Ultrasensitive Broadband Probing of Molecular Vibrational Modes with Multifrequency Optical Antennas

Heykel Aouani *†, Hana Šípová ‡, Mohsen Rahmani ¶§,Miguel Navarro-Cia , Kateřina Hegnerová ‡, Jiří Homola ‡, Minghui Hong §, and Stefan A. Maier †

^† The Blackett Laboratory, Department of Physics,Imperial College London, London SW7 2AZ, United Kingdom

^‡ Institute of Photonics and Electronics, Academy of Sciences of the Czech Republic, Chaberska 57, 18251 Prague, Czech Republic

^¶ Data Storage Institute, (A*STAR) Agency for Science, Technology and Research, 5 Engineering Drive 1, Singapore 117608

^§ Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576

 Department of Electronic & Electrical Engineering, University College London, London WC1E 7JE, United Kingdom

 Optical and Semiconductor Devices Group, Department of Electrical and Electronic Engineering,Imperial College London, London SW7 2BT, United Kingdom

ACS Nano, Article ASAP

DOI: 10.1021/nn304860t

Publication Date (Web): December 2, 2012

Copyright © 2012 American Chemical Society

Optical antennas represent an enabling technology for enhancing the detection of molecular vibrational signatures at low concentrations and probing the chemical composition of a sample in order to identify target molecules. However, efficiently detecting different vibrational modes to determine the presence (or the absence) of a molecular species requires a multispectral interrogation in a window of several micrometers, as many molecules present informative fingerprint spectra in the mid-infrared between 2.5 and 10 μm. As most nanoantennas exhibit a narrow-band response because of their dipolar nature, they are not suitable for such applications. Here, we propose the use of multifrequency optical antennas designed for operating with a bandwidth of several octaves. We demonstrate that surface-enhanced infrared absorption gains in the order of 10⁵ can be easily obtained in a spectral window of 3 μm with attomolar concentrations of molecules, providing new opportunities for ultrasensitive broadband detection of molecular species viavibrational spectroscopy techniques.