Spectral Sensitivity Research Articles

Enzymatic vitamin A2 production enables red-shifted optogenetics

Optogenetics is a technology using light-sensitive proteins to control signaling pathways and physiological processes in cells and organs and has been applied in neuroscience, cardiovascular sciences, and many other research fields. Most commonly used optogenetic actuators are sensitive to blue and green light, but red-light activation would allow better tissue penetration and less phototoxicity. Cyp27c1 is a recently deorphanized cytochrome P450 enzyme that converts vitamin A1 to vitamin A2, thereby red-shifting the spectral sensitivity of visual pigments and enabling near-infrared vision in some aquatic species.Here, we investigated the ability of Cyp27c1-generated vitamin A2 to induce a shift in spectral sensitivity of the light-gated ion channel Channelrhodopsin-2 (ChR2) and its red-shifted homolog ReaChR. We used patch clamp to measure photocurrents at specific wavelengths in HEK 293 cells expressing ChR2 or ReaChR. Vitamin A2 incubation red-shifted the wavelength for half-maximal currents (λ50%) by 6.8 nm for ChR2 and 12.4 nm for ReaChR. Overexpression of Cyp27c1 in HEK 293 cells showed mitochondrial localization, and HPLC analysis showed conversion of vitamin A1 to vitamin A2. Notably, the λ50% of ChR2 photocurrents was red-shifted by 10.5 nm, and normalized photocurrents at 550 nm were about twofold larger with Cyp27c1 expression. Similarly, Cyp27c1 shifted the λ50% of ReaChR photocurrents by 14.3 nm and increased normalized photocurrents at 650 nm almost threefold.Since vitamin A2 incubation is not a realistic option for in vivo applications and expression of Cyp27c1 leads to a greater red-shift in spectral sensitivity, we propose co-expression of this enzyme as a novel strategy for red-shifted optogenetics.

Membrane Protein Structures in Native Cellular Membranes Revealed by Solid-State NMR Spectroscopy.

The structural characterization of membrane proteins within the cellular membrane environment is critical for understanding the molecular mechanism in their native functional context. However, conducting residue site-specific structural analysis of membrane proteins in native membranes by solid-state NMR faces challenges due to poor spectral sensitivity and serious interference from background protein signals. In this study, we present a new protocol that combines various strategies for cellular membrane sample preparations, enabling us to reveal the secondary structure of the mechanosensitive channel of large conductance from Methanosarcina acetivorans (MaMscL) in Escherichia coli inner membranes. Our findings demonstrate the feasibility of achieving complete resonance assignments and the potential for determining the 3D structures of membrane proteins within cellular membranes. We find that the use of the BL21(DE3) strain in this protocol is crucial for effectively suppressing background protein labeling without compromising the sensitivity of the target protein. Furthermore, our data reveal that the structures of different proteins exhibit varying degrees of sensitivity to the membrane environment. These results underscore the significance of studying membrane proteins within their native cellular membranes when performing structural characterizations. Overall, this study opens up a new avenue for achieving the atomic-resolution structural characterization of membrane proteins within their native cellular membranes, providing valuable insights into the nativeness of membrane proteins.

Self-formed interfacial oxide layer minimizes reverse bias dark current in PbS colloidal quantum dot photodiodes

PbS colloidal quantum dot (CQD) photodiodes possess high photoresponsivity and broad spectral sensitivity, making them tremendously attractive for low-cost short-wave infrared (SWIR) sensing. A critical challenge in achieving high detectivity in SWIR photodiodes is to minimize their reverse bias dark current density (Jdark) and elucidate the origin of Jdark. We demonstrate in this work how the self-formed AlOx at the ZnO/Al interface dramatically reduced Jdark of the PbS CQD SWIR photodiodes. In such a simple and controlled way, the interfacial states were thoroughly passivated by post-exposure to dry air, which could block the dominant pathways for minority hole injection from Al electrode. The treated photodiode showed low Jdark down to 1.58 × 10−7 A/cm2 at –0.5 V, high photoresponsivity of 0.62 A/W, and high specific detectivity of 2.05 × 1012 Jones at 1413 nm, establishing a readily approach to optimizing detectivity in PbS CQD SWIR photodetectors.

