Nanooptics and photonics

Spectroscopic study of amphi-PIC J-aggregates interaction with bovine serum albumin
Sorokin A.V., Grankina I.I., Averchenko K.A., I.A. Borovoy, S.L. Yefimova, 
Yu.V. Malyukin Nanostructured Materials Department, Institute for Scintillation Materials of NAS of Ukraine, 60 Nauky Ave., Kharkiv-61072, Ukraine
E-mail: sorokin@isma.kharkov.ua

Cyanine dyes possess many attractive spectral properties like narrow bands, high molar extinction coefficients, high quantum yields, etc. In recent years, there is a growing interest in the use of cyanine dye and related compounds not only as fluorescent probes but as theranostic agents, especially the dyes absorbing in red and near-infrared regions. Another prominent feature of cyanine dyes is the ability to form ordered aggregates, called J-aggregates, which are low-dimensional molecular crystals. High ordering within 1D or 2D molecular aggregates results in electron excitation delocalization over some segments forming Frenkel excitons. Depending on the molecular arrangement, the excitonic band can be the red-shifted narrow one (called J-band) or the blue-shifted wide one (called H-band). Cyanine dye J-aggregates are also widely used as luminescent probes for biomedical applications.  
It is known that natural blood proteins like serum albumins can interact with different nanoparticles facilitating their penetration into the living cells. However, in the case of J-aggregates albumins typically destroy aggregates trapping separate cyanine dyes into their structure. Such albumin – cyanine dyes complexes are often used to deliver cyanines, primarily anionic ones, into cells. 
In the present report, we demonstrate the interaction of the bovine serum albumin (BSA) with amphi-PIC J-aggregates in an aqueous solution. Despite the BSA concentration slightly exceeds that for the amphi-PIC dyes, the J-aggregates are present in the solution with no disaggregation signs. Moreover, its spectral properties became improved showing static disordering decrease simultaneously with significant enhancement of the aggregate photostability. Low-temperature experiments revealed decreasing the efficiency of exciton self-trapping. We suppose that the BSA forms a protein corona around amphi-PIC J-aggregates leading to the separating the aggregates agglomerates into individual species. The obtained results are very promising for the application of J-aggregates-albumin complexes as luminescent probes for biological objects.