Topical Problems of Biophotonics

A special issue of Photonics (ISSN 2304-6732). This special issue belongs to the section "Biophotonics and Biomedical Optics".

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 31507

Special Issue Editors


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Guest Editor
Laboratory of Biophotonics, Institute of Applied Physics RAS, Ulyanov str., 46, Nizhny Novgorod, Russia
Interests: biophotonics; optical diagnostics; light scattering; photodynamic therapy
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Guest Editor
M.V. Lomonosov Moscow State University, Russia

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Guest Editor
Institute of Applied Physics RAS, Nizhny Novgorod, Russia
Interests: biophotonics;bioimaging;fluorescence imaging;diffuse optics;photoacoustics

Special Issue Information

Dear Colleagues,

This special issue will comprise papers related to recent achievements in biophotonics, including both optical diagnostics modalities and laser-based treatment approaches. The issue aims at giving a cross-section of state-of-the art research in the area of biomedical optics. This area has demonstrated a substantial development in the last two decades owing to both progress in the area of optical instrumentation and active introduction of optical techniques into biomedical studies. Principles on optical diagnostics are based on detection of photons scattered or emitted within biotissues, which provides wide possibilities for reconstruction of their structural or functional properties, while laser treatment approaches are related either to photoactivation of a drug within biotissue or employing high-power irradiation for tissue modification. The scope of this Special Issue covers the topics that are traditionally discussed within the frames of the international symposium on Topical Problems of Biophotonics held biannualy in Russia and gathering leading scientists in the area of biomedical optics.

The Special Issue scope includes but is not limited to following topics:

  • Coherence-based imaging and elastographic techniques;
  • Microcirculation and laser speckle contrast imaging;
  • Diffuse spectroscopy modalities;
  • Fluorescence imaging;
  • Optical nonlinear microscopy;
  • Optoacoustics;
  • Polarization Imaging;
  • Laser tweezers and micromanipulation;
  • Nanobiophotonics;
  • Translational biophotonics;
  • Photodynamic therapy;
  • Laser surgery;
  • Numerical simulations in optical diagnostics;
  • Machine and deep learning for optical diagnostics and imaging.

Dr. Kirillin Mikhail
Dr. Andrey Lugovtsov
Dr. Ilya Turchin
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Photonics is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (13 papers)

