## 3 Results
### Glucose-Dependent Optical Characteristics  
Next, we explored the fluorescence change of AcTDA with changes in the glucose concentration by collecting the emission spectra of the compound with various concentrations of glucose. Figure 3 shows the measured emission spectra of AcTDA mixed with glucose. In the presence of glucose, the emission spectra were blue-shifted by \(\sim\)20 nm, and the intensity increased. According to the mechanism of B-N bond formation, the formation of a boronic acid complex with the diols from a saccharide, such as glucose, created intramolecular interactions between the boronic acids and amines. As shown in Figure 4, the B-N bond prevented the nitrogen lone pair from participating in photoinduced electron transfer (PET) [14,31]. As a result, the quenched anthracene fluorescence was recovered. Thus, we could observe the increased fluorescence intensity of AcTDA as the glucose level of the mixture increased. Next, we measured the association constant of AcTDA with glucose using the modified Benesi-Hildebrand plot [25]:  
\[\frac{1}{F-F_{0}}=\frac{1}{Ka\times(F_{max}-F_{0})\times[Glucose]}+\frac{1}{F_ {max}-F_{0}} \tag{1}\]  
where \(F\) is the measured fluorescence intensity, \(F_{0}\) is the fluorescence intensity of free AcTDA, and \(F_{max}\) is the saturated fluorescence intensity of the AcTDA-glucose complex. We plotted \(1/[F-F_{0}]\) versus \(1/[glucose]\) and calculated the association constant for the obtained linear relationship (Figure 3d). The obtained association constant with glucose was 730 \(\pm\) 18 M\({}^{-1}\). We also measured the association constant of TDA with glucose. Figure 5 shows the fluorescence changes for TDA, depending on the quantity of added glucose. As shown in Figure 5, the fluorescence intensity of TDA increased proportionally with an increasing glucose concentration. The calculated association constant was 606 \(\pm\) 63 M\({}^{-1}\), which was approximately 20% lower than that of AcTDA. As shown in Figure 5c, no significant spectral shift was observed for glucose mixed with TDA. Instead, the emission peak became narrower. Because the portion of fluorescence from the unbound AcTDA that contributed to the association calculation was smaller than that of TDA, AcTDA could have a higher binding affinity for glucose than TDA. Meanwhile, there was no shift in the excitation spectrum of either dye by glucose (Figure S1). The excitation intensity near 300 nm was decreased for both dyes in the presence of glucose because the contribution of the plastic well plate to the excitation decreased. In addition, we compared the quantum yield of the two analogs by measuring the relative quantum yield [32]. The relative quantum yield is calculated using a flowing equation:  
\[Q_{S}=Q_{R}\bigg{(}\frac{m_{r}}{m_{s}}\bigg{)}\bigg{(}\frac{n_{s}}{n_{r}} \bigg{)}^{2} \tag{2}\]  
Figure 2: Comparison of oxidation resistance of AcTDA and TDA. Normalized fluorescence intensity after 4 mM H\({}_{2}\)O\({}_{2}\) was added to 20 \(\upmu\)M of (**a**) AcTDA and (**b**) TDA with 200 mg/dL glucose in 1\(\times\) PBS (pH7.4). where \(Q\) is the quantum yield, \(m\) is a gradient of the plot of the integrated fluorescence against absorbance, \(n\) is the refractive index of the solvent, and \(s\) and \(r\) are the sample and reference, respectively. In the equation, the quantum yield of reference is independent of the excited wavelength, but the ratio of the plot of integrated fluorescence against the absorbance is a function of the exciting wavelength [30]. Then, Equation (2) can be rearranged to the ratio of the quantum yield between two samples as follows:  
\[\frac{Q_{S1}}{Q_{S2}}=\bigg{(}\frac{m_{r1}}{m_{s1}}\bigg{)}\bigg{(}\frac{m_{r2} }{m_{s2}}\bigg{)} \tag{3}\]  
Figure 4: Glucose-dependent fluorescence change for AcTDA. Quenched fluorescence of AcTDA was recovered after formation of AcTDA–glucose because photoinduced electron transfer was blocked by the B-N bond pair. Figure 3: Glucose binding properties of AcTDA.