We have a 1mw-100mW 785nm Raman spectrometer. We have tried many commercially available SERS substrates (paper and AuNP). We are unable to see any Raman signal. Ideas on what we may doing wrong or how best to focus the substrate. We are looking at 0.1% solution of various drugs.
Thank you
Dear,
- Verify that the laser alignment and exposure time are adequate.
- Then as a start please start with pure 100% ethanol and try to establish a calibration curve with lower concentrations (1%, 0.1%, etc...) to verify that you have a Raman signal; and try to estimate the sensitivity (how far you can go) of the microscope.
- Then you can go for other products with the appropriate concentrations.
Thank you. Will try tomorrow and update you with results. Warm regards
What drugs are you measuring?
Depending on the drug, you may not require SERS - we have done quantification of drugs in aqueous and human serum samples using Raman spectroscopy, focussing through (rather than on) the solution to maximise the interaction of the focal depth with the solution. The verification process is initially similar to that proposed by Arno Germond .
You need a strong Raman scattering molecule to start with....usually some fused ring structure. The point is that you can detect amounts well below normal detection limits using SERS. Google Scholar SERS and start reading to get ideas.
785 nm on AuNP colloids in contact with the molecule of interest should work fine. Do you have a tight focus (microscope lense, 180 degree geometry) setup? There is some angular dependence for SERS, but having a high NA should
Also, remember that your Raman peaks with the SERS substrate will be shifted from corresponding peaks from normal Raman scans. Bear this in mind as you assign peaks for identification.
If you are reconstituting your sample, try using a buffer instead of for example D.I as this eliminates pH effects.
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