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Research

Scanning microscopy


Scanning microscopy


  Photonic nanostructures such as gold nanoparticles are being pursued for their use as light concentrators or antenna owing to the significant enhancement of local optical fields by their surface plasmon resonances. The imaging of these structures is achieved through laser light that is focused on the tip of a scanning microscope. The scattered light is then collected by a detector. As soon as the microscope tip encounters an object such as a gold nanoparticle, the scattering intensity increases dramatically. As the tip is scanned across the surface, a map of the nanoparticles is obtained. We have now developed a reliable and scalable method for the fabrication of scanning probes. Common fabrication methods for such probes rely on focused ion beam or directed assembly strategies, which are usually very slow and often result in irreproducible results. In our approach, the end of a silicon scanning probe was first coated with an aluminum film. Then the tip was grinded off so that the silicon was exposed locally at the end of the tip. The grinding was followed by the deposition of a thin gold film. As the aluminum was etched away, only the gold at the tip end remained. The same procedure could also be used to grow sharp structures such as ZnO nanorods at the tip end. These structures significantly enhanced the scattering of laser light in case another object was in close contact with the tip. Using these tips, we imaged and characterized individual 30 nm sized gold nanoparticles. Further improvements to the resolution could be achieved through the use of smaller nanostructures at the end of the probe tip, or by using probes with steeper angles. Eventually, we plan to use our method to mass-produce various nanostructure-terminated probes and make them commercially available for researchers employing such scanning probe microscopes.


Various Biosensors based on Carbon Nanotube Field Effect Transistor
Various Biosensors based on Carbon Nanotube Field Effect Transistor


  Portable nanosensor systems for the rapid detection of specific biomolecules are crucial for anti-bioterrorism, disease diagnostics, and food safety. Bio-sensors based on CNT-FET have been utilized for highly-sensitive chemical sensing because of following reasons. First single-walled CNTs have very small diameter, directly comparable to the size of single biomolecules and to the Debye length in solutions. And the low chargecarrier density of SWNTs is directly comparable to the surface charge density of biomolecules such as protein, which makes CNTs is good platform for electronic sensing.


Current Research Results - I. Bioelectronic Nose


Bioelectronic Nose


  We report the detection of odorant molecules with single-carbon-atomic resolution using a 'bioelectronic nose' based on human olfactory receptor-functionalized swCNT-FETs. In this device, lipid membranes that contain human olfactory receptor 2AG1 (hOR2AG1) were coated on swCNT-FET surfaces and the deformation of the hOR2AG1 protein upon binding specific odorant molecules was detected by the swCNT-FET. We demonstrate the detection of specific odorant molecules with single-carbon-atomic resolution and femtomolar sensitivity in real time. Furthermore, this is the first demonstration of monitoring the operation of G-protein-coupled receptors (GPCR) in a cell membrane with swCNT-FET sensors, and it should open various new applications in drug and fragrance development, because the olfactory receptor proteins are the largest family of GPCR, which is the most ubiquitous class of drug targets: up to 50% of current drugs are targeted at GPCR.


Current Research Results - II. Flexible DNA Sensor based on CNT-FET


Flexible DNA Sensor based on CNT-FET


  We report a simple but efficient method to massproduce flexible single-walled carbon nanotube (swCNT) devices. In this strategy, a solid substrate is first coated with a methyl-terminated self-assembled monolayer (SAM) as a release layer, and then swCNT-based devices fabricated on it are transferred directly into a poly(dimethylsiloxane) (PDMS) matrix, resulting in flexible swCNT-network devices embedded in PDMS. As a proof of concept, we demonstrate the fabrication of DNA sensors based on flexible swCNT devices embedded in PDMS. PDMS is a flexible, inert, non-toxic and non-flammable material which is ideal for flexible electronics, especially for biological applications. Furthermore, since this method is very simple and can be done via conventional micro-fabrication processes, it is readily available for mass-production of low-cost flexible devices such as biosensors.