Wavelength-multiplexed hook nanoantennas for machine learning enabled mid-infrared spectroscopy

• Published in: Nature communications 2022-07, Vol.13 (1), p.3859-3859, Article 3859
• Main Authors: Ren, Zhihao, Zhang, Zixuan, Wei, Jingxuan, Dong, Bowei, Lee, Chengkuo
• Format: Article
• Language: English
• Subjects: 140/125; 142/126; 147/135; 147/3; 49/62; 639/624/1075/1082; 639/624/1107/527/2257; 639/624/399; 639/766/400/1021; Alcohols; Broadband; Damping; Electric fields; Ethanol; Feature extraction; Humanities and Social Sciences; Infrared spectra; Infrared spectroscopy; Learning algorithms; Low concentrations; Machine learning; Microfluidics; multidisciplinary; Multiplexing; Nanoantennas; Plasmonics; Probes; Recognition; Resonance; Science; Science (multidisciplinary); Spectrum analysis; Wavelength; Wavelengths
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-022-31520-z

Infrared (IR) plasmonic nanoantennas (PNAs) are powerful tools to identify molecules by the IR fingerprint absorption from plasmon-molecules interaction. However, the sensitivity and bandwidth of PNAs are limited by the small overlap between molecules and sensing hotspots and the sharp plasmonic resonance peaks. In addition to intuitive methods like enhancement of electric field of PNAs and enrichment of molecules on PNAs surfaces, we propose a loss engineering method to optimize damping rate by reducing radiative loss using hook nanoantennas (HNAs). Furthermore, with the spectral multiplexing of the HNAs from gradient dimension, the wavelength-multiplexed HNAs (WMHNAs) serve as ultrasensitive vibrational probes in a continuous ultra-broadband region (wavelengths from 6 μm to 9 μm). Leveraging the multi-dimensional features captured by WMHNA, we develop a machine learning method to extract complementary physical and chemical information from molecules. The proof-of-concept demonstration of molecular recognition from mixed alcohols (methanol, ethanol, and isopropanol) shows 100% identification accuracy from the microfluidic integrated WMHNAs. Our work brings another degree of freedom to optimize PNAs towards small-volume, real-time, label-free molecular recognition from various species in low concentrations for chemical and biological diagnostics. Infrared spectroscopy with plasmonic nanoantennas is limited by small overlap between molecules and hot spots, and sharp resonance peaks. The authors demonstrate spectral multiplexing of hook nanoantennas with gradient dimensions as ultrasensitive vibrational probes in a continuous ultra-broadband region and utilize machine learning for enhanced sensing performance.