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Research

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16 pages, 2233 KiB  
Article
Problems of Red Blood Cell Aggregation and Deformation Assessed by Laser Tweezers, Diffuse Light Scattering and Laser Diffractometry
by Alexey Semenov, Andrei Lugovtsov, Petr Ermolinskiy, Kisung Lee and Alexander Priezzhev
Photonics 2022, 9(4), 238; https://doi.org/10.3390/photonics9040238 - 02 Apr 2022
Cited by 6 | Viewed by 2378
Abstract
This study aims to highlight the problems with implementing optical techniques (laser tweezers, diffuse light scattering and laser diffractometry) in clinical hemorheological practice. We provide the feasibility of these techniques to assess microrheological effects of various molecular mechanisms affecting RBC aggregation and deformability. [...] Read more.
This study aims to highlight the problems with implementing optical techniques (laser tweezers, diffuse light scattering and laser diffractometry) in clinical hemorheological practice. We provide the feasibility of these techniques to assess microrheological effects of various molecular mechanisms affecting RBC aggregation and deformability. In particular, we show that they allow assessment of changes in RBC aggregation in whole blood samples both on the level of single cells and on the level of large ensembles of cells. Application of these methods allows for studying the mechanisms of RBC aggregation because they are sensitive to changes in the medium which surrounds the RBC (i.e., blood plasma, serum or model solutions of blood plasma proteins) and to changes in the cellular properties of RBCs (i.e., effects on the cell membrane due to glycoprotein inhibition). Full article
(This article belongs to the Special Issue Topical Problems of Biophotonics)
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13 pages, 6847 KiB  
Communication
Changes in Optical Properties of Model Cholangiocarcinoma after Plasmon-Resonant Photothermal Treatment
by Vadim D. Genin, Alla B. Bucharskaya, Georgy S. Terentyuk, Nikolai G. Khlebtsov, Nikita A. Navolokin, Valery V. Tuchin and Elina A. Genina
Photonics 2022, 9(3), 199; https://doi.org/10.3390/photonics9030199 - 20 Mar 2022
Cited by 2 | Viewed by 1679
Abstract
The heating degree of the inner layers of tumor tissue is an important parameter required to optimize plasmonic photothermal therapy (PPT). This study reports the optical properties of tissue layers of transplanted cholangiocarcinoma and covering tissues in rats without treatment (control group) and [...] Read more.
The heating degree of the inner layers of tumor tissue is an important parameter required to optimize plasmonic photothermal therapy (PPT). This study reports the optical properties of tissue layers of transplanted cholangiocarcinoma and covering tissues in rats without treatment (control group) and after PPT using gold nanorods (experimental group). PPT was carried out for 15 min, and the temperature on the skin surface reached 54.8 ± 1.6 °C. The following samples were cut out ex vivo and studied: skin, subcutaneous connective tissue, tumor capsule, top, center, and bottom part of the tumor. The samples’ absorption and reduced scattering coefficients were calculated using the inverse adding–doubling method at 350–2250 nm wavelength. Diffuse reflectance spectra of skin surface above tumors were measured in vivo in the control and experimental groups before and immediately after PPT in the wavelength range of 350–2150 nm. Our results indicate significant differences between the optical properties of the tissues before and after PPT. The differences are attributed to edema and hemorrhage in the surface layers, tissue dehydration of the deep tumor layers, and morphological changes during the heating. Full article
(This article belongs to the Special Issue Topical Problems of Biophotonics)
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12 pages, 3949 KiB  
Communication
Adaptive Wave-Front Shaping and Beam Focusing through Fiber Bundles for High-Resolution Bioimaging
by Matvey S. Pochechuev, Ilya V. Fedotov, Maxim A. Solotenkov, Maria S. Andreeva, Aleksandr A. Lanin, Andrei B. Fedotov and Aleksei M. Zheltikov
Photonics 2022, 9(1), 21; https://doi.org/10.3390/photonics9010021 - 31 Dec 2021
Cited by 3 | Viewed by 2253
Abstract
We demonstrate an adaptive wave-front shaping of optical beams transmitted through fiber bundles as a powerful resource for multisite, high-resolution bioimaging. With the phases of all the beamlets delivered through up to 6000 different fibers within the fiber bundle controlled individually, by means [...] Read more.
