Ileana Rau and Francois Kajzar
This special issue is devoted to biopolymers and their potential applications in photonics technologies. It contains invited, revue papers written by the world leading specialists in this field, making an immense contribution to its development and is addressed particularly to the incomers to this very rapidly developing photonic and electronic materials field. For people already active in this research it may give a broader vision of very large potentialities for practical applications of biopolymers.
Biopolymers are abundant and practically unlimited supply materials, originating from renewable resources. People working in photonics technologies since a time already began to interest in these materials. This interest has grown significantly in recent years because of limited resources for synthetic polymers, synthesized mostly from the oil refineries sub products on one hand and on the increasing presence of polymers and their use in every day life on the second one. It is certain that the oil sources will dry soon and the synthetic polymers will have to be replaced by another materials.There are also another problems connected with the practical use of synthetic polymers. Principally it is the problem of their very slow degradation. Because of that they contribute significantly to the pollution of our planet. These problems became more and more crucial, particularly in terms of durable development of the planet.
Therefore the biopolymers appear to be a very interesting counterpart to synthetic polymers. They are abundant, their production is continuous by the nature and they are biodegradable. Already some biopolymers are used to replace ethylene, one of the most important pollutant of the planet, particularly that used in packaging. Biopolymers, particularly such as fluorescent proteins are largely utilized in medical imaging. Some of biopolymers, such as chitosan,  starch,  pectin  or agar  are used as polyelectrolytes (cf. paper by Firmino et al. ). Good results were also obtained with the protein gelatin .
Recently it was also shown that the biopolymers are very interesting candidates for practical applications in photonics and in electronics, particularly with the synthesis of stable and excellent optical propagation processes of DNA . This biopolymer, extracted from the waste produced in the salmon processing industry is commercially available from Ogata Photonics Laboratory, which elaborated a technique for its separation and purification. The practical used of this material was demonstrated in an excellent work by the J. Grote and co-workers  from US Air Force Wright Patterson Labs, Dayton, Ohio, USA. Compounds with good chemical stability up to ca. 230ºC were obtained by reaction of DNA with surfactants, particularly with CTMA (hexadecyltrimethyl chloride). They are soluble in common organic solvents, depending on the used surfactant and insoluble in water, the only solvent of DNA. The DNA-surfactant complex can be processed from solution into very good optical propagation properties thin film by such techniques like spin coating, deep drawing, doctor blade, etc.
The natural biopolymers are optically inactive materials because of the absence (proteins, starch) or little (DNA, collagen) π electron conjugation, providing high hyperpolarizability to conjugated polymers. Despite that they have shown interesting behaviours, such as ionic conductivity, exploited as solid polymers in electrochromic cells (see paper by Firmino et al ), particularly in smart windows or as buffer layers in electro-optic modulators, providing a beneficial electric field distribution between on the active and buffer layers, leading to the improvement of operation parameters (half wave voltage Vπ) [9,10].
As already mentioned most of research was done actually with DNA and DNA-CTMA complexes. These biopolymers can be doped or chemically functionalized with optically and electrically responsive molecules (cf. paper by I. Rau and F. Kajzar ). Due to the peculiar, double strand helical structure of DNA the possibilities of doping are increased and the properties of embedded molecules favourably modified. This is, e.g. the case of photoluminescence, which was found to be significantly enhanced in biopolymer matrix, as compared with synthetic polymers [12-13]. Also, potentially very important for practical applications photochromic processes are few orders of magnitude faster than in synthetic polymers This peculiar structure of DNA allowed several demonstrations of lasing, observed in doped DNA-CTMA-fluorescent dye systems [14-16]. Also improvement in organic light emitting diodes was observed by using DNA-CTMA as an electron blocking layer [17-18]. Kobayashi and co-workers demonstrated very recently the electric field controlled large wavelength emission spectrum of a DNA based BIOLED  (cf also the paper by N. Kobayashi ).
It is also worthy to note that the active molecules are more stable in DNA or DNA matrices than in synthetic polymer like polycarbonate and polyethyl glycol .
In electronics DNA-CTMA was used in fabrication of a field effect transistor  as a gate dielectric and variable capacitors . It is a well disposed material for fabrication of organic light emitting field effect transistors (OLEFETs). Interesting for practical application is the chemical and the tunability of the DNA-CTMA resistance by controlling its molecular weight .
We would also to attract your attention on the important and very interesting papers by A. Knoesen and K. Reisker  and by Y. Okada-Shudo . The first one describes the use of NLO parametric techniques for studying the crystalline and amorphous regions in intact samples of polysaccharides (cellulose, starch) and their relationship. The article by Y. Okada-Shudo describes application of bacteriorhodopsin for polarization recording and reconstruction in holography and its application in optical signal processing.
Angers – Bucharest, April 2011
 Pawlicka A., Danczuk M., Wieczorek W. and Zygadlo-Monikowska E. Influence of Plasticizer Type on the Properties of Polymer Electrolytes Based on Chitosan. J. Phys. Chem. A, 112, 8888–8895 (2008)
 Marcondes R. F. M. S., D’Agostinia P. S., Ferreira J., Girotto E. M., Pawlicka A. and Dragunski D. C., Solid State Ionics, 181, 586 (2010).
