples of sera taken from several individuals. The new ultralow fouling biorecognition layers open a feasible way to label-free biosensors capable of in real time detecting analytes in real samples of complex biological media tested for medical diagnostics or food control.