GA This study presents a novel approach for synthesizing CdS nanoparticles by employing tea (Camellia sinensis L.) leaf catechins as a potent chelating agent. The production of spherical, cubic, and crystallite CdS nanoparticles was confirmed by XRD and HRTEM investigations. The existence of biomolecules that encapsulated and stabilized the CdS nanoparticles was verified by UPLC and FTIR analysis. These nanoparticles demonstrated antimicrobial activity against microorganisms isolated from spoiled Capsicum chinense Jacq. Additionally, the cytotoxic effect of CdS nanoparticles on HEK 293 normal kidney cells showed safe level of cytotoxicity. The theoretical investigation reveals a substantial interaction between CdS nanoparticles and the bio- constituents of tea. Therefore, due to their favorable biocompatibility, antimicrobial activity, and low cytotoxicity, the green synthesized CdS nanoparticles hold promise as a preservative to control microbial contamination of Capsicum chinense Jacq., thereby enhancing its shelf life.

In light of the shifting global environment, ensuring food and nutritional security of the world's growing population is a difficult and demanding task. Hence, cutting-edge technologies like biotechnology and nanotechnology are thought to be the ideal ways to handle this difficult task by boosting production and lowering post-harvest losses. In developing countries , up to 30% of horticulture crop products are lost due to microbiological spoilage and physiological processes [1]. The majority of bacteria that were initially discovered on entire fruit or vegetable surfaces are found in soil. Studies have demonstrated that using contaminated irrigation water can raise the frequency of harmful microorganisms from harvest [2].In light of the shifting global environment, ensuring food and nutritional security of the world's growing population is a difficult and demanding task. Hence, cutting-edge technologies like biotechnology and nanotechnology are thought to be the ideal ways to handle this difficult task by boosting production and lowering post-harvest losses. In developing countries , up to 30% of horticulture crop products are lost due to microbiological spoilage and physiological processes [1]. The majority of bacteria that were initially discovered on entire fruit or vegetable surfaces are found in soil. Studies have demonstrated that using contaminated irrigation water can raise the frequency of harmful microorganisms from harvest [2].

Analytical grade chemicals were purchased from Sigma-Aldrich chemicals Pvt Ltd. (Bangalore, India) and used without further purification. Cadmium Sulphate (CdSO4) and Sodium Sulphate (Na2S) were used respectively as Cd2+ and S2- source and Camellia Sinensis L. was collected from Jorhat, Assam, India and used as plant material. The synthesis was carried out using double distilled water.

Twenty grams of dried tea leaves were infused in 200 ml boiling water for 5 min, after which the leaves were filtered out. The resulting infusion contained catechins along with other water-soluble compounds and pigments. To remove caffeine and other pigments, the infusion was extracted with dichloromethane. The aqueous layer, containing catechins, was then subjected to ethyl acetate extraction to obtain the catechin fraction. This extract was dried using a rotary evaporator to yield crude catechin. For the synthesis of CdS nanoparticles, equimolar solutions of CdSO4 and Na2S were prepared. 50 ml of Na2S solution was added drop wise to an equal amount of CdSO4solution. 5 ml of catechin extract was added drop wise to this mixture at 70oC with constant stirring. To complete the reaction and produce CdS nano colloids, the resulting solution was left at room temperature for the whole night. These nano colloids were centrifuged at 2,000 rpm for 15 min. The final product was ground into fine powder after being dried for 2 h at 120oC.

Figure 1. Symmetric representation of green synthesis steps of the CdS nanoparticles and their applications.

 After processing fresh tea leaves (1) into dried tea leaf powder (2), the powder was removed to create a tea leaf powder solution (3). By reacting with CdSO4 and Na2S under carefully regulated heating and centrifugation, the extract served as a stabilizing and reducing agent for the production of CdS nanoparticles (4). A powder of the resultant CdS nanoparticles was collected (5). The produced CdS nanoparticles were then used for biological assessments, such as determining their cytotoxic activity against the HEK-293 kidney cell line and evaluating their antimicrobial activity against isolated spoilage microorganisms from Capsicum chinense Jacq. (6), indicating their potential use in food safety and preservation investigations