Types

Method

Purpose

Ref.

Physical characterization

Dynamic light scattering

Determines the average size and size distribution of nanoparticles.

[5, 76, 77]

Transmission electron microscopy & scanning electron microscopy

Provide high-resolution images to analyze the shape, surface features and structure integrity of nanoparticles.

X-ray diffraction

Determines whether the nanoparticles have an amorphous or crystalline structure by analyzing the diffraction pattern of X-rays.

Zeta potential analysis

Measures the surface charge of nanoparticles, which is crucial for predicting their stability and aggregation tendencies in different pH environments.

Chemical characterization

Fourier transform infrared spectroscopy

Identify functional groups present in nanoparticles by analyzing their infrared absorption spectrum. Essential for confirming the pH-responsive group.

[5, 76, 77]

UV-visible spectroscopy

Analyzes optical properties and pH-dependent changes in the absorption spectrum of nanoparticles.

Nuclear magnetic resonance spectroscopy

Provides detailed information about the molecular structure and chemical bonding within nanoparticles.

pH-titration studies

It helps in evaluating how nanoparticles respond to different pH levels by monitoring their ionization behaviour.

Differential scanning calorimetry

Determines the thermal stability of nanoparticles by measuring heat flow changes under different temperature conditions.

Stability and self-life

Selection of suitable materials

The choice of polymers and stabilizing agents significantly impacts the stability of nanoparticles. Materials such as chitosan and alginate are commonly used due to their biocompatibility and ability to form stable structures.

[79, 80]

Encapsulation techniques

Encapsulation enhances the protection of nanoparticles from environmental factors that may cause degradation. Techniques like spray drying improve stability by creating a protective barrier around the nanoparticles, ensuring controlled release at the target site.

Freeze-Drying (Lyophilization)

Removing moisture through lyophilization enhances nanoparticle stability during storage by preventing hydrolytic degradation. This process transforms nanoparticles into a dry form, extending their shelf-life without compromising functionality.

Addition of Stabilizers

Stabilizing agents, including surfactants, polyols, and antioxidants, help prevent aggregation and chemical degradation of nanoparticles. These excipients are carefully selected based on the formulation requirements to enhance long-term stability.