Is it possible to observe redshift in plasmon resonance wavelength of gold nanoparticle colloids (13nm) by adding different concentration of glycerol to it?
Hi. This is a very interesting discussion. Due to influence of the glycerol refractive index, you can observe a shift by adding glycerol (if gold nanoparticles are in aqueous suspension). It is well-known that LSPR is shifted because of either the size and shape of the NPs or the refractive index of the surrounding medium. However I think the former article has a 'lack' in its discussion: Spherical particles of 15nm cannot be compared to nanorods of 100nm... both the spectral range where their LSPR are measured and their volume are different. Taking into account this fact, in my opinion a comparison of the 'resolutive power' of both systems is necessary (LSPR shift / LSPR wavelength). As matter of fact, under this consideration spheres become much more sensitive to changes in the refractive index of the sorrounding medium. Another question is the total contribution to Extinction of the scattering. In the case of tiny spheres there is a negligible contribution. On the other hand, nanorods of 100 nm or bigger can scatter even more than they can absorb, so scattering contribution to extinction measurements should be quantified. For instance, a gold nanosphere of R=10nm has 'no scattering' contribution and its LSPR is at 518 nm for n=1.4. On the contrary, a gold nanosphere of R=30nm has a shift from the absorption peak to the extinction peak of 4 nm -from 529nm to 533nm- at n=1.4. That is, both spheres will show similar shift in extinction, but only the smallest one takes into account only absorption (LSPR). In my opinion, the red shift can be demonstrated with small spheres in an easier way.
Thank you Prof. Juan for the somewhat in-depth discussion. But in my case 13 nm particles didn't show significant shift with change in glycerol concentration. So I am planning to execute the task with bigger sized spherical gold nanoparticles.
I am attaching herewith a PDF where 100 nm gold nanoparticles have been used.
Kindly suggest me whether bigger sized spherical gold NPs will work better or not.
Hi again. In my humble opinion smaller gold particles will give you a sharper LSPR (R=10-20 nm). You can also use other liquid, like PVP, with a bigger refractive index (1.57 approx.) than glycerol (1.48). Good luck
Hai
In My opinion, Surface Plasmon Resonance of gold nanoparticles not only depending on size and shape but also dependent on dielectric constant of surrounding medium. Please see the attached publications, may be helpful to clarify your doubts.
The inherent difficulty in this experiment is the relatively low refractive index sensitivity of spherical gold nanoparticles. Have you considered using rods or particles of different shapes, which will give you better sensitivity?
No I have not considered for other structures. I am only interested in spherical NPs which falls in visible domain
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