A near infra-red emitting supramolecular dye-polymer assembly as promising platform for protamine sensing

Detection and quantification of bioanalytes using near infra-red (NIR) probes provide several advantages, viz, negligible scattering of light, minimum interference from the background matrices, deep sample pen-etration, etc. Herein, we report a supramolecular dye-polymer complex, comprising of mono-cationic LDS-798 dye and multi-anionic polystyrene sulfonate (PSS), as a promising NIR emitting turn-on probe for protamine (Pr) sensing. The supramolecular complex displays moderate fluorescence enhancement for LDS-798 due to its binding onto PSS surface. Strikingly, in the presence of Pr, this complex displays further enhancement in its emission intensity, which is also substantiated by a significant increase in the excited-state lifetime of LDS-798 dye. This turn-on response is found to be highly selective towards Pr, which is attributed to the structural change taking place for the anionic PSS on its interaction with highly cationic Pr molecule. Such a conformational change creates several cavities into the modified PSS structure, which can suitably encapsulate LDS-798 dye via strong hydrophobic interaction. Accordingly, there is large decrease in the radiationless decay processes for the excited dye molecules, making them strongly emissive in nature. Furthermore, LDS-798-PSS complex is found to be quite robust against changing temperature and ionic strength of the medium, indicating its possible use as a fluores-cent probe over a wide range of temperature and salinity. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

Detection and quantification of bioanalytes using NIR probes have advantages of negligible light scattering, minimal interference from background matrices, and deep sample penetration. This study presents a supramolecular dye-polymer complex as a promising NIR emitting turn-on probe for protamine sensing. The complex shows fluorescence enhancement due to binding onto the polymer surface, and further enhancement in the presence of protamine. This selective turn-on response is attributed to a structural change in the polymer upon interaction with protamine.