Tuning assembly pattern of nanoparticle droplet deposits by varying nanoscale interaction

Evaporation based self-assembly technique offers easy and affordable methods for ordering nanoparticles in crystalline structures and design complex materials. Investigating nanoscale interactions are essential for tunable assembly of colloidal nanoparticles on solid substrates. Using in-situ contact angle meter and ex-situ scanning electron microscopy, we present a direct correlation of the drying profile of nanoparticle suspension with observed deposition pattern on hydrophilic silicon substrate. The assembly pattern of DNA-coated nanoparticles via stick-slip motion gives rise to periodic concentric rings in a stripe-like micropattern for a certain nanoparticle concentration range. The results indicate that the interplay between “stick-slip” motion of the droplet contact line and coulombic and steric NP interactions control the formation of the observed structures. The change in nanoparticle shape to gold nanorods leads to mixed mode of evaporation and formation of surface pattern that exhibits multiscale assembly.  Further, we will present the plasmonic application of the deposit pattern in determination of surface-enhanced Raman scattering signal of Rhodamine B analyte showing signal enhancement by factor of 7.6 * 10⁵ and detection limit to concentration as low as 10⁻⁸M.