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In this work, an NaYF4:Ho3+/Yb3+ upconversion phosphor in colloidal form was synthesized and then its suitability for image contrast enhancement in optical coherence tomography (OCT) and photothermal (PT) OCT imaging was analysed.

Currently, upconversion nanoparticles (UCNPs) implanted as a contrast agent for optical coherence tomography (OCT) system due to its biocompatibility, anti-stock emission, narrow emission bandwidth non-photobleaching effects etc., but it was not used as multi model imaging probe. We synthesized multimodal imaging probe having upconversion property along with paramagnetic property and used as dual contrast agents for Photothermal Optical Coherence Tomography (PTOCT) and Magnetomotive Optical Coherence Tomography (MMOCT). The synthesized Gd2O3:Er3+/Yb3+ UCNPs shows the bright yellow upconversion emission, biocompatibility with hydrophilic property. A custom built SSOCT setup modified for PTOCT and MMOCT imaging along with custom MATLAB algorithm for signal extraction. A dynamic study was performed with synthesized UCNPs as an imaging probe and functional OCT system for targeted imaging. This shows the utility of the Gd2O3:Er3+/Yb3+ UCNPs as molecular probe for targeted imaging applications.

Background and objectives The study presents a noninvasive, real-time monitoring technique for the cross-sectional imaging of the laser-tissue soldering process with a swept-source optical coherence tomography (SSOCT) system. The study also aims at performing a comparative study of the laser-tissue soldering (LTS) process using optimized compositions of albumin as solder biomaterials. Study design/materials and methods The experimental study was conducted both ex vivo and in vivo to assess the superiority of the LTS process over conventional methods using a noninvasive imaging tool. In our attempt to combine the two techniques into one diagnostic tool, we have used the SSOCT system for a thoroughgoing investigation of the process in real-time. Laser-assisted tissue soldering was performed using a pulsed near-infrared (NIR) laser with a central wavelength of 980 nm, an output power of 5 W, and beam diameter (1/e 2 ) of 6 mm. Here, the SSOCT system has been utilized to observe and analyze the transitions taking place in real-time without disrupting the process. For the comparative study, we have used serum albumin in a 70% w/v concentration and albumin-PEG conjugate in a 6:1 ratio as soldering materials. Different stages of the laser interaction process were monitored with OCT B-scans of the incision area. Also, the basis of biomaterial-tissue interaction was studied with the help of Fourier-transform infrared spectroscopy (FTIR) analysis of the soldering materials. Results FTIR spectrum alludes to the fact that the intertwining of the soldering biomaterial with tissue collagen creates adhesion. Biomaterial serum albumin with 70% w/v concentration as soldering material demonstrates complete sealing of tissue at the incision with 3 minutes of laser irradiation. SSOCT B-scans have been useful in imaging the incision noninvasively at different stages. Conclusion Both ex vivo and in vivo demonstration of the LTS process were presented with a clinical resemblance. OCT can be of great value to determine the wound contraction in case of incisional wounds or sealed wounds produced by the LTS procedure. Also, volumetric measurements of percentage reduction in wound area can be done with OCT. SSOCT system can be a potential imaging modality for real-time noninvasive imaging of surgical procedures like LTS. Lasers Surg. Med. © 2021 Wiley Periodicals LLC.

Swept-source optical coherence tomography (SSOCT) is a noncontact, noninvasive bioimaging tool that uses various probes to obtain high contrast images. Rare-earth based upconversion particles (UCPs...

The aim of the current study is to demonstrate the potential of rare earth (RE) based upconversion nanoparticles (UCNPs) as molecular probing agents for non-invasive depth-resolved bioimaging technique, swept-source optical coherence tomography (SSOCT). The Na+ doped La2O3:Er3+/Yb3+ UCNPs were synthesized using a solution combustion route with characterization for emission spectra and morphological study. A custom made SSOCT system was also incorporated for tissue imaging with an A-scan rate of 100 kHz/s, the central wavelength of 1060 nm, an axial and lateral resolution of ~ 4.5 µm and ~ 13 µm in tissue, respectively. UCNPs are utilized as exogenous molecular probing agents to improve local scattering in inner tissue layers. In vitro imaging of chicken breast tissue is functioned with and without excited UCNPs. Time-dependent dynamic changes in scattering coefficients of local tissue and contrast to noise ratio (OCT B-scans) is presented with a new mathematical model. Substantial enhancement in OCT image contrast, local scattering coefficients, and depth range of OCT was observed. The penetration dynamics of excited and non-excited UCNPs with time is reported. Excitation of the UCNPs enhance the scattering coefficients which lead to high contrast OCT images. It also enables the tunable characteristics of UCNPs as targeted molecular probes.

