The synthesis of silver nanoparticles (AgNPs) through green methods utilized Carica papaya L. flesh extract as both reducing and stabilizing elements. The color transformation of the solution from yellow to dark brown visually demonstrated Ag+ ion reduction to Ago during biosynthesis. Experimental parameters involved testing papaya extract concentrations ranging from 25% to 100% when using silver nitrate (AgNO3 ) as the starting material. UV-visible spectroscopy verified the formation of nanoparticles through surface plasmon resonance peaks which varied between 370 to 510 nm based on extract content. TEM microscopy showed that mostly spherical AgNPs existed with a standard size distribution averaging 21 nm. Zeta potential examinations showed outstanding colloidal stability across all extract levels starting from 25% to 50% and reaching 100% as indicated by -26 to -43.95 mV values. Research evidence shows that papaya extract contains enough phytochemicals to perform effective nanoparticle synthesis along with environmentally responsible manufacturing practices at affordable prices and in large volumes. The biologically produced silver nanoparticles show promise for it use in biomedical research alongside environmental applications.

• Green synthesis; Phytosynthesis; Silver nanoparticles; Bioactive compounds; Sustainability

Rosewan KI, Md Saad WM, Nasaruddin RR (2026) Green Synthesis of Silver Nanoparticles Using Carica papaya L. Flesh Extract and Evalu ation of its Characterization. JSM Chem 12(1): 1068.

Green synthesis offers a sustainable alternative by using plant extracts rich in natural phytochemicals that can reduce and stabilize nanoparticles. Carica papaya L., commonly known as papaya, is a tropical fruit abundant in enzymes (e.g., papain), vitamins, phenolics, and antioxidants. These components render papaya a viable candidate for the biosynthesis of nanoparticles. Green synthesis, utilizing microorganisms and plants, presents an eco-friendly alternative to traditional synthesis methods. It offers advantages like simplicity, low cost, short production time, and moderate operating conditions [1-26]. In contrast, the biological synthesis of nanoparticles, particularly using plants, provides an environmentally friendly and cost-effective alternative with easy scalability. Moreover, the small size of silver nanoparticles enhances their catalytic activity by providing more active sites [27]. Nanotechnology has revolutionized various scientific fields including biomedicine, catalysis, and environmental remediation. Among metal nanoparticles, silver nanoparticles (AgNPs) have gained immense attention for their strong antimicrobial and therapeutic properties. Traditional synthesis methods, however, involve toxic chemicals and energy-intensive processes.

The aim of this study was to synthesize AgNPs using papaya flesh extract and to evaluate the nanoparticles’ characteristics through various instrumental techniques, thereby proposing a non-toxic, cost-effective route for nanoparticle synthesis. Papaya, or Carica papaya L., is a tropical fruit plant that has demonstrated potential for the environmentally friendly synthesis of silver nanoparticles (AgNPs). The process of using plants to create AgNPs is a simple and efficient one that produces results quickly. Its abundance of metabolites grants it the capacity to reduce and stabilize nanoparticles. To produce AgNPs, active components have been extracted from various plant parts in the process of biosynthesis. Utilizing papaya extract not only optimizes the synthesis process but also improves the biocompatibility and functional characteristics of the resultant AgNPs. The present research investigates the process of synthesizing silver nanoparticles (AgNPs) from papaya extract and assesses their properties, thereby contributing to the progress of environmentally friendly nanotechnology.

Carica papaya L. (papaya) is a tropical fruit renowned for its abundant nutritional content and bioactive substances, such as β-carotene, vitamin B (thiamine, riboflavin, niacin, and folate), vitamin C, vitamin E, minerals; Na, K, Fe; Ca, and fiber [15]. These bioactive substances have the capability to function as reducing agents that reduce and stabilize nanoparticles during their synthesis, providing a more environmentally friendly option compared to traditional procedures. The Synthesis of silver nanoparticles can be achieved through various methods including chemical reduction, biological synthesis using plant or fruit extract and physical methods. Theoretically, the bioactive compound donates electrons to the Ag? ions to reduce them into Ag? (metallic silver). The chemical reaction can be represented as follows:

Ag+ + Reducing agent in papaya extract → Ag0 + Oxidized produced

The reduced silver atoms (Ag0) begin to nucleate, forming small clusters and these clusters grow into nanoparticles as more silver ions are reduced.

Preparation of Papaya Extract

Fully ripe papayas were purchased, washed under running tap water, and sanitized with ethanol. The whole fruit was weighed before peeling and deseeding. The peels were removed using a fruit peeler, the fruit was halved, and seeds were removed with a spoon. The papaya flesh was weighed, chopped, and blended using a hand blender to obtain a smooth puree.

Approximately 100 g of the papaya puree was mixed with 100 mL of ultrapure water in a 2000-mL beaker and heated at 65–70°C for 20 minutes. After cooling, the mixture was filtered twice: first using a nylon filter bag (20?cm × 15?cm), and then with a diaphragm vacuum pump at room temperature. The resulting orangish extract was used directly for silver nanoparticle synthesis.