Melanopsin enhances image persistence

Contributions of the inner retinal photopigment melanopsin to human visual perception are incompletely understood. Here, we use a four-primary display to produce stimuli differing in melanopsin versus cone contrast in psychophysical paradigms in eight subjects with normal color vision. We address two predictions from electrophysiological recordings of the melanopsin system in non-human mammals: melanopsin influences color and/or supports image persistence under visual fixation. We first construct chromatic contrast sensitivity contours for stimuli differing in melanopsin excitation presented as a central annulus (10°) or peripheral (22.5°) spot. We find that although including melanopsin contrast produces modest changes in the average chromatic coordinates in both eccentricities, this occurs equally at low (0.5Hz) and higher (3.75Hz) temporal frequencies, arguing that it reflects divergence in cone spectral sensitivity in our participants from that captured in standardized cone fundamentals rather than a melanopsin contribution to color. We continue to ask whether the established ability of melanopsin to sustain firing of visual neurons under extended light exposure has a visual correlate, using the optical illusion of Troxler fading in which blurred spots in periphery disappear during visual fixation. We find that introducing additional melanopsin contrast (+28% Michelson contrast) to either bright or dark spots increases fading latency by 35%± 8.8% and 41%± 13.6%, respectively. Our data argue that the primary contribution of melanopsin to perception under these conditions isnot to provide a color percept but rather to enhance persistence of low spatial frequency patterns during visual fixation.

Band selection pipeline for maturity stage classification in bell peppers: From full spectrum to simulated camera data

This paper describes a workflow for classifying the maturity of bell peppers using hyperspectral imaging and machine learning. The approach involves using spectral reflectance to determine the number of maturity stages, followed by a classification task using the optimal bands for accurate classification. The study explores a realistic scenario using simulated camera responses and investigates the use of real sensors with their spectral sensitivities and noise. Four classifier algorithms (RBFNN, PLS-DA, SVM, and LDA) were employed to predict the maturity stage based on spectral reflectance. The best results were achieved with the LDA algorithm, which was used in the optimization process for band selection. The optimized bands in the VISNIR range (400–1000 nm) were found to be [783.5, 844.1, and 905.4] nm, with an accuracy of 90.67% for spectral data. For camera responses with intermediate-level noise, the best bands were [760, 820, and 900 nm], achieving an accuracy of 81%. Overall, using three bands yielded satisfactory and practical results for real-world implementation.

Slow-wave-enhanced on-chip Michelson interferometer sensor.

We experimentally demonstrated slow-wave-enhanced phase and spectral sensitivity in asymmetric Michelson interferometer (MI) sensors. Compared to Mach-Zehnder interferometers (MZI) that experimentally demonstrated a phase sensitivity of 84,000 rad/RIU-cm, the reflected path enhancement of the optical path length coupled with slow light enhancement with photonic crystal waveguides in on-chip slow light Michelson interferometer sensors resulted in experimentally demonstrated phase sensitivity of 277,750 rad/RIU-cm with theoretical phase sensitivity as high as 461,810 rad/RIU-cm, at the same form factor as the MZI of identical interferometer arm lengths.

Electromagnetic heating-assisted metasurface for stably tunable, fast-responding chiroptics.

Herein, a graphene-dielectric metasurface with the function of stably tunable and fast responding on the chiroptics is theoretically investigated and numerically demonstrated. Via utilizing the intrinsic thermo-optical effect of the silicon, the circular dichroism (CD) peak position can be linearly scaled with a spectral sensitivity of up to 0.06 nm/K by artificially adjusting the temperature. Moreover, a perfectly adjusting manipulation with a wavelength shift of full width at half maximum for the resonant spectrum and the simultaneously maintained CD values can be realized by a slight temperature variation of ∼0.8 K. Additionally, we take a graphene layer as the heating source to actually demonstrate the ultra-fast thermal generation. Applying an input voltage of 2 V to the graphene with only 10 µs can rapidly increase the metasurface temperature of up to 550 K. Such performances hold the platform with wide applications in functional chiroptics and optoelectronics.

