Oct 19, 2020
Professor Ellen Sletten
Ellen Sletten’s group, in collaboration with scientists in Germany, develops new imaging probes and technologies to allow for real-time multicolor imaging. 
These combined technological advances provide simultaneous visualization of multiple biological structures in different colors at video speeds and has promise for applications in non-invasive and intraoperative diagnostics.
Professor Ellen Sletten (pictured above) joined the faculty in the Department of Chemistry & Biochemistry at UCLA as an Assistant Professor and the John McTague Career Development Chair in 2015.
The research was done in collaboration with Dr. Oliver Bruns’ laboratory at the Helmholtz Pioneer Campus at Helmholtz Zentrum München (Munich, Germany).
Figure 1. SWIR fluorophores and excitation multiplexed SWIR imaging. a) Heptamethine dyes reported in the study. b) Whole mouse multiplexed imaging in real time. c) Imaging of lymphatic vessels and vasculature in the hindlimb in two colors. 
The work, entitled “Shortwave infrared polymethine fluorophores matched to excitation lasers enable non-invasive, multicolour in vivo imaging in real time” was published in Nature Chemistry with authors from UCLA Chemistry & Biochemistry: graduate students Emily Cosco, Anthony Spearman, Monica Pengshung, and Kelly Wong and former undergraduate student Ryan McLaughlin (’19).
The Sletten group team - graduate students Emily Cosco, Anthony Spearman, Monica Pengshung, Kelly Wong, and alum Ryan McLaughlin (’19).
The UCLA team synthesized dyes with long wavelengths of absorption and emission, within the shortwave infrared region (SWIR, also referred to as the NIR-II region, 1000–2000 nm). Detection in the SWIR is essential for the non-invasive optical imaging method due to the high-resolution and deep-tissue penetration provided by SWIR light, in comparison to light at shorter wavelengths, such as visible light. Using physical organic chemistry principles, the researchers were able to tune the absorption profiles to shorter and longer wavelengths so that individual dyes could be preferentially excited by different lasers. This advance fueled the development of the imaging method “excitation-multiplexing with single-channel SWIR detection,” in which multiple excitation sources can be modulated and detected in tandem with a single detector, on the millisecond time scale. This work is in contrast to prior methods which have relied on different emission windows to observe multiple colors. 
Imaging experiments, conducted at the Helmholtz Pioneer Campus, with the German-based team and Cosco (as a visiting scientist at the research center), showed that two-and three-color images could be collected in high resolution at video-rate speeds (>25 frames per second). The multiplexing technology was leveraged to observe both biological structure and function, including liver function, lymphatic clearance, and vascular structures. Researchers envision that the method could be applied to observe both diseased tissue and healthy structures simultaneously, aiding clinicians in safe and non-invasive diagnoses, and during surgical procedures.
In a recent article in Nature Research Chemistry Community's "Behind the Paper" section, Cosco writes about her experience working between Sletten's lab at UCLA and the newly formed Bruns Lab at the Helmholtz Pioneer Campus.
Researchers from the Helmholtz Pioneer Campus include graduate students Jakob Lingg and Bernardo Arús, post-doc Dr. Mara Saccomano, engineer Shyam Ramakrishnan, and lab manager Martin Warmer. Members of the Institute of Biomedical Imaging (IBMI) at Helmholtz Zentrum München, Sarah Glasl and Professor Vasilis Ntziachristos are also co-authors. 
The work was funded by the National Institute of Health, the National Science Foundation, the Alfred P. Sloan Foundation, Emmy-Noether Program of the DFG, the Foote Family, UCLA, and Helmholtz Pioneer Campus Institute for Biomedical Engineering.
For further information, contact Professor Ellen Sletten, sletten@chem.ucla.edu.
Penny Jennings, UCLA Department of Chemistry & Biochemistry, penny@chem.ucla.edu.