Measurement of optical properties of pig esophagus by using a modified spectrometer set‐up

Optical properties (μ_a, μ_s and g) of certain human tissue types such as skin and blood have been very well investigated. However until today, for internal body organs such as the esophagus they are not well characterized. For ex‐vivo measurements “Inverse Adding Doubling” (IAD) and Inverse Monte‐Carlo‐Simulation (IMCS) are state of the art. Both methods need the measurement of the collimated transmission. Current methods lack a proper way of measuring the collimated transmission. Hence, this measurement of the g‐factor has a systematic error. Therefore, for the measurement of the collimated transmission, a new approach has been developed and evaluated with intralipid. Finally, the optical properties of mucosa, sub mucosa, muscularis and adventitia of pig esophagus tissue are calculated with IAD. The results are promising and in agreement with published literature.

     

Near‐infrared bulk optical properties of goat wound tissue and human serum: consequences for an implantable optical glucose sensor

Near‐infrared (NIR) spectroscopy offers a promising technological platform for continuous glucose monitoring in the human body. Moreover, these measurements could be performed in vivo with an implantable single‐chip based optical sensor. However, a thin tissue layer may grow in the optical path of the sensor. As most biological tissues are highly scattering, they only allow a small fraction of the collimated light to pass, significantly reducing the light throughput. To quantify the effect of a thin tissue layer in the optical path, the bulk optical properties of serum and tissue samples grown on implanted dummy sensors were characterized using double integrating sphere and unscattered transmittance measurements. The estimated bulk optical properties were then used to calculate the light attenuation through a thin tissue layer. The combination band of glucose was found to be the better option, relative to the first overtone band, as the absorptivity of glucose molecules is higher, while the reduction in unscattered transmittance due to tissue growth is less. Additionally, as the wound tissue was found to be highly scattering, the unscattered transmittance of the tissue layer is expected to be very low. Therefore, a sensor configuration which measures the diffuse transmittance and/or reflectance instead was recommended.

( a ) Dummy sensor; ( b ) explanted dummy sensor in tissue lump; ( c ) removal of dummy sensor from tissue lump; and ( d ) 900 µm slices of tissue lump.     

Feasibility study of using the dispersion of surface acoustic wave impulse for viscoelasticity characterization in tissue mimicking phantoms

The aim of this study was to investigate the feasibility of utilizing the phase velocity dispersion of impulse surface acoustic wave (SAW) for viscoelasticity characterization of soft materials. The focused ultrasound transducer and the phase‐sensitive optical coherence tomography were applied as the impulse SAW inducer and tracker, respectively. Three types of liquid‐paraffin‐based cream‐in‐agar phantoms were tested. Phase velocity dispersion curve was extracted using a Fourier transform‐based phase velocity analysis algorithm. Viscoelastic parameters were obtained by fitting the dispersion curve of SAW into Rayleigh wave dispersion equation. The estimated viscoelasticity was compared with that from spherical indenter, ramp‐hold relaxation testing for validation. Both results show an increasing trend in the elasticity and decreasing trend in the viscosity with the concentration of liquid‐paraffin‐based cream increasing in the samples. The proposed method has the capability of evaluating the viscoelastic properties of homogeneous soft tissue. By combining viscoelastic parameters estimated from the proposed method, the dispersive SAW‐impulse‐based viscosity‐compensated elastography could be further developed.      

Investigation of the source‐detector separation in near infrared spectroscopy for healthy and clinical applications