We demonstrate an adaptive wave-front shaping of optical beams transmitted through fiber bundles as a powerful resource for multisite, high-resolution bioimaging. With the phases of all the beamlets delivered through up to 6000 different fibers within the fiber bundle controlled individually, by means of a high-definition spatial light modulator, the overall beam transmitted through the fiber bundle can be focused into a beam waist with a diameter less than 1 μm within a targeted area in a biotissue, providing a diffraction-limited spatial resolution adequate for single-cell or even subcellular bioimaging. The field intensity in the adaptively-focused continuous-wave laser beam in our fiber-bundle-imaging setting is more than two orders of magnitude higher than the intensity of the speckle background. Once robust beam focusing was achieved with a suitable phase profile across the input face of the fiber bundle, the beam focus can be scanned over a targeted area with no need for a further adaptive search, by applying a physically intuitive, wave-front-tilting phase mask on the field of input beamlets. This method of beam-focus scanning promises imaging speeds compatible with the requirements of in vivo calcium imaging. Full article
(This article belongs to the Special Issue Topical Problems of Biophotonics)
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17 pages, 3290 KiB  
Article
Diffuse Optical Spectroscopy Monitoring of Experimental Tumor Oxygenation after Red and Blue Light Photodynamic Therapy
by Anna Orlova, Yulia Perevalova, Ksenia Pavlova, Natalia Orlinskaya, Aleksandr Khilov, Daria Kurakina, Maria Shakhova, Mikhail Kleshnin, Ekaterina Sergeeva, Ilya Turchin and Mikhail Kirillin
Photonics 2022, 9(1), 19; https://doi.org/10.3390/photonics9010019 - 30 Dec 2021
Cited by 7 | Viewed by 1985
Abstract
Photodynamic therapy (PDT) is an effective technique for cancer treatment based on photoactivation of photosensitizer accumulated in pathological tissues resulting in singlet oxygen production. Employment of red (660 nm) or blue (405 nm) light differing in typical penetration depth within the tissue for [...] Read more.
Photodynamic therapy (PDT) is an effective technique for cancer treatment based on photoactivation of photosensitizer accumulated in pathological tissues resulting in singlet oxygen production. Employment of red (660 nm) or blue (405 nm) light differing in typical penetration depth within the tissue for PDT performance provides wide opportunities for improving PDT protocols. Oxygenation dynamics in the treated area can be monitored using diffuse optical spectroscopy (DOS) which allows evaluating tumor response to treatment. In this study, we report on monitoring oxygenation dynamics in experimental tumors after PDT treatment with chlorin-based photosensitizers using red or blue light. The untreated and red light PDT groups demonstrate a gradual decrease in tumor oxygen saturation during the 7-day observation period, however, the reason is different: in the untreated group, the effect is explained by the excessive tumor growth, while in the PDT group, the effect is caused by the blood flow arrest preventing delivery of oxygenated blood to the tumor. The blue light PDT procedure, on the contrary, demonstrates the preservation of the blood oxygen saturation in the tumor during the entire observation period due to superficial action of the blue-light PDT and weaker tumor growth inhibition. Irradiation-only regimes show a primarily insignificant decrease in tumor oxygen saturation owing to partial inhibition of tumor growth. The DOS observations are interpreted based on histology analysis. Full article
(This article belongs to the Special Issue Topical Problems of Biophotonics)
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23 pages, 5825 KiB  
Article
Numerical Simulation of Enhancement of Superficial Tumor Laser Hyperthermia with Silicon Nanoparticles
by Olga I. Sokolovskaya, Ekaterina A. Sergeeva, Leonid A. Golovan, Pavel K. Kashkarov, Aleksandr V. Khilov, Daria A. Kurakina, Natalia Y. Orlinskaya, Stanislav V. Zabotnov and Mikhail Y. Kirillin
Photonics 2021, 8(12), 580; https://doi.org/10.3390/photonics8120580 - 15 Dec 2021
Cited by 9 | Viewed by 3215
Abstract
Biodegradable and low-toxic silicon nanoparticles (SiNPs) have potential in different biomedical applications. Previous experimental studies revealed the efficiency of some types of SiNPs in tumor hyperthermia. To analyse the feasibility of employing SiNPs produced by the laser ablation of silicon nanowire arrays in [...] Read more.
