Indian Journal of Biotechnology Vol 15, October 2016, pp 531-537 Properties and bioactivity of flavonoids and sugar induced gold nanoparticles Aishwarya Yadav and Suvidya Ranade* Department of Chemistry, Savitribai Phule Pune University (formerly Pune University), Pune 411007, India Received 24 June 2015; revised 17 November 2015; accepted 23 November 2015 The development of green method of metal nanoparticles (NPs) synthesis has become a major focus of researchers as the biogenic reduction of metals into NPs is eco-friendly, less expensive and free of hazardous chemicals. In the present study, we report the synthesis and characterization of gold (Au) NPs using aqueous Cassia fistula leaf extract. The reduction of 1 mM HAuCl4 (chloroauric acid) occurred within 7 min after addition of the leaf extract. These Au NPs were further characterized by using UV-visible spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), dynamic light scattering (DLS) and Fourier transform infrared spectroscopy (FTIR) analysis. MTT assay was carried out to check cytotoxicity of these Au NPs on MCF-7 cells. UV-Vis spectra confirmed the synthesis of Au NPs with SPR band obtained at 535 nm. The XRD analysis confirmed the crystalline nature of Au NPs. The average size of 27.21 nm was obtained by TEM analysis. The FTIR spectra explained the role of plant phyto-constituents in reduction and stabilization of Au NPs. We finally propose a reduction mechanism using HR-LCMS analysis of Cassia leaf extract showing the presence of flavonoids, sugar and antioxidants as supported by FTIR and NMR results. These bioreduced Au NPs showed no significant cytotoxicity to MCF-7 cells. Keywords: Cassia fistula, FE-SEM, gold nanoparticles (Au NPs), MCF-7, reduction mechanism Introduction The synthesis of gold (Au) nanoparticles(NPs) has gained great significance over the last few years because of its applications in various fields like biosensors, drug delivery, cancer therapy, catalysis and electronics 1 . Various chemical, physical and biological methods are being employed for the synthesis of Au NPs. Since chemical methods involve the use of hazardous chemicals, greener synthesis of metal nanoparticles (using plants, bacteria & fungi) is becoming popular worldwide 2 . In green synthesis of Au NPs, plant based materials are gaining more importance as they are easily available, suitable for large scale biosynthesis and can actually yield nanoparticles of a better defined size and morphology in comparison to other existing physico-chemical processes 3,4 . Many researchers have been reported the synthesis of Au NPs by using plants. The use of plant extracts of Pelargonium graveolens 5 , Cymbopogon flexuosus 6 , and Zingiber Officinale 7 have been reported in the synthesis of Au NPs. Cassia fistula L. (Family: Fabacae) is a medicinal plant. Its various plant parts are being used in treatment of jaundice, ulcers, rheumatism, skin eruptions etc 8 . Anticancer property of the plant has been reported on Ehrlich ascites carcinoma and oral cancer 9 . C. fistula has earlier been reported in the synthesis Au NPs using the stem bark 10 . In the present study, we have explored a simple and cost effective method for the synthesis of Au NPs using aqueous extract of C. fistula leaves. Gold nanoparticles were further analyzed for in vitro cytotoxicity on MCF-7 cells. Also, the mechanism of reduction of Au NPs by Cassia leaf extract was studied by high resolution-liquid chromatograph mass spectrometry (HR-LCMS) analysis. This is a preliminary study towards development of gold nanoconjugates for anticancer drug delivery. Materials and Methods Preparation of Leaf Extract The leaves (10 g) of C. fistula were cleaned, cut and crushed with liquid nitrogen, and the powder was soaked overnight in 100 mL milli-Q water. The resultant extract was filtered twice through Whatman filter paper to obtain a clear solution. Finally, a yellowish brown extract was obtained and used for the synthesis of the Au NPs. The phytochemical analysis of the aqueous leaf extract was carried out using standard tests. The protein and reducing sugar —————— *Author for correspondence: Tel: +91-20-25601395 extn 519; Fax: +91-20-25601265. suvidya@chem.unipune.ac.in