The importance of doping TiO2 into polypyrrol nanofibers to improve their optical sensitivity

In this study Electrochemical polymerization was used to make polypyrrol nanofiber. The in situ chemical oxidative polymerization approach was used to create a nanocomposite of polypyrrole PPy-TiO2. To achieve homogeneous dispersion inside the PPy matrix, the TiO2 was dissolved and ultrasonically dispersed. The surface morphology of polypyrrol and PPy/TiO2 nanocomposites was studied using field emission scanning electron microscopy (FE-SEM), which revealed of a polypyrrol nanofibre network and showed that the TiO2 nanoparticles was well incorporated. The produced PPy/TiO2 nanocomposite was characterized using XRD (X-Ray diffraction) and FT-IR (Fourier Transform Infrared). The formation of TiO2 nanoparticales on a PPy layer matrix was discovered, as well as homogeneous dispersion of TiO2 inside the PPy matrix and considerable interaction between PPy and TiO2. The produced PPy/TiO2 nanocomposite sensors’ response was investigated towards of light-power sensitivity. The PPy/TiO2 synergistic effects improve the light sensitivity qualities of the photodetector. The maximium sensitivity of PPy/TiO2 was around (188 %) at 20% TiO2 concentration at a light power of 30 mW for a laser diode 720 nm, while the rise time and fall time was ≈ 2.5sec.

Recent Technical Progression in Photoacoustic Imaging—Towards Using Contrast Agents and Multimodal Techniques

For combining optical and ultrasonic imaging methodologies, photoacoustic imaging (PAI) is the most important and successful hybrid technique, which has greatly contributed to biomedical research and applications. Its theoretical background is based on the photoacoustic effect, whereby a modulated or pulsed light is emitted into tissue, which selectively absorbs the optical energy of the light at optical wavelengths. This energy produces a fast thermal expansion in the illuminated tissue, generating pressure waves (or photoacoustic waves) that can be detected by ultrasonic transducers. Research has shown that optical absorption spectroscopy offers high optical sensitivity and contrast for ingredient determination, for example, while ultrasound has demonstrated good spatial resolution in biomedical imaging. Photoacoustic imaging combines these advantages, i.e., high contrast through optical absorption and high spatial resolution due to the low scattering of ultrasound in tissue. In this review, we focus on advances made in PAI in the last five years and present categories and key devices used in PAI techniques. In particular, we highlight the continuously increasing imaging depth achieved by PAI, particularly when using exogenous reagents. Finally, we discuss the potential of combining PAI with other imaging techniques.

Optical Sensitivity of Camera-Like Eyes to White Light

Gastropod mollusks are convenient model organisms for studying the functioning of the visual system. The purpose of this work is to estimate the value of the optical sensitivity to white light for the camera-like eyes of gastropod mollusks and humans and analyze its effect on the spatial resolving power in two regions of the retina: in the center—for single photoreceptors of the first/second type in a mollusk and single cones in humans—and in the periphery—for single photoreceptors of the first/second type in a mollusk, as well as for single rods/cones and their groups, subject to spatial summation in humans. The methods of histology, light and transmission electron microscopy, morphometry, calculations and methods of statistical analysis are used in the work. In a mollusk, with a fixed pupil area, the value of the optical sensitivity of the eye to white light in the center of the retina for single photoreceptors of the first/second type is 0.5/0.006 μm2·sr and in the periphery of the retina, 0.9/0.009 μm2·sr. In humans, at the minimum and maximum pupil area, respectively, the value of the optical sensitivity of the eye to white light in the center of the retina (foveola) for single cones varies from 0.00053 to 0.028 μm2·sr, and in the periphery of the retina (far periphery) for single rods from 0.011 to 0.575 μm2·sr, for single cones from 0.025 to 1.319 μm2·sr, for the groups of rods from 3859 to 204,094 μm2·sr and for the groups of cones from 2.5 to 131 μm2·sr. The value of the optical sensitivity of the eyes to white light for single photoreceptors of the first/second type in both regions of the retina in a mollusk, as well as for single cones in the center and groups of rods/cones in the periphery of the retina in humans, corresponds to the ambient light conditions during periods of activity and does not affect the spatial resolving power.

Advance Optical Properties and Emerging Applications of 2D Materials

In the last several decades, significant efforts have been devoted to two-dimensional (2D) materials on account of their optical properties that have numerous applications in the optoelectronic world in the range of light-emitting diodes, optical sensors, solar energy conversion, photo-electrochemical cells, photovoltaic solar cells, and even the biomedical sector. First, we provide an outline of linear optical properties of 2D materials such as graphene, TMDs, h-BN, MXenes, perovskite oxide, and metal-organic framework. Then, we discuss the optoelectronic properties of the 2D materials. Along with these, we also highlight the important efforts in developing 2D optical materials with intensive emission properties at a broad wavelength from ultraviolet to near-infrared. The origin of this tunable emission has been discussed decoratively. Thickness and layer-dependent optical properties have been highlighted and are explained through surface defects, strain, vacancy, doping, and dangling bonds emerging due to structural change in the material. The linear and nonlinear optical properties in 2D MXene and perovskite oxides are also impressive due to their potential applications in next-generation devices with excellent optical sensitivity. Finally, technological innovations, challenges, and possible tuning of defects and imperfections in the 2D lattice are discussed.

