Broadband graphene-based photoacoustic microscopy with high sensitivity

Area of Science:

• Biomedical Optics
• Materials Science
• Nanotechnology

Background:

• Photoacoustic microscopy (PAM) measures optical absorption in tissues but is limited by transducer frequency response, affecting depth resolution and accuracy.
• Existing PAM systems struggle with precise optical absorption coefficient measurements due to inadequate frequency response.

Purpose of the Study:

• To develop a novel photoacoustic microscopy (PAM) system with improved depth resolution and optical absorption measurement accuracy.
• To utilize a graphene-based sensor for enhanced photoacoustic (PA) wave detection.

Main Methods:

• A PAM system was configured using an attenuated total reflectance sensor with a ten-layer graphene film between a prism and water.
• Photoacoustic pressure transients altered water's refractive index, modulating the graphene film's polarization-dependent absorption.
• Signal detection involved recording reflectance intensity differences between orthogonally polarized probe beams.

Main Results:

• The graphene sensor demonstrated a noise-equivalent-pressure sensitivity of ~550 Pa within a 11.0-55.0 kPa linear response range.
• The system achieved a broad PA bandwidth detection of up to ~150 MHz, attributed to a localized evanescent field.
• In vivo, label-free PAM imaging of mouse ear microvasculature was achieved in 3D, leveraging hemoglobin's strong optical absorption.

Conclusions:

• The developed graphene-based PAM sensor significantly improves depth resolution and absorption coefficient measurements.
• The system enables high-bandwidth, label-free 3D imaging of microvasculature, demonstrating its potential for biomedical applications.
• Graphene-based PAM shows great promise for microcirculation studies and other biomedical investigations.