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Calcium imaging with protein-based indicators1,2is widely used to follow neural activity in intact nervous systems, but current protein sensors report neural activity at timescales much slower than electrical signalling and are limited by trade-offs between sensitivity and kinetics. Here we used large-scale screening and structure-guided mutagenesis to develop and optimize several fast and sensitive GCaMP-type indicators3–8. The resulting ‘jGCaMP8’ sensors, based on the calcium-binding protein calmodulin and a fragment of endothelial nitric oxide synthase, have ultra-fast kinetics (half-rise times of 2 ms) and the highest sensitivity for neural activity reported for a protein-based calcium sensor. jGCaMP8 sensors will allow tracking of large populations of neurons on timescales relevant to neural computation.

2,2′,7,7′-Tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9′-spirobifluorene (spiro-OMeTAD), the most widely used hole transport material in high-efficiency perovskite solar cells (PSCs), still has serious defects, such as moisture absorption and poor long-term conductivity, which seriously restrict further improvement of the power conversion efficiency (PCE) and stability of the cell. Herein, to overcome these problems, inorganic salt PbSO4(PbO)4quantum dots (QDs) are incorporated into spiro-OMeTAD as the hole transport layer (HTL) for the first time. The incorporated PbSO4(PbO)4QDs significantly hinder the agglomeration of lithium bis(trifluoromethanesulfonyl)-imide and improve the long-term conductivity through the oxidative interaction between PbSO4(PbO)4QDs and spiro-OMeTAD and hydrophobicity of the HTL. Furthermore, the spiro-OMeTAD:PbSO4(PbO)4composite film can effectively passivate perovskite defects at the perovskite/HTL interface, resulting in suppressed interfacial recombination. As a result, the PSC based on the spiro-OMeTAD:PbSO4(PbO)4HTL shows an improved PCE of 22.66%, which is much higher than that (18.89%) of the control device. PbSO4(PbO)4also significantly improves the moisture stability for 50 days at room temperature (at RH ∼ 40–50%) without encapsulation. This work indicates that inorganic PbSO4(PbO)4QDs are crucial materials that can be employed as an additive in spiro-OMeTAD to enhance the efficiency and stability of PSCs.

As a member of the seven-transmembrane rhodopsin-like G protein-coupled receptor superfamily, the melanocortin-3 receptor (MC3R) is vital for the regulation of energy homeostasis and rhythms synchronizing in mammals, and its pharmacological effect could be directly influenced by the presence of melanocortin receptor accessory proteins (MRAPs), MRAP1 and MRAP2. The tetrapod amphibian Xenopus laevis(xl) retains higher duplicated genome than extant teleosts and serves as an ideal model system for embryonic development and physiological studies. However, the melanocortin system of the Xenopus laevishas not yet been thoroughly evaluated. In this work, we performed sequence alignment, phylogenetic tree, and synteny analysis of two xlMC3Rs. Co-immunoprecipitation and immunofluorescence assay further confirmed the co-localization andin vitrointeraction of xlMC3Rs with xlMRAPs on the plasma membrane. Our results demonstrated that xlMRAP2.L/S could improve α-MSH-stimulated xlMC3Rs signaling and suppress their surface expression. Moreover, xlMC3R.L showed a similar profile on the ligands and surface expression in the presence of xlMRAP1.L. Overall, the distinct pharmacological modulation of xlMC3R.L and xlMC3R.S by dual MRAP2 proteins elucidated the functional consistency of melanocortin system during genomic duplication of tetrapod vertebrates.

To solve the problem of small field of view in traditional holographic waveguides, this paper proposes a waveguide-coupling technique using orthogonal superposition varied-line-spacing (VLS) gratings. These gratings expand the x and y directions and orthogonally superimpose to achieve transmission in a waveguide and enlarge the pupil field of view. At the optical coupling input end and the coupling output end of a waveguide, one-dimensional VLS gratings are used to realize horizontal expansion of the image. Then a vertical VLS grating is orthogonally superimposed at the exit end to realize vertical expansion of the image. Finally, the waveguide transmission and expansion of the image are completed. In the experiment, holographic polymer dispersed liquid crystal one-dimensional VLS gratings in the x and y directions are fabricated and coupled with a waveguide. An image source with a diameter of 0.5 cm is waveguide-transferred and coupled out, and then passed through the vertical grating. Amplification is performed to obtain an expanded image of a diameter of 2.28 cm. In this study, the diffraction characteristics of the grating used to realize pupil expansion in the holographic waveguide system are analyzed and simulated. It is calculated that the diffraction efficiency of the VLS gratings can reach 80% or more in the 532 nm band. Additionally, the characteristics of an electronically controlled switch are studied. Experimental results show that the method can be used for expanding the field of view and can be applied to waveguide systems for image transmission and expansion.

A varied-line-spacing switchable holographic grating is demonstrated through a changeable interference pattern recorded in polymer-dispersed liquid crystal. The pattern is generated by the interference between one plane wave and another cylindrical wave. The line spacing and the period of grating can be controlled by varying the distance between the cylindrical lens and the grating sample and by changing the exposure angle between the two beams. Experimental period measurements and calculations show good agreement with the theoretical results. High diffraction efficiency of more than 80% for the middle period of the grating has been achieved under appropriate exposure time of 120 s and intensity of 19.1  mW/cm^2. In addition, the diffraction can be switched on and off by virtue of the external driving voltage of approximately 120 V. The grating also possesses a fast response with a rise time of 300 μs and a fall time of 750 μs. This grating, which can change the period in the grating structure to allow switchable diffraction of transmitted light, shows great potential application for diffractive optics.

