In cell motility, researchers are usually used fluorescence microscopy, confocal microscopy, or total internal reflection microscopy to track a fluorescent labeled particle and reveal the dynamic trajectory in living. Because all fluorescent dyes have cell toxicity, quantum dots and gold nanoparticles can influence the structures and physical properties of biomolecules which they have labeled, to develop another label-free image approach becomes an important issue. We present here a Fourier-based cross-correlation process to analyze images of adhering living cell, including cell motility and single vesicle trajectory. We treated adhering MG-63 cell with 66 nM Epidermal growth factor (EGF) and observed its dynamic effect on cell motility based on the velocity fields of consecutive cell images. We also used crosscorrelation to track single vesicles in living cells. We found that EGF could rapidly activate the motility of adhering MG- 63 cell, and the vesicle exhibits either directed or diffusive motion.
Bovine serum albumin (BSA) solutions (2.5 %, PH 7.2) under heat treatment can result in structural changes. Some of
the α-helices are transformed at 67°C to random coils resulting in an increased rotation angle. With subsequent heating,
the transformed random coils may once again transform to non-native β-sheets and restore the optical rotation angle.
These two states are all reversible. However, when the heating temperature goes up to 69°C the denatured BSA starts to
transform into a rigid network and becomes an irreversible state. The reversible and irreversible temperatures of BSA
were determined and discussed.
Periodic nonlinearity is a systematic error limiting the accuracy of displacement measurements at the nanometer level. It results from many causes such as the frequency mixing, polarization mixing, polarization-frequency mixing, and the ghost reflections. An interferometer having accuracy in displacement measurement of less than one-nanometer is necessary in nanometrology. To meet the requirement, the periodic nonlinearity should be less than deep sub-nanometer. In this paper, a nonlinearity-reduced interferometry has been proposed. Both the linear- and straightness-interferometer were tested. The developed interferometer demonstrated of a residual nonlinearity less than 25 pm.
A nanometer-scale gap sensing technique based on surface plasmon resonance principle is presented. A simulation to the
gap sensing technique and an experimental setup to verify the simulation results have both done in this study. For
simulation, Fresnel's equation was used to derive the multilayer reflectivity of KR configuration of SPR devices. The
results show that the resonance angle increased when the air gap, which was within half a wavelength, between the SPR
device and the glass slide was decreased. For experiment, we measured the reflectivity versus incident angle. The results
verify the theoretical prediction. Utilizing this novel surface plasmon resonance gap sensing technique, we have
measured an air gap down to 100 nm. The technique is better than the other methods used in nanometer-scale gap
A Surface plasmon resonance (SPR) biosensor constructed with common path, heterodyne inteferometric system has been developed. The sensor ship consists of a BK7 substrate coated with gold film on which the receptor of the specific biomolecular or protein has been immobilized. The light source consisting of the s and p polarizations with heterodyne frequency of 60kHz is used to measure the phase difference between these two polarizations. Because the SPR sensor probes the changes of refractive index near the gold film (i.e. about one wave-length), the more the binding of molecules on the sensing surface results in the less sensitivity of the detection. In order to overcome this shortage, we set two quarter-wave plates before and after the SPR prism to make the sensitivity of measurement to be tunable. This sensor could detect the concentration of antibody of sheep IgG as low as several nanograms per milliliter. The results indicate that this system provides high sensitivity and is capable for detecting biomolecular interactions.
The interferometers which measure the displacement parallel to the measurement axis are called linear interferometers, while those measure the displacement orthogonal to the measurement axis are called straightness interferometers. Theoretically, the orthogonal characteristic between the displacement and the measurement axis does not introduce optical path difference (OPD) and thus, makes null signal. These lead to the straightness interferometer difficult to be implemented. A generalized laser interferometer system based on three design principles, the heterodyne frequency, the avoiding mixing, and the perfect symmetry, is described. These design principles give rise to the interferometer a highly stable system with no periodic nonlinearity. A novel straightness sensor, consisting of a straightness prism and a straightness reflector, is incorporated into the generalized system to form a straightness interferometer. With the help of a Hewlett-Packard commercial linear interferometer, the validity of the developed straightness interferometer has verified. Based on the present design, the interferometer has a gain of 0.348, a periodic nonlinearity of less than 40 picometers, and a displacement noise of 4 pm/√Hz at bandwidth 7.8 kHz. This system is useful in precision straightness measurement.
