Excitation energy migration in yellow fluorescent protein (citrine) layers adsorbed on modified gold surfaces

• Published in: Applied surface science 2013-09, Vol.280, p.776-782
• Main Authors: Yusoff, Hanis Mohd, Rzeźnicka, Izabela I., Hoshi, Hirotaka, Kajimoto, Shinji, Horimoto, Noriko Nishizawa, Sogawa, Kazuhiro, Fukumura, Hiroshi
• Format: Article
• Language: English
• Subjects: Anisotropy; Anisotropy decay; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Decay; Energy migration; Exact sciences and technology; Fluorescence; Fluorescence proteins; Gold; Migration; Photons; Physics; Proteins; Scanning tunneling microscopy; Scanning tunnelling microscopy
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2013.05.060

•Citrine (one of yellow fluorescent protein variants) was not denatured by the adsorption and drying on modified gold surfaces.•Fluorescence anisotropy decay was faster in dried protein layers than in solution, indicating the energy transfer among protein molecules.•Hydrophobic surface adsorbed protein more randomly while hydrophilic surface made more aligned layers.•Nano-scale observation of the morphology and fluorescence dynamics were connected, giving us consistent understanding. The nature of functional proteins adsorbed on solid surfaces is interesting from the perspective of developing of bioelectronics and biomaterials. Here we present evidence that citrine (one of yellow fluorescent protein variants) adsorbed on modified gold surfaces would not undergo denaturation and energy transfer among the adsorbed citrine molecules would occur. Gold substrates were chemically modified with 3-mercaptopropionic acid and tert-butyl mercaptan for the preparation of hydrophilic and hydrophobic surfaces, respectively. A pure solution of citrine was dropped and dried on the modified gold substrates and their surface morphology was studied with scanning tunnelling microscopy (STM). The obtained STM images showed multilayers of citrine adsorbed on the modified surfaces. On hydrophobic surfaces, citrine was adsorbed more randomly, formed various non-uniform aggregates, while on hydrophilic surfaces, citrine appeared more aligned and isolated uniform protein clusters were observed. Fluorescence lifetime and anisotropy decay of these dried citrine layers were also measured using the time correlated single photon counting method. Fluorescence anisotropy of citrine on the hydrophobic surface decayed faster than citrine on the hydrophilic surface. From these results we concluded that fluorescence energy migration occurred faster among citrine molecules which were randomly adsorbed on the hydrophobic surface to compare with the hydrophilic surface.