CONSALES ET AL . VOL. 6 ’ NO. 4 ’ 3163–3170 ’ 2012 www.acsnano.org 3163 March 08, 2012 C 2012 American Chemical Society Lab-on-Fiber Technology: Toward Multifunctional Optical Nanoprobes Marco Consales, † Armando Ricciardi, † Alessio Crescitelli, † Emanuela Esposito, ‡, * Antonello Cutolo, † and Andrea Cusano †,‡, * † Optoelectronic Division, Department of Engineering, University of Sannio, I-82100, Benevento, Italy and ‡ CNR-ICIB “E. Caianiello”, I-80078 Pozzuoli (NA), Italy. M. Consales and A. Ricciardi contributed equally to this work. T he “lab-on-fiber” concept essentially envisages the integration of highly functionalized materials at nano- and microscale within a single optical fiber and aims to develop a novel generation of minia- turized and advanced “all-in-fiber” technolog- ical platforms (namely “labs”) for both com- munication and sensing applications. The lab-on-fiber technology would thus represent the cornerstone of a photonics technological revolution enabling the im- plementation of fiber-based multifunction sensing and actuating micro- and nano- systems, showing unique advantages in terms of miniaturization, lightweight char- acteristic, cost effectiveness, robustness, power consumption, and information con- trol. Multifunctional laboratories integrated in a single optical fiber, exchanging infor- mation and combining sensorial data, could provide effective autodiagnostic features as well as new photonic and electro- optic functionalities useful in many strategic sectors such as optical processing, environ- ment, life science, safety, and security. The laboratories design deals with all those phenomena that provide light manipula- tion and control at the nanoscale, such as trapping and guiding effects in photonic crystals 1À3 and quasicrystals 4,5 as well as plasmonic nanostructures, 6À9 eventually combined all together in hybrid metallo- dielectric devices. 10À13 However, the realization of highly inte- grated optical fiber devices requires that several micro-and nanostructures be fabri- cated, embedded, and connected all to- gether in order to achieve the necessary lightÀmatter interaction and physical con- nection. As a consequence, a critical issue to be addressed consists in the definition of a reliable fabrication procedure able to integrate and process, at micro- and nanoscale, several ma- terials with the desired physical, mechanical, magnetic, chemical, and biological properties onto unconventional substrates such as the optical fiber tip. Promising approaches in this direction were recently introduced; 14,15 the proposed methodology relies on the preventive fabri- cation of metallic nanostructures on planar silicon wafers by means of electron- beam lithography (EBL), and their succes- sive transfer to small and/or nonconven- tional substrates (i.e., the fiber tip). 14 A further method in this direction was also recently demonstrated by the same group through the use of soft lithography and me- chanical sectioning, using an ultramicrotome * Address correspondence to e.esposito@cib.na.cnr.it; a.cusano@unisannio.it. Received for review December 19, 2011 and accepted March 8, 2012. Published online 10.1021/nn204953e ABSTRACT We propose a reliable fabrication process enabling the integration of dielectric and metallic nanostructures on the tip of optical fibers, thus representing a further step in the “lab-on- fiber” technology roadmap. The proposed fabrication procedure involves conventional deposition and nanopatterning techniques, typically used for planar devices, but here adapted to directly operate on optical fiber tip. Following this approach, we demonstrate a first technological platform based on the integration onto the optical fiber tip of two-dimensional hybrid metallo-dielectric nanostructures supporting localized surface plasmon resonances. By means of experimental measurements and full-wave numerical simulations, we characterize these resonant phenomena and investigate the underlying physics. We show that resonances can be easily tuned by acting on the physical and geometrical parameters of the structure. Moreover, with a view toward possible applications, we present some preliminary results demonstrating how the proposed device can work effectively as an optical probe for label-free chemical and biological sensing as well as a microphone for acoustic wave detection. KEYWORDS: lab-on-fiber . nanofabrication . fiber optics . localized surface plasmon resonances . metallo-dielectric nanostructures . acoustic wave detection . chemical and biological sensing ARTICLE