Carbon Nanostructure-Based Field-Effect Transistors for Label-Free Chemical/Biological Sensors

Over the past decade, electrical detection of chemical and biological species using novel nanostructure-based devices has attracted significant attention for chemical, genomics, biomedical diagnostics, and drug discovery applications. The use of nanostructured devices in chemical/biological sensors in place of conventional sensing technologies has advantages of high sensitivity, low decreased energy consumption and potentially highly miniaturized integration. Owing to their particular structure, excellent electrical properties and high chemical stability, carbon nanotube and graphene based electrical devices have been widely developed for high performance label-free chemical/biological sensors. Here, we review the latest developments of carbon nanostructure-based transistor sensors in ultrasensitive detection of chemical/biological entities, such as poisonous gases, nucleic acids, proteins and cells

SWCNT-Based Biosensor Modelling for pH Detection

Different forms of CNT delivery have been discovered with several biomedical functions during past decades. The mechanisms of the cellular uptake of CNTs are mainly maintained due to the chemical nature, the cell type, and the features of the molecules, which are used to functionalize the nanotube exterior. Since single-wall carbon Nanotube (SWCNT) has unique chemical and physical properties, it is a great applicant for pH sensing. In addition, ion sensitive FET (ISFET) base on nanostructured SWCNT have covered a new method to help genetic investigators restructure metabolic pathways in cells, recognize the progression of disease, and expand diagnostics and therapeutics. Particularly, because PH sensing is very crucial for the constancy of enzymes, it is essential to extend the cost efficient types of this sensing. In this research, the conductance changes of the CNT-based ISFET device with different pH values can be modelled by ion concentration of the solution. In addition, the electrical current of channel is imagined as a function of pH levels, which can be controlled by a control factor (α). Thus, ISFET based nanostructured SWCNT is proposed focusing on the area of electrical detection of hydrogen ions of the electrolyte membrane. Besides, electrical detection of hydrogen ion applications is suggested to be used by modelling the delivery of SWCNT sheets. In the end, after comparing the proposed model and experimental data, it has been reported that there is a good compatibility between them

Specific Binding of Alzheimer’s Aβ Peptide Fibrils to Single Walled Carbon Nanotubes

Amyloids constitute a class of protein and protein fragments believed to be involved in the pathologies associated with Alzheimer’s, Parkinson’s and Creutzfeldt‐Jakob diseases. These proteins can self‐assemble into unique fibrillar structures that are resistant to normal protein degradation. Interesting recent developments in the study of amyloid fibrils demonstrate that they bind carbon allotropes. In this study, using single‐walled carbon nanotube field-effect transistors (SWCNT‐FETs), we show that the fibrillar form of Alzheimer’s amyloid β (1‐40) and (1‐42) peptides specifically bind non‐functionalized SWCNT in a saturable manner. Both peptides exhibited near identical binding curves with half‐maximal binding concentrations of approximately 12 µg/ml. Binding of the peptides to SWCNTs was diminished by including dimethyl sulphoxide (DMSO) at concentrations that inhibits fibril formation. Lastly, a monoclonal antibody (BAM‐10), which binds to the N‐terminal region of Alzheimer’s amyloid fibrils, recognizes the amyloid peptides adhering to SWCNTs in the absence of DMSO, but not in the presence of 75% DMSO. Taken together, these results suggest that the fibrillar form of the Alzheimer’s amyloid peptides are specifically binding to SWCNTs

CMOS integration of inkjet-printed graphene for humidity sensing.

