Font Size: a A A

Design And Appiication Of Glucose Biosensors Based On Graphene Oxide

Posted on:2013-01-27Degree:MasterType:Thesis
Country:ChinaCandidate:J HuangFull Text:PDF
GTID:2218330374964080Subject:Analytical Chemistry
Abstract/Summary:PDF Full Text Request
Diabetes is a world-wide and common disease. It has been the third dangerous sicknesses inferior to cardiopathy and cancer. So it is very important to fleetly and exactly determine the concentration of glucose in blood. Glucose biosensor provides a convenient and fast method for concentration determination of glucose in blood and interests more and more people.The study of glucose biosensor can be fallen into three categories by glucose-responsive mechanism:the glucose oxidase (GOx), lectin and phenylboronic (PBA). Conventional carriers used were polymer, fiber, gel or Au, Ag and so on noble metal nanoparticles. They usually reduced the sensitivity of biosensor or they were too expensive to fulfill the detecting request or apply on a large scale.In this article, we used a novel home-made nanomaterial graphene oxide (GO) as carrier to study glucose biosensors based on three different glucose-responsive mechanism. GO has not only strong mechanical strength, high surface area and high electrical conductivity, but also low cost as well as good biocompatibility, which made biomolecule not only commendably immobilize on electrode but keep its activity well. In the design and fabrication of glucose biosensors, the crucial step is how to develop a simple and effective detection strategy for the construction of sensitive membrane. Aimed at the problems existed in immobilization technique of biosensors, the main work of this paper is focused on the development of novel biosensors based on GOx, lectin, PBA-modified system, respectively. They are as follows:1. A simple self-assembly approach was proposed for construction of the glucose biosensor by integrating ferrocene-branched chitosan (CS-Fc), graphene oxide (GO) and glucose oxidase (GOx) onto electrode surface. The intrinsic vander Waals interactions between layers of graphene easily results in irreversible agglomeration or even restack to form graphite. This limitation can be overcome by the attachment of CS onto the graphene surfaces. The uniformly dispersed GO within the CS matrix could significantly improve the stability of GO and make it exhibit a positive charge, which was more favorable for the further immobilization of GOx with higher loading. Further attaching redox mediator ferrocene group (Fc) to CS could not only effectively prevent the leakage of Fc from the matrix and retain its electrochemical activity, but also improve the electrical conductivity of CS and promote the electron-transfer between GOx and electrode. Moreover, GO acted as an electron relay in the biocomposite system significantly improved electronic conductivity of the biocomposite and facilitated electron transfer between the GOx and the electrode for the electrocatalysis of glucose. Thus, the present biosensor exhibited fast response, high sensitivity, excellent stability and reproducibility towards the quantification of glucose. Biosensors based on this CS-Fc/GO/GOx film showed a linear response to glucose in the concentration range from0.02to6.78mM with a detection limit of7.6juM at a signal-to-noise ratio of3and exhibited a higher sensitivity of10juA mM-1cm-2.2. A novel "smart" electrochemical affinity nanobiosensor ConA-DexP/GO with pH-sensitive "on-off" property was designed for the direct determination of glucose. The sensing interface could be easily fabricated by assembling DexP onto GO surface through π-π stacking, followed by incubation with pH-sensitive ConA. The sensing approach was based on the glucose-ConA-DexP competitive system induced charge evolution in the use of GO as transducer element, resulting in the enhancement of interfacial electron transfer kinetics between the redox probe and the electrode. With the isoelectric point at about5.0, ConA was positively charged at pH<5.0and negatively charged at pH>5.0. When the ConA-DexP/GO film electrode switched in the negatively charged probe [Fe(CN)6]3-/4-solution between pH4.0and8.0, the film is cycled between the "on" and "off' states due to the electrostatic attraction and repulsion between the ConA-confined film and [Fe(CN)6]3-/4-. Upon the introduction of different concentrations of glucose into the ConA-DexP/GO complex at pH8.0, the charge on the biosensor surface gradually decreased due to the displaced ConA, thus decreased the resistance of probe for electron communication on the sensor surface, accompanied by the switching from "off" state to "on" state. The decrease in electron-transfer resistance was proportional to the glucose concentration, which formed the concept for sensitively electrochemical sensing of glucose. This sensor which had advantages of fast response, excellent reproducibility and high selectivity showed a linear response to glucose in the concentration range from to5.0μmol L-1to9.0mmol L-1with a detection limit of0.34μmol L-1at a signal-to-noise ratio of3. This electronic detection scheme would open new opportunity for the design of more novel biosensors and bioelectronic devices.3. A novel fluorescence glucose biosensor based on the mechanism of photo-induced excited-state electron transfer was successfully constructed. The4-cyanophenylboronic acid (4-CN-PBA) adsorbed on the GO through π-π stacking interactions with the pendant aromatic moiety, causing a fluorescence quenching. Glucose binding disrupted this interaction, partially restoring the decreased emission. The complexation of glucose with aromatic boronic acids switched boronic acids from a trigonal neutral form with an sp2boron atom (an electron-deficient Lewis acid) to a tetrahedral boronate anionic form with an electron-rich sp3boron atom (increasing its inductive electron-donating ability) at the pH range of6to9. This complexation hence altered the reduction potential of the boronic acid more negatively, which reduced or reversed the potential difference between GO conduction band and the reduction potential of the boronic acid and can thus make an excited-electron transfer from GO to the boronic acid energetically less favorable, leading to a recovery of GO fluorescence. The fluorescence recovery was proportional to the glucose concentration, which formed the concept for sensitively glucose sensing. This sensor featured fast response, excellent sensitivity and good stability, which showed a simple and effective strategy for the clinical glucose diagnosis.
Keywords/Search Tags:glucose biosensors, chitosan-ferrocene, graphene oxide, competitive binding, pH-sensitive "on-off" property, decrease in electron-transfer resistance, photo-induced excited-state electron transfer, fluorescence recovery
PDF Full Text Request
Related items