Understanding near infrared light propagation in tissue is vital for designing next generation optical brain imaging devices. Monte Carlo (MC) simulations provide a controlled mechanism to characterize and evaluate contributions of diverse near infrared spectroscopy (NIRS) sensor configurations and parameters. In this study, we developed a multilayer adult digital head model under both healthy and clinical settings and assessed light‐tissue interaction through MC simulations in terms of partial differential pathlength, mean total optical pathlength, diffuse reflectance, detector light intensity and spatial sensitivity profile of optical measurements. The model incorporated four layers: scalp, skull, cerebrospinal‐fluid and cerebral cortex with and without a customizable lesion for modeling hematoma of different sizes and depths. The effect of source‐detector separation (SDS) on optical measurements' sensitivity to brain tissue was investigated. Results from 1330 separate simulations [(4 lesion volumes × 4 lesion depths for clinical +3 healthy settings) × 7 SDS × 10 simulation = 1330)] each with 100 million photons indicated that selection of SDS is critical to acquire optimal measurements from the brain and recommended SDS to be 25 to 35 mm depending on the wavelengths to obtain optical monitoring of the adult brain function. The findings here can guide the design of future NIRS probes for functional neuroimaging and clinical diagnostic systems.      

Comparison of spectroscopy technologies for improved monitoring of cell culture processes in miniature bioreactors

Cell culture process development requires the screening of large numbers of cell lines and process conditions. The development of miniature bioreactor systems has increased the throughput of such studies; however, there are limitations with their use. One important constraint is the limited number of offline samples that can be taken compared to those taken for monitoring cultures in large‐scale bioreactors. The small volume of miniature bioreactor cultures (15 mL) is incompatible with the large sample volume (600 µL) required for bioanalysers routinely used. Spectroscopy technologies may be used to resolve this limitation. The purpose of this study was to compare the use of NIR, Raman, and 2D‐fluorescence to measure multiple analytes simultaneously in volumes suitable for daily monitoring of a miniature bioreactor system. A novel design‐of‐experiment approach is described that utilizes previously analyzed cell culture supernatant to assess metabolite concentrations under various conditions while providing optimal coverage of the desired design space. Multivariate data analysis techniques were used to develop predictive models. Model performance was compared to determine which technology is more suitable for this application. 2D‐fluorescence could more accurately measure ammonium concentration (RMSE_CV 0.031 g L^?1) than Raman and NIR. Raman spectroscopy, however, was more robust at measuring lactate and glucose concentrations (RMSE_CV 1.11 and 0.92 g L^?1, respectively) than the other two techniques. The findings suggest that Raman spectroscopy is more suited for this application than NIR and 2D‐fluorescence. The implementation of Raman spectroscopy increases at‐line measuring capabilities, enabling daily monitoring of key cell culture components within miniature bioreactor cultures. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:337–346, 2017     

Specific anion effects on the optical rotation of glucose and serine

Optical activity is directly related to molecular conformation through the anisotropic polarizabilities of molecules and the refractive index of materials. L-amino acids and D-sugars are characteristic essential bioactive molecules. Since molecular recognition and enzyme activity are related to the conformation of substrates, the relevance of optical activity to biological processes is evident. Specific ion, or Hofmeister, effects that occur with electrolytes at moderately high concentrations modify the behavior of interfaces, molecular forces between membranes, of bulk solutions, of enzymes, and even of DNA. Such effects are universal. Here we report a study on the change in optical rotation induced by some sodium salts for the enantiomers of serine and glucose in water solution. The optical rotation is shown to depend on the kind of anion and on the salt concentration. To obtain further insights into the mechanism behind the phenomenon, Fourier transform infrared (FTIR) spectral studies of serine and glucose solutions in electrolytes were also carried out. The results suggest that it is the differences in interactions of anions at specific chemical sites of the solutes that are responsible for the effects. These forces depend strongly on anion polarizability in water. Such specific ion preferential interactions can affect conformation and internal field, and result in significant changes in optical rotation.     

