AixSense TBI: Field-Effect Biosensor for Traumatic Brain Injury : ERDNBT

AixSense TBI is a point-of-care electrochemical biosensor platform engineered to detect Traumatic Brain Injury (TBI) through rapid quantitative measurement of Glial Fibrillary Acidic Protein (GFAP) in blood samples. Developed by Team AixSense representing RWTH Aachen University for the SensUs 2023 competition, the device replaces subjective triage scoring with quantitative molecular diagnostics.

Project Document: Download Team Results Document (PDF)
Team Platform: aixsense.de
Affiliations: RWTH Aachen University, IWE1 Institute, Meyer Children’s Hospital

Project Showcase & Demonstration Video

AixSense 2023: Electrochemical ISFET Biosensor for TBI Detection Demonstration · Shot & edited by erdnbt

Clinical Urgency & Objective

Traumatic brain injury affects 50–69 million individuals globally each year. Current clinical triage relies heavily on the qualitative Glasgow Coma Scale (GCS) followed by expensive, radiation-heavy CT scans or MRI imaging:

GFAP Biomarker: Following axonal and astrocytic injury, GFAP rapidly crosses the compromised blood-brain barrier into peripheral circulation.
Triage Window: Rapid quantification of serum GFAP within minutes enables emergency physicians to rule out intracranial lesions without unnecessary neuroimaging, reducing healthcare expenditure and diagnostic delays.

Architecture: Indium Tin Oxide (ITO) ISFET Transducer

Rather than relying on fragile or costly nanomaterials (such as graphene or carbon nanotubes), AixSense pioneered an Ion-Sensitive Field-Effect Transistor (ISFET) platform leveraging custom RF-sputtered Indium Tin Oxide (ITO) thin-film channels.

                    [ Liquid Analyte Flow: Anti-GFAP + GFAP Complex ]
                                             │
      ┌──────────────────────────────────────▼──────────────────────────────────────┐
      │ Surface Biofunctionalization: APTES + EDC/NHS Crosslinking + BSA Block     │
      ├─────────────────────────────────────────────────────────────────────────────┤
      │ 30 nm Sputtered Semiconductive ITO Channel (Tailored Oxygen Vacancies)      │
      ├───────────────────────────────────┬─────────────────────────────────────────┤
      │ Source Contact (100nm Au / 30nm Ti)│ Drain Contact (100nm Au / 30nm Ti)     │
      ├───────────────────────────────────┴─────────────────────────────────────────┤
      │ Thermal SiO2 Dielectric / Passivation Barrier (SU-8)                        │
      └─────────────────────────────────────────────────────────────────────────────┘

1. Band Gap & Oxygen Vacancy Engineering

30 nm ITO channels were deposited on 4-inch oxidized silicon wafers via magnetron sputtering.
By strictly regulating the oxygen flow rate during sputtering, the team tuned oxygen vacancy density to shift the material into a controlled semiconducting regime with steep subthreshold slope and high transconductance.

2. Surface Chemistry & Oriented Immobilization

Surface activation via oxygen plasma followed by gas-phase silane deposition with (3-Aminopropyl)triethoxysilane (APTES).
Carboxyl-oriented crosslinking using EDC/NHS to anchor monoclonal anti-GFAP antibodies without occluding the antigen-binding Fab fragments.
Bovine Serum Albumin (BSA) passivation to eliminate non-specific background binding in complex serum matrices.

Dual-Channel Microfluidics & Detection Physics

The accumulation of net negative charge upon GFAP antigen-antibody binding at the gate modulates the channel's surface potential $\psi_0$ :

I_D = \mu C_{ox} \frac{W}{L} \left[ (V_{GS} - V_{TH}^*) V_{DS} - \frac{1}{2} V_{DS}^2 \right]

Where the shifted threshold voltage $V_{TH}^*$ reflects the analyte binding equilibrium:

V_{TH}^* = V_{TH} + \Delta \psi_0

Cartridge Integration: 24 individual ISFET comb structures per chip are encased in vacuum-cured PDMS microchannels.
Continuous Flow: Parallel dual microfluidic paths ensure uniform hydrodynamic delivery across all 24 sensors from a single sample loading well, maximizing signal-to-noise ratio.

Prototyping & System Integration

Custom Modular PCB Interface: Precision spring-loaded socket array connecting the delicate 24-channel ISFET cartridge directly to multichannel impedance and potentiostat instrumentation.
Point-of-Care Enclosure: Custom CAD-engineered, 3D-printed modular instrument housing facilitating rapid single-handed chip insertion by clinical personnel.