The plasmon band shifts to higher values with the increase of tomato concentration in the aqueous extract. At concentrations higher than this, the plasmon band shifts to 540 nm, and the extinction selleck products coefficient of the band decreases appreciably. Here, the tomato extract of 5:5 composition has been used throughout. Figure 2 UV–VIS absorption spectra of GNP at different compositions of tomato extract and SDS capped GNP in check details alkaline medium. UV-VIS spectra of (A) GNP at different compositions and (B) SDS-capped GNP. Insets
are digital photographic images of A and B. Shifting of gold plasmon band to the higher value may be explained as follows: tomato extract is a strong reducing agent but not a good capping agent. So, it induces rapid nucleation but cannot restrict FRAX597 cost the growth of gold nanoparticles. Hence, polydispersed gold nanoparticles are observed. When we use tomato extract (100%), the band shifts to 540 nm and the extinction coefficient decreases appreciably.
This might be due to colloidal instability. The polydispersity and the colloidal instability (agglomeration tendency of gold nanoparticle) may be the reason for a broad spectrum of gold sol along with a shift in the peak position. The shifting of the peak position may be related to the increase of the size of gold nanoparticles. To examine the sensor properties of the GNP, the solution was made Tyrosine-protein kinase BLK alkaline by adding different amounts of NaOH (0.15 (M)). For these studies, the pH of the solution was maintained near 9 to 9.5 by adjusting the amount of NaOH in the solution, and a surfactant SDS was added to stabilize the medium. Here, SDS acts as a capping agent, due to which the SPR band shifts to 532 nm (Figure 2B). A comparatively sharp spectrum with absorbance at 532 nm was observed in this case. This can be explained from the fact that SDS, being a strong capping agent, stabilizes the gold nanoparticles as soon as nucleation happens and so restricts the maximum size of the nanoparticles. As a result, we obtained nearly
monodispersed GNP. Methyl parathion was added to these alkaline solutions containing SDS in varying concentrations ranging from 10 to 200 ppm, and the change of absorption coefficient was observed. As soon as methyl parathion was added, we observed a new peak at around 400 nm in addition to the peak found at 532 nm. More interestingly, absorbance at 400 nm, the newly found peak, is seen to increase when the concentration of methyl parathion increased from 10 to 200 ppm (Figure 3A). Figure 3 UV–vis spectra of GNP and with methyl parathion, calibration curve (absorbance versus methyl parathion), and control spectrum. (A) UV–vis spectra of GNP and GNP with various concentrations of methyl parathion 10 to 200 ppm; (inset) digital photographic images of color changes due to addition of methyl parathion.