Development of Neutral Red as a pH/pCO2 Luminescent Sensor for Biological Systems

Neutral Red (NR), a eurhodin dye, is often used for staining living cells, but we demonstrated for the first time that NR can also serve as a CO2 sensor, because of NR’s unique optical properties, which change with dissolved carbon dioxide (dCO2) concentrations. In the present study, optical sensitivity of NR was quantified as a function of changes in absorption and emission spectra to dCO2 in a pH 7.3 buffer medium at eight dCO2 concentrations. NR exhibited a response time of two minutes for equilibration in pure N2 to 100% CO2 with an ~200% percent change (%∆) in emission intensity and >400%∆ in absorbance, with full reversibility. Important to its application to biological systems, NR exhibited zero sensitivity to dissolved oxygen, which has routinely caused interference for CO2 measurements. NR exhibited pH sensitive emission and excitation energies with dual excitation wavelengths at 455 nm and 540 nm, and a single emission at 640 nm. The CO2 sensing properties of NR were benchmarked by a comparison to pyranine (8-hydroxypyrene-1, 3,6-trisulfonic acid trisodium salt) (HPTS). Future studies will evaluate the feasibility of NR as an intracellular in vivo pCO2 sensor in aquatic organisms critically impacted by increasing global CO2 levels.

Self-Healing Polymers and Composites: Extrinsic Routes

: Polymers have the property to convert the physical stress to covalent bond shuffling thereby acting as the healing agents. Polymeric coatings, paints, electronic devices, drug delivery and many other applications find self-healing materials as a smart technique to prolong the life cycle of the end products. The idea behind these artificial materials is to make it behave like the human body. It should sense the failure and repair before it becomes worse or irreparable. Researchers have explored several polymeric materials which can self-heal through intrinsic or extrinsic mechanisms. This review specifically focusses on extrinsic routes governed by mechanical stress, temperature change in covalent bond, humidity, variation in pH, optical sensitivity and electrochemical effects. Each possible mechanism is further supported by the molecules or bonds which can undergo the transformations under given conditions. On a broader scale, bonds that can self-repair by mechanical force, thermal treatment, chemical modifications, UV irradiation, or electromagnetic phenomenon, are covered under this review. It brings into notice of the shortcomings or challenges in adopting the technology to the commercial scale. The possible molecules or bonds which can undergo the self-healing under certain conditions has been distinctly presented in a well-segregated manner. This review is envisaged to act as a guide for researchers working in this area.

Optical Response of Sila-Fulleranes in Interaction With Glycoproteins for Environmental Monitoring

In this paper, we introduce new features of silicon in fullerane structures. Silicon, when placed in a fullerane structure, increases its electron affinity and electrophilicity index, compared to placement in a diamondoids structure. These nanoparticles can be used to make optical sensors to detect viral environments. In this work, we theoretically examine the changes in the UV-Visible spectrum of sila-fulleranes by interacting with viral spikes. As a result, we find out how the color of silicon nanoparticles changes when they interact with viruses. We apply N- and O-Links for viral glycoprotein structures, and Si20H20 silicon dodecahedrane, respectively. Our computational method to obtain optimal structures and their energy in the ground and excited states, is density functional theory (DFT). Besides, to get the UV-Visible spectrum, time-dependent density functional theory (TD-DFT) approach has been used. Our results show that the color of sila-dodecahedrane is white, and turns green in the face of viral spikes. We can use the optical sensitivity of silicon nanoparticles, especially to identify environments infected with the novel coronavirus.

Run and hide: visual performance in a brittle star

Spatial vision was recently reported in a brittle star, Ophiomastix wendtii, which lacks discrete eyes, but little is known about its visual ecology. Our aim was to better characterize the vision and visual ecology of this unusual visual system. We tested animals’ orientation relative to vertical bar stimuli at a range of angular widths and contrast, to identify limits of angular and contrast detection. We also presented dynamic shadow stimuli, either looming towards or passing overhead the animal, to test for potential defensive responses. Finally, we presented animals lacking a single arm with a vertical bar stimulus known to elicit a response in intact animals. We found that O. wendtii orients to large (≥50°), high-contrast vertical bar stimuli, consistent with a shelter-seeking role and with photoreceptor acceptance angles estimated from morphology. We calculate poor optical sensitivity for individual photoreceptors, and predict dramatic oversampling for photoreceptor arrays. We also report responses to dark stimuli moving against a bright background - this is the first report of responses to moving stimuli in brittle stars and suggests additional defensive uses for vision in echinoderms. Finally, we found that animals missing a single arm orient worse to static stimuli, which requires further investigation.