Accurate measurements of the algal cell concentration are essential in microalgae culturing and ecological monitoring. Here, we propose a method based on optical coherence tomography (OCT) to assess green algae concentrations quantitatively and measure the depth distribution of green algae cells. The amplitude information of the complex OCT sequence was extracted to calculate the scattering coefficient. The results show that the scattering coefficient can be used to evaluate different concentrations of green algae suspensions by frequency statistics under non-contact conditions, and the scattering coefficient images can provide the depth distribution of green algae cells. This method provides an in situ, accurate and non-invasive tool for monitoring the growth of green algae and can effectively reflect the health status of water bodies.
Viscosity measurement is critical in the fields of biomedicine and industry. Here, we propose a method based on optical coherence tomography (OCT) to quantitatively assess the Doppler viscosity of the liquid in microfluidic devices. The velocity of the liquid in a silicone tube was obtained by Doppler optical coherence tomography (DOCT), by analysing the phase change between sequential B-Scan. Two manometers were used to measure the real-time pressure difference between the inlet and outlet of the silicone tube. Finally, the viscosity of the flow sample was calculated according to Poiseuille’s law. Different viscous liquids and blood samples were tested, and the results were consistent with data reported in the literature. Experimental results indicated that the proposed method can be a new tool for non-contact and fast liquid viscosity measurement and even be engineered in the future for daily monitoring of blood viscosity with only a small amount of blood.
Skin disease is one of the most common diseases affecting human health, and it is vital to detect and diagnose it rapidly and accurately through skin tissue. Terahertz metasurface sensors (THz MSs) offer the advantages of label-free and sensitive detection by virtue of the capacity to perceptively sense changes in the refractive index of substances and the dielectric environment on their surfaces. In this paper, an array of quadrupole metal split-ring resonators (SRRs) was proposed. For the purpose of achieving a high Q-factor and sensitivity at the same time, parameters including cell size and opening gap are tuned. On account of the centrosymmetric cell structure of the sensor, angle sensitivity-related experimental errors could be essentially eliminated. Resonant cavities and connecting arms excite LC resonance on metasurfaces upon interaction with THz waves, resulting in two resonant dips in the transmission spectrum. Using photolithographic processing techniques, periodic metallic patterns were formed on a thin quartz substrate to create the metasurface. In the experiments, skin disease tissue samples were taken from patients, and the transmission spectra of the metasurface sensor covered with skin tissue were obtained by a terahertz frequency domain spectroscopy system. The result shows that resonant frequencies of the sensors covered by skin tissues of disease are shifted towards the lower frequency region compared with normal tissues. This dual resonance frequency sensor made it possible to visually distinguish between diseased and normal tissues by analyzing the resonance frequency shift with superior sensing performance and accuracy without the necessity of analyzing the complex terahertz intrinsic spectrum and refractive index of the samples.
Optical coherence tomography-based angiography (OCTA) is a high-resolution imaging technology for mapping microvascular networks in vivo. Intensity variance OCTA methods have been developed for blood flow analysis. However, the complex statistical calculations of intensity variances result in high computational costs. In this study, we developed statistical algorithms for simplifying estimates of the intensity variances, including the range, the mean error, and the maximum error algorithms. A rat cerebral cortex was imaged by the simplified algorithms and the conventional algorithm. The number of repeated samplings was compared for the intensity variance analysis. Then the image quality and the calculation time were assessed. The results show that the simplified algorithms can shorten the calculation time and generate microvascular networks with similar image quality compared to the conventional intensity variance OCTA algorithm.
Coagulation tests are essential for diagnosis of blood disorders and treatment of cardiovascular diseases. Here, we developed a noncontact method for quantitative assessment of coagulation properties based on blood diffusion dynamics analysis using optical coherence tomography (OCT). After a blood sample was loaded into a centrifuge tube, an OCT Mscan was captured at a single lateral location. Then the amplitude components of the complex OCT sequences were extracted for autocorrelation analysis. The length of the OCT sequence was optimized for the autocorrelation calculation. The blood dynamics related to scattering particle diffusion were evaluated by the autocorrelation decay over the time delay. The results show that the OCT autocorrelation analysis can quantitatively assess the blood coagulation properties without contact. Therefore, it could be used for in situ monitoring and point-of-care testing of blood coagulation with high reliability.
Forces generated by cells are critical regulators of cell adhesion and function. Polymeric micropillar arrays have been widely used for measuring cellular traction forces, however, the sub-micron scale deflections of micropillars are typically measured with a high power microscope, leading to a limited field-of-view and reducing the measurement efficiency. Herein, we reports a typical 4F system used to monitor cell contraction force based on optical Fourier transform (OFT). Compared to conventional microscopy, with a field-of-view on the scale of millimeters and instant acquisition of the force map, this method makes high-throughput and real-time cell contraction monitoring possible. The cells growing on micropillar arrays were placed on the object plane of a typical 4F system, illuminated by a monochromatic plane wave. OFT was performed on the light field as it passed through the first Fourier lens. The spatial spectrum that consists of discrete light spots was projected on the back focal plane of the first Fourier lens and was then filtered by an optical stop, eliminating the extraneous frequency components while allowing the frequency spots corresponding to the period of the micropillar arrays to pass through the aperture. Inverse OFT was conducted as the filtered light passed through the second Fourier lens and an image was reconstructed on the image plane of the 4F system, which was recorded by a CCD camera with a 20X objective. The light intensity of the image directly represents the degree of periodicity of the micropillar arrays, in which low-intensity areas indicated that the micropillars in this area were deflected while high-intensity areas indicate the presence of uniform micropillar arrays. Using this method, cell contraction forces could be directly visualized based on the intensity distribution at the image plane with no need for further image post-processing, enabling direct visualization of cell contraction in a larger field-of-view.
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