Absolute calibration of the spectral sensitivity of an x-ray streak camera over the 0.1-10keV spectral range equipped with CsI photocathode.

In this paper, we report the absolute measurement of the spectral sensitivity of a bilamellar tube x-ray streak camera (XRSC) over the 0.1-10keV range equipped with a CsI photocathode for Laser MégaJoule (LMJ) fusion experiments. This calibration of the XRSC is performed in static mode by using two multi-anode x-ray generators. Two silicon drift detectors (SDDs) previously calibrated at the Physikalisch-Technische-Bundesanstalt radiometric laboratory are used as secondary standards. Both x-ray generators work with a specific monochromator for radiometric measurements. In the sub-keV region, a 1 m-grazing incidence Rowland geometry monochromator specifically developed to handle LMJ's x-ray camera is used, whereas for higher energies (>2keV), a double-crystal monochromator is employed. The absolute spectral sensitivity of the XRSC is obtained by comparing the CCD counts of the XRSC output with the output counts in x-ray lines recorded by the SDD. The results obtained below 1.2keV are, to our knowledge, the first measurements of the spectral sensitivity of an XRSC in the soft x-ray range with a CsI photocathode. Comparison with a model describing the spectral dependence of the sensitivity of the XRSC revealed that measurements obtained in the sub-keV region are greater than expected, whereas they agree with the model above 4.5keV. There may be several contributors to this behavior, including the grain morphology of the CsI layer and exposure to air.

A review of Cu2O solar cell

Cu2O-based solar cells offer a promising solution to address future energy challenges due to their affordability, eco-friendliness, and impressive power conversion efficiency (PCE). With the development of thin film deposition technology, the maximum PCE of single-junction solar cells fabricated based on Cu2O is 9.5%. Because the spectral sensitivity overlaps between Cu2O and crystalline silicon (c-Si) is small, Cu2O thin-film solar cells can be made into tandem solar cells with Si-based solar cells to achieve higher PCE. The Cu2O–Si tandem solar cell has been delivered 24.2% PCE in 2020, a time when the PCE of stand-alone silicon solar cells was 17.6%. The purpose of this paper is to summarize the development of Cu2O-based heterojunction, homojunction. The Cu2O material properties, n and p-type doping, the role of defects and impurities in bulk of films or at the interface of the p–n-junction and n-type buffer layer on the performance of Cu2O-based heterojunction like ZnO–Cu2O, and the difficulty in decreasing the interface state and doping in Cu2O homojunction solar cells are discussed. This review discusses the Cu2O film material preparation method, the history of Cu2O based solar cells, the essential factors required to enhance the performance of various types of Cu2O-based solar cells, and the potential future research opportunities for as a top subcells in Cu2O–Si tandem solar cells.

Diversity of rhodopsin cyclases in zoospore-forming fungi.

Light perception for orientation in zoospore-forming fungi is linked to homo- or heterodimeric rhodopsin-guanylyl cyclases (RGCs). Heterodimeric RGCs, first identified in the chytrid Rhizoclosmatium globosum, consist of an unusual near-infrared absorbing highly fluorescent sensitizer neorhodopsin (NeoR) that is paired with a visual light-absorbing rhodopsin responsible for enzyme activation. Here, we present a comprehensive analysis of the distribution of RGC genes in early-branching fungi using currently available genetic data. Among the characterized RGCs, we identified red-sensitive homodimeric RGC variants with maximal light activation close to 600 nm, which allow for red-light control of GTP to cGMP conversion in mammalian cells. Heterodimeric RGC complexes have evolved due to a single gene duplication within the branching of Chytridiales and show a spectral range for maximal light activation between 480 to 600 nm. In contrast, the spectral sensitivity of NeoRs is reaching into the near-infrared range with maximal absorption between 641 and 721 nm, setting the low energy spectral edge of rhodopsins so far. Based on natural NeoR variants and mutational studies, we reevaluated the role of the counterion-triad proposed to cause the extreme redshift. With the help of chimera constructs, we disclose that the cyclase domain is crucial for functioning as homo- or heterodimers, which enables the adaptation of the spectral sensitivity by modular exchange of the photosensor. The extreme spectral plasticity of retinal chromophores in native photoreceptors provides broad perspectives on the achievable spectral adaptation for rhodopsin-based molecular tools ranging from UVB into the near-infrared.

