A label-free aptamer-based nanogap capacitive biosensor with greatly diminished electrode polarization effects

Area of Science:

• Nanotechnology
• Biosensing
• Physical Chemistry

Background:

• Electrode polarization effects impede impedance spectroscopy in biosensing by masking biological signals.
• Electrical double layers (EDLs) at electrode-solution interfaces dominate low-frequency responses, obscuring crucial data.
• Nanogap capacitors with sub-EDL electrode separation can mitigate these effects and enhance sensitivity.

Purpose of the Study:

• To fabricate and characterize a horizontal thin-film nanogap capacitive sensor.
• To demonstrate the sensor's capability for label-free protein detection.
• To investigate fluid behavior in nanoscale confined geometries.

Main Methods:

• Fabrication of a 40 nm electrode separation nanogap capacitive sensor.
• Surface modification with thiol-functionalized DNA aptamers for specific protein capture.
• Impedance spectroscopy and permittivity measurements on various solutions.

Main Results:

• The nanogap sensor exhibited minimal electrode polarization effects with water and ionic buffers.
• Achieved label-free detection of human alpha thrombin with high sensitivity and selectivity.
• Observed large Debye lengths and a shift in Debye relaxation frequency in high ionic strength solutions, suggesting ordered water phases.

Conclusions:

• Nanogap capacitive sensors effectively reduce electrode polarization, enabling direct dielectric property quantification.
• The aptamer-functionalized sensor provides a sensitive platform for label-free protein detection.
• Understanding fluid behavior in nanoscale confinement is crucial for developing new sensing applications.