Fourier transform infrared (FTIR) spectroscopy is a popular technique for the analysis of biological samples, yet its application in characterizing live cells is limited due to the strong attenuation of...

Infrared spectroscopy has drawn considerable interest in biological applications, but the measurement of live cells is impeded by the attenuation of infrared light in water. Metasurface-enhanced infrared reflection spectroscopy (MEIRS) had been shown to mitigate the problem, enhance the cellular infrared signal through surface-enhanced infrared absorption, and encode the cellular vibrational signatures in the reflectance spectrum at the same time. In this study, we used MEIRS to study the dynamic response of live cancer cells to a newly developed chemotherapeutic metal complex with distinct modes of action (MoAs): tricarbonyl rhenium isonitrile polypyridyl (TRIP). MEIRS measurements demonstrated that administering TRIP resulted in long-term (several hours) reduction in protein, lipid, and overall refractive index signals, and in short-term (tens of minutes) increase in these signals, consistent with the induction of endoplasmic reticulum stress. The unique tricarbonyl IR signature of TRIP in the bioorthogonal spectral window was monitored in real time, and was used as an infrared tag to detect the precise drug delivery time that was shown to be closely correlated with the onset of the phenotypic response. These results demonstrate that MEIRS is an effective label-free real-time cellular assay capable of detecting and interpreting the early phenotypic responses of cells to IR-tagged chemotherapeutics.

Correction for ‘Metasurface-enhanced infrared spectroscopy in multiwell format for real-time assaying of live cells’ by Steven H. Huang et al., Lab Chip, 2023, 23, 2228–2240, https://doi.org/10.1039/d3lc00017f.

No abstract

Live-cell mid-infrared (MIR) imaging has always been challenging because of the absorptive nature of water. However, there is a strong drive to image this spectroscopic window–to see the protein and lipid vibrations directly without the help of dyes. Though the dyes are convenient for imaging, they interfere with the biological functions of live cells. In the past two decades, people have relied on attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopic imaging to probe such systems to reduce the infrared penetration depth to a few microns. In our previous works, we found a way to further restrict the penetration to a hundred nanometers with plasmonic nanoantennas, also known as the metasurfaces. We named the technique-metasurface-enhanced infrared reflection spectroscopy (MEIRS), and used it for either label-free spectroscopy or imaging. We had demonstrated MEIRS in various live-cell drug dynamics studies, including trypsin, cholesterol depleting agents, and chemotherapeutics, of live cells enclosed in microfluidics chambers. With the recent advancement of commercial mid-infrared quantum cascade laser (QCL), we now have a unique opportunity to acquire high-quality single-cell resolution metasurface-enhanced infrared reflection chemical imaging (MIRCI), which reveals the important protein information in real time. We built an inverted QCL microscope setup and cultured the cells on a cell-culture multiwell plate. The bottom of the multiwells is made of infrared-transparent window and with metasurface fabricated on. In this work, we demonstrated two proofs of concept of MIRCI on both fixed cells in water (single-cell resolution and spectroscopy) and live cells (capturing cell adhesion process). The application provides a novel tool to the drug discovery and fundamental cell biology research.