Enhanced deep-tissue photoacoustics by using microcomposites made of radiofrequency metamaterials and soft polymers: Double- and triple-resonance phenomena

Abstract: Photoacoustic imaging systems offer a platform with high resolution to explore body tissues, food, and artwork. On the other hand, plasmonics constitutes a source of resonant heating and thermal expansion to generate acoustic waves. However, its associated techniques are seriously limited to laser penetration and nonspecific hyperthermia in the sample. To address this issue, the present work adopts a paradigm shift in photoacoustics. By simulating microparticles made of random composites, the calculated pressure can be made similar or superior to that calculated via plasmonic optoacoustics. The improvement is due to a phenomenon called double or triple resonance, which is the excitation of one or both electric and magnetic plasmons within radiofrequency range and the simultaneous excitation of the particle's acoustic mode. Given that electromagnetic pulses are restricted to nanosecond pulse widths and MHz frequencies, the proposed method overcomes the poor penetration in tissues and reduces thermal damage, thereby offering a noninvasive technique of theragnosis. Moreover, the resonant pressure obtained lasts longer than with conventional photoacoustic pressure, providing a central feature to enhance detection. To fully comprehend the multi-resonance framework, we develop a complete photoacoustic solution. The proposed approach could pave the way to thermoacoustic imaging and manipulation methods for sensitive materials and tissues with micrometer resolution.