This article shows the adequacy of the custom-built optical imaging system in the advancement investigation of obese mice. Obesity is defined as increased adipose/fatty mass resulting from a chronic imbalance between energy intake and expenditure. The in vivo investigation was performed for the tissue characterization of obese mice utilizing swept-source optical coherence tomography (SSOCT) for in situ examination and histology of delicate tissues in mice skin. It provides a noninvasive, painless visualization of the subsurface in life systems. Our SSOCT system's data is comparable to the regular invasive histology. Cross-assessment is done in various skin layers in obese mice like epidermis, papillary dermis, dermis, and fat tissue, which are likewise separated from the nonobese mice group. Histopathology results were further assessed with the obtained SSOCT results. This high precision of characterizing tissues using SSOCT helps us perform in vivo imaging and can also be used for the variable purpose of clinical practice.

Monte Carlo simulations are an elementary approach towards modeling light propagation in tissues. The detection of subsurface temperature in tissues during laser mediated therapies and microsurgeries is crucial for estimating associated thermal damage. MC simulation provides with the possibility to optimize the process. The approach has been used to model light propagation, associated energy deposition, and the temperature distribution inside the tissue. Understanding the extent of laser light transmittance and heat distribution within the tissue is crucial for minimizing damage to the adjacent biological tissues. The total photon weight absorbed estimates the total heat distribution within the volume. A three-layer heterogeneous tissue was specified consisting of only the epidermis, dermis, and the subcutaneous fat tissue. The hop, drop, and spin trail of photons depends on the optical properties of these layers. The energy deposition and temperature distribution estimation are obtained by the MC simulation method. A real-time measurement of the temperature profile was also performed. The experimental results were in close congruence with the simulation result. The simulation results show good reproducibility of the real temperature distribution. Monte Carlo method can, thereby, be used in estimation and optimization laser induced processes.

Engineering of water-dispersible Gd3+ ions-decorated reduced graphene oxide (Gd-rGO) nanosheets (NSs) has been performed. The multifunctional capability of the sample was studied as a novel contrast agent for swept source optical coherence tomography and magnetic resonance imaging, and also as an efficient drug-delivery nanovehicle. The synthesized samples were fabricated in a chemically stable condition, and efforts have been put toward improving its biocompatibility by functionalizing with carbohydrates molecules. Gd incorporation in rGO matrix enhanced the fluorouracil (5-FU) drug loading capacity by 34%. The release of the drug was ∼92% within 72 h. Gd-rGO nanosheets showed significant contrast in comparison to optically responsive bare GO for swept source optical coherence tomography. The longitudinal relaxivity rate (r1) of 16.85 mM–1 s–1 for Gd-rGO was recorded, which was 4 times larger than that of the commercially used clinical contrast agent Magnevist (4 mM–1 s–1) at a magnetic field strength of 1.5 T.

The continuous development of microorganism colonies may lead to the development of biofilms. The ability to observe bacterial layers in real time using Optical Coherence Tomography (OCT) can be beneficial for cross-sectional growth studies of bacterial biofilms. A new mathematical model has been developed and utilized to calculate the backscattering optical properties of sample and estimate the necessary parameters. The spectroscopic based analytical method has been successfully demonstrated for characterization of different bacterial colonies and biofilms. The results were verified with conventional ‘Gram staining’ method. The proposed analytical method has potential to monitor realtime growth kinetics of bacteria. The quantities observed were cross-sectional growth and scattering using optical properties for the different bacterial layers.

We present an investigation on applicability of swept-source optical coherence tomography (SSOCT) to examine the internal structures of plant leaves. This study helps to identify the growth and spread of the leaf rust disease in leaves of wheat plants, caused by Puccinia triticina. The epidermal cell layer and parenchyma cell layer of the acquired OCT images are correlated with the histological images to show distinctive leaf morphological boundaries. In the OCT images, the thickness of the parenchyma cell layer in healthy and infected samples are compared and analyzed. Accurate morphological and quantitative information are obtained with our developed system for diagnostic evaluations of plant diseases. These results indicate that OCT modality is suitable for inspection of different categories of leaves at different stages of disease progression which may potentially lead to significant cost savings and better control of the spread of disease.

