Abstract
The secondary structures, i.e., the α-helix, β-sheet, and triple-helix, of protein may be denatured at a certain condition, for example, the pH-value, concentration of solvent, and beyond certain temperature. The transformation of denaturation is not well understood now. The X-ray diffraction crystallography and the nuclear magnetic resonance (NMR) can be used to detect the structures of protein; however, these two methods can not be applied to monitor the denaturation process of proteins at the present time. In addition, the X-ray diffraction crystallography can be only applied to observe protein powder or protein crystallization; therefore, it can’t observe the structures of protein dissolved in liquid. On the other hand, Circular dichroism (CD) spectroscopy is usually used to calculate the proportion of different protein structures; however, it is not a real-time system because the spectrum needs to be scanned. For this reason to construct a real-time detection system is highly required. In this study, we have built up a high resolution and real-time detection system to monitor the changes of secondary structure by utilizing a variable-retarder to amplify the rotation angle and a lock-in amplifier to enhance the signal-to-noise-ratio. We have verified that the structure changes and optical rotation changes of bovine serum albumin (BSA) were occurred via heating, the so-called thermal effect, where the thermal effect is directly related to denaturation of protein and therefore causes changes in optical rotation. We have demonstrated that by heating different concentrations of BSA, i.e., 0.67 % wt, 1.33 % wt, 2.66 % wt, the corresponding phase signal variations, as function of BSA concentration, are -0.012±0.009, -0.031±0.004 and -0.067±0.013, respectively, where the phase signal is directly corresponding to optical rotation.