New imaging technique homes in on electrocatalysis of nanoparticles

August 27, 2012

By modifying the rate at which chemical reactions take place, nanoparticle catalysts fulfill myriad roles in industry, the biomedical arena and everyday life. They may be used for the production of polymers and biofuels, for improving pollution and emission control devices, to enhance reactions essential for fuel cell technology and for the synthesis of new drugs. Finding new and more effective nanoparticle catalysts to perform these useful functions is therefore vital.

Now Nongjian (NJ) Tao, a researcher at Arizona State University’s Biodesign Institute, has found a clever way to measure catalytical reactions of single nanoparticles and multiple particles printed in arrays, which will help characterize and improve existing nanoparticle catalysts, and advance the search for new ones. Download Full Image

Most catalytic materials synthesized in labs contain particles with different sizes and shapes, each having different electrocatalytical activities, but the conventional methods measure the average properties of many nanoparticles, which smear out the properties of individual nanoparticles.

“The capability of measuring single nanoparticle catalytical reactions allows for determining the relationship between the efficiency of a catalytical reaction and the size, shape and composition of the nanoparticle,” Tao explained. “Such an imaging capability also makes it possible to image arrays of nanoparticle catalytical reactions, which may be used for fast screening of different nanoparticles,” he added.

In the current study, platinum nanoparticles acting as electrochemical catalysts are investigated by means of the new technique, known as plasmonic electrochemical imaging. The method combines the spatial resolution of optical detection with the high sensitivity and selectivity of electrochemical recognition.

Results of the study appear in this week’s advanced online edition of the journal Nature Nanotechnology.

Scanning electrochemical microscopy (SECM) has been used to image electrochemical reactions by mechanically scanning a sample surface using a microelectrode. In this process however, imaging speed is limited and the presence of the microelectrode itself may impinge on the sample and alter results.

The new method relies instead on imaging electrochemical reactions optically based on the phenomenon of surface plasmon resonance. Surface plasmons are oscillations of free electrons in a metal electrode, and can be created and detected with light. Every electrochemical reaction is accompanied by the exchange of electrons between reactants and electrodes, and the conventional electrochemical methods, including SECM, detect the electrons.

“Our approach is to measure electrochemical reactions without directly detecting the electrons,” Tao said. “The trick is to detect the conversion of the reactant into reaction products associated with the exchange of electrons.” Such conversion in the vicinity of the electrode affects the plasmon, causing changes in light reflectivity, which the technique converts to an optical image.

Using plasmonic electrochemical current imaging, Tao’s group examined the electrocatalytic activity of platinum nanoparticles printed in a microarray on a gold thin-film electrode, demonstrating for the first time the feasibility of high-throughput screening of the catalytic activities of nanoparticles.

Additionally, the new study shows that the same method can be used to investigate individual nanoparticles. As an electrical potential is applied to the electrode and cycled through a range of values, nanoparticles clearly appear as spots on the array. The effect can be seen in accompanying videos, where nanoparticle spots ‘develop’ over time as the potential changes, much like a polaroid picture gradually appears. 

Microarrays featuring different surface densities of nanoparticles were also produced for the study. Results showed that electrocatalytic current at a given potential increases proportionally with nanoparticle density. Further, when individual nanoparticles were characterized using SPR microscopy, atomic force microscopy (AFM) and transmission electron microscopy (TEM), good agreement was shown between the results, further validating the new technique.

Tao notes that in principle, plasmonic electrochemical imaging – a rapid and non-invasive technique offering the combined benefits of optical and electrochemical detection – may be applied to other phenomena for which conventional electrochemical detection methods are currently used.

In addition to his appointment as the Director of the Center for Bioelectronics and Biosensors at the Biodesign Institute, Tao is a professor in the School of Electrical, Computer and Energy Engineering, one of ASU’s Ira A. Fulton Schools of Engineering.

Richard Harth

Science writer, Biodesign Institute at ASU


Spread the word about the PeopleSoft upgrade

August 27, 2012

The entire ASU community will be affected by the Sept. 20-25  planned PeopleSoft outage. While the system is being upgraded, both PeopleSoft and My ASU will be READ-ONLY.

To minimize disruptions to university business, departments should use upcoming staff meetings to determine which of their business processes will be affected by the outage. Then consider the following questions to develop a comprehensive communications plan: Download Full Image

  • How will you minimize disruption to your business processes?
  • Who are your customers that will be affected?
  • How/when will you communicate with your customers?
  • What information will you give them?
  • How will your customers communicate with you during the outage?
  • How will you tell your customers the system is fully functional again?

ASU online, Blackboard, Google docs and apps, Gmail, and Outlook, will function normally and not be affected by the outage.

The upgraded PeopleSoft system will be split into two parts: one for human resources and payroll functions and another for student transactions. This upgrade is the first major one to the PeopleSoft system since it was installed at ASU in 2006.

Get More Information:

  • What’s New Informational Sessions -- Beginning Aug. 28, the University Technology Office will host one-hour sessions on all four campuses to explain the outage, where to find online resources and what the upgraded system will look like. Meeting schedule
  • -- Offers information about HR department functions, including payroll, benefits, PTR and time reporting plus a “Go Live” planning calendar
  • -- Provides outage information and includes a FAQ page, a link to the communication strategy, a list of applications unaffected by the outage, checklists to help you prepare for the outage and much more

If you have questions about the PeopleSoft outage, use the link in the Quick Links box on the page.

Paul Stoll,
University Technology Office

Wendy Craft

Marketing and communications manager, Business and Finance Communications Group