Boronic acid derivatives for indirect fluorescent glucose sensing
Bruen, Danielle and Delaney, Colm and Florea, Larisa and Diamond, Dermot (2016) Boronic acid derivatives for indirect fluorescent glucose sensing. In: 3rd Insight Student Conference 2016, 14 Sept. 2016, Dublin City University, Dublin, Ireland.
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Boronic acids (BAs) are well-known for their interactions with diol-containing compounds like glucose. Fluorescent moieties are commonly considered to enable monitoring of this interaction by changes in fluorescence. Hence, a novel cationic pyrimidine BA derivative, DBA2, has been investigated for it’s indirect glucose sensing capabilities. This approach aims to develop smart-contact lenses that will allow people suffering from diabetes to track their condition continuously and non-invasively in real-time using a mobile phone application.
Diabetes is a worldwide incurable disease known to have acute and chronic health effects . Blindness, heart or kidney failures are among the most common life-threatening effects of diabetes . Monitoring physiological blood-glucose concentrations is a means of managing the disease, however few non-invasive continuous monitoring methods currently exist . Consequently, there is considerable interested in using aqueous ocular fluid as a sample medium for tracking the disease marker glucose.
2. The Sensing Mechanism
Incorporation of a BA component into charged molecules, can be used to induce quenching in the emission of a known fluorescent molecule, thereby creating a two-component sensing system [1-2]. In this approach, the fluorescence of 7-hydroxycoumarin, is monitored. Increasing concentrations of our novel BA sensor, quenches the fluorescence of 7HC. The change in fluorescence intensity of the system is achieved via the formation of a ground-state complex, through electrostatic interactions between the fluorophore and BA-quencher [1-2]. In the presence of saccharides, the Lewis acidic BA moiety of the sensor is known to form strong, reversible interactions . This leads to the formation of a boronate diester , resulting in the dissociation of the BA-quencher and fluorophore ground-state complex, causing a sequential recovery of fluorescence in 7HC [1-2].
Figure 1: Indirect glucose-sensing mechanism.
3.1 Fluorescence Quenching
Photophysical characterisation shows that upon increased BA-quencher concentrations an extremely efficient and sequential decrease in the fluorescence intensity is observed in 7HC.
Figure 2: Fluorescence quenching of 7HC with DBA2 at pH 8.6 when excited at 370 nm.
3.2 Fluorescence Recovery
The introduction of glucose to this two-component system allows for a recovery in fluorescence, which can be used to indirectly quantify glucose concentrations.
Figure 3: Fluorescence recovery of 7HC with glucose (up to 100 mM) at pH 8.6 when excited at 370 nm.
To conclude, this glucose-sensing switch shows a high sensitivity for sugar detection, where DBA2 showed great potential to act as a glucose sensor exhibiting a decrease in fluorescence intensity by 98% and on incremental additions of glucose, the fluorescence can be recovered. Moreover, the inclusion of anchoring moieties to the BA-quencher shows wonderful potential for the incorporation of this molecule into porous hydrogel platforms.
The authors are grateful for financial support from SFI under the Insight initiative, grant number SFI/12/RC/2289.
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