SERS Substrate

Written by Takao Fukuoka, Oct. 2001.

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1. Principle

Metal colloid and its aggregation is stabilized even in aqueous medium by employing the interaction between dispersing particles.

The obtained dispersion is translucent and has slight Rayleigh scattering under 400 nm and no recrementitious absorption in visible nor near infrared region. The dispersion is fluid with low viscosity, so that it can be mixed with aqueous solution containing sample very easily.

This new stabilized aggregation is expected to perform excellently as a new substrate for Surface-enhanced Raman Scattering (SERS).

2. Amazing Stability of Aggregation

Plasmon absorption of metal colloid is a well-known indicator of aggregation as well as particle size.

Absorption spectra above show that three kinds of aggregated gold colloid ((1), (2), (3)) are stabilized in a aqueous medium for a long time over 20 days. Normal aggregated gold colloid tends to precipitate within days and doesn't show plasmon absorption any more.

These spectra also indicate aggregation of gold particles are under control. In selected situations, some aggregated gold colloid show excellent stability over months.

3. SERS Substrate with Excellent Performance

The Raman shift of pyridine 2.5mM aqueous solution is measured employing the substrate and commercial Raman spectrometer with Nd-YAG laser (Nicolet Magna 650 with Raman module).

Ring breathing (1010 cm-1) of pyridine appears immediately after mixing the substrate and analytic solution, while normal Raman gives weak signal even in 63mM concentration.

In addition, it is to be noted that this substrate was prepared by aggregation of gold colloid 138 h before mixing with analytic solution. State-of-the-art technique for synthesis of gold colloid elicits more availability and feasibility as SERS substrate

A bar chart shows effects of gold colloid on SERS intensity and stability. Particle size from 60 to 80nm is appropriate for SERS, which is in agreement with many published reports. Commercial gold colloid found elsewhere are, however, not good for SERS substrate in intensity and stability. The aggregated commercial gold colloid lost half of its activity within days, while homemade gold colloid found by our efforts holds over two months.

4. Now, SERS comes in your pocket tool

Previously, no one could prepare SERS substrate a few days before measurement. Now, with this stabilized substrate, you can !

This substrate makes SERS convenient, repeatable and reliable without much effort.