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One of the fundamental hurdles in infrared spectroscopy is the failure of molecular identification when their infrared vibrational fingerprints overlap. Refractive index (RI) is another intrinsic property of molecules associated with electronic polarizability, but with limited contribution to molecular identification in mixed environments currently. Here, we investigate the coupling mode of localized surface plasmon and surface phonon polaritons for vibrational de-overlapping. The coupling mode is sensitive to the molecular refractive index, attributed to the RI-induced vibrational variations of surface phonon polaritons (SPhP) within the Reststrahlen band, referred to as RI-dependent SPhP vibrations. The RI-dependent SPhP vibrations are linked to molecular RI features. According to the deep-learning-augmented demonstration of bond-breaking-bond-making dynamic profiling in biological reaction, we substantiate that the RI-dependent SPhP vibrations effectively disentangle overlapping vibrational modes, achieving a 92% identification accuracy even for the strongly overlapping vibrational modes in the reaction. Our findings offer insights into the realm of light-matter interaction and provide a valuable toolkit for biomedicine applications. Molecular vibrations serve as valuable signatures for the constituent elements and bonding in compounds. Here, using Surface-Enhanced Infrared Absorption spectroscopy, the authors study refractive index dependent vibrations of surface phonon polaritons and surface plasmon platform, targeting dynamic biomonitoring. [ABSTRACT FROM AUTHOR]

Infrared absorption spectroscopy is an effective tool for the detection and identification of molecules. However, its application is limited by the low infrared absorption cross-section of the molecule, resulting in low sensitivity and a poor signal-to-noise ratio. Surface-Enhanced Infrared Absorption (SEIRA) spectroscopy is a breakthrough technique that exploits the field-enhancing properties of periodic nanostructures to amplify the vibrational signals of trace molecules. The fascinating properties of SEIRA technology have aroused great interest, driving diverse sensing applications. In this review, we first discuss three ways for SEIRA performance optimization, including material selection, sensitivity enhancement, and bandwidth improvement. Subsequently, we discuss the potential applications of SEIRA technology in fields such as biomedicine and environmental monitoring. In recent years, we have ushered in a new era characterized by the Internet of Things, sensor networks, and wearable devices. These new demands spurred the pursuit of miniaturized and consolidated infrared spectroscopy systems and chips. In addition, the rise of machine learning has injected new vitality into SEIRA, bringing smart device design and data analysis to the foreground. The final section of this review explores the anticipated trajectory that SEIRA technology might take, highlighting future trends and possibilities. [ABSTRACT FROM AUTHOR]

Multifunctional chemical sensing is highly desirable in industry, agriculture, and environmental sciences, but remains challenging due to the diversity of chemical substances and reactions. Surface‐enhanced infrared absorption (SEIRA) spectroscopy can potentially address the above problems by ultra‐sensitive detection of molecular fingerprint vibrations. Here, a multifunctional chemical sensing platform based on dual‐resonant SEIRA device for sensitive and multifunctional on‐chip detection of poly(ethyl cyanoacrylate) (PECA) is reported. It is experimentally demonstrated that the SEIRA sensing platform achieves multiple functions required by the PECA glue industry, including vibrational detection, thickness measurement, and in situ observation of polymerization and curing, which are usually realized by separately using a spectrometer, a viscometer, and an ellipsometer in the past. Specifically, the all‐in‐one sensor offers a dual‐band fingerprint vibration identification, sub‐nm level detection limit, and ultrahigh sensitivity of 0.76%/nm in thickness measurement, and second‐level resolution in real‐time observation of polymerization and curing. This work not only provides a valuable toolkit for ultra‐sensitive and multifunctional on‐chip detection of PECA, but also gives new insights into the SEIRA technology for multi‐band, multi‐functional, and on‐chip chemical sensing. [ABSTRACT FROM AUTHOR]

MicroRNAs play an important role in early development, cell proliferation, apoptosis, and cell death, and are aberrantly expressed in many types of cancers. To understand their function and diagnose cancer at an early stage, it is crucial to quantitatively detect microRNA without invasive labels. Here, a plasmonic biosensor based on surface‐enhanced infrared absorption (SEIRA) for rapid, label‐free, and ultrasensitive detection of miR‐155 is reported. This technology leverages metamaterial perfect absorbers stimulating the SEIRA effect to provide up to 1000‐fold near‐field intensity enhancement over the microRNA fingerprint spectral bands. Additionally, it is discovered that the limit of detection (LOD) of the biosensor can be greatly improved by using tetrahedral DNA nanostructure (TDN) as carriers. By using near‐field enhancement of SEIRA and specific binding of TDN, the biosensor achieves label‐free detection of miR‐155 with a high sensitivity of 1.162% pm−1 and an excellent LOD of 100 × 10−15m. The LOD is about 5000 times lower than that using DNA single strand as probes and about 100 times lower than that of the fluorescence detection method. This work can not only provide a powerful diagnosis tool for the microRNAs detection but also gain new insights into the field of label‐free and ultrasensitive SEIRA‐based biosensing. [ABSTRACT FROM AUTHOR]

Surface-enhanced infrared absorption (SEIRA) spectroscopy is a powerful technique that overcomes the issue of low molecular absorption cross-sections in infrared spectroscopy. Due to the collective oscillations of electrons in the infrared regime, SEIRA using resonant metamaterial provides greatly enhanced (up to 107) electromagnetic fields extending up to tens of nanometers from the metamaterial. The enhanced near-field enables spectroscopic analysis and ultrasensitive on-chip sensing of molecules. This interesting characteristic has aroused widespread attention from researchers to SEIRA technology, and various SEIRA-based sensing applications have been continuously emerging. Optimization of the signal enhancement to obtain high sensing performance is the developing main thread of SEIRA technology. In this Review, we provide a basic understanding of SEIRA's sensing mechanism and theoretical model. With this background, several SEIRA optimizing methods are discussed, ranging from design, materials to algorithms. Additionally, perspectives about the future development trends of SEIRA technologies are discussed. [ABSTRACT FROM AUTHOR]

Simultaneous on‐chip sensing of multiple greenhouse gases in a complex gas environment is highly desirable in industry, agriculture, and meteorology, but remains challenging due to their ultralow concentrations and mutual interference. Porous microstructure and extremely high surface areas in metal–organic frameworks (MOFs) provide both excellent adsorption selectivity and high gases affinity for multigas sensing. Herein, it is described that integrating MOFs into a multiresonant surface‐enhanced infrared absorption (SEIRA) platform can overcome the shortcomings of poor selectivity in multigas sensing and enable simultaneous on‐chip sensing of greenhouse gases with ultralow concentrations. The strategy leverages the near‐field intensity enhancement (over 1500‐fold) of multiresonant SEIRA technique and the outstanding gas selectivity and affinity of MOFs. It is experimentally demonstrated that the MOF–SEIRA platform achieves simultaneous on‐chip sensing of CO2 and CH4 with fast response time (<60 s), high accuracy (CO2: 1.1%, CH4: 0.4%), small footprint (100 × 100 µm2), and excellent linearity in wide concentration range (0–2.5 × 104 ppm). Additionally, the excellent scalability to detect more gases is explored. This work opens up exciting possibilities for the implementation of all‐in‐one, real‐time, and on‐chip multigas detection as well as provides a valuable toolkit for greenhouse gas sensing applications. [ABSTRACT FROM AUTHOR]