Dear Ladan,

You can read the below article, that this paper can help you and relate to your question.

https://www.witec.de/assets/Literature/Files/WITec-AppNote-SERS.pdf

Thanks, Dear Mehdi Babaei

Dear Ladan Ajdanian , yes, you can. SERS is a surface induced effect and to induce it you need a substrate that is solid. It happens that it could appear like a liquid dispersion of metal nanoparticles, (solid nanoparticles) in a liquid solvent. If you add your target molecule to this dispersion and it is adsorbed on the nanoparticle surface (or just get close to it, say 10 or less nm from the metal NP) and you shot a laser the NP can increase locally the electromagnetic field of your laser, and if the molecule is excited and emits its Raman spectrum, this scattered radiation will be also enhanced by the surface of the NP.

Another way to perform the SERS experiment is like the one described in the link provided by Mehdi Babaei there you deposit the NP suspension over a substrate, like a microscope slide, allowing the solvent to evaporate, so that the metal NP´s remain in the glass surface, then you add your sample solution and again, allow it to evaporate. Some molecules could be attached or bonded to the metal NPs and when you shot the laser over the area loaded with sample and NP´s you can get something like it is described on the Witec article.

Most commercial SERS substrates are just that, some kind of NPs deposited on some kind of solid support (silicon, glass, paper... )

There are another kind of SERS substrates, basically metallic surfaces highly structured with nanostructures or nanopatterns, like the rough electrodes where the effect was initially described in 1974. Today it is possible to built nanostructured sustrates by means of nanofabrication techniques like litography and nanoimprint lithography. This is my field of work. Here you can make a regular structure over a supporting material like silicon, glass, polymers, or even metals. If your material is not a metal (or rich free electrons material) you need a plasmonic material on top of your structure to produce the SERS effect, something you can achieve by evaporating, by sputtering, by electrodeposition, by laser ablation, etc. There another kind of substrates that produce SERS like carbon nanotubes (with or without metal coat), some oxides also show this effect. With these solid substrates the way to procede is loading a tiny drop of your sample, often leave it dry and shine the laser on the spot wher the drop was deposited (this is the way I do it). Another way to deposit the sample consist in submerged your solid substrate in a solution of your sample, leave the substrate in the solution for several hours or even days to allow the molecules attach to the surface, then romove the substrate and clean it with water or the appropriate solvent (in this way only the bonded molecules remain on the surface), dry and perform the laser irradiation.

SERS can be done in shot or image mode. When you use the shot recording you select an area or region of interest in your substrate (where you think there are molecules), focus properly and hit the laser recovering the SERS spectra. In this case you can be lucky and get a nice spectrum, or just a bad one or nothing at all.

In the image configuration, -that showed in the Witec paper- you select an area of interest in your substrate and then define in the software the area you want to scan, so the spectrometer registered a lot of spectra from different points in the region. The software allows you to define filters, each associated to a Raman band, and then it shows you where in the image this band is present, where the intensity is higher the more concentrate is the analyte or the best positioned are the molecules on a hot-spot. This is very useful because you can identify different moleculecues simultaneously. Imagine your sample have two molecules (A and B) they are mixed but selecting a filter for a characteristic band of each molecule allow you to differenciate them.

Hope it helps.

Dear Manuel Gómez

Your answer is so good and sutiable for me.

Thanks a lot.

Dear Ladan,

I'd like to add a comment to the very nice answers above.

It is certainly possible to use a confocal Raman microscope to get SERS spectra. However, results will depend a lot on the kind of substrates you have, of course.

The thing is: many SERS substrates rely on the formation of "hot-spots", where most of the SERS signal is coming from relatively few spots. For these situations, a confocal setting will likely miss the signal from a lot of spots.

If you use colloidal substrates as liquids (e.g. as droplets made of a mix of metal colloid and analyte), then going for a confocal configuration will sensibly decrease the signal intensity, with respect to a non-confocal setting. For these samples, best results are obtained using a low-magnification objctive (10x or 20x), with a low N.A. With a bigger focal volume, more hot spots are probed, of course.

If you go for solid substrates, then results will depend on how "rough" your substrates are. For highly 3D porous substrates (e.g. NP deposited on paper), then confocality won't be and advantage, and best results will be obtained using a low-magnification objective.

A confocal configuration, on the ohter hand, will be very useful in case of relatively flat, homogeneous 2D SERS substrates. Or in case you want to locate NP aggregates inside complex structures (such as cells), or in general every time you want to pinpoint with a high later resolution where your signal does come from. However, spatial resolution always comes at the expense of signal intensity, as a general rule...

Dear professor Alois Bonifacio

In fact, this is the best answer for me.

Thanks a lot.

Best Regards

It is definitely possible. It also depends on the roughness/height consistency of your SERS substrate. The more homogeneous the 2D SERS substrates are, the more seamless you can scan the area without adjusting the focal plane everytime. In fact, 3D SERS platforms will provide a better tolerance to laser misalignment and you do not have to re-adjust your focal plane. --------------------------------- High quality Silver (Ag) nanocubes and Surface-enhanced Raman Scattering (SERS) substrates available at: https://silverfactorytechnology.com/

Dear Ladan,

Yes it is very possible, and well studied. In addition to the very helpful answers above, I would like to add the following: choose your laser settings appropriately! I worked with two avenues of interest, nanoscale roughness (a solid substrate) enabling the enhancement, and nanoparticles on a solid substrate to provide enhancement (with possible hot-spots). If you choose the nanoparticle route, it is very easy to provide enough laser power to damage nanoparticles with sub-nanometer features or nanoparticles made from poor conductors. When I encountered this first, I thought my experiment failed, but it turned out I was just ablating my nanoparticles. I also found, as Gc Phan mentioned, that having a consistent interaction volume, or focal plane, was essential to providing QUANTITATIVE results over just QUALITATIVE numbers. Here is a section from my thesis describing this,

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The most important similarity between the samples is not just their identical preparation, but also the establishment of the optical plane where the laser was focused. The plane of focus determines the interaction volume of the laser in the sample and can easily be tuned within thin films created on the sample by the poly-L-lysine or dye, making for inconsistent interaction volumes and artificially affecting the maximum signal obtained in counts/sec. In order to circumvent this, each sample was first moved so that an area with no optical sample present could be interrogated by the laser. The laser was then focused using an auto-focusing routine which sought to maximize the Raman signal of the Si spectral line at 520 cm\textsuperscript{-1} by adjusting the height of the sample. Once this height was established, samples were then mapped with all room lights turned off. Any further inconsistencies between samples was then limited to the distributions of particles and dye on the poly-L-lysine coated Si substrates.

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I hope this helps!

Cheers,

Rick