Evaluation of silver nanoparticles synthetic potential of Couroupita guianensis Aubl., flower buds extract and their synergistic antibacterial activity

Abstract

The present investigation demonstrates Couroupita guianensis flower buds extract mediated synthesis of stable silver nanoparticles (AgNPs). Instant formation of AgNPs was primarily confirmed by the appearance of yellowish brown colour and characteristic silver SPR band in the UV-visible spectrum. Elemental and crystalline natures of the AgNPs were identified from EDX and XRD pattern, respectively. Spherical morphology and the mono-disparity were revealed from TEM and AFM images. The particle size ranged from 5 to 30 nm and average size of 17 nm was consistent in XRD, TEM and AFM measurements. Possible reduction and stabilizing agents, viz., phenolics, flavonoids and proteins were identified from the characteristic FTIR peaks representing their functional groups. The strong antibacterial activity of synthesized AgNPs against Gram-positive and Gram-negative bacteria exhibited the potential for the formulation of synergistic bactericides by combining antibacterial properties of Couroupita flower buds extract and silver salts for biomedical applications.

Keywords: Antibacterial activity; Couroupita guianensis; Flower buds; Silver nanoparticles; Synergistic activity.

Fig. 1

UV–visible analysis of AgNPs showing a typical SPR band from 415–420 nm recorded as a function of reaction time of 10⁻³ M AgNO₃ aqueous solution with Couroupita guianensis flower bud extract

Fig. 2

XRD crystallography of phytosynthesized AgNPs showing four prominent peaks of a typical silver crystal

Fig. 3

TEM micrograph and SAED pattern of AgNPs. a TEM micrograph depicting uniformly dispersed spherical AgNPs. b SAED pattern revealing crystalline nature of AgNPs

Fig. 4

AFM analysis of AgNPs. a AFM 3D image depicting spherical shape of AgNPs. b Histogram showing the size range of AgNPs

Fig. 5

EDX spectrum showing the presence of silver nano crystallite

Fig. 6

FTIR spectra. A Flower bud extract. B Stabilized AgNPs showing peaks indicating functional groups of phenolics, aromatic compounds, alcohols and proteins

Fig. 7

Reduction reaction of silver ions to nanosilver by Quercetin

Fig. 8

Antibacterial activity of AgNPs on Gram positive and Gram negative strains. 1 AgNO₃, 2 silver nano solution, 3 flower bud extract, 4 gentamicin, 5 sterile distilled water