Detection of Thermal Denaturation and Renaturation of Collagen: Optical Characteristics Using Angular Displacement-Enhanced Heterodyne Polarimeter

An angular displacement-enhanced heterodyne polarimeter has been employed to investigate the optical properties and thermal denaturation of collagen. In the angular measurement, the phase change of the collagen at different temperatures can be enhanced using a null-detection technique with a retardation-tunable wave-plate and analyzer into our common-path heterodyne polarimeter. Also, the environmental noise can be reduced by the interference of transverse magnetic (TM) and transverse electric (TE) waves from the optical common-path setup. We first measured the optical rotation of deionized water, glucose solution (dextrorotatory), and bovine serum albumin (BSA, levorotatory) to ensure the accuracy and high signal-to-noise ratio (SNR) of the experimental setup. It was found that the optical rotation from the measured phase difference can be enhanced up to 40-fold amplification with a soleil babinet compensator (SBC). Moreover, we have investigated the thermal denaturation from the denaturation temperature defined by the change of optical rotation, and the thermal renaturation of collagen has been studied by heating the samples to 55°C followed by cooling down to 25°C and then heating back to 55°C. The results reveal that 63% triple helices in the collagen structure have been refolded during the renaturation stage. This approach successfully provides with a real-time, noninvasive, and high resolution detection for thermal denaturation and renaturation of collagen.