Study Of The Synthesis Of Phenylboronic Acid-based Compounds And Their Applications In Biosensors

Boronic acid compounds have attracted more attention just because their unique chemical property that they could react with1,2-or1,3-diols forming five-or six-membered cyclic complexes in solution under mild and easily controllable conditions. The binding reaction between phenyboric acid and its derivatives with polyhydroxy-compound such as polysaccharides, glycoproteins, glycolipids and nucleotide, has been widely used in biological sensor and identification, isolation and purification of glycoprotein. In addition, boric acid and its derivatives have a broad application in the field of medicine. On the basis of boric acid, DTBA-PBA and BBV have been synthesized, realizing the detection of H2O2and glucose. The details are summarized as follows:1. We have developed a new current of hydrogen peroxide (H2O2) biosensor utilizing the specific interaction between phenyboric acid self-assembled monolayer and glycosylated protein. Firstly, disulfide compound DTBA-PBA that carried phenylboronic acid groups at its ends was prepared by coupling of3-aminophenylboronic acid (PBA) with4,4’-Dithiodibutyric acid (DTBA), and it was fastened to gold electrode surface through self-assembly technique. Phenylboronic acid could react with1,2-or1,3-diols forming five-or six-membered cyclic complexes in solution under mild and easily controllable conditions. Aware of this nature, horseradish peroxidase (HRP) which has a high degree of glycosylation of about16.8%-21%, covalently bonded to the gold electrode surface for H2O2detection. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) have proved that the dense phenylboronic acid monolayer was forming onto the surface of gold electrode through self-assembly technique compact, and HRP was successfully bonded to the DTBA-PBA film. The performance of the biosensor was characterizeed by cyclic voltammetry and the chronoamperometry. The results showed that the linear response of the HRP modified Au electrode to H2O2was in the concentration range of8.3×10-6～5.3×10-2mol·L-1with a detective limit was2.24×10-6mol/L (S/N=3), the equation of linear regression was Ip (μA)=0.01889C[H2O2](mmol/L)+0.08415with a linear correlation coefficient of0.9992.2. In this part, a novel fluorescent glucose sensor based on graphene quantum dots (GQDs) and boronic acid-substituted bipyridinium salt (BBV) was proposed. Firstly, the GQDs were synthesized from graphene sheets (GSs) by a hydrothermal approach, showing that the GQDs are single-layer, good stability of optical properties, mono-dispersed with average size of about8.0nm. And then, BBV was prepared using a one-step procedure by reacting2-bromomethylphenylboronic acid with4,4’-bipyridyl, and it was characterized by Fourier transform infrared (FTIR) and1H NMR spectra. The pristine GQDs act as fluorescent reporting unit in our sensing system, and BBV serves as a fluorescence quencher and a glucose receptor simultaneously. It is postulated that electrostatic attraction between anionic GQDs that bear polar surface groups of carboxy and hydroxy groups and cationic BBV results in the formation of a ground-state complex which facilitates the excited-state electron transfer from GQDs to bipyridinium, leading to a decrease in the FL intensity of the GQDs. When glucose is added to the system, the boronic acids are converted to tetrahedral anionic glucoboronate esters, which effectively neutralize the net charge of the cationic bipyridinium, thus greatly diminishing its quenching efficiency, and the FL intensity of GQDs is recovered. To our knowledge, this is a unique realization of sugar sensor based on the GQDs, which does not rely on enzymes or electrochemical redox mediators, but rather on a combination of affinity sensing and electrostatic attraction. The sensor is simple, low cost, and has a certain practical value.