Anti-IgG-anchored liquid crystal microdroplets for label free detection of IgG

The orientational variation of 4-cyano-4'-pentyl biphenyl (5CB) molecules in LC microdroplets in response to IgG antigen (IgG) interactions has been utilized to develop a biosensor for rapid and label-free detection of IgG in biological fluids. In order to prepare a LC microdroplet-based biosensor, the anti-IgG (AIgG) anchored 4-cyano-4'-pentyl biphenyl LC microdroplets were prepared in the presence of sodium dodecylsulfate (SDS) as a mediator and amphiphilic poly(styrene-b-acrylic acid) (PS-b-PA) as a modifier of the LC/water interface. The AIgG-anchored LC microdroplets with a size variation from 20 to 30 μm have been used successfully for the detection of IgG within a concentration range of 20 to 1000 ng mL^-1, at a detection limit of as low as 16 ng mL^-1, and a response time of 30 min in PBS solution at room temperature. The LC microdroplets anchored with 5 μg mL^-1 of AIgG were found to be more sensitive for the detection of IgG in the concentration range from 20 to 800 ng mL^-1 in PBS. The AIgG-anchored LC microdroplets have shown a delayed response of 90 minutes for IgG in a solution containing 10% FBS or 10% blood plasma in comparison to PBS solution. The LC microdroplets anchored with 5 μg mL^-1 (34 pmol) of AIgG have shown a recovery of 106% of IgG, a coefficient of variance of ±4% and a precision within a limit of 1-6% for a spiked sample of 25 ng mL^-1 of IgG. The results indicated that orientational response of LC microdroplets is potentially useful to develop a biosensor for in vivo detection of proteins or pathogens in a biological fluid.