Surface enhanced vibrational spectroscopy using ultra narrow-band perfect absorber

In this work, we present a narrow-band (sub-100 cm-1 ) and multi-band metamaterial perfect absorber operating in the mid-IR frequency regime for analysis of biomolecules with vibrational spectroscopy. The presented perfect absorber is based on multi-layer metamaterial plasmonic nanoantennas. We used numerical and experimental work to fine tune the parameters of the PA and control its spectral response. The suggested PA system provides high absorbance values (100%) in the mid-IR region and near-field enhancement factor of 103 at the corresponding resonance values. The experimental results are well agreeing the numerical results. The working principle of the presented perfect absorption can be both explained by impedance matching and critical coupling phenomenon. The fabricated PA shows strong narrow band resonance and all the resonance energy could be transferred to thin films (10 nm) for higher sensitivity. In addition, PA shows multi-band resonances within the mid-IR region, thus it can be effectively used for simultaneously detecting the different biomolecular fingerprints. In this sense, we experimentally observed absorption of carbonyl (C=O) and asymmetric methyl (-CH3) stretching bands of thin polymethyl methacrylate (PMMA) film on the narrow band resonance of PA.