Figure 1. (a) Schematic diagrams of longitudinal plasmonic nanomotor and (b) 3 by 3 array assembly by using electric tweezers.

Xiaobin Xu: Surface Enhanced Raman Scattering

Xiaobin Xu is a fourth year PhD student under the supervision of Prof. Donglei (Emma) Fan. The main focus of his research is on investigating innovative mechanisms and approaches to design, synthesize, and assemble plasmonic nanostructures for biochemical detection, delivery, and manipulation using surface enhanced Raman scattering (SERS).

Figure 1. (a) Schematic diagrams of longitudinal plasmonic nanomotor and (b) 3 by 3 array assembly by using electric tweezers.

Figure 1. (a) Schematic diagrams of longitudinal plasmonic nanomotor and (b) 3 by 3 array assembly by using electric tweezers.

Surface enhanced Raman scattering is an effect that can substantially increase the finger-print Raman signals of biochemicals, owing to the highly enhanced electric fields in the vicinity of noble nanoparticles. Recently SERS has attracted intensive research interest due to its great potential in label-free and multiplex biochemical detection. The enhancement of SERS can be so pronounced that single molecules can be readily detected. However, the practical applications of SERS for ultrasensitive biochemical detection has not been materialized. First, it is extremely difficult to create a large number of hotspots with controlled junctions at a low cost for sensitive and reproducible detection. Second, it is even more arduous to assemble the hotspots at desirable positions for location predicable sensing. Third, the sensing of molecules is largely carried out in a passive fashion. New mechanism is in dire needs to motorize the SERS nanosensors for active detection.

Xiaobin’s research focuses on address all the aforementioned problems. Longitudinal plasmonic nanoparticles (NPs) consisting of three functional layers were rationally designed and synthesized. The outer sensing layers, made of a large number of plasmonic Ag nanoparticles with controlled diameters and junctions, offer ultrasensitive biochemical detection, with an enhancement factor of 1010 on the entire surface of the NPs. The silica layer in the center supports the outer Ag layers and removes the plasmonic quenching effect. The inner metallic Ag/Ni/Ag core is the key component for robotizing the NPs into motors by the electric tweezers— our recent invention.  Arrays of SERS nanomotors can be manipulated and assembled into ordered arrays for location predicable sensing [Fig. 1], delivered to a single live cell amidst many for single-cell bioanalysis [Fig. 2]., and rotated with controlled angle, speed, and chirality for multiplex biochemical release and detection [Fig. 3].

Figure 2. Delivery of a nanomotor to a single cell admist many for single cell bioanalysis.

Figure 2. Delivery of a nanomotor to a single cell admist many for single cell bioanalysis.

This research may inspire a new paradigm of plasmonic nanosensors for biochemical sensing, delivery, and manipulation.

Figure 3. (a) Illustration of rotation controlled release. The plasmonic nanomotor is functionalized with Nile blue (in pink). (b) The release rate k monotonically increases with the rotation speeds of nanomotors.

Figure 3. (a) Illustration of rotation controlled release. The plasmonic nanomotor is functionalized with Nile blue (in pink). (b) The release rate k monotonically increases with the rotation speeds of nanomotors.