Label- and enzyme-free detection of glucose by boronic acid-coupled poly(styrene-b-acrylic acid) at liquid crystal/aqueous interfaces.

A glucose biosensor was developed based on a 4-cyano-4'-pentylbiphenyl (5CB)-filled transmission electron microscopy (TEM) grid cell by coating poly (styrene-b-acrylic acid) (PS-b-PAA) at the 5CB/aqueous interface and immobilising 3-aminophenyl boronic acid (APBA) on the PAA block chains by N-(3-dimethylaminopropyl)-N-ethylcarbodiimide coupling. Binding events between APBA and glucose were translated into homeotropic-to-planar configurational changes of 5CB, which were observed by polarised optical microscopy (POM) under crossed polarisers. This liquid-crystal-based glucose biosensor exhibited high sensitivity (limit of detection: 0.1 mM), even in complex serum and urine samples, high selectivity (against cholesterol, haemoglobin, and urea), and good stability for 40 d. This new and sensitive glucose biosensor has the advantages of low production cost, a simple immobilisation technique, and easy detection with POM, and may be useful for pre-screening glucose levels in human samples (serum and urine).