. Author manuscript; available in PMC: 2012 May 15.

Published in final edited form as: Anal Chem. 2011 Apr 25;83(10):3750–3757. doi: 10.1021/ac2001302

Table 1.

Comparison of the different models used to study protein-antibody interactions on the surface via AIR.

Protein	Array Format	One-site Langmuir	Two-site Langmuir	Sips Isotherm
FGF-2	Macro spots	K_D = 1.6 nM^b t_max = 1.3 nm^c R² = 0.98^d	NS^d	K_Da = 1.6 nM^b t_max = 1.3 nm^c a = 1 R² = 0.98

FGF-2	Microarrays	K_D = 1.6 nM^b t_max = 1.3 nm^c R² = 0.82	K_D1 = 1.6 nM^b K_D2 = 27.2 pM t_max1 = 0.51 nm t_max2 = 0.79 nm R² = 0.98	K_Da = 122.2 pM t_max = 1.3 nm^c a = 0.52 R² = 0.98

VEGF	Microarrays	K_D = 100 pM^b t_max = 0.8 nm^c R² = 0.97^e	K_D1 = 100 pM^b K_D2 = 0.36 pM t_max1 = 0.57 nm t_max2 = 0.23 nm R² = 0.99^e	K_Da = 27.2 pM t_max = 0.8 nm^c a = 0.53 R² = 0.99

Determined by SPR.

Measured by spectroscopic ellipsometry for saturating concentrations of the protein. t_max = t_max1+ t_max2 was fixed at 1.3 nm for FGF-2 and 0.8 nm for VEGF, as measured by ellipsometry.

NS (Not Significant); for FGF-2 macro spot data a two-site based Langmuir model was fit and an F-test was utilized to statistically compare the two models.⁵³ The analysis resulted in a P value of 0.0680; for a 99% confidence interval this indicates that there is not a significant difference between the one-site and the two-site-based Langmuir fits.

Similarly, an F-test was utilized to compare the one-site and two-site Langmuir fits for the VEGF microarray data. A P value of 0.0036 was obtained and at a 99 % confidence interval this indicated that the two-site based model was statistically better than the one-site model.