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Posted: Jan 22, 2015

Multiplexing biosensors on a chip for human metabolite detection

(Nanowerk Spotlight) The convergence of nanotechnology, biology, and photonics opens the possibility of entirely new classes of biosensing and imaging nanodevices. The application of nanomaterials such as carbon nanotubes, nanowires, and graphene to biosensor design and fabrication promises to revolutionize diagnostics and therapy at the cellular and even molecular level (see for example: "Nanotechnology biosensor to detect biomarkers for Parkinson's disease"). These nanoprobes and nanosensors have the potential for a wide variety of medical uses down to the cellular level.
So far, there have been very few research reports on single electrode materials that enable the simultaneous detection of different metabolites – such as glucose, urea, cholesterol, and triglycerides – in whole blood. Moreover, it is a considerable challenge to integrate all required materials and devices on a single chip to ultimately produce a multiplexing biosensor array.
In new work, researchers demonstrate that biosensors based on conducting polymer hydrogels (CPHs) enable the precise and full-range detection of different metabolites in human blood.
The results, published in the January 8, 2015, online edition of Nano Letters ("A Nanostructured Conductive Hydrogels-Based Biosensor Platform for Human Metabolite Detection"), represent a significant step towards fabricating integrated sensor arrays on a chip to recognize different metabolites with the simplified technology of only one single electrode material system.
"We wanted to demonstrate that there is a kind of nanomaterials that can meet the requirements of a biosensing platforms to detect all metabolites simultaneously with high sensitivity while being compatible with simple patterning technology," Guihua Yu, an Assistant Professor of Materials Science at the University of Texas at Austin, tells Nanowerk. "Synergizing the advantages of both organic conductors and hydrogels, nanostructured CPHs present excellent electrochemical performance and good biocompatibility. They also provide an advantageous interface between the substrates and electrode. All these advantages make CPHs excellent candidates for high-performance biosensors – as we confirmed in our recent work."
 CPH-based bioelectrode platform with sensing capability for different human metabolites
Schematic illustration of the general sensing mechanism of our CPH-based electrode platform. (a) Platinum nanoparticles (PtNP) and enzymes were loaded onto hierarchically three-dimensional (3D)-porous polyaniline hydrogel matrices to form polyaniline hydrogel/PtNPs hybrid electrodes. (b) The PtNP-catalyzed sensing process of the biosensor based on polyaniline/PtNPs/enzyme hybrid films. (Reprinted with permission by American Chemical Society)
To develop their biosensor platform, Yu's team fabricated a platinum nanoparticle modified CPH electrode. Polyaniline hydrogels provide hierarchically porous, nanostructured matrices, and particularly, solvated surfaces resulted from the hydrophilic nature of the hydrogels. The team homogeneously dispersed enzymes and platinum nanoparticles in the hydrogel matrix to catalyze the electrochemical oxidization of the hydrogen peroxide molecules generated in the enzymatic reaction between the substrates and enzymes and to enhance the current collection in electrochemical processes.
"Owing to the unique features of conducting polymer hydrogels, such as high permeability to biosubstrates and rapid electron transfer, our biosensors demonstrate excellent sensing performance with a wide linear range (uric acid, 0.07-1 mM; cholesterol, 0.3-9 mM, and triglycerides, 0.2-5 mM), high sensitivity, low sensing limit, and rapid response time of about 3 seconds," says Lijia Pan, a Professor at the School of Electronic Engineering, Nanjing University, who, together with Yu, led the project.
In their experiments, the researchers demonstrated the detection of different metabolites separately on the same conductive-polymer based bioelectrode platform.
However, there still are some hurdles to overcome before we will see multiplexing biosensors on a chip that are fabricated at low cost and large scale: Eliminating the mutual interference between the various metabolites is the next key challenge to solve. The related work is now ongoing in Yu's lab.
"We envision that, once it is possible to successfully fabricate these multiplexing biosensors, we will see a very sensitive yet inexpensive 'vital reader' on the market that can tell people accurately the values of 3-4 key human metabolites with only one single drop of blood," says Yu.
His team is already working towards building such multiplexing biosensors on a chip and designing and implementing the seamless connection of the biosensor and a portable terminal (e.g. a smartphone) by wireless communication.
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