Towards the real-time monitoring of glucose in tear fluid: holographic glucose sensors with reduced interference from lactate and pH.

Glucose-selective holographic sensors were fabricated from unique tetrahedral 2-acrylamidophenylboronic acid (2-APB) incorporated with co-monomers poly(ethylene glycol) acrylate (PEG), (3-acrylamidopropyl)trimethylammonium chloride (ATMA) and [2-(acryloyloxy)ethyl]-trimethylammonium chloride (AETA) into thin hydrogel films which were transformed into volume holograms using a diffusion method coupled with holographic recording using a frequency-doubled Nd:YAG laser (532 nm). The results showed that the 2-APB-based holographic sensors contracted upon addition of glucose due to the formation of a 2:1 complex between the tetrahedral 2-APB and glucose. More significantly, the 2-APB-based holographic sensors had greatly reduced lactate dependence and a hugely reduced pH effect over the physiological range of pH. These features are vital for development of contact lens-based glucose sensor, where the pH variability is greater (pH 5.8-7.8) and the lactate concentration is substantially higher than in blood. Furthermore, the 2-APB-based holographic sensors also displayed fast response to glucose. The successful union of holograms and the tetrahedral 2-APB receptor for glucose detection in artificial tear fluid is also demonstrated. This new type of holographic sensors responding to glucose with features of minor pH effect and negligible interference from lactate is applicable to the detection of glucose concentrations in tear fluid for the management of diabetes.