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Published November 2023 | Published
Journal Article Open

Photoacoustic imaging of the dynamics of a dye-labeled IgG4 monoclonal antibody in subcutaneous tissue reveals a transient decrease in murine blood oxygenation under anesthesia



The aim of this research is to understand the dynamics of monoclonal antibodies at the injection site as well as how the antibody itself affects the functional characteristics of the injection site [e.g., blood oxygen saturation (sO2)].


We employed triple-wavelength equipped functional photoacoustic imaging to study the dynamics of dye-labeled and unlabeled monoclonal antibodies at the site of injection in a mouse ear. We injected a near-infrared dye-labeled (and unlabeled) human IgG4 isotype control antibody into the subcutaneous space in mouse ears to analyze the injection site dynamics and quantify molecular movement, as well as its effect on local hemodynamics.


We performed pharmacokinetic studies of the antibody in different regions of the mouse body to show that dye labeling does not alter the pharmacokinetic characteristics of the antibody and that mouse ear is a viable model for these initial studies. We explored the movement of the antibody in the interstitial space to show that the bolus area grows by ∼300 % over 24 h. We discovered that injection of the antibody transiently reduces the local sO2 levels in mice after prolonged anesthesia without affecting the total hemoglobin content and oxygen extraction fraction.


This finding on local oxygen saturation opens a new avenue of study on the functional effects of monoclonal antibody injections. We also show the suitability of the mouse ear model to study antibody dynamics through high-resolution imaging techniques. We quantified the movement of antibodies at the injection site caused by the interstitial fluid, which could be helpful for designing antibodies with tailored absorption speeds in the future.

Copyright and License

© The Authors. Published by SPIE under a Creative Commons Attribution 4.0 International License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.


A.K., C.D.P., J.M.B., S.O., and L.V.W. conceived the project and the ideas. C.D.P. and A.K. designed the chemistry and parameters for dye labeling. P.G. labeled the antibody with the dye and characterized them. P.G. and A.K. prepared the antibody and dye buffer solutions. A.K. and K.M. designed and built the scanning photoacoustic microscope. A.K. designed and performed the photoacoustic experiments and analyzed the photoacoustic data. A.K. interpreted all the results and conclusions. R.C. and J.S. wrote the LabVIEW software for photoacoustic data acquisition. P.B.A., E.L., and R.L.B. designed, performed, and analyzed the pharmacokinetic experiments. L.V.W., S.O., and J.M.B. supervised the project. A.K. wrote the manuscript. C.D.P., P.B.A., J.M.B, S.O., and LV.W. contributed to writing the manuscript.

Data Availability

The data that support the conclusions of this paper are mentioned in the main text or the supplementary information.

Conflict of Interest

A.K., R.C., and J.S. declare no competing interests. C.D.P., P.G, P.L.B.A., E.L., R.L.B, J.M.B, and S.O. are employees and stockholders of Eli Lilly and Company. L.V.W. and K.M. have financial interests in Microphotoacoustics, Inc.; CalPACT, LLC; and Union Photoacoustic Technologies, Ltd., which did not support this work.


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Additional details

February 29, 2024
February 29, 2024