This paper reports on a new microfluidic system for at-line bioprocess monitoring of human immunoglobulin G (IgG). This is the first report on the successful integration of supercritical angle fluorescence (SAF) detection with a centrifugal microfluidic "lab-on-a-disc" cartridge, enabled using novel SAF detection optics incorporated onto the microfluidic device. The microfluidic cartridge utilizes serial siphon valving to show for the first time sequential release of the sample, wash, and fluorescence-labeled solutions required to perform a quantitative IgG sandwich immunoassay. Using a custom, compact, benchtop instrument with integrated spinning motor and SAF optical components, a microfluidic, flow-through, IgG immunoassay on a Zeonor ® surface was developed and successfully tested for IgG concentration monitoring. Copyright © (2011) by the Chemical and Biological Microsystems Society.