Localized surface plasmon resonance

Localized surface plasmon resonances of AgNPs depend on the size, shape, as well as the surrounding dielectric medium. Usually the spherical nanoparticles in the range of 10–50 nm show an extinction peak at ~400 nm, leading to a characteristic yellow colour and changing the size of spherical particles can induce small shifts in the peak position.

Figure 1 shows the UV absorption of synthesized AgNPs, which is capped with phospholipids membrane. The fresh synthesized silver nanoparticles have a yellow colour which has higher absorption than the capped AgNPs. But they have a short lifetime and their colour changes to dark yellow, and then black suspension and slowly turn to macro particle and settle. AgNPs have a localized peak at 405 nm and their colour shift to darker by adding lecithin which causes their absorption to reduce. This is because of the lack of absorption for lecithin suspension at this position