Effects of organic solvents on immunosensing assays for small molecules based on an optofluidic immunosensing platform

Highly sensitive and selective immunosensors are widely applied to detect small molecules. Organic solvent extraction of small molecules in samples is generally required when the small molecules have poor solubility in water. Immunosensing assays should tolerate at least some organic solvents to rapidly detect small molecules on-site. Herein, the effects of four organic solvents (methanol, acetone, acetonitrile, and n-hexane) on the homogenous and heterogeneous interactions between two small molecules (bisphonel A (BPA) and aflatoxin M1 (AFM1)) and their respective antibodies were studied using an optofluidic immunosensing platform. To evaluate the influences of these solvents on immunoassays for small molecules, indirect competitive immunoassays of BPA and AFM1 were conducted using organic solvents at various concentrations. Antibody–antigen binding reaction and inhibition depends on the concentration and water-miscibility of organic solvents as well as their chemical features. The homogenous and heterogeneous binding reactions of small molecules and their antibodies were almost uninfluenced by water-immiscible n-hexane even at a concentration of 40% (v/v). The quantitative immunoassays of small molecules could be carried out in water-miscible organic solvents at low concentrations, including methanol, acetone, and acetonitrile. However, increasing the concentrations of these organic solvents variably affected the immunoassays of the small molecules. The effects of the three water-miscible organic solvents at relatively high concentrations on homogenous binding reactions are more significant than the effects on heterogeneous binding reactions. The homogenous binding reactions between small molecules and their antibodies were inhibited completely by acetone and acetonitrile solutions at high concentrations. The susceptibilities of the binding reactions between different small molecules and their antibodies in response to different organic solvents were variable. To rapidly detect small molecules on-site, an organic solvent should be carefully selected on the basis of its extraction efficiency and effect on the immunoassay.