Study Of Graphene-based Biosensors

A biosensor is a device that combines a biological component (e.g. enzyme, antibody, nucleic acids, cell, tissue, etc.) and chemical or physical detector for concentration detection. Taking advantage of high sensitivity, high specificity and real-time monitoring, biosensors are widely used in clinical diagnosis, biotechnology, environmental monitoring, etc. Graphene, a two-dimensional and one-atom-thick material in a honeycomb crystal lattice, has gained considerable attention due to its unique electronic, optical, electrochemical, mechanical, and thermal properties. The discovery of graphene greatly favors the design of various biosensor platforms, and lays the foundation of our works.1. A dual-colorimetric signal strategy for DNA detection based on graphene and DNAzymeIn this work, by employing graphene together with a peroxidase-mimic DNAzyme, we have developed a novel dual-colorimetric strategy for DNA detection. In this strategy, a bi-functional probe DNA with both the sequence to have peroxidase activity and the sequence to be complementary to the target DNA is designed. Through π-π stacking, the probe DNA can interact with graphene; however, when the target DNA is present, the graphene-probe DNA interaction will be interrupted, resulting in the peroxidase activity to be transferred from the precipitated graphene to the supernatant under centrifugation. Consequently, colorimetric signals can be obtained due to the catalytic reactions by the formed DNAzyme. By observing the changes of the color depth of either the precipitate or the supernate, we are able to detect the target DNA very easily and sensitively with naked eyes. The dual colorimetric signals (signal-off for the precipitate and signal-on for the supernate) can also be integrated through mathematical operations, which may greatly improve the performance of the sensing platform.2. Colorimetric detection of ATP based on graphene oxide and aptamer functionalized gold nanoparticlesAptamer, a single-stranded DNA or RNA, may attach to graphene oxide (GO) via π-π interaction. In this chapter, a novel colorimetric strategy for ATP detection using aptamer functionalized gold nanoparticles (AuNPs) and GO is proposed. In the absence of ATP, aptamers on AuNPs may adsorb on both sides of GO, to form super sandwich-like packed GO/aptamer/AuNP flakes, eventually leading to precipitation. In the presence of ATP, the aptamer binds ATP and folds into specific tertiary structure, which hinders aptamer terminal bases approaching GO. In this case, aptamer/AuNPs are stable in the solution. UV-vis analysis even naked eyes may be applied to monitor such changes.3. Electrochemical detection of trypsin using thionine-graphene nanocompositeIn this work, a simple and label free electrochemical method is proposed for trypsin detection based on peptide graphene interaction. A peptide, substrate of trypsin with cysteine on C-terminus, is immobilized onto gold electrode through Au-S bond, while histidine on N-terminus may adsorb graphene via π-π interaction and electrostatic adsorption. In the presence of trypsin, the peptide is cleaved, remaining serine residues on N-terminus, which may not adsorb graphene. As graphene may load large amount of thionine due to large surface, electrochemical signal is greatly amplified. This method is simple and label-free. Besides, this method may extend to detect other proteases by replacing the cleavage site.4. Fabrication of a3D nanoshelter for small molecules using DNA functionalized grapheneNanostructures on electrode interface endow the electrode with multiple functions. Taken advantage of DNA functionalized GO, a3D nanoshelter is assembled on electrode so as to protect signal molecules. In a typical procedure, DNA1is firstly immobilized on gold electrode via Au-S bond. Then, DNA2functionalized GO is introduced and tethered with DNA1by a linker DNA which is complementary to DNA1and DNA2. Thus, a3D nanoshelter with a graphene roof and DNA columns is achieved. Afterwards, a small electroactive molecule is chosen to investigate the diffusion process of getting in and out of the nanoshelter. Results show that the nanoshelter may significantly hinder electroactive molecule diffusing from bulk solution into nanoshelter and the reverse process is also attenuated. Therefore, the nanoshelter can prolong reserve time in nanoshelter and impede disturbance from outside, which may be helpful to increase the sensitivity and specificity of the detection.5. Fabrication of a smart small molecule-responsive switch using graphene oxide and anodic aluminum oxideA smart small molecule-responsive gate is fabricated in this work by employing ATP aptamer and GO, where aptamer serves as a novel recognition and response element. ATP aptamer is firstly immobilized on a gold-coated anodic aluminum oxide membrane. In the absence of ATP, the aptamer may adsorb GO via π-π interaction, with the switch off, and molecules may not pass though the covered pores. However, when pretreated with ATP, the aptamer binds with ATP and may not bind with GO, with switch on. Results show that good response to ATP can be achieved, and the regulation is related with ATP concentration, which allows continuous regulation. Regarding the diversity of aptamers, much more stimulus-response switches may be developed by adopting proper aptamer, consequently expanding its application in the future.