# Presentation: 278819

## Nanotubes and Nanowires as Chemical and Biological Sensors

- Through the EAGLE school science mentor program, 8th grade student Adam Schneider worked with students Sarah Baker and Lu Shang to synthesize and manipulate nanowires.  We have mentored an 8th-grade EAGLE  student for each of the last 5 years. We have also mentored a high school student as part  of the Madison Metropolitan School District’s Summer Science Intern Program for each of the last 4 years

- Our NSF-funded scanning electron microscope system has been used for many hands-on demonstrations targeting students from underrepresented groups.
- Here a middle-school girl prepares to to operate the SEM while other girls watch on a second monitor.

***R. Hamers, L.M. Smith, and D .van der Weide, Univ. of Wisconsin, DMR-0210806***
***http://hamers.chem.wisc.edu/***

**Notes:**
The top images shows Adam Schneider an 8th-grade at Eagle School, standing beside graduate student Sarah Baker and our home-built plasma chemical vapor-deposition system for growing carbon nanofibers. Adam conducted an 8-week science project growing nanofibers and nanowires and then manipulating them with electric fields. This year we participated in day-long workshops done as part of a “Women of Science” initiative on campus.  This initiative was targeted principally toward middle-school girls but was open to anyone.  It included a number of different workshops; we hosted two workshops on scanning electron microscopy.  The bottom image shows middle-school students in our laboratory. Every participant was given the opportunity to operate the controls of the SEM.  This is one of many demonstrations presented through the year.   Other demonstrations and workshop have targeted a number of different sectors, principally (but not exclusively) targeted toward underrepresented groups.

## Nanotubes and Nanowires as Chemical and Biological Sensors

***R. Hamers, L.M. Smith, and D .van der Weide, Univ. of Wisconsin, DMR-0210806***
***http://hamers.chem.wisc.edu/***

- The top images shows Adam Schneider an 8th-grade at Eagle School, standing beside graduate student Sarah Baker and our home-built plasma chemical vapor-deposition system for growing carbon nanofibers. Adam conducted an 8-week science project growing nanofibers and nanowires and then manipulating them with electric fields. This year we participated in day-long workshops done as part of a “Women of Science” initiative on campus.  This initiative was targeted principally toward middle-school girls but was open to anyone.  It included a number of different workshops; we hosted two workshops on scanning electron microscopy.  The bottom image shows middle-school students in our laboratory. Every participant was given the opportunity to operate the controls of the SEM.  This is one of many demonstrations presented through the year.   Other demonstrations and workshop have targeted a number of different sectors, principally (but not exclusively) targeted toward underrepresented groups.

## Nanotubes and Nanowires as Chemical and Biological Sensors

- Prof. Clark Miller organized a “Citizen’s Consensus Conference” on Nanotechnology.  Robert Hamers participated an open panel discussion with local citizens about nanotechnology and it societal implications.  A diverse group of citizens was selected to participate in the writing of a report summarizing their views on nanotechnology, based upon selected reading materials and what they learned in the forum with Prof. Hamers and other nanotechnology experts. The report of the consensus conference was presented to local and state legislators in a press conference at the Wisconsin State Capitol and is on the web at http://www.lafollette.wisc.edu/research/Nano/nanoreport42805.pdf.

***R. Hamers, L.M. Smith, and D .van der Weide, Univ. of Wisconsin, DMR-0210806***
***http://hamers.chem.wisc.edu/***

## Nanotubes and Nanowires as Chemical and Biological Sensors

***R. Hamers, L.M. Smith, and D .van der Weide, Univ. of Wisconsin, DMR-0210806***
***http://hamers.chem.wisc.edu/***

- This slide shows photographs from the Citizens’ Consensus Conference. The citizens engaged in a series of three meeting. In the first one they identified appropriate reading materials about the field of nanotechnology.  In a second meeting, the citizens met with R. Hamers and other UW-Madison scientists working on different aspects of nanotechnology (physical science, societal implications, medicine, etc); this was open to all interested citizens and was well attended.  The photo at lower left shows the “expert” panel (far side of room) and interested citizens. The right panel shows R. Hamers and two other panelists who participated as experts.  In a third meeting, the citizens wrote a report on nanotechnology that was presented to our state legislators at a press conference at the State Capitol.  The conference was organized primarily by Professor Clark Miller.  R. Hamers participated as an expert and participated in the press conference at the Capitol.     More information is at: http://www.lafollette.wisc.edu/research/Nano/index.htm

## Nanotubes and Nanowires as Chemical and Biological Sensors

- Current, pA

- Voltage, V

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- Semiconducting nanowires have the potential to act as highly sensitive detector elements. We are characterizing the electrical response of semiconducting nanowire “bridges”, such as the 45-nanometer-diameter Si nanowire shown here. By using two electrodes of different materials, an inherent asymmetry can be built into the junction. This asymmetry is clearly reflecting the current –voltage characteristics of the junction when a silicon nanowire bridges across the gap between electrodes. The optical and electrical response of nanowire junctions are currently being measured.  The electrical properties are expected to change in response to chemical and/or biological molecules, leading to new types of nanoscale biosensors.