Biodegradable and low-toxic silicon nanoparticles (SiNPs) have potential in different biomedical applications. Previous experimental studies revealed the efficiency of some types of SiNPs in tumor hyperthermia. To analyse the feasibility of employing SiNPs produced by the laser ablation of silicon nanowire arrays in water and ethanol as agents for laser tumor hyperthermia, we numerically simulated effects of heating a millimeter-size nodal basal-cell carcinoma with embedded nanoparticles by continuous-wave laser radiation at 633 nm. Based on scanning electron microscopy data for the synthesized SiNPs size distributions, we used Mie theory to calculate their optical properties and carried out Monte Carlo simulations of light absorption inside the tumor, with and without the embedded nanoparticles, followed by an evaluation of local temperature increase based on the bioheat transfer equation. Given the same mass concentration, SiNPs obtained by the laser ablation of silicon nanowires in ethanol (eSiNPs) are characterized by smaller absorption and scattering coefficients compared to those synthesized in water (wSiNPs). In contrast, wSiNPs embedded in the tumor provide a lower overall temperature increase than eSiNPs due to the effect of shielding the laser irradiation by the highly absorbing wSiNPs-containing region at the top of the tumor. Effective tumor hyperthermia (temperature increase above 42 °C) can be performed with eSiNPs at nanoparticle mass concentrations of 3 mg/mL and higher, provided that the neighboring healthy tissues remain underheated at the applied irradiation power. The use of a laser beam with the diameter fitting the size of the tumor allows to obtain a higher temperature contrast between the tumor and surrounding normal tissues compared to the case when the beam diameter exceeds the tumor size at the comparable power. Full article
(This article belongs to the Special Issue Topical Problems of Biophotonics)
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19 pages, 4018 KiB  
Article
Dynamic Light Scattering by Foamed Polymers during Preparation of Scaffold Prototypes: Events Statistics Analysis versus Evaluation of Correlation Time in Data Interpretation
by Dmitry Zimnyakov, Marina Alonova, Ekaterina Ushakova, Olga Ushakova, Anna Isaeva and Elena Isaeva
Photonics 2021, 8(12), 549; https://doi.org/10.3390/photonics8120549 - 03 Dec 2021
Viewed by 1993
Abstract
Polylactide foaming as the key stage in laboratory preparation of highly porous biocompatible matrices used as scaffold prototypes was monitored based the effect of dynamic light scattering in expanding polylactide foams. Intensity fluctuations of scattered laser radiation in the course of foam expansion [...] Read more.
Polylactide foaming as the key stage in laboratory preparation of highly porous biocompatible matrices used as scaffold prototypes was monitored based the effect of dynamic light scattering in expanding polylactide foams. Intensity fluctuations of scattered laser radiation in the course of foam expansion were analyzed using ensemble-averaged estimates of the speckle lifetime within a running window in the time domain. It was found that, in contrast to the commonly used correlation time of intensity fluctuations, the values of the average speckle lifetime are invariant with respect to the type of dynamics of phase fluctuations of partial components in scattered radiation. This makes it possible to relate this parameter to microscopic mobility of interphase boundaries in the foam in the absence of a priori information on the law of motion relating these boundaries at the microscopic level. The proposed approach in combination with the developed phenomenological model describing the relationship between the average speckle lifetime and the current values of the foam volume, as well as its first-time derivative made it possible to interpret the features of foam structure formation. Full article
(This article belongs to the Special Issue Topical Problems of Biophotonics)
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10 pages, 1179 KiB  
Communication
An Improved Analytical Model of a Spectrometer for Optical Coherence Tomography
by Evgeny P. Sherstnev, Pavel A. Shilyagin, Dmitry A. Terpelov, Valentin M. Gelikonov and Grigory V. Gelikonov
Photonics 2021, 8(12), 534; https://doi.org/10.3390/photonics8120534 - 26 Nov 2021
Cited by 2 | Viewed by 1584
Abstract
We present an improved analytical model of a spectrometer for optical coherence tomography (OCT), which more accurately describes the OCT in-depth sensitivity fall-off. The model considers the intrinsic spectral resolution of the dispersive element and the influence of additional components (inequidistance-correcting prism). The [...] Read more.