Preparation of Extract Concentrations

As shown in Table 1, to determine the optimal extract concentration, dilutions were prepared at 25%, 50%, 75%, and 100% using the stock extract (15 mg/mL). For example, 2.5 mL of extract was diluted with 10 mL of ultrapure water to obtain 25%. Similar steps were followed for 50% and 75%, while 100% was used undiluted.

Table 1: Concentration of papaya extract

Preparation of Silver Nitrate (AgNO?) Stock Solution

A 0.2 M silver nitrate (AgNO?) stock solution was prepared using AgNO? (99.8% purity, Guaranteed Reagent grade, Nacalai Tesque, Japan). Precisely 1.00 g of AgNO? was weighed and dissolved in 29 mL of ultrapure water in a volumetric flask. The solution was mixed thoroughly using a Pasteur pipette until complete dissolution was achieved. The molarity of the prepared solution was calculated as follows:

Moles of  =0.0059 mol

Molarity +  = =0.20 M

Synthesis of Silver Nanoparticles

A total of 1 mL of filtered Carica papaya L. extract was mixed with 3 mL of 20 mM AgNO? solution in a 15 mL clear vial. The mixture was stirred thoroughly using a magnetic stirrer and heated at 55?°C for 2 hours on a constant-temperature magnetic stirrer. A gradual colour change from light yellow to brown was observed, indicating the formation of silver nanoparticles (AgNPs).

Visual Observation of Nanoparticle Formation

The reaction mixture was monitored at regular intervals to observe any visual changes. Initially, the papaya extract appeared yellowish, while the silver nitrate solution was clear. As the reaction progressed, a color change from yellowish or colorless to brown was observed, indicating the reduction of silver ions and the formation of silver nanoparticles (AgNPs). The time required for the color change was recorded, and photographs were taken to visually document the synthesis process.

UV-Visible Spectroscopy

AgNPs solution was transferred into a clean cuvette, and the instrument was calibrated using ultrapure water as the blank. The blank cuvette was inserted to set the baseline to zero absorbance. The AgNPs sample was then placed into the spectrophotometer, and the measurement was performed within a wavelength range of 350–600?nm. Absorbance values were recorded, and the spectrum displayed characteristic absorbance peaks at specific wavelengths, indicating the formation of silver nanoparticles.

Transmission Electron Microscopy (TEM)

TEM was used to observe the size and shape of AgNPs. A volume of 5?µL of AgNPs solution was placed onto 3?mm copper grids and allowed to dry at room temperature for 30 minutes. A drop of 2% phosphotungstic acid (PCA) was then added to the inverted grid and left to dry. The TEM was calibrated to ensure all settings were optimized for imaging. The grid containing the sample was inserted into the TEM, and the desired magnification was set to capture the nanoparticle images. The detailed setup and configuration parameters used for TEM analysis are summarized in Table 2.

Table 2: Setup and configuration parameters for Transmission Electron Microscopy (TEM)

Zeta Potential

During sample preparation, the AgNPs solution was diluted by adding 2 to 6 drops into 20 µL of ultrapure water to ensure good nanoparticle dispersion. A clear disposable zeta cell was carefully filled with the sample to avoid air bubbles and inserted into the instrument. Relevant parameters were entered into the software, and the measurement was initiated. The setup and configuration parameters for the zeta potential analysis are detailed in Table 3.

Table 3: Setup and configuration parameters for zeta potential

Visual Observation

The initial solution appeared yellowish with no precipitate. After the synthesization process, distinct colour changes were observed. At 25% concentration of papaya extract with 10 mM AgNO?, the solution turned brownish, suggesting a lower concentration of nanoparticles. As the concentration increased to 50%, the solution exhibited a brown colour, while at 75%, it became a darker brown and slightly turbid. At 100% concentration, the solution appeared the darkest brown with slight turbidity Figure 1.

Figure 1: Silver nanoparticle solutions using different extract concentrations and 10 mM AgNO3 before and after reaction (a) 25%, (b) 50%, (c) 75%, (d) 100%

UV-Vis Analysis

UV-visible absorption spectra of AgNPs synthesized with different papaya extract amounts combined with 10 mM AgNO? were shown in Figure 2.

Figure 2: UV-Visible spectra of papaya-synthesized silver nanoparticles using different papaya extract concentrations and AgNO3

Plotted against wavelength (350–600 nm) the x-axis shows absorbance values that serve as the y-axis. Table 4 summarizes the highest wavelength peaks and corresponding absorbance values for each concentration of papaya extract. The blue line representing 25% papaya extract solution achieved 0.853 absorption at 420 nm wavelength. The red line reflecting 50% concentration displayed an intense peak reaching an absorbance value of 1.808 at 510 nm wavelength. The absorbance reading at 470 nm reached 1.158 for the extract containing 75% concentration (yellow line). Meanwhile the 100% concentration (green line) demonstrated the most intense peak with 2.448 absorbance at 510 nm.

