An LSPR-Based Kinetic Framework for Polyelectrolyte Molecular Weight Determination: A Proof-of-Concept Study

Area of Science:

• Polymer Science
• Analytical Chemistry
• Materials Science

Background:

• Determining polyelectrolyte molecular weight is challenging due to limitations of conventional methods like size-exclusion chromatography (SEC).
• SEC often requires added salt, calibration with neutral polymers, and complex optimization to manage polymer-surface interactions.
• Existing methods struggle with accurate characterization under dilute, salt-free conditions crucial for many applications.

Purpose of the Study:

• To introduce a novel kinetics-based method for determining polyelectrolyte molecular weight.
• To establish a calibration-free approach using Localized Surface Plasmon Resonance (LSPR).
• To demonstrate the feasibility of measuring real-time electrostatic complexation for molecular weight determination.

Main Methods:

• Utilized Localized Surface Plasmon Resonance (LSPR) to monitor the real-time electrostatic complexation between poly(ethylenimine) (PEI) and poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt] (PAZO).
• Extracted association (k_on) and dissociation rate constants from concentration-dependent binding data.
• Calculated the number-average molecular weight (Mn) based on kinetic parameters, assuming symmetrical binding.

Main Results:

• Successfully established a calibration-free method for determining the number-average molecular weight (Mn) of polyelectrolytes under dilute, salt-free conditions.
• Calculated the Mn of PAZO to be 257,400 g mol⁻¹, with a degree of polymerization of 642, using the known Mn of PEI.
• Demonstrated LSPR-based kinetics as a powerful, surface-sensitive alternative to traditional characterization techniques.

Conclusions:

• LSPR-based kinetic analysis provides a broadly adaptable strategy for characterizing charged polymers and other biomolecular systems.
• The developed method overcomes key limitations of conventional techniques, offering a more direct and efficient approach.
• This proof-of-concept study highlights a generalizable framework for polyelectrolyte characterization with potential for future refinement and application.