Organic acids and protein compounds causing the photoluminescence properties of natural rubber membranes and the quenching phenomena from Au nanoparticle incorporation

Natural rubber membranes were fabricated using latex from Hevea brasiliensis trees (clone RRIM 600) by casting, and controlling the time and temperature of thermal treatment. Three temperatures were used: 65, 80 and 120 °C and the corresponding annealing times of 6, 8, 10 and 12 h. The centrifugation of the latex produces the constituent phases: solid rubber (F1), serum or protein components (F2) and bottom fraction (F3). The photoluminescence properties could be correlated with organic acid components of latex. Natural rubber membranes were used as the active substrate (reducing agent) for the incorporation of colloidal Au nanoparticles synthesized by in situ reduction at different times. The intensity of photoluminescence bands assigned to the natural rubber decreases with the increase in amount of nanoparticles present on the membrane surface. It can be assumed that Au nanoparticles may be formed by reduction of the Au cation reacting with functional groups that are directly related to photoluminescence properties. However, the quenching of fluorescence may be attributed to the formation of a large amount of metal nanostructures on the natural rubber surface. Copyright © 2014 John Wiley & Sons, Ltd.     

Calculated vibrational properties of semiquinones in the A1 binding site in photosystem I

Time-resolved (P700⁺A₁^? – P700A₁) FTIR difference spectra have been obtained using photosystem I (PSI) particles with several different quinones incorporated into the A₁ protein binding site. Difference spectra were obtained for PSI with unlabeled and ¹⁸O labeled phylloquinone (2-methyl-3-phytyl-1,4-naphthoquinone) and 2-methyl-1,4-naphthaquinone (2MNQ) incorporated, and for PSI with unlabeled 2,3-dimethyl-1,4-naphthoquinone (DMNQ) incorporated. (¹⁸O – ¹⁶O), (2MNQ – PhQ) and (DMNQ – PhQ) FTIR double difference spectra were constructed from the difference spectra. These double difference spectra allow one to more easily distinguish protein and pigment bands in convoluted difference spectra. To further aid in the interpretation of the difference spectra, particularly the spectra associated with the semiquinones, we have used two-layer ONIOM methods to calculate corresponding difference and double difference spectra. In all cases, the experimental and calculated double difference spectra are in excellent agreement. In previous two and three-layer ONIOM calculations it was not possible to adequately simulate multiple difference and double difference spectra. So, the computational approach outlined here is an improvement over previous calculations. It is shown that the calculated spectra can vary depending on the details of the molecular model that is used. Specifically, a molecular model that includes several water molecules that are near the incorporated semiquinones is required.     

Time-resolved step-scan FTIR difference spectroscopy for the study of photosystem I with different benzoquinones incorporated into the A1 binding site

Time-resolved step-scan FTIR difference spectroscopy has been used to study photosystem I (PSI) with plastoquinone-9 (PQ) and two other benzoquinones (2,6-dimethyl-1,4-benzoquinone and 2,3,5,6-tetrachloro-1,4-benzoquinone) incorporated into the A₁ binding site. By subtracting a (P700⁺A₁^????P700A₁) FTIR difference spectrum for PSI with the native phylloquinone (PhQ) incorporated from corresponding spectra for PSI with different benzoquinones (BQs) incorporated, FTIR double difference spectra are produced, that display bands associated with vibrational modes of the quinones, without interference from features associated with protein vibrational modes.Molecular models for BQs involved in asymmetric hydrogen bonding were constructed and used in vibrational mode frequency calculations. The calculated data were used to aid in the interpretation and assignment of bands in the experimental spectra. We show that the calculations capture the general trends found in the experimental spectra.By comparing four different FTIR double difference spectra we are able to verify unambiguously bands associated with phyllosemiquinone in PSI at 1495 and 1415?cm^?1. We also resolve a previously unrecognized band of phyllosemiquinone at 1476?cm^?1 that calculations suggest is due in part to a C₄$\stackrel{?}{?}$O stretching mode.For PSI with PQ incorporated, calculations and experiment taken together indicate that the C₁$\stackrel{?}{?}$O and C₄$\stackrel{?}{?}$O vibrational modes of the semiquinone give rise to bands at 1487 and 1444?cm^?1, respectively. This is very distinct compared to PSI with PhQ incorporated.From the calculated and experimental spectra, we show that it is possible to distinguish between two possible orientations of PQ in the A₁ protein binding site.