z Materials Science inc. Nanomaterials & Polymers Green Synthesis of Silver Nanoparticles Using Tea Leaves from Three Different Elevations Abhishek Chandra, [a] Ajaya Bhattarai, [b] Ashok K. Yadav, [b] Janak Adhikari, [b] Man Singh, [a] and Basant Giri* [c] Green synthesis of nanoparticles offers numerous advantages over the conventional methods. This work provides a compre- hensive understanding on the effect of tea cultivation elevation on the formation of silver nanoparticles (AgNPs) using green tea (Camellia Sinensis) leaves. The green tea leaves were collected from three different elevations: 86, 1700, and 2000 m above sea level in eastern Nepal. We found that AgNPs synthesized using tea leaves from 1700 m were homogene- ously dispersed and smallest size, when compared to AgNPs synthesized using tea leaves from remaining two elevations. All aqueous dispersed AgNPs were sensitive towards mercury (II) ion over a range of other metal ions tested. However, the AgNPs synthesized using tea leaves from 1700 m resulted in better detection limit of 9.79 μM for sensing mercury (II) ions. Interestingly, the nanoparticles when additionally stabilized in aqueous trimethyloctylammonium bromide, a cationic surfac- tant among seven other surfactants tested, improved the detection limit to 0.71 μM. Introduction Nanoparticles have been widely used in medicine, water purification, laser technology, cosmetic industry, pollution control, etc. for the betterment of humankind. [1–4] Among various types of nanoparticles, silver nanoparticles (AgNPs) are found to be particularly useful because of their applications in food storage, textile coatings, water treatment, catalysis, as antibacterial agents, optical data storage, nanoscale sensors, etc. [5] The AgNPs are generally synthesized by chemical reduction, [6,7] photochemical reduction, [5] electrochemical re- duction, and laser ablation methods. [5] These methods are quite rigorous, but are not always environmental friendly. Recently, alternative green synthesis methods that reduce or eliminate the usage and generation of hazardous substances are becoming popular because of environmental, health, and economic concerns. Most of the reported green synthesis methods for AgNPs involve the use of locally available plant materials as reducing agent. [8,9] Green tea leaves are one of the commonly used plant materials for green synthesis of AgNPs. [5] Tea leaves have one of the highest flavonoids content among the common food and beverage products, resulting in high antioxidant activity. The secondary metabolites such as phytochemicals and amino acids present in tea leaves are responsible for the reduction of silver ions during silver nanoparticles (AgNPs) synthesis. Among these active components, the major bioactive compounds in tea are catechins. [10] The polyphenols constitute up to 30% of the dry weight of young shoots of fresh tea leaves. [11] The content and composition of secondary metabolites in tea depend on ecological and environmental factors such as temperature, humidity, solar radiation, elevation of growing field, etc. [12–14] High elevation (1400 m) tea contained statisti- cally higher concentrations of volatile compounds and amino acids, compared to low elevation tea (600 m). [13] The alteration of content and composition of secondary metabolites due to elevational gradient has been clearly documented in previous studies. [9,10] However, there are no studies on how elevational gradient influences the nanoparticle synthesis potential of tea leaf extract. To fulfil this gap, we have investigated the effect of tea cultivation elevation on AgNPs formation from tea lea extract. We used green tea leaves (Camellia sinensis) from following three locations in eastern Nepal for the synthesis of AgNPs: (a) Gauradaha Municipality-9, Baigundura, Jhapa, (b) Chamaita Rural Municipality-9, Ilam, and (c) Pathibhara Multiple Campus, Phuiling, Taplejung. Jhapa represents southern flat land region, Ilam is hilly region, and Taplejung is mountainous region representing 86, 1700, and 2000 m above sea level, respectively. We found that the elevation of tea plant cultivation field plays a crucial role in tailoring the physical and chemical properties of the synthesized AgNPs. The tea leaves collected from hilly region of Nepal produced homogeneous and smaller sized AgNPs. To our best knowledge, such elevation-based approach has never been reported for the synthesis of AgNPs using any plant extract. Additionally, we have also explored various types of surfactants: cationic, anionic and nonionic, as a stabilizing agent for AgNPs dispersion and their potential for [a] Dr. A. Chandra, Prof. M. Singh School of Chemical Sciences, Central University of Gujarat, Gandhinagar, India [b] Dr. A. Bhattarai, A. K. Yadav, J. Adhikari Department of Chemistry, M.M.A.M.C., Tribhuvan University, Biratnagar, Nepal [c] Dr. B. Giri Center for Analytical Sciences, Kathmandu Institute of Applied Sciences, Kathmandu, PO Box 23002, Nepal E-mail: chembasant@gmail.com bgiri@kias.org.np Supporting information for this article is available on the WWW under https://doi.org/10.1002/slct.201904826 Full Papers DOI: 10.1002/slct.201904826 1 ChemistrySelect 2000, -15,1–9 © 2000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim