Photoacoustic shadow-casting microscopy.

Area of Science:

• Biomedical Optics
• Microscopy Techniques
• Biophotonics

Background:

• Imaging weakly absorbing biological samples is challenging due to low contrast.
• Conventional photoacoustic microscopy (PAM) can cause photothermal damage at high excitation fluences.
• There is a need for high-sensitivity, low-damage microscopy techniques.

Purpose of the Study:

• To introduce and demonstrate photoacoustic shadow-casting microscopy (PASM).
• To achieve high-resolution imaging of weakly absorbing biological samples.
• To improve signal-to-noise ratio and reduce photothermal damage.

Main Methods:

• PASM utilizes a uniform optical absorbing layer in contact with the sample.
• The absorbing layer is excited by light transmitted through the sample, generating photoacoustic waves.
• A 0.30 numerical aperture (NA) microscope objective lens was used, providing 5 μm lateral resolution.

Main Results:

• PASM achieved an increased signal-to-noise ratio compared to conventional PAM.
• The technique significantly reduced the required excitation fluence, minimizing photothermal damage.
• High-resolution images of bovine red blood cells and microbeads were successfully acquired.

Conclusions:

• PASM offers unprecedented sensitivity and high resolution for imaging weakly absorbing biological specimens.
• The method effectively mitigates photothermal damage, enabling safer imaging.
• PASM represents a significant advancement in photoacoustic microscopy for biological applications.