Label Free Quantitation of Immunoglobulin G using the Stagnant Cap Hydrodynamic Retardation Effect Detector (SHRED)

Immunoglobulin G (IgG) is an essential antibody that helps fight pathogens and protect the body from infections. Measurement of IgG is useful in assessing immunity to measles, mumps, rubella (MMR), varicella, and in the diagnosis of autoimmune hepatitis, food allergy, liver diseases etc. High performance liquid chromatography (HPLC) and enzyme-linked immunosorbent assay (ELISA) are widely employed technologies for detection of IgG. HPLC-MS systems are fast and sensitive with a detection limit of 0.4 ng/mL but are bulky and expensive. ELISA, despite having a very good sensitivity of <; 0.02 ng/ml, requires antibody and labels. In this study, we demonstrate label-free detection of IgG using a novel sensor concept of a stagnant cap hydrodynamic retardation detector (SHRED). SHRED detects IgG by leveraging its amphiphilic structure. The IgG adsorbs to the interface of water-in-oil droplets and retards the motion of droplets by the stagnant cap effect. The frequency shift of the droplets is measured downstream with a light scattering detector. Measured parameters such as peak area, time constant, and percentage frequency drop were all found to increase linearly for the 3 different concentrations of IgG. The detection method is comparatively simple, inexpensive, label-free and real time with a current sensitivity of 150 ng/ml.