Fabrication of temperature- and pH-sensitive liquid-crystal droplets with PNIPAM-b-LCP and SDS coatings by microfluidics.

Dual responsive (temperature and pH) 4-cyano-4'-pentylbiphenyl (5CB) droplets were fabricated by coating with PNIPAM-b-LCP (PNIPAM: poly(N-isopropylacrylamide) and LCP: poly(4-cyanobiphenyl-4'-oxyundecylacrylate)) and sodium dodecyl sulfate (SDS) using a microfluidic method, and were tested for protein detection. The PNIPAM-b-LCP/SDS-functionalized 5CB droplets were effective in detecting proteins in water through a radial-to-bipolar (R-B) orientational change, with detection limits of 0.95, 1.1, 0.12, and 0.07 μM for bovine serum albumin (BSA), lysozyme (LYZ), hemoglobin (Hb), and chymotrypsinogen (ChTg), respectively. The R-B change of the 5CB droplet occurred above the lower critical solution temperature (LCST) of PNIPAM and at pH values below the pI values of the tested proteins, and was reversible by heating/cooling at the LCST of PNIPAM. These sensitive 5CB droplets are simple to prepare, cost-effective, easily detectable, and re-usable (by temperature control) for protein detection. Further, they can be applied to a biosensor after employing the selective units such as aptamers, antibodies, single-stranded DNA, proteins, peptides, and aptamer-binding RNA on the droplet.