Engineering novel gold nanoparticles using Sageretia thea leaf extract and evaluation of their biological activities

Abstract

An eco-friendly method for biogenic synthesis of gold nanoparticles (AuNPs) was developed using leaf extract of Sageretia thea as a reducing, stabilizing, and capping agent. AuNPs synthesis was immediately confirmed from a color change in the gold solution from yellow to ruby red. UV–visible spectroscopy technique showed a sharp narrow peak at 535 nm that confirmed the presence of spherical and cubic-shaped nanoparticles. SEM and TEM analyses revealed that the average size of AuNPs was 36 and 13 nm, respectively. XRD revealed the pure crystalline nature of AuNPs. The sharp narrow peaks corresponding to (111), (200), (220), and (311) Bragg's planes at 2θ position denoted the cubic shape of AuNPs with a crystallite size of 18 nm. FTIR analysis showed the existence of various reducing metabolites, which capped over the surface of Au. The biological efficacy of AuNPs was tested against Klebsiella pneumonia, Staphylococcus aureus, and Bacillus subtilis. K. pneumonia was the most susceptible strain with an inhibition zone of 12 ± 0.2 mm (200 µg/mL dose), while the most tolerant strain was B. subtilis with a 6 ± 0.4 inhibition zone. The antioxidant potential was detected with DPPH scavenging activity, where the maximum scavenging activity was recorded at100 µg/mL. In analgesic activity, AuNPs showed superior efficiency as compared to leaf extract. The maximum latency time observed was 77.15 ± 0.39 s at a dose level of 300 mg/kg followed by 6.77 ± 0.30 s at 200 mg/kg, demonstrating 80.16% and 75.90% of analgesia, respectively. While diclofenac sodium was used as a standard with a latency time of 8.92 ± 0.32 s. The maximum metabolic activity of promastigote was seen at 150 µg/mL, which shows 91.21% lethality at 150 µg/mL with LD50 28.15, LD70 98.72, LD90 605.70, and 2.106 Chi-square values. In conclusion, the present findings demonstrate that AuNPs synthesized by plant extract might be applied as an alternative to synthetic drugs for different pathogenic diseases.