Phase control of nanostructured iron oxide for application to biosensor

Area of Science:

• Materials Science
• Nanotechnology
• Electrochemistry

Background:

• Bare iron oxide nanoparticles (Fe3O4 NPs) can transform to alpha-iron oxide (α-Fe2O3 NPs) during electrophoretic deposition.
• This phase transformation can alter nanoparticle properties and performance in applications.
• Controlling nanoparticle phase stability is crucial for reliable device fabrication.

Purpose of the Study:

• To investigate the phase transformation of Fe3O4 NPs during electrophoretic film deposition.
• To explore methods for preventing in situ oxidation of Fe3O4 NPs.
• To compare the performance of biosensors fabricated with phase-stabilized Fe3O4 NPs versus α-Fe2O3 NPs.

Main Methods:

• Electrophoretic deposition of Fe3O4 nanoparticles onto ITO-coated glass.
• Surface passivation of Fe3O4 NPs using carbon (organic) and silica (inorganic) shells.
• X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) for phase analysis.
• Scanning Electron Microscopy (SEM) for morphological studies.
• Fabrication and characterization of cholesterol biosensors.

Main Results:

• Electrophoretic deposition of bare Fe3O4 NPs resulted in transformation to α-Fe2O3 NPs.
• Surface passivation with carbon or silica shells successfully prevented phase transformation, retaining Fe3O4 NPs.
• Encapsulated NPs showed reduced agglomeration during film deposition.
• A cholesterol biosensor using Fe3O4@C NPs demonstrated a rapid response time (60 s), wide linearity (25-500 mg dl⁻¹), high sensitivity (193 nA mg⁻¹ dl cm⁻²), and a Michaelis-Menten constant of 1.44 mg dl⁻¹.

Conclusions:

• Surface passivation is an effective strategy to maintain the phase integrity of Fe3O4 NPs during electrophoretic deposition.
• Stabilized Fe3O4 NPs are suitable for fabricating high-performance cholesterol biosensors.
• The carbon-shelled Fe3O4 nanoparticle-based biosensor offers promising characteristics for cholesterol detection.