Currently, upconversion nanoparticles (UCNPs) implanted as a contrast agent for optical coherence tomography (OCT) system due to its biocompatibility, anti-stock emission, narrow emission bandwidth non-photobleaching effects etc., but it was not used as multi model imaging probe. We synthesized multimodal imaging probe having upconversion property along with paramagnetic property and used as dual contrast agents for Photothermal Optical Coherence Tomography (PTOCT) and Magnetomotive Optical Coherence Tomography (MMOCT). The synthesized Gd

We demonstrate a photothermal optical coherence tomography (PTOCT) system, with upconversion nanoparticles (UCNPs) as a molecular probe. We synthesized hydrophilic, biocompatible upconversion nanoparticles (UCNPs) using hydrothermal synthesis. We developed the PTOCT system along with the signal processing tool and applied this technique on animal tissue phantom for targeted imaging. The ‘lock-in detection’ of the amplitude modulated photothermal beam (980 nm), which used to excite the UCNPs was the backbone of the signal processing algorithm. The signal processing was further established in different aspects. As an application part, the diffusion dynamics of the UCNPs was performed inside the tissue to study molecular movement and subsequent changes in tissue properties. A comparison of photothermal optical coherence tomography (PTOCT) with phase variance optical coherence tomography (PVOCT) for targeted molecular imaging also presented.

The current study presents a method based on Optical Coherence Tomography (OCT) for non-destructive, real-time analysis and portrayal of immobilization efficacy for lipase on a natural matrix namely, eggshell. Subsequently, qualitative biochemical reaction kinetics of immobilized lipase was also studied. Successful immobilization of lipase on eggshell was confirmed by the presence of a clear peak in ‘A’ scan of OCT image. From immobilization kinetics it is clearly observed that the thickness of the highest peak of the A-scan increases significantly and peak intensity saturated after 90 min of incubation. Hydrolysis of oil using immobilized lipase indicated that the release of free fatty acids increased up to 8 h during reaction and the result was in accordance with the ‘B’ scan data of the OCT system. Changes in scattering coefficient-based analysis were performed with respect to incubation time to showcase the immobilization process and hydrolysis reaction of lipase. Scanning electron microscope analysis with smoother surface indicated presence of lipase on eggshell matrices, with no further change after oil hydrolysis.

We present applicability of ZnO nanoparticles (ZnONPs) as a potential contrast agent for Optical Coherence Tomography (OCT) imaging. A 1064 nm laser source was used in a swept source configuration capable of a scanning rate of 100 kHz (100,000 A-lines/s). Swept Source Optical Coherence Tomography (SSOCT) is a variation of OCT, offering greater scan rates, higher resolution and signal-to-noise ratios. To enhance the contrast of an OCT frame, ZnO nanoparticles were used as an exogeneous contrast agent, which were fabricated using zinc acetic acid derivation and oxalic acid via precipitation. The particles were characterized using UV–vis Spectroscopy, Dynamic Light Scattering (DLS), Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDX). In-vitro imaging was performed on chicken breast tissue, with and without the application of ZnONPs. The contrast enhancements of the ZnONPs was determined at various time from the time of application, with calculation of the scattering coefficient and Contrast-to-Noise Ratio (CNR).

Nitrilase enzyme (a green catalyst) is an industrially important enzyme which hydrolyses various nitrile compounds (containing -CN functional group) into amides and corresponding carboxylic acids. The current study explored the binding affinity and a method to enhance the catalysis activity of the enzyme using computational approaches. Four mutants were generated using sequential site-directed mutagenesis aiming that an increase in hydrogen bonds that will further increase binding efficiency towards the ligand. Molecular dynamics simulation was rigorously performed to check the stability of those mutants followed by docking to verify its interaction with the ligand. Various statistical dynamics analyses were performed to validate the structure. All the studies predict that built mutants are stable. Mutants 2 and 3 showed a better affinity towards acrylamide by forming the highest number of hydrogen bonds implying better catalysis. The binding affinity values of the Mutant 2 and Mutant 3 with acrylamide are -7.44 kcal/mol and -7.17 kcal/mol, respectively. This study may prove useful for the industry to develop efficient nitrilase enzymes with improved catalytic activity.Communicated by Ramaswamy H. Sarma.