The absorbance readings at 25% concentration indicate either low nanoparticle size or low particle quantity formation. The peaks observed in the 50% concentration maintained higher intensity at 510 nm which suggests successful AgNP synthesis. The absorbance peak for 75% concentration appeared at a slightly shorter wavelength while being more intense because the reaction generated larger nanoparticles or multiple small nanoparticles. The 100% concentration yielded the greatest absorbance values while showing a distinct peak at 510 nm which indicates its dominance over other samples as the most efficient production method for AgNPs.

TEM Morphology

As shown in Figure 3 (a) and (b), the synthesized AgNPs were predominantly spherical in shape (indicated by red arrows), with some particles appearing slightly elongated (indicated by yellow arrows). The nanoparticles exhibited a relatively uniform size distribution, with an average diameter of 21 nm at 136,000× magnification. The smallest particle size recorded was 16.3 nm. Minor signs of aggregation were observed, as some nanoparticles appeared closely spaced upon visual inspection.

Figure 3: (a) and (b) TEM images under 136000X magnification

Zeta Potential

The papaya concentrations synthesized with AgNO3 solution were considered stable due to measurement of zeta potential values within expected range. Greater zeta potential values indicate stronger repulsive forces among particles, resulting in enhanced dispersion and stability of the nanoparticles. Zeta potential values ranged from −26 to −32 mV, confirming good colloidal stability. The negative charge suggests the presence of anionic functional groups from papaya compounds on the nanoparticle surfaces (Table 5).

Table 5: Average zeta potential of papaya extract and AgNO3

The reaction solution indicated the formation of silver nanoparticles (AgNPs) through its observed colorimetric changes. At the beginning the solution showed a yellow in colour corresponding to plant extract properties. The synthesis process resulted in a brown colour transition in the mixture which represents the important of visual signature indicating the Ag? conversion to Ag? which produces AgNPs. Renuka et. al., reported identical colour transitions during Phyllanthus emblica extract-induced nanoparticle synthesis which featured a transition from clear to brown as a confirmed sign of nanoparticle formation. The surface plasmon resonance bands detected by UV Visible spectrophotometry proved the synthesis of AgNPs. Selvaraj et. al., presented similar data showing flavonoids along with other phytochemicals that perform as reducing and stabilizing agents during nanoparticle synthesis. The SPR peaks identified in lemon leaf extract studies align with current results because the peaks appeared between 350 to 440 nm as researchers manipulated particle size [28-31]. The spectral resonance peak of the 25% extract solution appeared at 420 nm while the baseline AgNO? spectrum displayed its peak at 380 nm implying the presence of slightly larger or smaller nanometer particles. The sharp red shift from 420 nm to 510 nm observed in UV-Vis spectra measurements prove excessive phytochemicals in the solution caused the formation of bigger nanoparticles or aggregate clusters. Among the various phytochemical extract concentrations, 75% extract produced particles with 470 nm absorption peak indicates medium-sized formations showing less aggregation than particles created with lower or higher phytochemical amounts. The detected SPR values ranging from 400–450 nm in the research by Soliman et. al., corresponded with the experimental results and indicated that some samples contained polydisperse entities or aggregated structures. The high-resolution details about nanoparticle dimensions and structure were obtained through Transmission electron microscopy (TEM) examinations. Through TEM analysis the nanoparticles produced from 100% papaya extract showed spherical shapes while having elongated appearance. The synthesized nanoparticles displayed uniform distribution while having sizes between 16.3 nm and 21 nm with almost no sign of aggregation observed between particles. The different reducing agents in the synthetic process between this study and Cao et. al., might have led to slightly larger size of AgNPs synthesized from watermelon peel extract (8–19 nm). The zeta potential values generated from 10 mM AgNO? reached -43.95 mV and produced more potent electrostatic stabilization than the 20 mM samples did. A lower concentration of silver nitrate results in stronger electrostatic stabilization according to these findings. A zeta potential range between -12.3 mV to -52.4 mV was reported by Revathi et. al., while using Carica papaya extract and confirms the vital importance of extract concentration and silver precursor ratio for nanoparticle stability.

This study successfully demonstrated the green synthesis of silver nanoparticles using Carica papaya L. flesh extract has succeed. The biosynthesized nanoparticles were spherical, uniformly distributed, and stable. The method offers a non-toxic, economical, and sustainable alternative to conventional synthesis methods. These AgNPs from carica papaya flesh hold potential for applications in wound healing, antimicrobial treatments, and other biomedical uses.

The authors gratefully acknowledge Universiti Teknologi MARA (UiTM) Puncak Alam and the Faculty of Health Sciences for their generous support and for providing the laboratory facilities essential to the successful completion of this project.

Consent for publication

All authors have reviewed and approved the final manuscript and consent to its publication.

Data Availability

The datasets generated and/or analyzed during the current study are available from the corresponding author upon reasonable request. All relevant data are included within the article.

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