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. Author manuscript; available in PMC: 2008 Sep 20.
Published in final edited form as: Anal Chem. 2007 Apr 17;79(10):3549–3553. doi: 10.1021/ac062350v

Figure 1.

Figure 1

Schematic of the concentration gradient immunoassay (not drawn to scale). Antibody and a fast-diffusing analyte (e.g., phenytoin) are introduced to a T-sensor. Antibody and analyte interdiffuse and bind at the fluidic interface. The diffusion front of the fast-diffusing analyte traverses into the antibody stream (y-dimension) as the fluids travel down the length of the channel where it binds to the relatively slow-diffusing antibody to form antibody-analyte complex. The surface downstream is functionalized with immobilized analyte. Free antibody binds to the surface and is detected with a surface-sensitive technique – SPR imaging. Due to computational limitations, only the central 1.6 mm of the 3 mm wide (y-dimension) device located 22 mm downstream of the inlet could be modeled in three dimensions. A two-dimensional model that was connected to the three-dimensional model simulated the upstream portion of the assay.