To better understand any tumor, first, we need to know the characteristic features. The tumor microenvironment is that the signature helps us know the dermatological condition for biopsy. Some traditional optical imaging methods have restricted properties to visualize shallow skin highlights, and boundary data is missing to identify pathophysiology relationships of skin infections. Here, we illustrate a swept-source optical coherence tomography (SSOCT) technique that non-invasively visualizes (in-vivo) the tissue micro-structure/neoplastic changes during tumor development as optical biopsy in real-time with pathophysiological correlations in the mice model. To further validate the current study, we perform the corresponding histopathology (ex-vivo) of that tumor region. Furthermore, the scattering coefficient and the optical penetration depth analysis prove that SSOCT imaging can provide detailed findings and treatment in dermatology.

We present noninvasive depth-resolved imaging of human retinal and choroidal microcirculation with an ultrahigh-speed (1.7 MHz A-scans/s), Fourier-domain mode locked (FDML) swept-source optical coherence tomography (SS-OCT) system having a central wavelength of 1065 nm. Three OCT angiography (OCTA) motion based contrast methods, namely phase variance (PV), amplitude decorrelation (AD) and Joint Spectral and Time domain OCT (STdOCT) were implemented. The OCTA imaging was performed with a field of view of 16° (5 mm × 5 mm) and 30° (9 mm × 9 mm), on the retina. A qualitative comparison of images obtained with all three OCTA methods is demonstrated using the same eye of a healthy volunteer. Different parameters, namely acquisition time, scanning area, and scanning density, are discussed. The phase-variance OCTA (PV-OCTA) method produced relatively better results than the other two. Different features regarding the retinal and choroidal vessels are described in different subjects.

We demonstrate the synthesis, characterization, and potential application of polymerically modified superparamagnetic nanoparticles over bare SPIONs, as a multi-model molecular probe for functionalized optical coherence tomography (fOCT). The synthesized magnetic nanoparticles (MNPs) also have the ability of photo thermionic excitation under near-infrared irradiation (980 nm). By having dual excitation properties, the SPIONs are used as exogenous contrast agents for magnetomotive optical coherence tomography (MMOCT) as well as photothermal optical coherence tomography (PTOCT). We developed a functionalized OCT system and signal processing algorithms for MMOCT and PTOCT. Further, non-invasive in-vivo imaging was performed on swiss-albino mice to demonstrate the potential application of polymerically modified SPIONs. A diffusion dynamics study and contrast-to-noise ratio (CNR) study of the dispersed synthesized SPIONs inside skin tissue of mice as a function of time and depth is also reported. We found that PEG-SPIONs are excellent candidate for molecular contrast agent of functional OCT.

In-vitro imaging by swept-source optical coherence tomography (OCT) represents a class of advanced tomography that provides comprehensive and accurate clinical diagnostics. Here colloidal NaGdF4:Er3+/Yb3+ particles having an average size of 32 nm were successfully synthesized by a facial thermal decomposition method and then used as a contrast agent in OCT imaging. Prepared phosphor has shown bright green upconversion emission under 976 nm diode laser. The phosphor particles had increased the scattering of OCT scanning radiation, and thus higher image contrast was observed. The results indicate that upconversion phosphors may work as suitable contrast agents for OCT imaging.

Upconversion nanoparticles (UCNPs) are widely recognized exogenous contrast agents for bioimaging. Swept source optical coherence tomography (SSOCT) is a non-invasive imaging tool commissioned for cross-sectional imaging of the biological sample. We present polymerically modified UCNPs as a potential contrast agent for SSOCT. In this communication, functionalized NaYF4: Ho3+/Yb3+ UCNPs were synthesized for more bioavailability with a coating of two different polymers namely, polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP). Time-dependent diffusion dynamics of functionalized UCNPs were performed in-vivo with a mice model. Imaging was performed with both inactive and excited UCNPs. A separate optical system was developed with an amplitude modulated 980 nm laser source to excite UCNPs. UCNPs with PVP coating shows better results compared to others in terms of increase of scattering coefficients and contrast-to-noise ratio. The complete system is designed with purpose to enhance imaging contrast of tissue at molecular level with further possible extension as a theranostics system for tumor imaging during photodynamic therapy.

Candida albicans infections and their resistance to clinically approved azole drugs are major concerns for human. The azole antifungal drugs inhibit the ergosterol synthesis by targeting lanosterol 14α-demethylase of cytochrome P450 family. The lack of high-resolution structural information of fungal pathogens has been a barrier for the design of modified azole drugs. Thus, a preliminary theoretical molecular dynamic study is carried out to develop and validate a simple homologous model using crystallographic structure of the lanosterol 14α-demethylase of Mycobacterium tuberculosis (PDB ID-1EA1) in which the active site residues are substituted with that of C. albicans (taxid 5476). Further, novel designed pyrazole analogs (SGS1-16) docked on chimeric 1EA1 and revealed that SGS-16 show good binding affinity through non-bonding interaction with the heme, which is different from the leading azole antifungals. The ADME-T results showed these analogs can be further explored in design of more safe and effective antifungal agents.

