Pentacene-based organic thin-film transistors were used to create highly sensitive, real-time electronic sensors for selective antibody detection. Bovine serum albumin was covalently attached to a modified pentacene surface to selectively detect the label free monoclonal antiBSA. These sensors displayed a high affinity constant (K-A) of (1.1 +/- 3) x 10(7) M-1 at pH 7, which is 1 order of magnitude higher than those obtained with a highly sensitive surface plasmon resonance spectroscopy detection system. Furthermore, a high degree of discrimination in the hybrid antiBSA charges was achieved at different pH values. This demonstration of fast, label-free, real-time detection of nanoscale biomolecules in aqueous buffer solutions using the organic transistor sensing platform will have a significant impact on high-performance microarrays in addition to discriminating the presence of ionizable groups.