Why the gold nanoparticles synthesized from leaf extract get negatively charged?

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Poonam G Gawali

Negative value of zeta potential indicates stability of your nanoparticles. It measures the effective electric charge on the nanoparticle surface. What is your negative value of zeta potential..? If it is -25mV to -30mV then its stable.

Syed Salman Hashmi

When synthesizing gold nanoparticles, the positive gold ions capped by the negatively charged functional groups of phytochemicals present in leaf extracts are responsible for the net negative charge.

Vijay Kumar

Thanks Salman...the major phytochemicals in the leaf extracts were flavonoids and tannin. How they can add negative charge on the surface of AuNPs?

Joseph Owusu

Thanks ... the major phytochemicals in the leaf extracts were flavonoids and tannin. How they can add negative charge on the surface of AuNPs?

Dear Vijay Kumar

The exact capping mechanism for nanoparticles is still an unsolved mystery. Questions like yours are answered hypothetically. Simply, when the precursor salt is dissolved in aqueous medium, positively charged gold ions are generated. Since opposite charges attract each other, the negatively charged phytochemicals (can be any phytochemical belonging to the classes you mentioned) starts capping the positively charged gold ions. Since the phytochemicals present upon the surface of AuNPs are negatively charged, your nanoparticles will be detected as negatively charged entities. Consider a DNA molecule as an example, which is negatively charged due to the presence of phosphate group at its surface. Similarly, the AuNPs you synthesized contains negatively charged phytochemicals on its surface.