Abstract
Bioinspired fluorescence, being widely explored for imaging purposes, faces challenges in delivering bright biocompatible sources. While quite a few techniques have been developed to reach this goal, encapsulation of high-quantum yield fluorescent dyes in natural biological forms suggest achieving superior light-emitting characteristics, approaching amplified spontaneous emission and even lasing. Here we compare gain capabilities of highly concentrated Rhodamine B solutions with a newly synthesized biocompatible peptide derivative hybrid polymer/peptide material, RhoB-PEG1300-F6, which contains the fluorescent covalently bound dye. While concentration quenching effects limit the maximal achievable gain of dissolved Rhodamine B, biocompatible conjugation allows elevating amplification coefficients towards moderately high values. In particular, Rhodamine B, anchored to the peptide derivative material, demonstrates gain of 22–23 cm−1 for a 10−2 M solution, while a pure dye solution possesses 25% smaller values at the same concentration. New biocompatible fluorescent agents pave ways to demonstrate lasing in living organisms and can be further introduced to therapeutic applications, if proper solvents are found.
Highlights
Bioimaging is a widely used technique, contributing to a broad range of applications, spanning from fundamental cellular studies to applied t herapeutics[1]
Peptide derivative Rho-PEG1300-F6, of which the molecular structure appears in the inset to Fig. 1, was synthetized in a solid phase according to the Fmoc/OtBu strategy[14], purified by RP-HPLC and characterized by electrospray ionization (ESI) mass spectrometry (Fig. 1)
We characterized the peptide in HFIP/H2O (20/80, v/v) mixture, in which peptide arrangement into β-sheet macrostructures is expected. This consideration is based on different studies previously performed on hexaphenylalanine analogues[15,16,17]
Summary
Bioimaging is a widely used technique, contributing to a broad range of applications, spanning from fundamental cellular studies to applied t herapeutics[1]. While each specific investigation might demand having a certain set of properties, there are several typical requirements common to a majority of bioimaging applications Those requirements include biocompatibility (or at least a low level of toxicity), high quantum yield and resistance against bleaching and quenching. Typical concentrations where collective effects start playing a role for Rhodamine dyes are around ~ 1 0−2 mol/L5–8, though there is a strong dependence on the solvent used for dye dissolution In this case, further increasing the concentration does not lead to a boost in the fluorescent signal but rather causes its decrease. We show that the Rhodamine conjugation allows preventing concentration quenching effect and provides moderately higher values of gain within an optically pumped solution It is worth noting, that threshold concentrations strongly depend on an embedding environment (typically a solvent) and on the experimental technique which has been used. Comparative studies of samples, which undergo the same fabrication and characterization path are required—this is what will be done here
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