Attenuated total reflectance - Fourier transform infrared (ATR-FTIR) spectra of ethylene glycol–water (abbreviated as EG–H₂O) mixtures were measured at 298 K with the ethylene glycol molar ratio ranging from 0.01 to 1400. The two bands at 1033 and 1082 cm^-1 were assigned to be the C-C stretching vibration modes related to the trans- and gauche- conformation of EG. The absorbance of the two bands was found to be sensitive to the molar ratios. We made theoretical calculation for ten conformations of the EG molecules to understand the conformational transformation of EG molecules changing with EG–H₂O molar ratios. The absorbance ratio (A₁₀₃₃/A₁₀₈₂) was used to determine the trans- and gauche- conformation ratio with the calculated (Aν_O-C-C-O-T/Aν_O-C-C-O-G) as standard. When the molar ratio of water and EG (x_H2O/x_EG) is smaller than 0.4, strong associations formed by the intermolecular hydrogen bonds were dominant in the solutions and the proportion of gauche- conformation was about 0.5. Within the region of 0.4< x_H2O/x_EG < 20, the intermolecular hydrogen bonds structure between EG molecules were broken by the water molecules and the structure of most EG molecules changed from trans- to gauche- conformation. The blue shift of the peaks indicated the increasing hydrogen bonding between water and EG. When x_H2O/x_EG is larger than 20, the monomers of molecules started to appear in the EG–H₂O solution. The gauche- conformation was the dominated conformation in the dilute EG–H₂O solution with proportion of 0.87. In the CH₂ rocking vibration (δ_C-H) region, the computational results showed that the majority bands in this region were influenced by the gauche- conformation which can be divided into group G₁ or G₂. The transformation between the gauche- conformations of EG molecules can be studied by combining the experimental results and the computational results, The proportion of G₁ for the EG-rich solution was about 0.71 while it decreased to 0.55 for the H₂O–rich solution.

Optical techniques for visualization and quantification of chemical and biological analytes are always highly desirable. Here we show a hyperspectral surface plasmon resonance microscopy (HSPRM) system that uses a hyperspectral microscope to analyze the selected area of SPR image produced by a prism-based spectral SPR sensor. The HSPRM system enables monochromatic and polychromatic SPR imaging and single-pixel spectral SPR sensing, as well as two-dimensional quantification of thin films with the measured resonance-wavelength images. We performed pixel-by-pixel calibration of the incident angle to remove pixel-to-pixel differences in SPR sensitivity, and demonstrated the HSPRM’s capabilities by using it to quantify monolayer graphene thickness distribution, inhomogeneous protein adsorption and single-cell adhesion. The HSPRM system has a wide spectral range from 400 nm to 1000 nm, an optional field of view from 0.884 mm² to 0.003 mm² and a high lateral resolution of 1.2 μm, demonstrating an innovative breakthrough in SPR sensor technology.

Here we present methods to simultaneously investigate diffusivities and volatilities in studies of evolving single aerosol particle size and composition.

Optical interferometric sensors have been widely used for highly sensitive detection of various physical quantities, and most of them operate in simple intensity interrogation mode. The deviation between the sensor's operating point and its quadrature point (Q-point) can cause signal distortion and sensitivity reduction. In this work, a new method for judging and compensating the above-mentioned deviation is proposed for improving sensor performance. Judgment of the degree of deviation is performed using the amplitude of the second harmonic (SH) component derived from the sensor's output signal, and the deviation compensation is achieved through wavelength tuning. The wavelength tuning direction is determined by the relationship between the two phases of fundamental frequency (FF) and SH components, which eliminates the ambiguity of the sign of wavelength change and expedites the tuning speed. The method was fully verified by simulation and experiment based on a Fabry-Perot interferometer (FPI) based fiber-optic microphone with a tunable laser. Experimental results show that the FF and SH amplitudes oppositely changes with changing the ambient temperature after fixing the laser wavelength and fast tuning of the laser wavelength minimizes the SH amplitude close to zero and simultaneously maximizes the FF amplitude, consequently maintaining the operating point of the microphone at its Q-point. Moreover, the proposed method shows high precision and strong robustness to the laser power fluctuation. According to the criterion that the total harmonic distortion allowed is less than 3%, the phase deviation between the microphone's operating point and its Q-point should be smaller than 0.004°, which can be easily satisfied by the method proposed in this work.