Boronic acid fluorophores for saccharide sensing
Bruen, Danielle and Delaney, Colm and Florea, Larisa and Diamond, Dermot (2016) Boronic acid fluorophores for saccharide sensing. In: CASi Ireland 2016, 14-15 Apr 2016, Dublin City University, Dublin, Ireland.
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Lewis acidic boronic acids (BAs) have been widely reported for their strong and reversible interactions with diol-containing compounds like sugars1,2. In many examples, fluorescent structures are incorporated into a BA derivative’s framework in order to monitor the effect of sugar concentrations by changes in fluorescence1,2. Due to the pKa of the BA at ~9 and the one for the sugar bound form at ~6, BA type sensors exhibit sugar sensing capabilities between a pH range of 6-9. This is advantageous for applications in sugar sensing under physiological conditions, where the pH for blood and ocular fluid is approximately 7.4.
Here, we report novel carboxylic acid BA fluorescent sensors, o-COOHBA and m-COOHBA, respectively, that have been synthesised via a one-step nucleophilic substitution reaction, and have been investigated for their glucose sensing capabilities in solution. Upon addition of glucose the electron density on the boron atom is increased, facilitating the partial neutralization of the positively charged quaternary nitrogen of the quinolinium moiety through a neutralisation-stabilisation interaction. This leads to a quenched state and hence a decrease in fluorescence of the COOHBA probe with increased glucose concentration. The sensor’s response was investigated in various pH buffer solutions, where the sensing range was determined to be between pH 6-92, which correlates to the pKa of the BA and the sugar-bound form. As pH 7.4 lies within the sensing range, these sensors have been directed towards physiological monitoring of glucose for personalised sensing, where the sensors can be incorporated in to wearable platforms, such as a disposable contact lens, for continuous and non-invasive glucose monitoring.
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