Magnesium Plasmonic Nanoparticles in Water

Abstract

A plasmonic resonance in the UV promises entirely new possibilities in conjunction with molecular sensing, as most organic molecules show resonances in the UV.1 Aluminium (Al) nanoparticles are therefore currently being investigated for UV plasmonics.2 However, theory predicts that magnesium (Mg) provides both a substantially higher far-field absorption efficiency and a higher near-field electric field enhancement (highest in the UV).3 In conjunction with its plasmonic performance, Mg also possesses several other advantages; it is abundant, biocompatible, and lightweight (two-thirds lighter than Al).4 Nevertheless, it appears that Mg nanoparticles are so far not investigated for UV plasmonics in water. One major challenge is the fabrication of such structures and their stability once they are transferred to an aqueous environment. Here, we report the successful fabrication of Mg colloids5 as well as their corrosion protection6 and use as refractive index sensors.7 We demonstrate that colloidal solutions of Mg nanoparticles in the form of nanohelices give rise to a large extinction and chiroptical response in the UV and are therefore extremely promising for plasmonic sensing applications. A physical shadow growth method, which we reported in the earlier paper,8 is used to grow large-area arrays of Mg nanostructures. The particles then subjected to a coating procedure which ensures their stability for applications in water. We discuss how the chiral shape of the Mg nanocolloids enables high LSPR enhancements and thus permits new sensing tasks in complex fluids. In particular, we show that the refractive index dispersion of a small molecule in the UV gives rise to correspondingly larger plasmonic resonance shifts than in the visible.

1. M. W. Knight, N. S. King, L. Liu, H. O. Everitt, P. Nordlander and N. J. Halas, ACS Nano, 2014, 8, 834-840. 2. K. M. McPeak, C. D. van Engers, S. Bianchi, A. Rossinelli, L. V. Poulikakos, L. Bernard, S. Herrmann, D. K. Kim, S. Burger, M. Blome, S. V. Jayanti and D. J. Norris, Advanced Materials, 2015, 27, 6244-6250. 3. J. M. Sanz, D. Ortiz, R. Alcaraz de la Osa, J. M. Saiz, F. González, A. S. Brown, M. Losurdo, H. O. Everitt and F. Moreno, The Journal of Physical Chemistry C, 2013, 117, 19606-19615. 4. L.-Y. Chen, J.-Q. Xu, H. Choi, M. Pozuelo, X. Ma, S. Bhowmick, J.-M. Yang, S. Mathaudhu and X.-C. Li, Nature, 2015, 528, 539-543. 5. H.-H. Jeong, A. G. Mark and P. Fischer, Chemical Communications, 2016, 52, 12179-12182. 6. H.-H. Jeong, M. Alarcon-Correa, A.G. Mark, K. Son, T.-C. Lee, and P. Fischer, Corrosion protection of nanoparticles (In preparation). 7. H.-H. Jeong, A. G. Mark, M. Alarcon-Correa, I. Kim, P. Oswald, T.-C. Lee and P. Fischer, Nature Communications, 2016, 7, 11331. 8. A. G. Mark, J. G. Gibbs, T.-C. Lee and P. Fischer, Nature Materials, 2013, 12, 802-807