Enzyme Immobilization in Polyelectrolyte Brushes: High Loading and Enhanced Activity Compared to Monolayers.

Enzyme immobilization on surfaces is a widely studied topic in biocatalysis and biosensing. Despite its potential, achieving high enzyme loading while maintaining activity remains a challenge. Prior research has shown that traditional methods like self-assembled monolayers often limit enzyme density and activity. This gap motivated the search for alternative surface architectures that could support more efficient enzyme immobilization. Polyelectrolyte brushes have emerged as a promising platform due to their tunable properties and three-dimensional structure. However, the exact impact of brush architecture on enzyme behavior is not fully understood. This study contributes by comparing two brush preparation techniques and their effects on enzyme binding and activity. The research fills a need for better strategies to enhance surface-based enzymatic reactions. By exploring both grafting-to and grafting-from methods, the work advances understanding of how brush structure influences enzyme performance.

The study aimed to evaluate how polyelectrolyte brushes affect enzyme immobilization and activity compared to self-assembled monolayers. The goal was to determine whether brush-based surfaces could support higher enzyme loading and better catalytic performance. Researchers focused on glucose oxidase as a model enzyme and used both anionic and cationic polymers to create brush layers. The investigation sought to identify the conditions under which enzyme binding and activity are maximized. The motivation stemmed from the need for improved immobilization strategies in biosensors and biocatalytic devices. By comparing grafting-to and grafting-from techniques, the study aimed to clarify the role of brush architecture in enzyme behavior. The research also aimed to assess the influence of pH and ionic strength on binding and activity. The ultimate purpose was to provide a foundation for designing more effective enzyme-functionalized surfaces.

The study employed two methods to prepare polyelectrolyte brushes: grafting-to and grafting-from. Both anionic and cationic polymers were used to create brush layers on surfaces. Surface plasmon resonance and spectroscopic ellipsometry were used to measure enzyme binding and surface coverage. The model enzyme glucose oxidase was immobilized using both covalent and noncovalent interactions. The researchers compared the results with those from self-assembled monolayers using the same chemical interactions. The experiments were conducted under varying pH and ionic strength conditions to assess their impact. The study also evaluated the effect of brush thickness and charge state on enzyme activity. The methods allowed for precise quantification of enzyme loading and catalytic performance.

The study found that polyelectrolyte brushes supported significantly higher enzyme loading than self-assembled monolayers. Enzyme binding reached up to 50% of the polymer mass, with thousands of ng/cm² immobilized. The 3D-like brush environment enhanced specific activity compared to monolayer immobilization. For grafting-from brushes, multilayer enzyme immobilization occurred without conjugation chemistry. At pH between the enzyme's pI and the polymer's pKa, binding was strong even at physiological ionic strength. Neutral brushes also showed considerable enzyme binding. Acidic brushes demonstrated higher activity with covalent immobilization than with noncovalent. Grafting-from brushes achieved full preservation of specific activity, both covalently and noncovalently. Catalytic activity of hundreds of pmol cm⁻² s⁻¹ was observed in polybasic brushes only tens of nanometers thick.

The study concluded that polyelectrolyte brushes offer a superior platform for enzyme immobilization compared to self-assembled monolayers. The brush environment supports higher enzyme loading and enhanced catalytic activity. The results suggest that brush architecture plays a key role in enzyme performance. Grafting-from brushes enabled multilayer immobilization without additional chemistry. The findings indicate that pH and ionic strength significantly affect binding and activity. The study supports the use of acidic brushes for covalent immobilization to maximize activity. Neutral brushes also showed promise for enzyme binding under certain conditions. The results provide new insights for designing functional interfaces based on enzymatic catalysis.