We present an improved analytical model of a spectrometer for optical coherence tomography (OCT), which more accurately describes the OCT in-depth sensitivity fall-off. The model considers the intrinsic spectral resolution of the dispersive element and the influence of additional components (inequidistance-correcting prism). The model is validated by experimental data obtained both from other studies and our own experiments. The influence of the frequency response of the CCD electrical circuit and the analog-to-digital converter to the OCT signal fall-off was also detected and was shown to be significant in some cases. Full article
(This article belongs to the Special Issue Topical Problems of Biophotonics)
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21 pages, 3257 KiB  
Article
Real-Time Strain and Elasticity Imaging in Phase-Sensitive Optical Coherence Elastography Using a Computationally Efficient Realization of the Vector Method
by Vladimir Y. Zaitsev, Sergey Y. Ksenofontov, Alexander A. Sovetsky, Alexander L. Matveyev, Lev A. Matveev, Alexey A. Zykov and Grigory V. Gelikonov
Photonics 2021, 8(12), 527; https://doi.org/10.3390/photonics8120527 - 24 Nov 2021
Cited by 16 | Viewed by 1977
Abstract
We present a real-time realization of OCT-based elastographic mapping local strains and distribution of the Young’s modulus in biological tissues, which is in high demand for biomedical usage. The described variant exploits the principle of Compression Optical Coherence Elastography (C-OCE) and uses processing [...] Read more.
We present a real-time realization of OCT-based elastographic mapping local strains and distribution of the Young’s modulus in biological tissues, which is in high demand for biomedical usage. The described variant exploits the principle of Compression Optical Coherence Elastography (C-OCE) and uses processing of phase-sensitive OCT signals. The strain is estimated by finding local axial gradients of interframe phase variations. Instead of the popular least-squares method for finding these gradients, we use the vector approach, one of its advantages being increased computational efficiency. Here, we present a modified, especially fast variant of this approach. In contrast to conventional correlation-based methods and previously used phase-resolved methods, the described method does not use any search operations or local calculations over a sliding window. Rather, it obtains local strain maps (and then elasticity maps) using several transformations represented as matrix operations applied to entire complex-valued OCT scans. We first elucidate the difference of the proposed method from the previously used correlational and phase-resolved methods and then describe the proposed method realization in a medical OCT device, in which for real-time processing, a “typical” central processor (e.g., Intel Core i7-8850H) is sufficient. Representative examples of on-flight obtained elastographic images are given. These results open prospects for broad use of affordable OCT devices for high-resolution elastographic vitalization in numerous biomedical applications, including the use in clinic. Full article
(This article belongs to the Special Issue Topical Problems of Biophotonics)
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11 pages, 1451 KiB  
Communication
Efficacy of Photodynamic Inactivation against the Major Human Antibiotic-Resistant Uropathogens
by Nadezhda Ignatova, Tatiana Ivanova, Artem Antonyan, Ivan Budruev, Olga Streltsova, Vadim Elagin and Vladislav Kamensky
Photonics 2021, 8(11), 495; https://doi.org/10.3390/photonics8110495 - 05 Nov 2021
Cited by 6 | Viewed by 1668
Abstract
Photodynamic inactivation (PDI) is considered to be an effective method of prevention of postoperative complications of urolithiasis. The present study shows a complex approach to assess the efficacy of PDI of drug resistant bacteria associated with renal calculi. Bacterial strains associated with renal [...] Read more.
Photodynamic inactivation (PDI) is considered to be an effective method of prevention of postoperative complications of urolithiasis. The present study shows a complex approach to assess the efficacy of PDI of drug resistant bacteria associated with renal calculi. Bacterial strains associated with renal calculi were isolated and identified using standard methods of bacteriological analysis and tested for drug resistance to 10 antibiotics by the disco-diffusion method. Uropathogenic bacterial strains present in 78.7 ± 5.2% of the infected samples from the total number of analyzed calculi. The most frequent representatives belonged to the genera Staphylococcus, Escherichia, and Enterococcus. All tested strains showed high antibiotic resistance. Representatives of the most common bacterial genera in the calculi were used as models for the selection of PD exposure modes. It was found that the maximum time of photosensitizer accumulation depends on the structure of the bacterial cell wall: 30 min for Gram-negative strains and 60 min for Gram-positive ones. Optimal modes of PD exposure to antibiotic-resistant uropathogenic microorganisms were selected: 50 µg/mL Fotoditazin and 150 mW laser power. The maximal bactericidal activity of PDI against uropathogenic microorganisms was shown for Enterococcus faecalis, and Staphylococcus aureus. The bacteriostatic effect was found against Escherichia coli and Proteus mirabilis. Full article