A novel heterodyne polarimeter is designed to measure the concentration of chiral media. Optical common-path for the interference of the TE and TM waves, after a polarizer, is set up in our system to reduce noises from the environment. A phase-variable waveplate is placed behind the sample to enhance the phase signal change of rotation of polarization introduced by the sample itself. This enhancement can be excess two orders in amplitude when the retardation of the phase-variable plate is set close to 180 degree. With this polarimeter, the measurement of optical rotation angle with high sensitivity of 6.5×10-4 degree experimentally can be achieved when phase retardation of the phase-variable waveplate is 178.5 degree. We expect that, by further improvement, it can be applied in noninvasive blood glucose concentration monitoring for diabetics in the future.
We present an improved interferometric system based on surface plasmon resonance (SPR) and phase detection. The system incorporates a SPR device and a total internal reflection (TIR) device used not only to enhance the relative phase-shift between the TE and TM waves but also to keep the output beam to be anti-parallel to the input beam. A pair of quarter-wave-plates (QWPs) is placed in front of and behind, respectively, to the system. This gives rise to optimize the response curve and then the sensitivity. Theoretical simulations have been developed and verified by experimental results. By using this new design, we can always get the best sensitivity regardless weather the systems are manufactured in perfect conditions or not.
A novel compact roll angular displacement measurement system based on the use of wave retarder is presented. It utilizes the technique of common-path, heterodyne interferometry to detect the phase shift caused by roll angular displacement of a wave retarder fixed on a moving system. This novel system is set up and verified both theoretically and experimentally. Demonstrated by experiments, it can measure the roll angular displacement of a moving system down to microradian over the range of a half-degree.
A common-path, heterodyne interferometric system for studying the phase variations under surface plasmon resonance (SPR) is presented. The reflected beam from SPR is further going into a total internal reflection device (TIR) for increasing the sensitivity by the phase shift between TE-wave and TM-wave, as described by the Fresneli's equation. With the combination of a SPR prism and a TIR prism, the system can avoid the change of direction in the output light, which is always happened when only a SPR prism has been used. An unaltered output light is convenient for the detection devices. The system utilizes a pair of orthogonally linearly polarized beams with heterodyne frequency of 60 kHz as the light source. They are perfectly collinear so that the noises resulting from the ambient conditions are greatly reduced. Compared with the technique of reflectivity variation measurement, which is widely used in traditional SPR, the phase variation measurement using common-path, heterodyne techniques is estimated to be higher in sensitivity and thus can be used as a high-sensitivity-demanded biosensor.
The vibration displacement of a shaker in an accelerometer calibration system is detected by a Michelson type of a phase quadrature laser interferometer. The interferometric signals are stored in a digital storage scope and transferred to a computer for displacement calculation. Due to the high resolution, fast acquisition speed, and large memory capacity of the scope, this system demonstrates a measuring range from about 10 nm to 100 micrometers at the frequency range of DC to 20 kHz. A cyclical signal- preserving algorithm is developed to preserve the signal's phase and amplitude while reducing the drift and random noise level. The standard deviations of the measured displacements are 1.3% for 13 nm and rapidly lower to 0.04% for 500 nm or greater. The measured displacement in conjunction with the vibration frequency and the output voltage of the accelerometer then give its sensitivity. Preliminary results demonstrate that the sensitivities calibrated by both the direct displacement measuring method (our experiment) and the conventional fringe-disappearance method agree within 0.6%.