Development of Activity-Based Sensors and Biomarkers
Unlock the power of NIR-II imaging for your biomarker discovery research
Transitting from NIR-I to NIR-II in vivo imaging
The discovery of long tails of emission of NIR-I contrast agents that extend into the second biological window called NIR-II (or SWIR) has changed the way of visualizing small animals. Imaging in the SWIR region has enabled it to look clearer and deeper because of the transparency of the tissues with the NIR-I dyes that have long emission tails like ICG (indocyanine green). To take advantage of this transparency, research groups around the world have developed NIR-II activity-based sensors such as small molecule-based dyes, single-walled carbon nanotubes, semiconductor quantum dots, graphene dots, nanoparticle alloys, down conversion rare-earth nanoparticles, semiconducting polymer-based nanoparticles (SPNPs), aggregation-induced emission (AIE) probes, etc.
See sooner, see deeper
These contrast agents can be observed in vivo thanks to the superior penetration depth (10x more than the visible wavelengths) in the SWIR region. Each of them has unique properties that have shown great promise to generate new tools for diverse applications such as surgery guidance to treatment efficacy assessment, theranostics, disease monitoring and diagnosis.
The characterization tools present a challenge
Nonetheless, the development of these agents comes with the challenge that very few characterization tools are optimized for these wavelengths. In order to push further the development of NIR-I and NIR-II biomarkers for NIR-II imaging applications, we must have the appropriate tools to detect the fluorescence signal in this region, either using point-by-point spectroscopy or real-time imaging of probes in vivo, in vitro or in solution. Efforts must be made to continue optimizing quantum yields of dyes with emissions tails in the NIR-II to develop new applications in biological research.