May 4, 2011
Hexagon-like nanopattern amplifies virus fingerprint
Focused ion beam (FIB) processing is a useful technique for fabricating uniform micro/nanostructured patterns on gold thin film. Building on its wide advantages, the method has been applied to create surface-enhanced Raman scattering (SERS) substrates. The FIB-made pattern (denoted here as "the fibAu") is assessed to have high electromagnetic effect and thus increases the enhancement factor for detecting target species. The nanoscale SERS-active pattern is very suitable to detect size-comparable pathogens such as viruses. The illustration below describes the procedures for detecting a molecular probe or target virus.
Researchers at National Cheng Kung University, Taiwan, have shaped micro/nanostructured patterns using a physical process such as vertically sensitive nano-indentation or FIB (described here). These identified SERS-active substrates were applied for the detection or distinction of different viruses.
First, the SERS mechanism on these fibAu patterns is estimated by low-concentration molecular probes as the target molecules with respect to a suitable laser wavelength as the excitation source. Second, these SERS-active fibAu patterns are further optimized by considering geometrical, dimensional and spacing factors.
The results indicate that a hexagon-like fibAu pattern may induce a very high electromagnetic mechanism based on the availability of multiple edges and small curvature. By decreasing the dimensions from 300 to 150 nm, the laser-focused area contains an increasing number of micro/nanostructures and therefore intensifies the excitation of SERS signals.
If the geometry and dimensions of the micro/nanostructures are optimized, the relative intensity/surface area value may reach a maximum as the spacing approaches 22 nm. However, an exponential decrease is found as the spacing increases, which most probably results from the loss of electromagnetic effect.
Comparing the factors of geometry, dimension and spacing between two micro/nanostructures, a statistical analysis indicates that spacing is the dominant factor for the effect of SERS.
Third, the optimized fibAu pattern has been experimentally configured to detect the influenza virus. Based on the resulting SERS spectrum, the major part of the fingerprint information from the outermost surface of the influenza virus can be clearly assigned.
Accordingly, the group will now tailor these fibAu patterns and enable them for fast-screening detection of size-dependent or envelop-sensitive viruses.
The researchers presented their work in the journal Nanotechnology.
About the author
This study was conducted by researchers from the Department of Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan. The corresponding author, Prof. Dr Jiunn-Der Liao, is currently chairman of the department. His research focuses on engineering materials for biomedical applications using nanofabrication methods and nano-characterization tools. The first author, Ying-Yi Lin, is currently a PhD candidate and Yu-Hung Ju is a graduate masters student in the department. They performed all the FIB experiments and the related Raman analyses. Dr Chia-Wei Chang is a fresh PhD, who gave assistance on the Raman analyses. His major study is focused on SERS-active substrates fabricated by a vertically sensitive nano-indentation method. Prof. Ai-Li Shiau is a virus expert and responsible for the virus purification. She is currently a professor in the Department of Microbiology and Immunology at National Cheng Kung University.