Peak at 300 nm may be from some bacterial residues? For example, most proteins have local absorbance maximum at around 280 nm. It may be wise to measure silver nanoparticles without the bacterial extract to see if this second peak is produced by nanoparticles. Regarding broad spectral signals which are not smooth, this may be due to oversaturation. So I would try to measure in a thin cuvette or try to dilute the samples and measure the diluted samples. I would avoid measuring absorbances over 2-2.5 for most UV-Vis instruments.

Short and Broad Spectrum

• Concentration Optimization: Start by varying the concentrations of the plant extract and the silver precursor (e.g., silver nitrate). A higher concentration of the silver precursor typically enhances nanoparticle formation.
• Reaction Time: Extend the reaction time to allow for more complete formation of nanoparticles. Monitor the spectra at different time intervals.

2. Non-Smooth Progression

• Stirring and Mixing: Ensure that your reaction mixture is well-stirred to promote uniform dispersion of the reactants. Inconsistent mixing can lead to uneven reactions, resulting in broad and jagged spectra.
• Temperature Control: Maintain a constant reaction temperature, as fluctuations can affect the kinetics of nanoparticle formation.

3. Two Peaks Issue

• Peak at 300 nm: This peak may be due to the absorption of the plant extract or other organic components. To minimize this interference, consider Dilution: Dilute your sample further and check if the peak at 300 nm diminishes while retaining the 420 nm peak. Purification: If feasible, purify the nanoparticles from the plant extract using centrifugation or filtration to isolate them from the organic components.
• Characterization: Use additional techniques (like FTIR or chromatography) to analyze the compounds in your extract that may contribute to the 300 nm peak.

4. Control Experiment

• Run a control experiment with the plant extract and the silver precursor without reducing agents to see if the broadness and other peaks still appear. This will help you identify if the interference is from the extract or the synthesis process.

5. Adjustment of Parameters

• pH: The pH of your reaction can significantly impact nanoparticle size and shape. Try varying the pH to find the optimal condition for silver nanoparticle synthesis.
• Temperature: Conduct the synthesis at different temperatures. Higher temperatures can accelerate the reaction, but be cautious as they may also lead to uncontrolled growth.

6. Characterization Techniques

• After optimizing conditions, use techniques such as DLS (Dynamic Light Scattering) to measure particle size distribution and TEM (Transmission Electron Microscopy) for shape and size confirmation.

7. Documentation and Iteration

• Keep detailed records of each experiment, including concentrations, times, and results, to help identify trends and optimize further.

Thanks for your suggestions. I will conduct the trial experiments as soon as possible.