## 1 Introduction  
Metal nanoparticles are utilized not only in research but in many fields of applications, especially in the pharmaceutical and biomedical fields, owing to their improved physical and chemical properties upon size reduction. These particles have a broad range of applications, such as catalysis, biosensing, optoelectronics, chemical sensing, and medical diagnosis [1]. Out of various nano-structured materials under research, gold nanoparticles (AuNPs) are of particular interest to scientific community owing to their stability, inertness, and potential applications in biotechnology [2]. Additionally, AuNPs can efficiently bind to thiol and amine groups, which help with surface modification and increase their effectiveness in biomedical applications. Various physical and chemical processes have been involved in the synthesis of AuNPs. However, these processes generate a large amount of hazardous byproducts [3]. Hence, there has been a growing interest to make a remarkable improvement in the ability to synthesize AuNPs to overcome the disadvantages of the physical and chemical process. It is suggested that the use of plant materials for the synthesis of AuNPs could be more advantageous than the physical and chemical method. Several studies have shown that biomolecules like amino acids, organic acids, phenols, and flavonoids present in plants play a vital role in reducing the metal ions to their respective nanomaterials as well as aid in the capping of the metal NPs, which keeps them stable for a longer period. In addition to this, plant extracts are secure to handle, readily available, and have a wide variety of metabolites that may aid in the reduction of metal salts to NPs [4]. Application of nanotechnology to herbal drugs may lead to the development of nano herbal products possessing high bioavailability and less toxicity, which consequently will open a new era of herbal drug discovery [5]. Several plants were productively used for efficient and rapid extracellular production of stable dispersions of AuNPs. Apart from this, plant extracts used for the biosynthesis of gold nanoparticles have gained much more importance due to their simplicity, eco-friendliness, and non-toxic nature [6]. Recently, AuNPs were used for cancer cell detection, encapsulation of drugs, nerve cell signaling stimulator, luminescent biomarker, drug delivery, sensor analysis, and membrane filtration, and as nano barcodes, and antimicrobial agents [7]. Cancer is one of the most challenging diseases to cure and the second leading cause of death in developed countries. Over the past few decades, it continues to be a worldwide health problem despite the rising number of nanoscaled technologies [8]. The synthesis of AuNPs was mediated by an extract of _Allium cepa_ and it was internalized by MCF-7 breast cancer cells via endocytosis [9]. AuNPs have recently been investigated for biocompatibility according to their interactions with human breast epithelial MCF-7 cells, which were assessed by cytotoxicity by MTT assay and caspase 3, 9, Bax, and Bcl expression by real-time PCR assays [10]. In addition, green synthesis of gold nanoparticles has been previously achieved using different parts of various plants like _Ginkgo biloba_[11], _Nepenthes khasiana_[12], _Panax ginseng_[13], _Mentha piperita_[14], _Mappia foetida_[15], _Bambusa chungii_[16], _Ocimum santum_[17], and _Butea monosperma_[18]; there are no reports of the biosynthesis of AuNPs using _Eclipta prostrata_. _Eclipta prostrata_ (Asteraceae) is a perennial herb distributed in the tropical and sub-tropical regions of the world. It is a common weed in moist regions throughout India. There is a potential for medicinal use of this plant as an antiseptic, stringent, depurative, emetic, febrifuge, ophthalmic, purgative, style, and tonic, for use against hepatitis, jaundice, liver cirrhosis, aching and weakness of the knees and loins, hematuria and diarrhea with bloody stools, and abnormal uterine bleeding [19]. Also, previous phytochemical studies on _E.