Synthesis of silver nanoparticles employing Polyalthia longifolia leaf extract and their in vitro antifungal activity against phytopathogen

Abstract

The P. longifolia mediated silver (PL-AgNPs) nanoparticles are very stable and efficient. UV-Vis spectroscopy, dynamic light scattering (DLS), X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDX) were used to characterize the produced AgNPs. UV-Vis analysis showed a characteristic peak at 435 nm corresponding to surface plasmon resonance. The synthesis process was spectrophotometrically optimized for various parameters. After optimization, highly stable AgNPs were prepared using 3.0 ml of P. longifolia leaf extract, pH 7.0, 1.0 mM AgNO₃, and 60 °C. The zeta potential was measured by DLS, which showed -20.8 mV and the PDI value was 5.42. TEM and SEM analysis shows a spherical shape of the synthesized nanoparticles, and the size was measured between 10 and 40 nm. EDX analysis showed intense peaks from silver and oxygen and small peaks from various metal atoms such as Na, P, S and Al indicating their presence in trace amounts. The average size of the PL-AgNPs was 14 nm. The phytochemical analysis shows that the presence of alkaloids, essential oils and saponins seems to be responsible for the synthesis of nanoparticles. PL-AgNPs were further investigated for their antifungal activity against Alternaria alternata. The minimum inhibitory concentration (MIC), minimum fungicidal concentration (MFC) and effect of nanoparticles on cytomorphology of A. alternata have also been reported. Biosynthesized nanoparticles have proven to be inexpensive, environmentally friendly, stable, easily reproducible, and highly effective against plant-pathogenic fungi.

Keywords: Antifungal activity; Cyto-morphology; Green synthesis; Polyalthia longifolia; Silver nanoparticle.

Fig. 1

A. UV–visible spectrum of plant extract and AgNPs, B. before, C. after reduction.

Fig. 2

P. longifolia aqueous leaf extract phytochemical screening i. Alkaloids, ii. Carbohydrates, iii. Tannins, iv. Volatile Oils, v. Phytosterol, vi. Saponins and vii. Flavonoids.

Fig. 3

Optimization of synthesis of PL-AgNPs at different A. Concentration of AgNO₃, B. pH, C. Temperature D. Time.

Fig. 4

Zeta potential of synthesized PL-AgNPs.

Fig. 5

X-ray diffraction of synthesized PL-AgNPs.

Fig. 6

A-C. SEM micrograph of synthesized PL-AgNPs, D. EDX spectrum of elemental composition of PL-AgNPs.

Fig. 7

A-C. TEM micrograph of synthesized PL-AgNPs, D. Histogram of particles size.

Fig. 8

Antifungal activity of PL-AgNPs against A. alternataA.P. longifolia aqueous leaves extract, B. 100 ppm PL-AgNPs, C. 200 ppm PL-AgNPs, D. 300 ppm PL-AgNPs, E. 400 ppm PL-AgNPs, F. 500 ppm PL-AgNPs.

Fig. 9

MIC and MFC of PL-AgNPs (A). Minimum inhibitory concentration, Control, P1: 500 ppm, P2: 250 ppm, P3: 125 ppm, P4: 62.5 ppm, P5: 31.25 ppm, P6: 15.62 ppm, P7: 7.81 ppm. (B). Minimum fungicidal concentration, Control, P1: 500 ppm, P2: 250 ppm, P3:125 ppm, P4: 62.5 ppm, P5: 31.25 ppm, P6: 15.62 ppm, P7: 7.81 ppm.