Optical detection of bovine serum albumin using charged cholesteric liquid crystal droplets functionalized with surfactant

Monodispersed micrometer-sized Cholesteric liquid crystal (CLC) droplets were prepared by using the flow-focusing microfluidic device, which was used for the detection of protein bovine serum albumin (BSA). The PVA/SC12S stabilized micro-sized CLC droplets (CLCPVA/SC12S) exhibited flashing spots with red reflection. These CLC droplets were effective in the detection of BSA in an aqueous solution through a configurational change from red reflection flashing spots (homeotropic configuration) to a central spot of red reflection (planar configuration) with a detection limit of 0.15 µM. We found that the electrostatic interaction caused by the adsorption of negatively charged BSA below isoelectric point on the positively charged CLC droplets can cause the arrangement of the CLC molecules in droplets to change from flashing spot to central spot reflection. Our results also highlight that the limit of detection and response times of CLCPVA/SC12S droplets are tunable as a function of the concentration and pH of protein. These CLCPVA/SC12S droplets are highly sensitive and are inexpensive and simple to make. With this novel approach, we can detect protein by observing optical reflection patterns with/without crossed polarizers in CLCPVA/SC12S droplets, which, on the contrary, are required in the case of the nematic biosensors.