I want to calculate EF in SERS spectra for powder of Azo-dye molecules and an aqueous solution of that. I know I must use that equation. but I don't know what is concentration of that powder(solid) of Azo-dye molecules. Can I put this 100? I think that it's pure(100%).
Thanks
Hi Arezou
From your question I am assuming you are doing the Raman of your Azo solid and SERS of your Azo solid in solution and then using them together to calculate an EF value.
First to answer your question, yes you can assume your solid azo is pure (as long as you've done the HNMR and so on to roughly prove this), because as you probably will know the calculation of the EF value includes many estimations so is not a super accurate number anyways.
But I would also suggest you to make a concentrated solution of your azo dye to acquire a Raman spectrum instead of using the solid directly. This is because when using the solid you would often get a lot of fluorescence signals. also more importantly, in order for you to calculate your EF value, you'll need to know how much effective analyte molecules there are. If you are doing this with a solid, you won't be able to know this number. because the surface of the solid would be lumpy so you won't be able to estimate a surface area, also you won't be able to know how deep the laser has penetrated your sample. Therefore doing a Raman of a solution would be much more accurate and convenient at the same time.
Thanks for your answer, But what concentration I can consider instead of solid one? As you know I obtain different EFs when I choose different concentrations. So what do you think about it? How Can I choose the best one?
Hi Arezou
First to answer your question, I would suggest you start off trying a 10-2 M solution and make your way up. The more concentrated your solution is the stronger signal intensity you'll have but also probably more fluorescence as well. So the trick is to find a good balance between signal intensity and fluorescence. Of course this would largely depend on your sample and equipment as well, so you might need to test out a few different concentrations before you decide on one.
The other thing is, for different concentrations, your EF value should be technically the same (but realistically a little bit different due to some experimental error). I take that's what you meant by saying 'obtain different EFs when I choose different concentrations'?
Ok. I understand what you say. As you know we obtain EF by equation 2 in attachment. So I calculate our EFs by different concentrations of Azo dye molecule instead of solid one and I obtain different EFs. In this case, Do you think it's ok if I use different solutions and obtain different EFs? How can I compare my results with other authors?
Hi Arezou
I know where the problem is now after I've read your attached paper. I must say I can't agree with their way of calculating EF values.
The true definition of an EF value should be
(SERS intensity x effective SERS analytes) / (Raman intensity x effective Raman analytes)
In the equation you are using at the moment, they have simply used their 'analyte concentration' as 'effective analytes' which is just simply too much of an estimation and this is why:
In SERS, the effective analytes are the molecules that are within the plasmonic region of your enhancement material. normally this is only a few nanometers from the surface. This means your effective anaytes would be the amount of molecules you have that is within both your laser beam and plasmonic region.
On the other hand, in Raman there is no plasmonic region to worry about, so the amount of effective NPs is all the analytes in the laser beam. This means if you are hitting your laser into a 1 cm deep solution, than here your effective Raman analytes would be the amount of molecules in that volume.
Normally EF values would range from 10-4 to 10-9. It must be said that everyones EF value is an estimation of some kind. So we are all comparing rough calculations with each other anyways, which is why a high EF value is normally only seen as a plus but not a big selling point in good papers.
I've a attached a PDF which has detailed steps of how to calculate EF values. Hope it helps.
Wow!!!!
Thank you very much. Your answer was very useful. I don't know how can I say "Thanks"! Thanks Mr. Yikai Xu .
Yikai Xu
hello,
can you please assist me, how to calculate "h" in Vthiol
Hi Gagandeep Kaur
If you picture your Raman analysis, there will be a thickness to the laser spot making it a volume that you are probing. More specifically, your laser spot is likely to be round, and there will be a thickness to it, so your probe volume is a cylinder shape and "h" is the height of this cylinder. If you are using a commercial instrument, you might be able to get this number off your supplier. If you need to determine this yourself, then you can use a model sample such as a silicon or polymer film to get a rough estimate. First focus the sample so you get optimal signal, then slowly move it out if focus until the signal disappears. The distance that you have moved is "h".
Yikai Xu
Is penetration depth changes with type of excitation like if using 532nm laser and 785 nm laser. will it change or its just a instrument factor?
- Badges
- Science topic
- Similar topics
- Correction