Nonlinear optical properties of fluorescent proteins
Research carried out by and Evelien De Meulenaere, coordinated by Jos Vanderleyden and Stijn Spaepen
Apart from a list of linear optical properties like absorption, (1-photon) fluorescence, optical rotation, reflection and refraction, certain molecules can also exhibit nonlinear optical properties, like two-photon excited fluorescence, multiple photon absorption and sum frequency generation. Second harmonic generation (SHG) is a special case of sum frequency generation, where 2 photons of the same energy (or the same wavelength) interact at exactly the same moment with each other and with a specific molecule, to form a photon of double the frequency, or half the wavelength.
Fluorescent proteins are very well known for their easy application in biochemical experiments, usually to track other proteins inside cells. Fluorescent proteins have been known to exhibit SHG for several years (Khatchatouriants et al., 2000; Knöpfel et al., 2003), but these properties haven’t been characterized until recently (Asselberghs et al.,2008; De Meulenaere et al., 2009; De Meulenaere et al., 2010). We are investigating this nonlinear optical property of several existing fluorescent proteins and the ability to use SHG of this rainbow of fluorescent proteins expressed in living cells to extract structural and environmental data from microscopy experiments.
Artist’s impression of second harmonic generation (SHG) and two photon excited fluorescence (TPEF) of fluorescent proteins (eGFP, eYFP and DsRed).
This picture was published as inside cover in the Journal of Materials Chemistry, 2009.
References:
Asselberghs I, Flors C, Ferrighi L, Botek E, Champagne B, Mizuno H, Ando R, Miyawaki A, Hofkens J, Van der Auweraer M, Clays K (2008) Second-harmonic generation in GFP-like proteins. J Am Chem Soc 130: 15713-15719. PubMed
De Meulenaere E, Asselberghs I, de Wergifosse M, Botek E, Spaepen S, Champagne B, Vanderleyden J, Clays K (2009) Second-order nonlinear optical properties of fluorescent proteins for second-harmonic imaging. J Mater Chem19: 7514-7519. J Mater Chem
De Meulenaere E, De Wergifosse M, Botek E, Spaepen S, Champagne B, Vanderleyden J, Clays K (2010) Nonlinear optical properties of mStrawberry and mCherry for second harmonic imaging. J Nonlinear Opt Phys 19: 1-13. Worldscinet
Khatchatouriants A, Lewis A, Rothman Z, Loew L, Treinin M (2000) GFP is a selective non-linear optical sensor of electrophysiological processes in Caenorhabditis elegans. Biophys J 79: 2345-2352. PubMed
Knöpfel T, Tomita K, Shimazaki R, Sakai R (2003) Optical recordings of membrane potential using genetically targeted voltage-sensitive fluorescent proteins. Methods 30: 42–48. PubMed
