A*STAR Singapore - Plasmonics as growth lamps for nanoparticles

It is claimed that the illuminating of Silver nanoparticles (AgNP) within a narrow-bandwidth light at or nearby the Near Infrared (NIR) region will allow them to grow uniformly, and, therefore, improve their potential for imaging and sensing applications.  For instance just as gardeners can employ 'growth lamps' to promote plant growth - material scientists are capable of promoting uniform growth of decahedron-shaped AgNPs whilst they are in solution.  The 10-faced solids (as shown below) could help in surface enhancing for bio-imaging and bio-sensing techniques.  Such a new photo-assisted method for use during crystal growth was developed by Xia Yu of the Singapore Institute of Manufacturing Technology with collaborators in Hong Kong and Singapore.

Excitingly Yu and her co-workers based their method on a well known phenomenon of localised surface plasmons (LSP), which initiate through the movement of electrons - typically at the metal-air interface.  Employing plasmons at the surface of AgNPs, whereby the researchers have succeeded in specifically growing these particles to be decahedron-shaped and uniform in size.  The principle idea was based on previous work, which demonstrated that crystal growth of decahedral AgNPs can be promoted by white-light illumination.  However, on this occasion the researchers targeted the di-electric moments in the plasmons more specifically - rather than use the white light, which contains a variety of wavelengths across the visible

DCN Corp - Scanning-electron micrograph (SEM) of an ensemble of highly uniform silver (Ag) nano-decahedrons.  Each particle is approximately 50 nanometers (nm) across.  Credit - © 2011 Springer Science+Business Media, LLC

spectrum, instead a more narrower spectrum was employed, which tailored to the frequency of the LSPs.  Testing by Yu and co-workers was undertaken on a range of light-emitting diodes (LED) of different wavelengths, and interestingly it was found that illumination with narrow-band lights sources did in fact facilitate the growth of uniform Silver (Ag) nano-decahedrons.  Yu went onto state "Also, when precursor solutions containing very small seed particles are irradiated with light of different wavelengths, we can form AgNPs of other shapes,"

During Yu's photo-assisted growth process - particles of varying porosity formed initially, but after several hours they reached a sphere of uniformity.  Some of the Ag nano-decahedrons grow to a relatively large size - though such particles are unstable, they are useful, as according Yu.  In addition, Yu explains that "the Ag atoms on their surface etch away and then serve as a source of Ag atoms for smaller nano-decahedrons," - "this dynamic process stabilises after prolonged irradiation and finally we have uniform Ag nano-decahedrons."

Yu and her co-workers are exploring the commercial practicality of their unique Ag particles - she states "Ag nano-decahedrons strongly enhance electrical fields when they are illuminated with light," - which can be used to detect trace amount of molecules on a solid surface.  Interestingly composite materials incorporating the team's particles could also be applied in bio-imaging and bio-sensing techniques, whereby the interaction of light with such materials could help to visualise anatomical structures or detect tiny amount of molecules.  Original article available here.

DCN Corp finds Yu's research extremely interesting - especially when considering that DCN Corp's Proof-of-Principle (PoP) research was based on surface-enhancement at a NIR laser inducement.  Moving forward - if you or your colleagues are interested in making the above a reality - please ensure to contact the company as soon as practicably possible.