Whole serum BSA antibody screening using a label-free biophotonic nanoparticle array

Bovine serum albumin antibodies (aBSA) have been screened from whole leporine anti serum on a biophotonic array. The array was initially printed with seed gold nanoparticles into a 96-spot configuration, and 130-nm gold nanoparticles were synthesised in situ on the surface of each spot. The gold nanoparticle surface was then functionalized with the proteins bovine serum albumin (BSA), fibrinogen, and immunoglobulin G (IgG) and with the amino acid glycine. The concentration of aBSA in the whole serum was determined using a kinetic analysis of the time-dependent light scattering from the nanoparticles. The aBSA-BSA kinetic parameters derived from the array are k_a = (1.3 ± 0.3) × 10⁵ M⁻¹ s⁻¹, k_d = (4 ± 2) × 10⁻⁴ s⁻¹, and K_D = 3 nM, which compare favorably with those from continuous gold surfaces. The ultimate sensitivity of the array reader to the bulk refractive index (RI) is 1 × 10⁻⁴ refractive index units (RIU), corresponding to 1 μg ml⁻¹ for aBSA. The nanoparticles appear to be more sensitive than the continuous gold surface to the aBSA binding event from whole serum, and this is interpreted in terms of the difference in RI contrast in the plasmon fields.