I think that your reaction was not completed and it proceed during the storage. Otherwise you had wrong zeta potential reading due to low or large concentration or other reason. Chitosan stabilized AgNPs should have zeta potential + something at slightly acidic pH.

Hi Subhadarshani Dhall,

The change in pH conditions can indeed affect the surface charge (Zeta potential) of chitosan-coated silver nanoparticles. Chitosan is a pH-sensitive polymer that can undergo protonation or deprotonation reactions depending on the pH of the surrounding environment. These reactions can impact the surface charge of the nanoparticles.

In your case, the change in Zeta potential from a negative charge (-39) to a positive charge (+50) after storing the sample at 4 degrees Celsius could be attributed to pH changes. When you store the sample at a lower temperature, it can result in a decrease in pH, leading to the protonation of the chitosan coating and subsequently changing the surface charge from negative to positive. Consider using pH buffers to maintain a consistent pH during storage. Buffers help resist changes in pH, ensuring that the environment remains suitable for the stability of the chitosan coating and the surface charge of the nanoparticles.

Good luck

Jakub Knurek Could you please suggest some of the commonly used buffers to stabilize the pH of Chitosan solution? Also, could you add insight into the stability of chitosan nanoparticles synthesized by ionic gelation using TPP as a cross-linker?

Thank you

Hi Subhadarshani Dhall,

The choice of the buffer used for ionic gelation in the synthesis of chitosan nanoparticles depends on the parameters of the nanoparticles one wants to obtain (e.g., chitosan concentration, size of nanoparticles or their morphology). I, when choosing a particular buffer, am mainly guided by the table available on the website: https://www.sigmaaldrich.com/PL/pl/technical-documents/protocol/protein-biology/protein-concentration-and-buffer-exchange/buffer-reference-center

As an introduction to the issue, I recommend the Norwegian NOBIPOL publication Article Chitosan: Gels and Interfacial Properties

I further recommend the following articles, which expand on the topic of chitosan nanoparticles synthesized by ionic gelation using TPP:

Article Synthesis and Properties of Chitosan Nanoparticles CrossLink...

Article Physicochemical Properties of TPP-Crosslinked Chitosan Nanop...

Article Preparation of Chitosan Nanoparticles and their In-vitro Cha...

Article Synthesis and characterization of TPP/chitosan nanoparticles...

Article Factors determining the stability, size distribution, and ce...

Article Chitosan and crosslinked chitosan nanoparticles: Synthesis, ...

Article Synthesis and Characterization of Chitosan Nanoparticles wit...

Article Understanding the mechanism of ionic gelation for synthesis ...

https://www.sciencedirect.com/science/article/abs/pii/S0022286021022493

https://www.mdpi.com/1420-3049/28/11/4328

Best