EAGER: A New Multiphoton Luminescence Imaging Approach to Interrogate the Fate of Metallic Nanoparticles in a Living System

Over the last 20-years, metallic nanoparticles have been utilized across a wide range of fields from cosmetics to renewable energy to electronics to biomedical applications. Their size gives them unique properties, and the use of metallic nanoparticles has revolutionized several technological and industrial sectors. As a result, inadvertent human exposure rates to engineered metallic nanoparticles are increasing, generating the need to better understand their short- and long-term effects to ensure the public’s safety.

This project will focus on utilizing a new imaging strategy that can offer important insights on how metallic nanoparticles behave in living systems. The imaging strategy is different than conventional imaging techniques in that it does not require an exogenous label to track metallic nanoparticles. Instead, the imaging strategy can detect and follow the metallic nanoparticles in a label-free manner by exploiting a luminescent signal that is generated from the metals that comprise the nanoparticles themselves.

The imaging technique can offer real-time tracking of metallic nanoparticles to observe their physiological interactions while in circulation. The images generated will also be able to reveal where they ultimately reside in the body and determine if any toxic effects or morphological changes are resulting. Gaining an improved fundamental understanding of these biological interactions could 1) better discern the safety of metallic nanomaterials in living subjects, 2) lead to informing new environmental policies, 3) generate new disease targeting strategies with therapeutic metallic nanoparticles to improve patient outcome.

Additionally, further development and assessment of this transformative imaging strategy could open new avenues of investigation throughout the nano-community to further exploit this unique imaging technique. Local Los Angeles high school students will be introduced to the physical concepts and imaging approaches utilized here and the various nanoparticle types encountered as environmental pollutants.

The goals for the educational plan are to 1) generate enthusiasm and spark creativity among students from under-represented groups in the Los Angeles area by showing different ways that nanoparticles are used to solve problems and 2) introduce new imaging concepts to students that can allow them to watch where nanoparticles are located in the body.

The research objective of this project is to explore a new multiphoton luminescence imaging strategy and its ability to develop a deeper understanding of how metallic nanoparticles behave in living systems. Researchers have previously reported on specific endpoints of nanoparticle interactions studied in cell culture on a macroscopic scale, e.g., cellular stress, inflammatory or mutagenic responses, or biodistribution profiles observed in preclinical models.

However, this does not give a complete or biologically accurate depiction of how nanomaterials behave in a dynamic living system. Metallic nanoparticle biodistribution has been previously studied, but their real-time dynamics in circulation and ultimate fate are poorly understood on the microscopic level. This research project addresses this critical need by using a new and innovative multiphoton luminescence microscopy imaging approach.

Intravital microscopy (IVM) has emerged as a profound imaging modality for gaining insight into dynamic processes on the cellular and sub-cellular level and is particularly suitable for visualizing nanoparticles in real time. IVM has enabled observation of several fundamental nanoparticle processes such as extravasation, tumor accumulation, and blood elimination in real time within a living organism.

A current problem is that most nanoparticles must be exogenously labeled with fluorophores for visualization with conventional single-photon IVM. As the fluorophore may dissociate from the nanoparticle, it is challenging to determine the true behavior of nanoparticles within the blood stream using this approach. This project will use a new label-free multiphoton luminescence imaging approach that was recently uncovered in the principal investigator’s (PI’s) lab to study the native behavior of metallic nanoparticles in mouse models.

Intrinsic broad-band luminescence has previously been observed in noble metals under multiphoton excitation conditions but has yet to be applied successfully in vivo to track nanoparticles flowing within the vasculature in real time. Luminescent properties associated with metals have yet to be applied successfully in vivo to track nanoparticles flowing within the vasculature in real time.

This underutilized intrinsic luminescence will be used to 1) track metallic nanoparticles flowing in the vasculature to assess their rates of clearance from blood, and 2) determine their toxicities on major organs where they ultimately reside by analyses of harvested tissues. This is an immensely powerful tool, as the intrinsic luminescence of metallic nanoparticles could finally give the research community the ability to follow native flow in the blood while providing dynamic physiological information and ultimately localizing their accumulation within tissues on a microscopic scale.

Consumers may be inadvertently exposed to various metallic nanoparticles. The results generated from this project are meant to enable a better understanding of the cellular interactions taking place within the body and where these nanoparticles ultimately reside. This information will be important in determining how to better regulate these nanomaterials as new nano-enabled products are engineered.

A multi-year outreach and educational training plan will be pursued that is closely integrated with the proposed research, emphasizing how people use and encounter nanomaterials day to day. High school students from underrepresented groups across the Los Angeles area will be introduced to nanoparticles and the imaging techniques utilized to study their interactions in the body.

The PI will connect with a Hispanic serving institution in her hometown, University of Texas Rio Grande Valley (UTRGV). UTRGV currently lacks Ph.D. curricula in STEM and this research opportunity will enable the participation of these students in this research lab, providing interaction with Ph.D. students. This will promote higher education paths for students who otherwise would not get exposed to these careers.

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.