Shaking up reaction-site selectivity: It seems intuitive that putting vibrational energy into a chemical bond ought to promote selective cleavage of that bond. In fact, the relation of vibrational excitation to reactivity has generally proven subtler and more complex. Thomas et al. studied how strong coupling of specific vibrational modes to an optical cavity might influence a molecule with two competing reactive sites. The molecule had two silicon centers that could react with fluoride by respective cleavage of a Si–C or Si–O bond. Exciting the vibrations at either center slowed down the overall reaction while favoring otherwise disfavored Si–O cleavage. Science , this issue p. 615

Vibrational strong coupling (VSC) has recently emerged as a completely new tool for influencing chemical reactivity. It harnesses electromagnetic vacuum fluctuations through the creation of hybrid states of light and matter, called polaritonic states, in an optical cavity resonant to a molecular absorption band. Here, we investigate the effect of vibrational strong coupling of water on the enzymatic activity of pepsin, where a water molecule is directly involved in the enzyme's chemical mechanism. We observe an approximately 4.5‐fold decrease of the apparent second‐order rate constant k_cat/K_m when coupling the water stretching vibration, whereas no effect was detected for the strong coupling of the bending vibration. The possibility of modifying enzymatic activity by coupling water demonstrates the potential of VSC as a new tool to study biochemical reactivity.

Vibrational strong coupling (VSC) has recently emerged as a completely new tool for influencing chemical reactivity. It harnesses electromagnetic vacuum fluctuations through the creation of hybrid states of light and matter, called polaritonic states, in an optical cavity resonant to a molecular absorption band. Here, we investigate the effect of vibrational strong coupling of water on the enzymatic activity of pepsin, where a water molecule is directly involved in the enzyme's chemical mechanism. We observe an approximately 4.5‐fold decrease of the apparent second‐order rate constant k_cat/K_m when coupling the water stretching vibration, whereas no effect was detected for the strong coupling of the bending vibration. The possibility of modifying enzymatic activity by coupling water demonstrates the potential of VSC as a new tool to study biochemical reactivity.

The TM and TE guided modes in the coupled plasmon-waveguide resonance configuration are investigated in the spectral domain. Here we use the modes dispersion to study their capability for sensing in the near infrared region. It is shown that the spectral widths of the guided modes are, at least, one order of magnitude smaller than the conventional surface plasmon resonance counterpart. The enhanced sensitivity and figure of merit of the guided modes reveal their potential for sensing in the spectral interrogation method where the traditional configurations are inherently limited. Moreover, the high resolution associated with the narrow resonances and the polarization dependence make these modes very promising for anisotropic biosensing in the spectral interrogation approach. The extremely high figure of merit, large penetration depth, and propagation distance in the near infrared region open the possibility of combining the plasmon-waveguide configuration with absorption spectroscopy techniques for molecular recognition.

Plasmon waveguide resonances (PWRs) have been widely used to enhance the interaction between light and matter. PWRs have been used for chemical and biological sensing, molecular detection, and boosting other optical phenomena, such as Raman scattering and fluorescence. However, the performances of plasmon-waveguide-based structures have been investigated in the angular interrogation mode, and their potential in different spectral regions has hardly been explored. Moreover, the applications of PWRs have been limited to the weak light–matter coupling regime. In this study, we investigate leaky coupled waveguide plasmon resonances (LCWPRs) and explore their potential to enhance light–matter interaction in different spectral regions. In the weak coupling regime, we demonstrate the potential of LCWPRs for sensing in the near-IR region by detecting heavy water (D₂O) and ethanol in water. The experimental results show spectral sensitivity of 15.2 nm/% and 1.41 nm/% for ethanol and D₂O detection, respectively. Additionally, we show that LCWPRs can be used to achieve vibrational strong coupling (VSC) with organic molecules in the mid-IR region. We numerically show that the coupling between LCWPRs and the C=O stretching vibration of hexanal yields a Rabi splitting of 210 cm⁻¹, putting the system in the VSC regime. We anticipate that LCWPRs will be a promising platform for enhanced spectroscopy, sensing, and strong coupling.