Characterizing the Electrophoretic Mobility, Charge, And Zeta Potential of Biopolymers

Importance of Topic

Measurement of electrophoretic mobility, effective molecular charge, and zeta potential of biopolymers is essential for understanding their behavior in biological and industrial processes. This rapid, nondestructive approach allows characterization even in high ionic strength environments, overcoming traditional electrolysis limitations.

Study Objectives and Overview

This work examines the relationship between molecular weight, surface functionality, pH, and ionic strength on the electrophoretic properties of poly(amidoamine) (PAMAM) dendrimers and heparin polymers. Key goals include:

• Assessing effective charge and size of amine-terminated (G4–G7) and hydroxyl-terminated (G3–G6) PAMAM dendrimers under neutral and acidic high-salt conditions.
• Determining charge-to-mass ratios of unfractionated heparin standards from different suppliers.
• Identifying contaminated heparin lots via altered electrophoretic behavior.

Methodology and Instrumentation

Electrophoretic mobility (µ) and hydrodynamic radius (rH) were measured simultaneously using massively parallel phase-analysis light scattering (MP-PALS) combined with dynamic light scattering (DLS). Key experimental parameters:

• Instrument: Wyatt Möbiuζ with Atlas autosampler.
• Samples: 2 mg/mL in water and in 500 mM NaNO3 with 500 mM acetic acid (conductivity 34 mS/cm).
• Measurement settings: 30 s acquisition, 3 V electric field, 30 parallel detectors.

Instrumentation Used

• Wyatt Möbiuζ MP-PALS module for electrophoretic mobility.
• Dynamic Light Scattering (DLS) for hydrodynamic radius determination.
• Atlas autosampler for automated sample handling.

Results and Discussion

For PAMAM dendrimers, amine-terminated samples exhibited a marked increase in effective charge under acidic conditions, whereas hydroxyl-terminated analogs showed only slight positive charge. Heparin standards displayed consistent charge-to-mass ratios across suppliers, with super-sulfated contaminants identified by a ~30% higher ratio, demonstrating the method’s sensitivity to structural modifications.

Benefits and Practical Applications

This combined mobility and size measurement approach offers:

• Rapid analysis (<30 s per sample) with improved statistical reliability.
• Nondestructive evaluation applicable to fragile biopolymers.
• Capability to operate at physiological and high ionic strengths.

Future Trends and Potential Applications

Advancements may include integration with microfluidic platforms for high-throughput screening, real-time process monitoring in biomanufacturing, and extension to a broader range of charged macromolecules such as nucleic acids and proteins.

Conclusion

The study demonstrates that simultaneous MP-PALS and DLS measurements provide a powerful, efficient tool for characterizing the electrophoretic and structural properties of biopolymers, enabling improved quality control and deeper insights into molecular functionality.