Photo sensing analysis of T-shape TFET sensor under visible range of spectrum

This paper presents the optical performance of T-shape TFET based photo sensor under visible range of spectrum using a technology computer-aided design (TCAD) Synopsys simulator. The optical analysis of a photo device results in enhancement of spectral sensitivity (Sn), Signal to noise ratio (SNR), Responsivity (R), recombination rate, drain current, and optical generation rate. The result reveals that device under illumination reports magnitude of SNR are 67.79, 47.38, and 38.3 dB at λ= 300, 500, and 700 nm, respectively. The primary objective for investigating the optical operation of TFET is to detect Sn at low gate voltage and make it suitable for low power optical applications in the visible range of spectrum. Finally, a comparison table is introduced to compare the sensitivity of proposed TFET based photo sensor with the existing FET based sensor. TFET based photo sensors have found widespread applications in electronic devices such as wearable bands, smart watches, and IoT appliances, where power efficiency is critical.

Visible-Blind Narrowband Near-Infrared Photodetector for Precise Real-Time Photoplethysmography Measurement.

The visible-blind narrowband photodetector (NPD) with spectral selective sensitivity to near-infrared (NIR) light is an important technology in the field of cardiovascular health assessment. However, the biological information carried by NIR light constantly changes signals with small amplitude and fast speed, which puts high requirements on the performance of detectors. Herein, visible-blind NIR NPDs were constructed by integrating solution-processable films of perovskite, CuSCN, and organic semiconductors. The NIR response was provided by the organic bulk heterojunction (OBHJ) film with a narrow band gap. A thick perovskite layer was applied to screen the incident visible light and suppress the leakage current in the dark state. CuSCN with a high LUMO level blocked the extraction of the visible-light-induced free electrons. The width of the response window was restricted by adjusting the band gap of the perovskite and the donor/acceptor ratio of the OBHJ film. The optimized NIR NPD exhibits a comprehensive performance including visible-blind response, a tunable response spectrum, a high responsivity/detectivity, and a short response time. In practical photoplethysmography measurements, the detector can record the human heart rate in real time through a noninvasive technique and precisely monitor the whole cardiac cycle, which provides an effective method for early detection of cardiovascular symptoms for timely diagnosis and treatment.

Integration and first operation of the Gotthard-II detector at European XFEL

Gotthard-II (G-II) is a 1-D silicon microstrip hybrid detector developed by the Paul Scherrer Institut within the framework of a collaboration agreement with the European XFEL. The ASIC features a dynamic gain switching architecture, in order to cope with the luminosity of European XFEL, and a 12-bit analog-to-digital converter with a sampling/conversion rate of more than 18 MS/s as well as a Static random-access memory, making it capable of matching the European XFEL pulse train structure, thus acquiring up to 2700 images at 4.5 MHz per burst. The sensor’s strip pitch can be either of 50 μm or 25 μm , for a total of 1280 or 2560 output channels per detector, respectively, with a spectral sensitivity that allows either X-ray detection (optimized in the 5–20 keV range) or visible light detection. Its exceptionally good compliance with the European XFEL beam conditions will make G-II the most widely employed detector across the facility, with a total of 29 modules of different flavors that will be installed in scientific instruments and beam diagnostic setups. Although the detector will be predominantly used for spectroscopic measurements it will have a variety of other applications, including X-ray diffraction/emission/absorption experiments, relative pulse arrival time monitoring (of fundamental importance for pump–probe experiments), spectral diagnostics, and beam quality monitoring, with the possibility for the detector itself to generate a veto patterns for the large area MHz framerate pixel detectors employed at the scientific instruments, such as AGIPD, LPD and DSSC. In this paper, an overview of G-II detector technology and its usage at the European XFEL will be presented; the focus will then move on towards the process of detector integration in the European XFEL control system, data acquisition, and data correction infrastructure, highlighting its challenges. Finally, an overview of the first results obtained at scientific instruments will be given.

