The Electrochemical Sugar Recognition Using a β-Cyclodextrin Assembled on the Gold Electrode

Abstract

Introduction Cyclodextrin has a hydrophobic field inside of its structure and includes various molecules to form complexes. The inclusion occurs when the size of the cyclodextrin cavity matches that of the guest molecules. Therefore, a molecule recognition probe which is not soluble to water can be dissolved in an aqueous solution by the inclusion of cyclodextrin. This type of sensing using a cyclodextrin complex is widely researched. Hayashita’s group conduct alkali metal ion recognition using crown ether type azo probe and sugar recognition using boronic acid type azo probe. Both of them utilize the cyclodextrin inclusion ability. Moreover, electrochemical molecule recognition, which involves fixing cyclodextrin on electrodes and utilizing the inclusion ability, is also widely researched. purpose In our laboratory we have various probes that utilize cyclodextrin and in our experiments we conduct an electrochemical molecular recognition by impedance measurements in aqueous solutions. We composed β-CyD whose alkyl chains were stretched (β-CyD-R10SH) and we also modified the gold electrode with it. This improved the coverage and stabilization of the modification to CyD gold electrode by van der Waals forces of each other alkyl chain. We successfully improved sensitivity of the carbohydrate recognition. In addition, we succeeded in recognition of phosphoric acid salts such as ATP by having the dipicolylamino group included. In this study, my purpose was to find an electrochemical molecular recognition by impedance measurements of monosaccharide such as D-fructose, D-glucose and D-galactose, disaccharide, trisaccharides, tetrasaccharide, polysaccharides and the rare sugar based on the impedance measurements. Materials and Method Synthesis of β -CyD-(CH2)10S(CH2)11CH3 ( β -CyD-R10SH ): Primary amino was introduced at the 6th carbon of cyclodextrin by the Appel reaction, nucleophilic substitution reaction and the Staudinger reaction. A solution of the Synthesized heptakis(6-deoxy-6-amino)-b-cyclodextrin and 11-(thiododecyl)undecanoic acid were stirred for 18 hours with DCC, in order to create a white powder (β-CyD-R10SH). Modification: modification was conducted in 3 steps. First, β-CyD-R10SH was attached onto the gold electrode by the SAM method. Second, the octadecanthiol was attached onto the gold electrode to fill gaps among β-CyD-R10SH. Third, 1-pyreneboronic acid was included by β-CyD-R10SH. Measurement: EIS were measured while adding sugar solution using the modified electrode prepared above. Through the results of measurements, the relationship between concentration and charge transfer resistance was investigated by making a Nyquist plot. Results and Discussion Modification of β-CyD-R10SH and 1-octadecanethiol to the gold disk electrode was identified by a decrease of the current response of CV. The Nyquist plots at that point with the inclusion of 1-pyreneboronic acid were shown in Fig. 2 when sugar was added to the solution. With the addition of D-fructose and D-psicose, the increase in charge transfer resistance (Rct) was observed. This confirmed the inclusion of 1-pyreneboronic acid / Bp-amido-adamantane and monosaccharide / rare sugar recognition. However, with the addition of D-psicose when 1-pyreneboronic acid was used as a probe, the increase in charge transfer resistance (Rct) was not observed. It showed that using an appropriate probe for each molecule was necessary. Conclusion We conduct an electrochemical molecular recognition using modified cyclodextrin on gold electrode by impedance measurements. The results mentioned above indicate that the method is applicable to recognition of various molecules by changing probes and show high sensitivity. Figure 1