**Gold**

**Silver**

**2 ********m**

***R. Hamers, L.M. Smith, and D .van der Weide, Univ. of Wisconsin, DMR-0210806***
***http://hamers.chem.wisc.edu/***

**Notes:**
This slide shows a scanning electron microscopy image of a 45-nanometer-diameter silicon nanowire bridging across a pair of electrodes.  The left electrode is made from gold, and the on one the right is made from silver.  The difference in work function between gold and silver creates a “built-in” potential across the nanowire that makes its current-voltage response asymmetric, as shown by the curve in red.  This asymmetric behavior assists in separating the response of the nanowire from other possible sources of conduction.  We are investigating the electrical properties of these nanowires and how they change in response to a variety of stimuli including optical excitation and exposure to chemical and/or biological molecules.  Functionalization of the nanowires with specific biomolecules of interest is expected to provide selectivity toward specific chemical or biological molecules of interest, while the electrical response provides a way to detect the binding of molecules to the surface of the functionalized nanowires.

## Nanotubes and Nanowires as Chemical and Biological Sensors

***R. Hamers, L.M. Smith, and D .van der Weide, Univ. of Wisconsin, DMR-0210806***
***http://hamers.chem.wisc.edu/***

- This slide shows a scanning electron microscopy image of a 45-nanometer-diameter silicon nanowire bridging across a pair of electrodes.  The left electrode is made from gold, and the on one the right is made from silver.  The difference in work function between gold and silver creates a “built-in” potential across the nanowire that makes its current-voltage response asymmetric, as shown by the curve in red.  This asymmetric behavior assists in separating the response of the nanowire from other possible sources of conduction.  We are investigating the electrical properties of these nanowires and how they change in response to a variety of stimuli including optical excitation and exposure to chemical and/or biological molecules.  Functionalization of the nanowires with specific biomolecules of interest is expected to provide selectivity toward specific chemical or biological molecules of interest, while the electrical response provides a way to detect the binding of molecules to the surface of the functionalized nanowires.

## Nanotubes and Nanowires as Chemical and Biological Sensors

***R. Hamers, L.M. Smith, and D .van der Weide, Univ. of Wisconsin, DMR-0210806***
***http://hamers.chem.wisc.edu/***

**CV in Hexaammine ruthenium (II/III) chloride**

**1 ********m**

**Notes:**
These images are top-view images showing carbon nanofibers grown at precise locations on molybenum electrodes, on a SiO2/Si substrate.  The position of the nanofibers was controlled using electron-beam lithography to control the spatial location of a nickel catalyst.  When placed in a plasma-enhanced chemical vapor deposition system leads to nanofibers at these predefined locations.  The fibers shown here were then insulated with a thin coating of SiO2, leaving only the ends of the nanofibers exposed.  The carbon shows up as the small,  bright spots at the center of each nanofiber.  The underlying electrodes are completely insulated as well, but this coating is partially transparent to the scanning electron microscope electron beam, making it possible to view the underlying electrodes even though they are completely insulated. When the nanofibers are placed in solution, one can measure the electrochemical response of the exposed nanofiber ends. We have functionalized nanofiber electrodes with molecules such as horeradish peroxidase and are currently exploring their electrochemical response as way to achieve nanoscale biosensing.

## Nanotubes and Nanowires as Chemical and Biological Sensors

***R. Hamers, L.M. Smith, and D .van der Weide, Univ. of Wisconsin, DMR-0210806***
***http://hamers.chem.wisc.edu/***

- These images are top-view images showing carbon nanofibers grown at precise locations on molybenum electrodes, on a SiO2/Si substrate.  The position of the nanofibers was controlled using electron-beam lithography to control the spatial location of a nickel catalyst.  When placed in a plasma-enhanced chemical vapor deposition system leads to nanofibers at these predefined locations.  The fibers shown here were then insulated with a thin coating of SiO2, leaving only the ends of the nanofibers exposed.  The carbon shows up as the small,  bright spots at the center of each nanofiber.  The underlying electrodes are completely insulated as well, but this coating is partially transparent to the scanning electron microscope electron beam, making it possible to view the underlying electrodes even though they are completely insulated. When the nanofibers are placed in solution, one can measure the electrochemical response of the exposed nanofiber ends. We have functionalized nanofiber electrodes with molecules such as horeradish peroxidase and are currently exploring their electrochemical response as way to achieve nanoscale biosensing.