Black mesoporous silicon as contrast agent for LED-based 3D photoacoustic tomography.

Mesoporous silicon (PSi) nanoparticles have been widely studied in different biomedical imaging modalities due to its several beneficial material properties. However, they have not been found suitable for photoacoustic imaging due to their poor photothermal conversion performance. In the present study, biodegradable black mesoporous silicon (BPSi) nanoparticles with strong light absorbance were developed as a superior image contrast agent for photoacoustic tomography (PAT), which was realized with light emitting diode (LED) instead of commonly used laser. LED-based PAT offers the advantages of low cost, compactness, good mobility, and easy operation as compared to the traditional laser-based PAT modality. Nevertheless, the poor imaging sensitivity of the LED-PAT systems has been the main barrier to prevent their wide biomedical application because the LED light has low optical energy. The present study demonstrated that the imaging sensitivity of the LED-PAT system was significantly enhanced with the PEGylated BPSi (PEG-BPSi) nanoparticles. The PEG-BPSi nanoparticles were clearly detectable with the low concentration of 0.05 mg/mL in vitro and with the LED radiation energy of 5.2 μJ. The required concentration of the PEG-BPSi nanoparticles was ten-times less than that of the reference gold nanoparticles to reach the corresponding level of the imaging contrast. The ex-vivo studies demonstrated that the submillimeter BPSi nanoparticle-based absorbers were distinguishable in chicken breast tissues. The strong contrast provided by the BPSi particles indicated that these particles can be utilized as novel contrast agents in PAT, especially in LED-based systems with low light intensity.