(This article belongs to the Special Issue Topical Problems of Biophotonics)
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9 pages, 1355 KiB  
Article
Diode Laser Lithotription Technique Based on Optothermal Converter
by Olga S. Streltsova, Evgeny V. Grebenkin, Nikita M. Bityurin, Vladimir I. Bredikhin, Vadim V. Elagin, Vasily V. Vlasov and Vladislav A. Kamensky
Photonics 2021, 8(10), 452; https://doi.org/10.3390/photonics8100452 - 18 Oct 2021
Cited by 2 | Viewed by 1963
Abstract
Purpose: evaluation of the efficiency of the “hot spot” method for the fragmentation of urinary stones. Materials and methods: A retrospective analysis of clinical records of 1666 patients with urolithiasis who underwent percutaneous nephrolithoextraction/tripsy and contact ureterolithotripsy/extraction in the period from 2014 to [...] Read more.
Purpose: evaluation of the efficiency of the “hot spot” method for the fragmentation of urinary stones. Materials and methods: A retrospective analysis of clinical records of 1666 patients with urolithiasis who underwent percutaneous nephrolithoextraction/tripsy and contact ureterolithotripsy/extraction in the period from 2014 to 2017 at the urology clinic was performed to assess the incidence of postoperative infectious and inflammatory complications. The research objects were postoperative urinary stones (n-78). The X-ray density and linear dimensions of the stones were determined. Stone fragmentation was performed with a continuous-wave diode laser operating at wavelengths of 0.81 μm, 0.97 μm, and 1.47 μm. An absorbing coating of micro-size graphite powder was applied on the working tip of the optical fiber. In vitro fragmentation was carried out in liquid. Results: A group of patients (224/1666) (13.4 ± 0.86%) was identified, who developed infectious and inflammatory complications after: percutaneous nephrolithotripsy, 123/361 (34.1 ± 2.5%) cases; percutaneous nephrolithoextraction, 59/240 (24.6 ± 2.78%); contact ureterolithotripsy, 23/294 (7.8 ± 1.57%); and ureterolithoextraction, 19/771 (2.5 ± 0.56%). In liquid, the “hot spot” technique made it possible to fragment stones with an X-ray density of up to 1000 HU at a laser wavelength of 0.81 µm, up to 1400 HU at 0.97 µm, and up to 1400 HU at 1.47 µm. Full article
(This article belongs to the Special Issue Topical Problems of Biophotonics)
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10 pages, 2109 KiB  
Article
Tumor Phantom with Incorporated SERS Tags: Detectability in a Turbid Medium
by Boris Khlebtsov, Daniil Bratashov, Andrey Burov and Nikolai Khlebtsov
Photonics 2021, 8(5), 144; https://doi.org/10.3390/photonics8050144 - 26 Apr 2021
Cited by 2 | Viewed by 1876
Abstract
Surface-enhanced Raman scattering (SERS) tags have proven to be excellent labels for tissue bioimaging because of their low interference from biological matrices, high photostability, and possibility for using as theranostic agents. Although SERS tags are widely used for the imaging of tumors in [...] Read more.
Surface-enhanced Raman scattering (SERS) tags have proven to be excellent labels for tissue bioimaging because of their low interference from biological matrices, high photostability, and possibility for using as theranostic agents. Although SERS tags are widely used for the imaging of tumors in vivo, in practice, the low contrast of the tag accumulation in the tissue and strong light scattering can significantly affect their detectability. In this work, we studied these effects by using a phantom of tumor tissue with incorporated SERS tags. The phantom is a 2 mm sphere of calcium alginate with incorporated SERS tags at a concentration of 0.625 × 108–2 × 109 cm−3. To simulate the surrounding medium with differing turbidities, the phantom was placed in a 4 mm thick agarose gel containing intralipid at a concentration of 0–1%. SERS bioimaging was carried out using standard backscattering geometry with different light focusing conditions. We found that shielding the phantom with a turbid medium led not only to a decrease in detectability but also to a decrease in the apparent size of the imaging object. Our results can help develop more accurate algorithms for processing SERS data for bioimaging. Full article
(This article belongs to the Special Issue Topical Problems of Biophotonics)
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Review

