Aggregation of Gold Nanorods by Optical Forces for SERS Biosensing in Liquid Environment

Here we report on a novel concept of label-free, all-optical SERS biosensor for proteins detection in liquid, based on the laser-induced aggregation of gold nanorods (NRs) in proteins buffered solution. Commercial gold NRs dispersed in deionized water and capped with CTAB molecules are mixed with the target proteins dissolved in PBS in a glass microcell. A laser beam is then focused on a micron scale spot inside the liquid solution. Due to repulsive optical interaction, NRs-protein complexes thermally drifting through the laser spot pushed towards the bottom of the glass microcell. Here they stick and accumulate, forming SERS-active aggregates. BSA has been used as a model protein to test the sensor performances. We reach sensitivities down to 10^-7 M (blue line), whereas solution phase Raman spectroscopy of BSA is already impossible at concentrations of 10^-4 M (black line). This methodology can pave the way to a new generation lab-on-chip sensors that implies user-friendly experimental set up allowing for highly sensitive vibrational spectroscopy of biomolecules in their natural habitat.

gucciardi@me.cnr.it