Tunable fluorescence quenching near the graphene-aqueous interface

Area of Science:

• Materials Science
• Biophysics
• Nanotechnology

Background:

• Graphene-based sensors are increasingly used for biomolecule detection.
• Understanding environmental factors affecting sensor performance is crucial.
• Fluorescein is a common labeling agent for biomolecules.

Purpose of the Study:

• To investigate the effect of ionic strength on fluorescein-labeled proteins adsorbed on graphene.
• To explore the implications of the aqueous environment near graphene surfaces.

Main Methods:

• Utilized fluorescein-tagged fibrinogen as a model system.
• Studied steady-state fluorescence emissions from adsorbed proteins on chemical vapor deposited (CVD)-graphene/silica.
• Varied salt concentration and employed Guoy Chapman modeling.

Main Results:

• Fluorescein emission intensity on adsorbed fibrinogen was highly sensitive to salt concentration, unlike in solution.
• Fluorescence quenching was linked to fluorescein's pH sensitivity and an acidic near-surface environment.
• The acidic environment is attributed to negative charge on the graphene or underlying silica support.

Conclusions:

• The aqueous interface near silica-supported graphene is acidic due to negative surface charge.
• Ionic strength can be used as a 'molecular ruler' to assess fluorescence emissions near graphene.
• Findings are relevant for any fluorescein-tagged species near graphene, impacting sensor design and interpretation.