The control of light with artificial structures is one of the key issues in modern photonics. The last decade has been characterized by artificial electromagnetic (EM) materials, including photonic crystals (PCs) and photonic quasi-crystals (PQCs), making these very attractive given that there are new possibilities to control the EM field in innovative way. Quasiperiodic crystals (QCs) are a new class of materials that have fascinating optical properties lying somewhere between those of disordered and period structures.[1-3] With the use of PCs and PQCs, it is possible to synthesize novel artificial structures characterized by selective EM responses, which, in turn, undergo significant frequency shifts, in presence of biological material. Since the initial discovery of Surface-Enhanced Raman Scattering (SERS), an increased amount of work has been done on the research of substrates for highly efficient Raman scattering enhancement due to their extraordinary potential for trace analysis and biological tags. Recently, the plasmonic optical responses of metal nanoparticles, based on Localized Surface Plasmon Resonances (LSPR) in the visible and near IR region, has been intensively researched. It has been demonstrated that the plasmon resonance is closely related to the size and shape of metal nanoparticles and to the dielectric properties of the surrounding medium. In SERS spectroscopy it is of crucial importance to develop systems of interacting metal nanostructures capable of producing high field enhancement with highly reproducible characteristics on controllable metal-dielectric substrates. In the present work we studied artificial electromagnetic (EM) nanomaterials to develop innovative plasmonic nanobiosensors based on SERS and working in the visible frequency band. Au photonic crystals (PCs) and photonic quasi crystals (PQCs) are proposed for the engineering of reproducible SERS substrates. Using a molecular monolayer of pMA (p-mercaptoaniline) as a Raman reporter, we show that high values of SERS enhancement factors can be achieved in photonic structures. We have demonstrated experimentally measured SERS enhancement 1) GSERS=1.3*107 in lithographically defined Square-based periodic PCs of triangular-shape with side size d=200nm and pitch A=300nm, 2) GSERS=1.4*107 in Thue Morse (ThMo) PQC arrays of Au nano cylinders with 185nm side size and 80nm minimum interparticle separation, and, 3) GSERS=1.4*108 in 8-fold PQC arrays of cylinders with diameter D=125nm and FF= 0.18. The resulting PQC nanostructured films, both ThMo and octagonal arrangements, can serve as good SERS substrate, exhibit large electromagnetic field enhancement factors for pMA, and can readily be used in ultrasensitive, molecule-specific sensing utilizing vibrational signatures. To demonstrate the feasibility of the fabricated nanostructures as efficient SERS substrates for biological applications, we devised a method to deposit single cells (human prostatic) on the photonic surfaces. Preliminary results on SERS sampling of single prostatic human cells indicated that the present engineered metamaterials may be used as an ultrasensitive Raman probe to monitor subtle molecular changes in the cell and open up interesting new opportunities in biosensing.
2D Plasmonic Quasi Crystals for Surface-enhanced Raman scattering
M Pannico;P Musto;L Petti
2014
Abstract
The control of light with artificial structures is one of the key issues in modern photonics. The last decade has been characterized by artificial electromagnetic (EM) materials, including photonic crystals (PCs) and photonic quasi-crystals (PQCs), making these very attractive given that there are new possibilities to control the EM field in innovative way. Quasiperiodic crystals (QCs) are a new class of materials that have fascinating optical properties lying somewhere between those of disordered and period structures.[1-3] With the use of PCs and PQCs, it is possible to synthesize novel artificial structures characterized by selective EM responses, which, in turn, undergo significant frequency shifts, in presence of biological material. Since the initial discovery of Surface-Enhanced Raman Scattering (SERS), an increased amount of work has been done on the research of substrates for highly efficient Raman scattering enhancement due to their extraordinary potential for trace analysis and biological tags. Recently, the plasmonic optical responses of metal nanoparticles, based on Localized Surface Plasmon Resonances (LSPR) in the visible and near IR region, has been intensively researched. It has been demonstrated that the plasmon resonance is closely related to the size and shape of metal nanoparticles and to the dielectric properties of the surrounding medium. In SERS spectroscopy it is of crucial importance to develop systems of interacting metal nanostructures capable of producing high field enhancement with highly reproducible characteristics on controllable metal-dielectric substrates. In the present work we studied artificial electromagnetic (EM) nanomaterials to develop innovative plasmonic nanobiosensors based on SERS and working in the visible frequency band. Au photonic crystals (PCs) and photonic quasi crystals (PQCs) are proposed for the engineering of reproducible SERS substrates. Using a molecular monolayer of pMA (p-mercaptoaniline) as a Raman reporter, we show that high values of SERS enhancement factors can be achieved in photonic structures. We have demonstrated experimentally measured SERS enhancement 1) GSERS=1.3*107 in lithographically defined Square-based periodic PCs of triangular-shape with side size d=200nm and pitch A=300nm, 2) GSERS=1.4*107 in Thue Morse (ThMo) PQC arrays of Au nano cylinders with 185nm side size and 80nm minimum interparticle separation, and, 3) GSERS=1.4*108 in 8-fold PQC arrays of cylinders with diameter D=125nm and FF= 0.18. The resulting PQC nanostructured films, both ThMo and octagonal arrangements, can serve as good SERS substrate, exhibit large electromagnetic field enhancement factors for pMA, and can readily be used in ultrasensitive, molecule-specific sensing utilizing vibrational signatures. To demonstrate the feasibility of the fabricated nanostructures as efficient SERS substrates for biological applications, we devised a method to deposit single cells (human prostatic) on the photonic surfaces. Preliminary results on SERS sampling of single prostatic human cells indicated that the present engineered metamaterials may be used as an ultrasensitive Raman probe to monitor subtle molecular changes in the cell and open up interesting new opportunities in biosensing.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
