Self-assembly of α,ω-aliphatic diamines on Ag nanoparticles as an effective localized surface plasmon nanosensor based in interparticle hot spots

The adsorption and self-assembly of a, alpha,omega-aliphatic diamines on silver nanoparticles is studied in this work by surface-enhanced Raman scattering (SERS) spectroscopy and plasmon resonance. These bifunctional diamines can act as linkers of metal nanoparticles (NPs) inducing the formation of hot spots (HS), i.e. interparticle junctions or gaps between metal NPs, which are points where a huge intensification of the electromagnetic field occurs. In addition, the dicationic nature of these diamines leads to the formation of cavities just at the induced hot spots which can be applied to molecular recognition of analytes. The influence of the surface coverage and the aliphatic chain length in diamines on their self-assembly was tested by the vibrational spectra and correlated to the different plasmon resonances of the dimers detected in the extinction spectra. These factors can be used for tuning the plasmon resonance of dimers formed by two metal nanoparticles where interparticle hot spots are formed. Finally, the analytical potential of these functionalized Ag nanoparticles is demonstrated for the trace detection of the pesticide aldrin.