Accuracy Assessment of different classifiers for Sustainable Development in Landuse and Landcover mapping using Sentinel SAR and Landsat-8 data

Sentinel satellites make use of Synthetic Aperture Radar (SAR) which produces images with backscattered signals at fine spatial resolution from 10 m to 50 m. This study is mainly focused on evaluating and assessing the accuracy of various supervised classifiers like Random Forest classifier, Minimum Distance to mean classifier, KDTree KNN classifier, and Maximum Likelihood classifier for landuse / landcover mapping in Maduranthakam Taluk, Kancheepuram district, Tamilnadu, India. These classifiers are widely used for classifying the Sentinel SAR images. The SAR images were processed using speckle and terrain correction and converted to backscattered energy. The training datasets for the landcover classes, such as vegetation, waterbodies, settlement, and barren land, were collected from Google Earth images in high-resolution mode. These collected training datasets were given as input for the various classifiers during the classification. The obtained classified output results of various classifiers were analyzed and compared using the overall classification accuracy. The overall accuracy achieved by the Random Forest classifier for the polarization VV and VH was 92.86%, whereas the classified accuracy of various classifiers such as KDTree KNN, Minimum distance to mean, and Maximum Likelihood are found to be 81.68%, 83.17%, and 85.64% respectively. The random forest classifier yields a higher classification accuracy value due to its greater stability in allocating the pixels to the right landuse class. In order to compare and validate the results with sentinel data, the random classifier is applied with optical Landsat-8 satellite data. The classification accuracy obtained for Landsat-8 data is 84.61%. It is clearly proved that the random forest classifier with sentinel data gives the best classification accuracy results due to its high spatial resolution and spectral sensitivity. Thus accurate landuse and landcover mapping promote sustainable development by supporting decision-making at local, regional, and national levels.

Spectral Tunability, Luminescence Enhancement, and Temperature Sensitivity of Sb3+-Doped Bismuth-Based Halide Emission Crystals for Anti-Counterfeiting Applications.

The synthesis of sustainable luminescent materials with simplicity, low energy consumption, and nontoxicity is of great importance in the field of chemistry and materials science. In this study, a room temperature evaporation method was employed to synthesize Sb3+-doped bismuth-based halide emission crystals, allowing for investigation of spectral tuning, luminescence enhancement, and temperature sensitivity. By substitution of Rb+ with varying concentrations of Cs+ in Rb3BiCl6 (RBC), the luminescent color of the crystals can be tuned from orange to yellow. The resulting alloyed yellow-emitting crystals were identified as Rb2CsBiCl6 (RCBC). Remarkably, when one-third of the Rb+ ions were replaced by Cs+ in the RBC, the crystals exhibited improved thermal stability and a 20-fold increase in luminescence intensity. The temperature-sensitive behavior was observed for RBC:Sb, with emission shifting from 590 to 574 nm upon heating while the yellow emission of RCBC:Sb exhibited no significant peak shift with temperature. Notably, the yellow emission of RBC:Sb could be reversibly converted back to orange light upon cooling to room temperature. In contrast, RCBC:Sb exhibited no significant peak shift with temperature. The differential temperature sensitivity between RBC:Sb and RCBC:Sb offers potential applications in anti-counterfeiting measures.

Switching and photosensitive analysis of dopingless tunnel field effect transistor based on cladding layer concept

— In this paper, the switching and photo sensing analysis of cladding layer based dopingless Tunnel FET (CDL-TFET) has been examined under visible range of spectrum. Initially, the impact of cladding layer in DL-TFET on electrical parameter is observed by varying the source material and thickness of source region. Furthermore, CDL-TFET is used for photo sensing application under the light state at various wavelength of light incident. The various optical figure of merits (FoMs) like spectral sensitivity (Sn), Signal to noise ratio (SNR), Responsivity (R), and quantum efficiency (η) is extracted to realize the behavior of photosensor. The maximum value of Sn is 48, R of 0.74 (A/Watt), SNR of 68.8 dB, and η of 3 are obtained at λ = 300 nm. Further, impurity trap charge effects are also observed at the interface and bulk of TFET. Finally, a comparison table has been presented to signify the importance of cladding layer based DL-TFET photo sensor with existing literature.

Photon-Counting CT Material Decomposition in Bone Imaging.

