One- and Two-Photon Excited Autofluorescence of Lysozyme Amyloids

Abstract

Autofluorescence properties of amyloid fibrils are of much interest but, to date, the attention has been given mostly to one-photon excited fluorescence (1PEF), while the two-photon excited fluorescence (2PEF) properties of amyloids are much less explored. We investigate 1PEF and 2PEF of hen egg-white lysozyme (HEWL) in the form of monomers and fibrils. HEWL monomers feature some autofluorescence, which is enhanced in the case of fibrils. Moreover, by varying NaCl content, we introduce changes to fibrils morphology and show how the increase of the salt concentration is linked with an increase of 1PEF and 2PEF intensities. Interestingly, we observe 2PEF emission red-shifted in comparison to 1PEF. We confirm the presence of different relaxation pathways upon one- or two-photon excitation by different lifetimes of the fluorescence decays. Finally, we correlate the changes in optical properties of HEWL fibrils and monomers with salt-mediated changes in their morphology and the secondary structure.

Non-toxic Polymeric Dots with the Strong Protein-Driven Enhancement of One- and Two-Photon Excited Emission for Sensitive and Non-destructive Albumin Sensing

“…According to the literature, BSA and HSA plasma proteins display nine characteristic absorption peaks (i.e., amide bands A–B and I–VII), which are assigned to different vibrations from N–H, CO, and C–N bonds. , The major absorption signals correspond to the amide I band (CO stretching) and amide II band (C–N stretching and N–H bending). They are located in the range of 1500–1750 cm –1 , considered as the fingerprint region of proteins and usually studied in the quantitative conformational analysis. ,− All normalized amide I bands of proteins–PDs samples exhibit only a small broadening and a blue shift. Amide II bands decrease slightly in the presence of varying contents of PDs (see Figure S22).…”

“…30 Similar trends were reported for protein assemblies (i.e., amyloid fibrils). 38 In contrast, organometallic supramolecular assemblies and molecular cocrystals possess the constant positions of their OPE and TPE emission peaks. 39−43 The TPE bands of the PDs are also located at wavelengths shorter than the doubled wavelength maxima of the OPE spectrum (Figure 1), in agreement with the previous nonlinear optical (NLO) studies on carbon dots.…”

Revealing two chemical strategies to tune bright one- and two-photon excited fluorescence of carbon nanodots

“…The TPEF spectra are slightly red shifted (by 2–7 nm) with respect to their one-photon excited analogues. The spectral red shifts were also observed for other CDs 3,39 and fluorescent peptide assemblies; 72 however, these bathochromic shifts were larger (∼20–60 nm). In the case of PG CNDs, we can confirm the similar relaxation pathways in one- and two-photon regimes, with only minor modifications of the vibrational structure.…”

Strongly Emitting Folic Acid-Derived Carbon Nanodots for One- and Two-Photon Imaging of Lyotropic Myelin Figures

“…It should be noted that in some CDs the TPE bands are blue-shifted with respect to the doubled-wavelength position of their OPA spectra. , The TPE fluorescence band of the FA CNDs is red-shifted (by 17 nm) with respect to their OPEF spectra (Figure f). Such a feature was reported for a variety of fluorescent species containing polymeric sub-structures, including other CNDs, polymer dots (PDs), peptide aggregate forms (i.e., amyloids), etc.…”