Two-Dimensional Correlation Spectroscopy (2DCOS)
Two-dimensional correlation spectroscopy (2DCOS) has been used as an analytical method to study changes induced by external perturbations such as temperature, surface reactions, pH, and adsorbate concentrations. In typical one-dimensional spectroscopic experiments, an electromagnetic probe is used to investigate interactions of the probe and system. However, once an external perturbation is used to stimulate the system, spectral intensity changes can occur. 2DCOS is a way of aggregating spectra to establish whether intensity fluctuations are correlated and to determine the sequential sequence of peak changes
2DCOS can be considered a quantitative intensity comparison of two spectra between some perturbation interval. This is a way to visualize similarity or dissimilarity of the correlations between intensity fluctuations. Importantly, recent 2DCOS experiments have been used along with IR spectroscopy to investigate different NP surface interactions such as oxyanion adsorption, protein conformational change, and displacement reactions.
(a) Original attenuated total reflectance–Fourier transform infrared (ATR-FTIR) spectra for environmental DNA (eDNA) in 30 mM NaCl at pH 5, 1.5 ug/mL in solution phase (top), adsorbed on hematite nanoparticles at 0.1 ug/mL shown every 10 min for 150 min (middle) and desorbed with NaCl shown every 10 min for 60 min (bottom). (b) Two-dimensional correlation spectroscopy (2DCOS) maps for eDNA adsorption onto a hematite nanoparticle surface at pH 5 using ATR-FTIR spectra. Autocorrelation spectrum (top), synchronous 2DCOS map (middle), and asynchronous 2DCOS map (bottom). The dotted line in the synchronous 2DCOS corresponds to the intensity line trace autocorrelation spectrum, highlighting the peaks most responsive to the external perturbation, time. Red and blue for the synchronous and asynchronous 2DCOS map correspond to positive and negative values, respectively
Izaac Sit, Haibin Wu, Vicki H. Grassian
Annual Review of Analytical Chemistry 2021 14:1