Enzyme-induced modulation of the emission of upconverting nanoparticles: Towards a new sensing scheme for glucose

A new approach for the design of a fluorometric biosensor for continuous monitoring of glucose levels in biological samples based on near-infrared (NIR) excitation is described. The sensor combines the fluorescence of the enzyme glucose oxidase (GOx) chemically modified with a fluorescein derivative (FS) and the luminescent properties of upconverting luminescent nanoparticles (UCLNPs). Both, the chemically modified enzyme (GOx-FS) and the UCLNPs are immobilized in a poly(acrylamide) film as a physical support. The excitation of the UCLNPs with NIR light is of major advantage, since fluorescence background from the matrix is minimized. The upconverted luminescence is used to excite GOx-FS, which undergoes a change in the fluorescence intensity during the enzymatic reaction with glucose. The sensor comprises sufficient stability and covers the physiological range of glucose levels in blood. Furthermore, in a proof of principle experiment, the sensor system responds linearly to glucose concentrations in the range from 33 to 16.6 mM in flow injection analysis mode. (C) 2014 Elsevier B.V. All rights reserved.