Microscale photoacoustic imaging via laser-induced ultrasound in microfluidic environments

Abstract Photoacoustic (PA) imaging offers a powerful non-invasive approach for visualizing optically absorbing structures within biological tissues and microfluidic (MF) devices. While conventional PA imaging often relies on complex inverse problem solutions and physical models to reconstruct images, these approaches can be computationally intensive and limit real-time application in dynamic microenvironments. This study presents a knowledge gap in developing a simplified high-performance PA imaging method, based directly on the acquired PA signals, directly related with in situ geometric sample variations such as width and volume. This optimized method enables direct reconstruction of optically absorbing objects from their intrinsic PA signal characteristics, significantly reducing the reliance on intricate data processing or complex physical models. Utilizing a compact PA setup with acoustic transducers integrated into a MF system, we successfully imaged objects buried up to 3 mm deep with a resolution of 110 µ m. The system’s overall performance spans its resolution depth characterization, the use of water-soluble optical absorber material (copper(II) nitrate, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mtext>Cu</mml:mtext> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mtext>NO</mml:mtext> <mml:mn>3</mml:mn> </mml:msub> <mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math> ) and surfactant, to its application in detecting melanoma cells and rat blood within microdroplets. Our approach overcomes limitations of traditional model-based techniques, offering a high-resolution, non-invasive option for investigating the internal dynamics of absorbing objects. This advancement holds promise for valuable applications in fundamental MF research, biomedical diagnostics, and industrial quality control, where simplicity, speed, and precision are paramount.