We report on the integration of inkjet-printed graphene with a CMOS micro-electro-mechanical-system (MEMS) microhotplate for humidity sensing. The graphene ink is produced via ultrasonic assisted liquid phase exfoliation in isopropyl alcohol (IPA) using polyvinyl pyrrolidone (PVP) polymer as the stabilizer. We formulate inks with different graphene concentrations, which are then deposited through inkjet printing over predefined interdigitated gold electrodes on a CMOS microhotplate. The graphene flakes form a percolating network to render the resultant graphene-PVP thin film conductive, which varies in presence of humidity due to swelling of the hygroscopic PVP host. When the sensors are exposed to relative humidity ranging from 10-80%, we observe significant changes in resistance with increasing sensitivity from the amount of graphene in the inks. Our sensors show excellent repeatability and stability, over a period of several weeks. The location specific deposition of functional graphene ink onto a low cost CMOS platform has the potential for high volume, economic manufacturing and application as a new generation of miniature, low power humidity sensors for the internet of things.S.S. acknowledges Department of Science and Technology (DST), India for Ramanujan Fellowship to support the work (project no. SR/S2/RJN-104/2011). This work was (partly) supported through the EU FP7 project MSP (611887). T.H. acknowledges support from the Royal Academy of Engineering through a fellowship (Graphlex).This is the final version of the article. It was first available from NPG via http://dx.doi.org/10.1038/srep1737

Targeting Antibodies to Carbon Nanotube Field Effect Transistors by Pyrene Hydrazide Modification of Heavy Chain Carbohydrates

Many carbon nanotube field-effect transistor (CNT-FET) studies have used immobilized antibodies as the ligand binding moiety. However, antibodies are not optimal for CNT-FET detection due to their large size and charge. Their size can prevent ligands from reaching within the Debye length of the CNTs and a layer of charged antibodies on the circuits can drown out any ligand signal. In an attempt to minimize the antibody footprint on CNT-FETs, we examined whether pyrene hydrazide modification of antibody carbohydrates could reduce the concentration required to functionalize CNT circuits. The carbohydrates are almost exclusively on the antibody Fc region and this site-specific modification could mediate uniform antibody orientation on the CNTs. We compared the hydrazide modification of anti-E. coli O157:H7 polyclonal antibodies to pyrenebutanoic acid succinimidyl ester-coated CNTs and carbodiimide-mediated antibody CNT attachment. Our results show that the pyrene hydrazide modification was superior to those methods with respect to bacteria detection and less than 1 nM labeled antibody was required to functionalize the circuits

Optimisation of carbon nanotubes growth conditions by CVD and its application in amperometric glucose biosensor

This thesis presents the fabrication of glucose biosensor by modifying the surface of the glassy carbon electrode (GCE) using optimized carbon nanotubes (CNTs). Chemical vapor deposition (CVD) method was utilized to grow vertically aligned carbon nanotubes (VACNTs) with various aspect ratios. Field emission scanning electron microscopy (FESEM) images coupled with Raman spectroscopy results highlighted the high aspect ratio as well as uniformity of the high crystalline carbon nanotubes. Transmission electron microscopy (TEM) images of the grown CNTs confirm the successful synthesis of multiwall carbon nanotube (MWCNTs) due to larger outer diameter of the CNTs. Furthermore, to increase the graphitic ratio of synthesized CNTs, sequential experimental strategies based on response surface methodology (RSM) was employed to investigate the crystallinity model of CNTs. In the next step, glucose oxidase (GOx) was immobilized on the optimized multiwall carbon nanotubes/gelatin (MWCNTs/Gl) composite using the entrapment technique to achieve enzyme-catalyzed oxidation of glucose at anodic potentials, which was drop-casted onto the GCE. Cyclic voltammetry (CV) results coupled with the chronoamperometric response obtained from modified GCE indicates that, GOx/MWCNTs/Gl/GC electrode can be utilized as a glucose biosensor with high direct electron transfer rate (8.42 s-1) between GOx and MWCNTs/Gl in a wide linearity range (8.9 mM) to glucose. The detection limit of the fabricated biosensor recorded was 0.59 mM by keeping its initial stability of 75.4% after 25 days. The performance of the fabricated biosensor as an electronic tongue was also investigated by designing a frequency based circuit attached to the electrochemical cell. The resistivity alteration of GOx/MWCNTs/Gl/GCE was recorded after each drop of glucose in the electrochemical cell. The oscilloscope results clearly showed that, by adding glucose to the circuit design, the output oscillation frequency changed and the square wave frequency reached a new stable value. These results indicated that, the modified GCE with the GOx/MWCNTs/Gl showed potential application in the determination of glucose in human serum samples as well as voltammetric based electronic tongue