A Quantum Leap in Glucose Sensing: the Application of Fluorescent Quantum Dots with Boronic Acid-Substituted Viologens to Sense Glucose in Aqueous Solution

General. The following two sets of fluorescent quantum dots were acquired from Evident Technologies (Troy, NY) as buffered aqueous stock solutions of 7.76 nmols/mL concentration: a. CdSe/ZnS Fort Orange COOH-functionalized QDs b. CdSe/ZnS Fort Orange NH2-functionalized QDs The preparation of o-BBV2+ has been previously described.[1] Benzyl viologen dichloride (BV2+) was purchased from Aldrich and used as received. Fluorescence Quenching Studies with 3-nitrophenylboronic acid: These studies were conducted to help determine the effect of the boronic acid moiety on fluorescence quenching. A quartz cuvette filled with the quantum dot solution (2 mL of 5 x 10-8 M in pH 7.4 buffer) was excited at 460 nm. The emission of unquenched quantum dot solution was first obtained, then aliquots of 3-nitrophenylboronic acid (0.001 M) were added, the solution gently shaken for 60 sec, and the new fluorescence was measured. Fluorescence intensity was taken as the area under the emission curve. Experiments with both amine and carboxyl substituted quantum dots showed that the boronic acid quenching was insignificant (less than 2 % of that observed with the viologen-based quenchers o-BBV2+ and BV2+). Temperature-dependent quenching studies using NH2 substituted Fort Orange Quantum Dots (5 x 10-8 M) at pH 7.4 at 15, 25, and 65 oC: We observed that quenching became more efficient at reduced temperatures. Such behavior is consistent with a static quenching mechanism involving complex formation between quencher and fluorophore.[3]