CAREER: Photoacoustic-Brillouin microscopy for multimodal mechanical imaging of tumor growth

Tumor tissues are usually harder than surrounding healthy tissues, leading to a different microenvironment for cancer cells inside. Since the behaviors and functions of cells are regulated by physical cues from their microenvironment, emerging research has suggested that the altered mechanics of tumor tissue plays a crucial role in the progression of metastatic cancers. To understand the relationship between the properties of the microenvironment and tumor growth, it is essential to quantify these mechanical properties with high spatial resolution in three dimensions. However, existing mechanical testing tools are mostly contact-based and invasive, making such measurement highly challenging. This Faculty Early Career Development (CAREER) project aims to address the current technical challenge by developing an optical technology named photoacoustic-Brillouin microscopy (PABM), which can measure the mechanical properties of cancer cells and their microenvironment in a non-contact, non-invasive, and high-resolution manner. In concert with the research goal, this project will develop educational modules to promote the dissemination of the innovative Brillouin technology and to stimulate a lasting interest in biophotonics for high school, undergraduate, and graduate students. Confocal Brillouin microscopy has been recently demonstrated as a promising non-contact mechanical testing tool. However, due to the lack of knowledge on refractive index and density of the sample under test, existing Brillouin microscopy is mostly used to estimate the relative mechanical change, rather than to provide an absolute measurement of mechanical modulus, making it inapplicable for heterogeneous tumor microenvironment, benchmarking, and comparison across studies. In this project, a novel optical technique named PABM will be developed based on the colocalized excitation of scattered Brillouin light and time-resolved photoacoustic signals. In addition to directly quantifying mechanical modulus, the PABM can provide complementary contrast mechanisms, including stiffness, optical absorption, and acoustic speed. This capability will enable a comprehensive understanding of heterogeneous processes in tumor growth. Taken together, the PABM addresses a significant gap in current cancer research methodologies. The new data and insights gained from this technology holds a unique potential to advance a wide range of research in both biophotonics and cancer diseases. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.