Fibrinogen monolayer characterization by colloid deposition.

Area of Science:

• Surface science
• Biophysics
• Materials science

Background:

• Understanding protein adsorption is crucial for biomaterials and biosensors.
• Fibrinogen (Fb) adsorption on surfaces influences biological interactions.
• Characterizing protein monolayers requires advanced surface analysis techniques.

Purpose of the Study:

• To characterize bovine and human fibrinogen (Fb) monolayers on mica at pH 3.5.
• To investigate the electrokinetic properties and adsorption mechanisms of Fb on mica.
• To evaluate the orientation and conformation of adsorbed Fb molecules.

Main Methods:

• Colloid particle deposition using AFM and streaming potential measurements.
• Controlled adsorption under diffusion transport.
• Enumeration of single adsorbed molecules via AFM.
• In situ streaming potential measurements for electrokinetic properties.
• Deposition of negatively charged polystyrene latex microspheres.

Main Results:

• Fibrinogen adsorbs irreversibly on mica across a wide ionic strength range (4 × 10⁻⁴ to 0.15 M NaCl).
• Overcharging of the negative mica surface occurred at high Fb concentrations (>1400 μm⁻²).
• Anomalous deposition of negative latex particles on negatively charged Fb monolayers was observed, contradicting DLVO theory.
• End-on adsorption of Fb with extended conformations and positive charge in αA chains was confirmed.

Conclusions:

• Colloid particle deposition is an effective method for studying protein adsorption mechanisms at solid/electrolyte interfaces.
• The observed anomalous latex deposition provides insights into Fb orientation and surface charge distribution.
• The findings challenge conventional theories and offer a more nuanced understanding of protein-surface interactions.