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27 pages, 2485 KiB  
Review
Application of Reflectance Indices for Remote Sensing of Plants and Revealing Actions of Stressors
by Anastasiia Kior, Vladimir Sukhov and Ekaterina Sukhova
Photonics 2021, 8(12), 582; https://doi.org/10.3390/photonics8120582 - 16 Dec 2021
Cited by 27 | Viewed by 4646
Abstract
Environmental conditions are very changeable; fluctuations in temperature, precipitation, illumination intensity, and other factors can decrease a plant productivity and crop. The remote sensing of plants under these conditions is the basis for the protection of plants and increases their survivability. This problem [...] Read more.
Environmental conditions are very changeable; fluctuations in temperature, precipitation, illumination intensity, and other factors can decrease a plant productivity and crop. The remote sensing of plants under these conditions is the basis for the protection of plants and increases their survivability. This problem can be solved through measurements of plant reflectance and calculation of reflectance indices. Reflectance indices are related to the vegetation biomass, specific physiological processes, and biochemical compositions in plants; the indices can be used for both short-term and long-term plant monitoring. In our review, we considered the applications of reflectance indices in plant remote sensing. In Optical Methods and Platforms of Remote Sensing of Plants, we briefly discussed multi- and hyperspectral imaging, including descriptions of multispectral and hyperspectral cameras with different principles and their efficiency for the remote sensing of plants. In Main Reflectance Indices, we described the main reflectance indices, including vegetation, water, and pigment reflectance indices, as well as the photochemical reflectance index and its modifications. We focused on the relationships of leaf reflectance and reflectance indices to plant biomass, development, and physiological and biochemical characteristics. In Problems of Measurement and Analysis of Reflectance Indices, we discussed the methods of the correction of the reflectance indices that can be used for decreasing the influence of environmental conditions (mainly illumination, air, and soil) and plant characteristics (orientation of leaves, their thickness, and others) on their measurements and the analysis of the plant remote sensing. Additionally, the variability of plants was also considered as an important factor that influences the results of measurement and analysis. Full article
(This article belongs to the Special Issue Topical Problems of Biophotonics)
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10 pages, 2149 KiB  
Review
Probing Small Distances in Live Cell Imaging
by Verena Richter, Peter Lanzerstorfer, Julian Weghuber and Herbert Schneckenburger
Photonics 2021, 8(6), 176; https://doi.org/10.3390/photonics8060176 - 21 May 2021
Cited by 4 | Viewed by 2147
Abstract
For probing small distances in living cells, methods of super-resolution microscopy and molecular sensing are reported. A main requirement is low light exposure to maintain cell viability and to avoid photobleaching of relevant fluorophores. From this point of view, Structured Illumination Microscopy (SIM), [...] Read more.
For probing small distances in living cells, methods of super-resolution microscopy and molecular sensing are reported. A main requirement is low light exposure to maintain cell viability and to avoid photobleaching of relevant fluorophores. From this point of view, Structured Illumination Microscopy (SIM), Axial Tomography, Total Internal Reflection Fluorescence Microscopy (TIRFM) and often a combination of these methods are used. To show the high potential of these techniques, measurements on cell-substrate topology as well as on intracellular translocation of the glucose transporter GLUT4 are described. In addition, molecular parameters can be deduced from spectral data, fluorescence lifetimes or non-radiative energy transfer (FRET) between a donor and an acceptor molecule. As an example, FRET between the epidermal growth factor receptor (EGFR) and the growth factor receptor-bound protein 2 (Grb2) is described. Since this interaction, as well as further processes of cellular signaling (e.g., translocation of GLUT4) are sensitive to stimulation by pharmaceutical agents, methods (e.g., TIRFM) are transferred from a fluorescence microscope to a multi-well reader system for simultaneous detection of large cell populations. Full article
(This article belongs to the Special Issue Topical Problems of Biophotonics)
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