Brightly Fluorescent Self-Assembled Supra-J-Aggregate Nanoparticles for Bioanalysis and Imaging

J-aggregates of molecular dyes have the potential to serve as bright fluorophores with spectrally narrow emission for bioanalysis and imaging; however, this potential is largely untapped due to challenges in developing an architecture that stabilizes the J-aggregates, minimizes nonspecific binding interactions, and facilitates bioconjugation. Here, we develop and deploy colloidal supra-nanoparticle assemblies of J-aggregates as fluorescent labels. The assemblies, denoted as (Supra-J)-Dex, form via the spontaneous layer-by-layer assembly of a polycation, a cyanine dye (TDBC), and a dextran amphiphile on a silica nanoparticle scaffold. The (Supra-J)-Dex, which are characterized at both the ensemble and single-particle levels, are many-fold brighter than a benchmark monomeric fluorophore (rhodamine B) and far narrower in emission bandwidth. The minuscule Stokes shift associated with J-aggregates is neither an obstacle to one-photon-excitation fluorescence microscopy nor to imaging with a smartphone-based device equipped with an LED light source. It is also outrightly avoidable by two-photon excitation of fluorescence. (Supra-J)-Dex outperformed rhodamine B-labeled dextran and a semiconductor quantum dot in a mock lateral flow assay and in the immunofluorescent labeling of breast cancer cells via tetrameric antibody complexes. The assembly method appears generally applicable to cyanine dyes with anionic side chains, where future work will need to identify dye structural features that lead to bright fluorescence on par with supra-nanoparticle assemblies of TDBC dye. Overall, the (Supra-J)-Dex architecture simply and effectively harnessed J-aggregates for sensitive and selective fluorescent detection in bioanalysis.