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Site Updated:
09/18/2008

Surface Enhanced Raman Scattering

Objective

To design a tunable plasmon resonant SERS active substrate with enhanced local electromagnetic field for ultrasensitive biomolecule detection.

Background material

Raman spectroscopy provides a label-free technique for biomolecule detection due to the distinctive signature of each molecule vibrational bands of chemical bonds. However, the scattering cross section of Raman processes is extremely small. Therefore, in order for practical applications, Raman signal must be significantly enhanced. Nano noble metallic particles have exhibited exceptional optical properties when interact with visible-infrare lights. The collective oscillations of conduction electrons of nanoparticles upon excitation, donated as surface plasom (SP) or particles plasmons, induce strong local and scattered fields. As a result, these strong local fields can be used to enhance the Raman intensity by amplifying several or even tens orders of magnitude, known as surface-enhanced Raman scattering (SERS).

Fig. 1: Schematic illustration of tunable plasmonic resonator (TNPR)	Fig. 2: Optical microscope image (Left) and SEM image of TNPR (Right)

Fig. 3: Measured enhanced Raman spectrum of pMA via TNPR

Results

Our current researches are focus on developing a good SERS active substrate. The plasmon resonance of metal/dielectric multi-layered nanoparticles, named tunable nano-plasmonic resonantor (TNPR), has been exhibited several distinctive properties including significantly enhanced plasmon resonances and tunable resonance (Figure1). By varying the thickness of dielectric layer, we are able to fabricate the plasmon resonant frequency of TNPR at laser excitation (Figure 2). At resonance, the strength of local electromagnetic field near the TNPR surface is strongly enhanced making TNPR a great candidate serve as s surface-enhanced Raman scattering (SERS) active substrate. We have examined the SERS response of individual NPR by directly comparing with non-enhanced absorbates. Effective SERS enhancements of ~10^10 are observed experimentally for individual NPR which opens the door to applications in ultrasensitive biomolecular deteaction (Figure3). Furthermore, TNPR nanofabrication is reproducible and precisely located at desired location to avoid nanoparticle cluster aggregation for SERS measurement errors occurred in other methods. Therefore, our measurement brings a more reliable SERS measurement for individual nanoparticles. The merits of TNPR open the door to applications where it can be used as the detection tool for integrated on-chip devices.