We present a spectroscopic OCT (sOCT) system to extract spectroscopic properties of turbid liquid media using principle component analysis (PCA) and swept source optical coherence tomography (SSOCT). Extracted results are well comparable with the standard photo spectrometer technique. This system has potential for real time measurement of blood oxygen saturation and monitoring of relative concentration for other metabolic compounds inside human body. Liquid media was prepared with ethanol (10% v/v), citric acid (5% v/v) and water. A linear mathematical model for depth resolved diffuse reflectance was build from sOCT signal. Then PCA was applied on resultant model to extract absorption coefficients of different constituents of the media. Extracted information is well comparable with the standard photo spectrometer technique. This system has potential to monitor relative concentration change of metabolic compounds inside any system.

Magnetomotive optical coherence tomography (MMOCT) is a functional modification of conventional optical coherence tomography (OCT). It utilizes the nano-scale displacement embedded magnetic nanoparticles (MNPs) and subsequent amplitude and phase changes in OCT interferogram scattered from samples. We report a new robust method for ‘phase-lock-in’ detection of MMOCT signals and subsequent imaging. We validated this method utilizing iron-gold (Fe-Au) composite nanoparticles as an exogenous contrast agent for MMOCT. High contrast and specific background-subtracted images was generated for Fe-Au MNPs targeted samples. MMOCT with MNPs imaging systems was corroborated with tissue phantoms and in-vivo swiss albino mice model with modulating external magnetic field (resonant frequency of 30 Hz). A time-dependent dynamics study of diffusion for MNPs inside the tissue of mice as a function of time and depth is also reported.

We present monitoring of nitrilase enzyme assay in real-time by means of Spectroscopic Optical Coherence Tomography (sOCT). Combination of principal component analysis (PCA) algorithm with Swept Source Optical Coherence Tomography (SSOCT), to extract the absorption spectra of the sample, termed as sOCT. Spectroscopic information of nitrilase enzyme obtained from sOCT is used to investigate dynamic enzyme kinetic reactions. Different principle components give complete information regarding the composition of the samples. Further, Fourier Transform Infrared Spectroscopy (FTIR) analysis has been also performed to validate the PCA absorption spectra. Samples were prepared in controlled condition and evaluated at a regular time interval of the incubation period. The developed algorithm and system are combinedly capable of in-vitro real-time, study of enzyme kinetics with respect to time as biosensor.

Optical coherence tomography is non-invasive diagnostic technique for performing high resolution (~µm) cross sectional imaging. In this article, we demonstrate characterization and oxygen saturation studies of human retinal blood vessels with Principal Component Analysis (PCA) based Spectroscopic Optical Coherence Tomography-based Angiography. A Fourier Domain Mode-Locked laser having an axial imaging resolution of ~7.5 µm, with an A-scan sweep rate of 1.7 MHz and centre wavelength of 1060 nm, was utilized as an OCT source. PCA has been used in conjunction with a scanning Short Time Fourier Transform, procedure to isolate the probable amount of oxygenated and deoxygenated haemoglobin and extract the information from individual OCT frames, without any external fitting model. This technique could provide useful insight into an effective blind source data extraction technique for medical image analysis. The technique proposed in this article, has a significant advantage in requiring no additional filtering or noise reduction technique in order to accurately extract the required information. It can also be used for ophthalmological research to determine the oxygen saturation of human retinal blood circulation, which may be helpful for identification of abnormalities related to human eye.

A complex conjugate resolved, extended depth range, high speed 1 μm swept-source optical coherence tomography (SSOCT) provides a dense three-dimensional (3-D) imaging of the entire anterior segment of eye. SSOCT system utilizes “coherence revival” characteristics of the light source (external cavity tunable laser, ECTL), which is automatically phase modulated. We describe implementation of this with a common swept laser with built-in k-clock to allow imaging in high depth range, 10.5 mm in air, without any external MZI clock. The system is capable of generating long depth range without any modulators or frequency shifter. Most of the commercially available OCT systems are limited with this type of application due to low acquisition speed, resolution, and axial imaging range. The sensitivity fall-off profiles for extended imaging depth range were also presented with matched and mismatched interferometer optical path delays. The imaging feasibility of this system is demonstrated by in vitro 3D imaging of the full anterior segment of lamb eye.