**1. Introduction**

The capability for realizing high density nanostructures over large areas is important for the sensing of chemical and biological molecules based on localized surface plasmon resonance (LSPR) of metallic nanoparticles (Jensen et al., 1999; Barbillon et al., 2008; Faure et al., 2008). To characterize these plasmonic nanosensors on an area of <sup>∼</sup> <sup>100</sup> <sup>×</sup> <sup>100</sup> *<sup>μ</sup>m*<sup>2</sup> (Barbillon et al., 2009; Anker et al., 2008; Barbillon et al., 2008), extinction spectroscopy measurements are mainly used. In order to study multiple biomolecular interactions on the same surface, very large areas need to be fabricated. Various techniques such as focused ion beam lithography and electron beam lithography are available to design these large surfaces. However, these two techniques are slow to obtain these surfaces. Moreover, charge effect on insulating surface can alter the regularity of the pattern shape. Thus, these techniques will not be suitable for a large scale production. Other lithographic techniques such as extreme UV lithography are also used, but these techniques (fabrication of masks) are expensive and allow with difficulty to realize samples in small quantity. In addition, alternative methods emerged, and among these methods we find soft UV nanoimprint lithography (UV-NIL). The UV-NIL process is fast to realize high density nanostructures, not very expensive and compatible with biological and biochemical applications (Krauss & Chou, 1997). With UV-NIL, samples can be fabricated at room temperature and low pressure. A limiting factor of UV-NIL exists and this factor is the resolution of the fabricated molds (Jung et al., 2006; Austin et al., 2005). Flexible molds of the soft UV-NIL technique were fabricated by cast molding processes, in which an appropriate liquid mold material is deposited on a patterned master mold, followed by optical curing of the material. Moreover, a great homogeneity of patterns is obtained with soft UV-NIL on a large zone. Thus, the purpose of this chapter is to present in details the principle of soft UV-NIL and the results of plasmonic structure fabrication on glass substrates obtained by this technique in order to realize LSPR nanosensors for biological molecules. To finish, a plasmonic sensing of biomolecules is investigated in order to validate the use of soft UV-NIL.
