A label-free indicator for tumor cells based on the CH2-stretch ratio

Thermal effect on dispersive infrared spectroscopic imaging of prostate cancer tissue

A system that combines dispersive infrared micro-spectroscopic imaging and thermography has been developed to study the effect of thermal radiation on the infrared absorption spectra of prostate biopsy samples. The system allows the distribution of thermal signal intensity as a function of emissivity to be interpreted from the integrated absorbance obtained by spectroscopic imaging. Biochemical differences between cancer and benign areas within the specimens are identified in the spectra. Side-by-side comparison of H&E stained adjacent tissue sections with infrared images constructed before and after the removal of thermal effect showed that the latter strongly support differentiation of regions within tissues. The use of spectral bands at discrete wavelengths significantly reduced spectral acquisition time, making this technique promising as a future clinical diagnostic tool. A systemic methodology was implemented to process the data, first by k-means clustering on the second derivative spectra without a priori knowledge, followed by principal component analysis (PCA). Four distinct regions within the tissue samples were successfully classified based on the antisymmetric stretching mode of the methylene functional group. Separation between data in clusters occurs when projecting spectra on a PCA score plot on a plane made by first 2 principal components. The significance of the disparity was verified with statistical test. Regulation of signal to chopper and detector enables simultaneous acquisition of infrared and thermal images of the prostate biopsy tissues.

An Infrared Absorbance Sensor for the Detection of Melanoma in Skin Biopsies

An infrared (IR) absorbance sensor has been designed, realized and tested with the aim of detecting malignant melanomas in human skin biopsies. The sensor has been designed to obtain fast measurements (80 s) of a biopsy using a small light spot (0.5 mm in diameter, typically five to 10 times smaller than the biopsy size) to investigate different biopsy areas. The sensor has been equipped with a monochromator to record the whole IR spectrum in the 3330-3570 nm wavelength range (where methylene and methyl stretching vibrations occur) for a qualitative spectral investigation. From the collected spectra, the CH₂ stretch ratio values (ratio of the absorption intensities of the symmetric to asymmetric CH₂ stretching peaks) are determined and studied as a cancer indicator. Melanoma areas exhibit different spectral shapes and significantly higher CH₂ stretch ratios when compared to healthy skin. The results of the infrared investigation are compared with standard histology. This study shows that the IR sensor is a promising supportive tool to improve the diagnosis of melanoma during histopathological analysis, decreasing the risk of misdiagnosis.

Dual-band perfect absorber for multispectral plasmon-enhanced infrared spectroscopy

Metamaterial-based perfect absorbers utilize intrinsic loss, with the aid of appropriate structural design, to achieve near unity absorption at a certain wavelength. For most of the reported absorbers, the absorption occurs only at a single wavelength where plasmon resonances are excited in the nanostructures. Here we introduce a dual-band perfect absorber based on a gold nanocross structure. Two bands of maximum absorption of 94% are experimentally accomplished by breaking the symmetry of the cross structure. Furthermore, we demonstrate the two bands can be readily tuned throughout the mid-infrared with their associated resonances giving rise to large near-field enhancements. These features are ideal for multiband surface-enhanced infrared spectroscopy applications. We experimentally demonstrate this application by simultaneously detecting two molecular vibrational modes of a 4 nm thick polymer film utilizing our proposed absorber. Furthermore, in response to variations in the interaction strength between the plasmonic and molecular dipoles, we observe an anticrossing behavior and modification in the spectral line shape of the molecular absorption peak, which are characteristic of the coupling between the two modes.