Self-assembled noble-metal nanoparticles and applications

F.  Toderas, M. Baia and S. Astilean

Faculty of Physics, Babes-Bolyai University Cluj-Napoca, Romania, E-mail: ftoderas@phys.ubbcluj.ro 

Much recent research effort has been focused on the fabrication of large-area periodic nanostructures with reasonable control over their size and periodicity. In particular, highly organized and regular arrays of noble-metal nanoparticles are of great research interest for optimizing many current applications in ultrasensitive surface-enhanced spectroscopies, biosensors, chemical sensors and photonic devices 1, 2.   
Fabrication of nanostructures by self-assembled methods has attracted much attention due to their simplicity and flexibility. A method for control of surface morphology is through assembly of small, spherical, uniformly sized particles at an interface, imparting a repeating feature size that is dependent upon the particles used. Gold colloids were prepared and self-assembled onto glass substrates by using an organic coupling agent as a 3-aminopropyltrimethoxysilane (APTMS)3. The size and spatial distribution of immobilized metal nanoparticles was characterized by transmission electron microscopy (TEM). The substrates have a surface roughness that is defined by the colloid diameter (16-18 nm) and an average interparticle spacing that is continuously variable. Optical extinction spectra of self-assembled noble-metal monolayers exhibit well-defined surface plasmon resonance peaks located at 524 nm. Gold assemblies could play a major role in bio- and chemo- detection because they are able, under a resonant laser excitation, to induce a huge local electromagnetic field  and sense at the nanoscale the local chemical environment 
In order to make correlations between nanometer-scale morphology, surface plasmons resonances and the amplification of surface-enhanced Raman scattering (SERS), the nanostructures were locally characterized by using atomic force microscopy (AFM), optical extinction and reflection spectra as well as SERS measurements. We believe that the ability to optimize the surface plasmon resonances can have impact on several analytical applications of optical spectroscopy, mainly in Raman scattering (SERS), infrared absorption and molecular fluorescence.  

References :
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2. J. B.  Jackson, S. L. Westcott, L. R. Hirsch, J. L. West, N. J. Halas,  Appl. Phys. Lett., 82, 257, (2003).
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