Label-Free Neuropeptide Detection beyond the Debye Length Limit

Area of Science:

• Nanomaterials and Sensor Technology
• Biomedical Engineering
• Analytical Chemistry

Background:

• Graphene field-effect transistor (GFET) biosensors are promising for wearable diagnostics and real-time biomarker monitoring.
• Conventional direct current (DC)-mode GFET biosensors suffer from reduced sensitivity in high ionic strength fluids due to Debye length screening.
• Accurate detection of biomarkers like neuropeptide-Y (NPY) in physiological fluids such as sweat is crucial for health monitoring.

Purpose of the Study:

• To develop and characterize alternating current (AC) mode heterodyne-based GFET biosensors.
• To overcome the Debye screening limitation of DC-mode GFET biosensors for sensing in physiological fluids.
• To detect the stress biomarker neuropeptide-Y (NPY) in artificial sweat at physiologically relevant ionic concentrations.

Main Methods:

• Fabrication and testing of AC-mode heterodyne-based GFET biosensors.
• Characterization of sensor performance across a range of carrier frequencies (30 kHz to 2 MHz).
• Evaluation of sensor response in artificial sweat with varying salt concentrations (10, 50, and 100 mM).

Main Results:

• Achieved a record ultralow detection limit of 2 × 10^-18 M for NPY.
• Demonstrated an extensive dynamic range of 10 orders of magnitude in sensor response.
• Observed increased AC-mode sensor response with higher salt concentrations, contrary to DC-mode behavior.
• Identified an optimal response frequency of 400-600 kHz for specific salt concentrations.
• Explained the observed phenomena using an electrolyte-gated capacitance model.

Conclusions:

• AC-mode heterodyne GFET biosensors effectively overcome Debye length screening limitations.
• The developed sensors offer ultra-high sensitivity and a broad dynamic range for biomarker detection in complex fluids.
• Optimizing carrier frequency and understanding salt concentration effects are key for enhanced biosensor performance.