The accurate screening of osteoporosis is important for identifying persons at risk. The diagnosis of bone conditions using dual X-ray absorptiometry is limited to extracting areal bone mineral density (BMD) and fails to provide any structural information. Computed tomography (CT) is excellent for morphological imaging but not ideal for material quantification. Advanced photon-counting detector CT (PCD-CT) possesses high spectral sensitivity and material decomposition capabilities to simultaneously determine qualitative and quantitative information. In this study, we explored the diagnostic utility of PCD-CT to provide high-resolution 3-D imaging of bone microarchitecture and composition for the sensitive diagnosis of bone in untreated and ovariectomized rats. PCD-CT accurately decomposed the calcium content within hydroxyapatite phantoms (r = 0.99). MicroCT analysis of tibial bone revealed significant differences in the morphological parameters between the untreated and ovariectomized samples. However, differences in the structural parameters of the mandible between the treatment groups were not observed. BMD determined with microCT and calcium concentration decomposed using PCD-CT differed significantly between the treatment groups in both the tibia and mandible. Quantitative analysis with PCD-CT is sensitive in determining the distribution of calcium and water components in bone and may have utility in the screening and diagnosis of bone conditions such as osteoporosis.

Utilising spectral lighting simulation technique for evaluating transmitted daylight through glazing: Exploring the non-visual effects and colour appearance

Modern humans spend more time indoors than their ancestors. In indoor environments, windows are the primary building elements that provide access to daylight and views. The advancement of the building industry has introduced new glazing and coating technologies for windows. Electrochromic glazing, in particular, has gained popularity in recent decades. These glazings’ tint varies with light exposure and electrical voltage, affecting the spectral power distribution of transmitted daylight. The growing knowledge of the impacts of light on sleep and health encourages an evaluation of the non-visual effects of daylight transmitted through glazing. Therefore, the aim of this paper is to investigate the non-visual effects of transmitted daylight through one clear and one smart glazing and evaluate the colour appearance variations. However, conventional visualisation tools are inadequate for this purpose, necessitating the use of alternative techniques that consider the spectral power distribution of light. To accomplish this, the Radiance-based Lark spectral lighting simulation tool was utilised. The non-visual effects were analysed by examining the responses of the five photoreceptors (Short-, Medium-, Long-wavelength cones, Rods, and ipRGCs) to light using the CIE spectral sensitivity functions. Additionally, the changes in colour appearance were assessed using six attributes: lightness, hue, chroma, vividness, depth, and clarity. The results demonstrate the effect of the studied glazing on non-visual light stimulation and colour appearance while presenting the challenges, applicability, and limitations of spectral simulation techniques. The proposed method yields promising results and can be a valuable tool for evaluating the effects of glazing on humans.

Design of a novel D-shaped SPR sensor with high sensitivity based on PCF for ultra-low refractive index detection

In this paper, a novel D-shaped plasmon resonance sensor based on photonic crystal fiber (PCF) is proposed to detect analytical materials with low refractive index. There are three arc-shaped small holes on both upper and lower edges of the fiber core, which can enhance the surface plasmon effect. The operation wavelength of the sensor is from 2243 nm to 2651 nm when its measurable refractive index range is between 1.17 and 1.27. The maximum spectral sensitivity of the sensor can be reached to 20 300 nm RIU−1, and the optimal resolution is 4.93 × 10−6 RIU. In our knowledge, the current literature indicates that when the refractive index is less than 1.3, this is the sensor with the highest spectral sensitivity among the reported low refractive index PCF-surface plasmon resonance sensors.

Fiber-optic temperature sensor based on glass Fabry–Perot interferometer

The paper presents a theoretical and experimental study of a fiber-optic all-glass microthermometer based on a Fabry–Perot interferometer. The interferometer is fabricated by applying borosilicate glass to the cleaved end of a standard telecom single-mode optical fiber using a microforge. According to the results of experimental studies, the spectral sensitivity of the fabricated interferometer was about 40 pm/°C. A mathematical model of the Fabry–Perot interferometer based on the method of scattering and transfer matrices is presented and verified, which makes it possible to calculate the spectral response of an interferometer with arbitrary structure parameters.