That is correct

Which concentration are you using for Uv-Vis spectroscopy?

Do you have other means of checking your particle size (e.g. DLS?) ?

Dear Rabia look:Biophysics 11/2013; 58(6). DOI:10.1134/S0006350913060146

Inorganic Materials 10/2013; 49(10). DOI:10.1134/S0020168513090094 · 

Dear you should choose the range of 200 to 800 nm for UV VIS spectroscopy. Moreover silver nanoparticles also show colour variation depending upon size variation.

Cheers

Dear Rabia,

This peak shift may be due to presence of active elements / components which may be present over your particles , like a capping layer the active elements present in the plants will adhere to the surface of the nanoparticles during reduction of AgNO3 ; do one thing , you can check with DLS for size distribution of your particles , and you should check with the concentration of your sample before dispersion for analysis , may be centrifuge can be performed , so first try to check out the effect of active elements [ plant extract ] adhered to your nanoparticle system and variation of colours due to change in particle size , good luck.

Actually I do not think the size variability can explain the shift. The Smaller Ag nanoparticles should have a peak around 400nm (eg 7nm particles), and the peak shifts to larger wavelength for larger particles.

thanx Respected Orsi :

       i m taking 1,2,3........10 ml of plant extract in 10 ml of 1mM AgNO3,,and take uv-vis reading after 12, 24, 48, 78 hour,,,, but the results are same although absorbance increase but position is same i mean lamda max is around 320 to 350 nm. we have SEM (scanning electron microscopy) but not DLS.

respected Vikram:

                          thanx,,, can you help me to tell the procedure that how can i check out the effect  of active element adhaere on surface of nanoparticle,, n what can i do if i dont have DLS facility

Dear Rabia Shafiq,

I agree with dr. Vikram that you should first compare your UV-vis spectra with the UV-vis spectra of the plant extract alone, without nanoparticles, to see if the peak is due to something inside the plant: this is likely, since many bio components absorb UV light.

Dear Rabia. Did you read my article? From the article:The UV spectrum of tea (Fig. 1) has three absorption bands, centered at 226 (not shown in Fig. 1), 296, and

370 nm. The bands can be assigned to arbutin, С12Н16О7 (226 nm); quercetin, С15Н10О7 (296 nm),and pheophytin (370 nm), which are present in tea. It

seems likely, however, that the spectrum, corresponds to

all of the substances present in tea. The absorption spec

tra of reaction mixtures of tea and AgNO3 solutions

contain plasmon bands of Ag nanoparticles, centered at

410 (0.1 mL) and 450 nm (0.2 mL). Best regards.

Dear Rabia,

Many researchers are provided valuable suggestions. In addition, I too think you should take separate UV-Visible analysis for extract and then go with nanoparticle colloids. From this result, you can come to conclusion which peak is SPR peak of Ag. As Prof.Yuri suggested that the extracts peaks comes only between 200 and 400nm. check out separately and let us see.

Best regards

Hello Rabia,

Spherical AgNPs (50-90 nm) exhibit a SPR peak centred between 400-480 nm which is dependent on NP size and the surrounding liquid medium as per Mie's Theory. However, in case of a a significant population  of disc-shaped NPs or other forms, a SPR peak may be expected at 500 nm or beyond. Pure ionic Ag exhibits a SPR peak in the UV range of 270-300 nm. Considering your peak positions for AGNPs, a narrow size distribution (5-25 nm) may be assumed. The lower values of SPR peak may be attributed to the presence of ionic Ag species in the colloidal solution. It is also noteworthy to mention that pH also plays a role in the shift in SPR peak. UV-vis analysis of NP solutions is not  conclusive . I suggest you to carry out TEM and DLS to support your findings. Thanks and regards. 

I think your sample does not show SPR and the result you mentioned show band-band transition in silver nanoparticles. You check the size of your samples, if it is too small then try to increase the size of Ag nanoparticles and again check its SPR peak.

thanks Abhisek Sasmal, can u kindly suggest me some protocols on comprehensive  SPR peak  of AGNPs, and tell is dilution factor effect the SPR peak or not? i mean by increasing the dilution factor the spectrophotometric analysis disturb or not?

Please wash your sample at least three times with a suitable solvent and check SPR peak again.

That is correct