Control of Probe Density at DNA Biosensor Surfaces Using Poly(l-lysine) with Appended Reactive Groups

Area of Science:

• Biomaterials Science
• Surface Chemistry
• Nanotechnology

Background:

• Biosensors and biomedical materials require surface functionalization for specific molecular recognition and antifouling properties.
• Modified poly(l-lysine) (PLL) polymers with oligo(ethylene glycol) (OEG) and maleimide (Mal) groups (PLL-OEG-Mal) allow controlled presentation of functional groups for conjugation.
• Thiol-functionalized probes, like peptide nucleic acid (PNA), can be readily attached to these reactive groups.

Purpose of the Study:

• To demonstrate reliable conjugation of thiol-functionalized PNA probes onto PLL-OEG-Mal layers.
• To show control over the surface density of conjugated probes through modification of the PLL polymer synthesis.
• To establish a quantitative relationship between probe density and the density of maleimide groups on the polymer.

Main Methods:

• Synthesis of poly(l-lysine) modified with oligo(ethylene glycol) and maleimide (PLL-OEG-Mal).
• Quartz crystal microbalance (QCM) to monitor DNA probe binding and correlate it with PLL grafting density.
• Cyclic voltammetry using Methylene Blue-labeled DNA to determine absolute probe density.

Main Results:

• Reliable conjugation of thiol-PNA probes onto PLL-OEG-Mal surfaces was achieved.
• A linear relationship was observed between probe density and the density of maleimide groups grafted to PLL.
• An absolute probe density of 1.2 × 10^12 probes/cm^2/% grafted Mal was determined, validating synthetic density control.

Conclusions:

• The synthetic modification of PLL-OEG-Mal provides precise control over the surface density of conjugated biomolecular probes.
• This method allows for the rational design of biosensor surfaces without requiring extensive post-conjugation characterization.
• The findings are crucial for developing high-performance biosensors for biomedical applications, including DNA detection.