Stability and binding interaction of bilirubin on a gold nano-surface: steady state fluorescence and FT-IR investigation

Abstract

A gold nanoparticle exhibits strong absorption and emission due to its unique physical geometry and surface plasmon resonance phenomena. A further modification with organic molecules makes it more appropriate for biological applications. The current manuscript illustrated the optical behavior and stability of bilirubin (BR) coated gold (AuBR) nanoparticles, using BR itself as a reducing agent. In addition, FT-IR and steady state fluorescence measurements were performed to illustrate the binding interaction of BR with the Au(III) ion and the nanoparticles. BR showed a strong affinity towards Au(III) and the measured binding constant was ∼4.3 × 10(5) M(-1). It caused reduction of the Au(III) ion and rendered the formation of cubic face centered AuBR nanoparticles, which were ∼20 nm in diameter. The particles were stabilized as BR was bound to the gold nanoparticle surface, which was confirmed by FT-IR measurement. An intense carboxyl C=O stretching vibration at 1695 cm(-1) was observed for the BR powder but was absent for the AuBR nanoparticles. However, two weak bands at ∼1563 and 1391 cm(-1), presumably due to the asymmetric and symmetric stretching vibrations of the carboxylate form (COO(-)), were found for the AuBR nanoparticles. A stretching vibration of lactam C[double bond, length as m-dash]O appeared at 1645 cm(-1) for BR and the band was shifted to 1647 cm(-1) for the AuBR nanoparticles. The stretching modes of pyrrole N-H and lactam N-H were detected at 3406 cm(-1) and 3267 cm(-1), respectively, for BR. However, the pyrrole N-H band shifted to 3446 cm(-1) and became broader for the AuBR nanoparticles. The observed blue shift in the lactam C[double bond, length as m-dash]O and N-H vibrations of the AuBR nanoparticles indicated a weakening/absence of internal hydrogen bonds between the carboxyl groups and the four N-H bonds in the BR moiety. The binding of BR to the surface provides great stability to the nanoparticles, which remained monodispersed in the large pH range (pH 4 to 12) for more than a month. However, under acidic pH conditions the particles associated to form bigger particles and the plasmon resonance band shifted as they grew; the plasmon resonance band shifted from 525 nm (at pH 7.0) to 555 nm (at pH 3.0). The particles also remained stable in the presence of a higher concentration of salt (KCl and NaCl) in the dispersing media.

Porphyrin–Gold Nanomaterial for Efficient Drug Delivery to Cancerous Cells

“…The surface plasmon resonance (SPR) peak of TPPS-AuNPs appeared at 523 nm, and for the bare gold nanoparticles (AuNPs) in aqueous suspension, the peak was at 515 nm. 40 Thus, an ∼8 nm shift in the peak position was observed. The presence of porphyrin also resulted in the broadening of the plasmonic band, indicating a strong association of TPPS with the gold nanosurface.…”

Near-infrared autofluorescence induced by intraplaque hemorrhage and heme degradation as marker for high-risk atherosclerotic plaques

“…Fluorescence signals of these compounds are not constant in intensity and can change markedly with protein binding. Bilirubin’s fluorescence is enhanced with albumin binding 37–39 or binding with metals (e.g., tetrapyrroles fluorescence quenches significantly with iron 40 and bilirubin fluorescence quenches with gold 41 ). Even interaction with human erythrocyte ghosts seems to enhance the fluorescence of bilirubin 42 .…”

Optimization and Structural Stability of Gold Nanoparticle–Antibody Bioconjugates

“…Particularly, FT-IR allows for descriptions of pAb–AuNP complex interactions in the corona layer assemblies. 31,32 This technique allows the analysis of the stability changes in the secondary structure of the biomolecule. 33−36 Hence, specific information on the structural effects of pAb–AuNPs interactions at specific solvent conditions can be obtained.…”