 Andrade J. R., Raphael E. and Pawlicka A., Electrochimica Acta, 54, 6479 (2009).
 Raphael E., Avellaneda C. O., Manzolli B. and Pawlicka A., Electrochimica Acta, 55, 1455 (2010).
 Firmino A., Grote J. G., Kajzar F., Rau I. and Pawlicka A., Application of DNA in electrochromic cells with switchable transmission, Nonl. Opt. Quant. Opt., this issue.
 Vieira D. F., Avellaneda C. O. and Pawlicka A., Electrochimica Acta 53, 1404 (2007).
 Wang L., Yoshida J., Ogata N., Sasaki S. and Kajiyama T., Self-assembled supramolecular films derived from marine deoxyribonucleic acid (DNA)-cationic surfactant complexes: large-scale preparation and optical and thermal properties, Chem. Mater. 13(4), 1273–1281 (2001).
 Grote J., Biopolymer materials show promise for electronics and photonics applications, , SPIE Newsroom., 15 May 2008, DOI: 10.1117/2.1200705.1082,http://spie.org/x24479. xml?ArticleID=x24479
 Grote J., Ogata N., Diggs D.and Hopkins F., Deoxyribonucleic acid (DNA) cladding layers for nonlinear-optic-polymer-based electro-optic devices, Proc. SPIE, 4991, 621–625 (2003).
 Grote J., Hagen J., Zetts J., Nelson R., Diggs D., Stone M., Yaney P., Heckman E., Zhang C., Steier W., Jen A., Dalton L., Ogata N., Curley M., Clarson S. and Hopkins F., Investigation of polymers and marine derived DNA in optoelectronics, J. Phys. Chem. B, 08(25), 8589–8591 (2004).
 Rau I. and Kajzar F., Nonlinear Optical Properties of Functionalized DNA-CTMA Complexes, Nonl. Opt. Quant. Opt., this issue.
 Yu Z., Hagen J., Zhou Y., Klotzkin D., GroteJ. and Steckl A., Photoluminescence and stimulated emission from deoxyribonucleic acid thin films doped with sulforhodamine, Appl. Opt. 46(9), 1507–1513 (2006).
 Yu Z., Zhou Y., Klotzkin D., Grote J. and Steckl A., Stimulated emission of sulforhodamine 640 doped DNA distributed feedback (DFB) laser devices, Proc. SPIE, 6470, 64700V (2007).
 Y., Wang, L., Nakamura, T. and Ogata, N., Thin-film lasers based on dye-deoxyribonucleic acid-lipid complexes. Appl. Phys. Lett. 81, 1372–1374 (2002).
 Mysliwiec J., Sznitko L., Miniewicz A., Kajzar F. and Sahraoui B., Study of the amplified spontaneous emission in a dye-doped biopolymer-based material, J. Phys. D: Appl. Phys., 42(8), 085101 (2009).
 Kawabe Y. and Sakai K.-I., DNA Based Solid-State Dye Lasers, Nonl. Opt. Quant. Opt., this issue.
 Diggs D., Hagen J., Yu Z., Heckman E., Hopkins F., Grote J. and Steckl A., Molecular binding and enhanced photoluminescence of bromocresol purple in marine derived DNA, Proc. SPIE, 5934, 071–078 (2005).
 Hagen J., Li W., Steckl A., Grote J. and Hopkins F., Enhanced emission efficiency in organic light emitting diodes using deoxyribonucleic acid complex as electron blocking layer, Appl. Phys. Lett., 88, 171109 (2006).
 K. Nakamura, T. Ishikawa, D. Nishioka, T. Ushikubo, and N. Kobayashi, Appl. Phys. Lett., 97, 193301 (2010).
 Kobayashi N., BiOLED with DNA/Conducting Polymer Complex as Active Layer, Nonl. Opt. Quant. Opt., this issue.
 Popescu R., Pîrvu C., Moldoveanu M., Grote J. G., Kajzar F. and Rau I., Biopolymer thin films for optoelectronics applications, Mol. Cryst. Liq. Cryst., 522, 229–237 (2010).
 Singh B., Sariciftci S., Grote J. and Hopkins F., Bio-organic-semiconductor field-effect transistor (BiOFET) based on deoxyribonucleic acid (DNA) gate dielectric, J. Appl. Phys. 100, 024514 (2006).
 Subramanyam G., Bartsch C. M., Grote J. G., Naik R. R., Brott L., Stone M., Campbell A., Effect of external electrical stimuli on DNA based biopolymers, NANO, 4(2), 1–8 (2009).
 Bartsch C., Subramanyam G., Axtell H., Grote J., Hopkins F., Brott L. and Naik R., A new capacitive test structure for microwave characterization of biopolymers, temperature and bias dependent microwave dielectric properties of new biopolymers, Microwave Opt. Technol. Lett. 49(6), 1261–1265 (2007).
 Reiser K. and Knoesen A., Parametric Nonlinearity in Plant Polysaccharides: A New Harvest, Nonl. Opt. Quant. Opt., this issue.
 Okada-Shudo Y., Polarization Recording and Reconstruction in Bacteriorhodopsin Films, Nonl. Opt. Quant. Opt., this issue.