We report on the synthesis and characteristics of a holographic polymer dispersed liquid crystal (H-PDLC) switchable grating based on nano-Ag particles. The influence of doping different concentrations of nano-Ag on the diffraction efficiency, driving voltage, and response time of the H-PDLC grating is investigated. The best grating characteristics were achieved with 0.05% nano-Ag doping. Calculated and experimental results reveal that the improvement of the characteristics is likely due to the surface plasmon effect of nano-Ag.

Tunable photonic crystals (PCs), which are infiltrated with nematic liquid crystals (LCs), tune photonic band gap (PBG) by rotating directors of LCs when applied with the external electrical field. Using the plane wave expansion method, we simulated the PBG structure of two-dimensional tunable PCs with a triangular lattice of circular column, square column and hexagon column, respectively. When PCs are composed of LCs and different substrate materials such as germanium (Ge) and silicon (Si), the influence of structural parameters including column shape and packing ration on PBG is discussed separately. Numerical simulations show that absolute PBG can't be found at any conditions, however large tuning range of polarized wave can be achieved by rotating directors of LCs. The simulation results provide theoretical guidance for the fabrication of field-sensitive polarizer with big tunable band range.

The optical chopper array based on Holographic Polymer Dispersed Liquid Crystal (H-PDLC) working at high frequencies, for example 1KHz, 2KHz, and its application in an improved Frequency Division Multiplexed Fluorescence Confocal Microscope (FDMFCM) system are reported in this article. The system is a combination of the confocal microscopy and the frequency division multiplexing technique. Taking advantages of the optical chopper array based on H-PDLC that avoids mechanical movements, the FDMFCM system is able to obtain better Signal-Noise Ratio (SNR), smaller volume, more independent channels and more efficient scanning. What's more, the FDMCFM maintained the high special resolution ability and realized faster temporal resolution than pervious system. Using the proposed device, the FDMFCM system conducts successful parallel detection of rat neural cells. Fluorescence intensity signals from two different points on the specimen, which represent concentration of certain kind of proteins in the sample cells, are achieved. The experimental results show that the proposed H-PDLC optical chopper array has feasibility in FDMFCM system, which owes to its unique characteristics such as fast response, simple fabrication and lower consumption etc. With the development of H-PDLC based devices, there will be prospective in upgrading FDMFCM system's performance in the biomedical area.

An experimental investigation on a novel electrically controlled optical chopper based on holographic polymer dispersed liquid crystal (H-PDLC) gratings is presented in this paper. In order to realize the chopping function, a corresponding electrical driving source and controlling circuit are developed for the phase type H-PDLC grating, so that the H-PDLC chopper can not only modulate a light beam with variable frequencies at different duty ratios but also generate other types of waveform modulation such as the sinusoidal modulation to replace the traditional rectangular modulation. Experimental results on one-channel, two-channel and four-channel H-PDLC optical choppers showed that, in comparison with the mechanical chopper counterpart, this device had the advantages of (1) lower noise without mechanical moving part, (2) higher conveniences in terms of changing its operational frequencies, duty ratios and modulation curves, and (3) multi-channel modulation capability. Therefore, it will have a great potential for applications that requires frequency modulations such as frequency modulated confocal microscopy system.

An electrically controlled optical chopper based on switchable holographic polymer dispersed liquid crystal (H-PDLC) gratings is demonstrated through a programmable, adjustable, and periodic external driving source. Compared with traditional mechanical optical choppers, the H-PDLC chopper exhibits many advantages, including faster response time, less waveform deformation, as well as easier integration, control, and fabrication, to name a few. Its excellent performance makes the device potentially useful in frequency modulation optical systems, such as frequency division multiplexed microscopy system.

Machine learning can effectively accelerate the runtime of a computer-generated hologram. However, the angular spectrum method and single fast Fresnel transform-based machine learning acceleration algorithms are still limited in the field-of-view angle of projection. In this paper, we propose an efficient method for the fast generation of large field-of-view holograms combining stochastic gradient descent (SGD), neural networks, and double-sampling Fresnel diffraction (DSFD). Compared with the traditional Gerchberg–Saxton (GS) algorithm, the DSFD-SGD algorithm has better reconstruction quality. Our neural network can be automatically trained in an unsupervised manner with a training set of target images without labels, and its combination with the DSFD can improve the optimization speed significantly. The proposed DSFD-Net method can generate 2000-resolution holograms in 0.05 s. The feasibility of the proposed method is demonstrated with simulations and experiments.

The electron transport layer (ETL) plays an important role as a buffer layer in the efficient n-i-p planar heterojunction perovskite solar cells (PSCs). Recently, a new ETL, (CH3)2Sn(COOH)2(CSCO), with excellent conductivity and defect passivation of perovskites at the ETL/perovskite interface is synthesized by our group, which leads to a high-performance n-i-p PSC. Nevertheless, the effect of CSCO film thickness on the power conversion efficiency (PCE) of PSCs is unclear. In this work, we systematically explore the influence of CSCO film thickness on photovoltaic performance of Cs0.05FA0.81MA0.14PbI2.55Br0.45(CsFAMA)-based PSCs. When the thickness of the CSCO film is less than 42 nm, the coverage of CSCO on an indium tin oxide (ITO) substrate becomes more complete as the CSCO film thickness increases, which reduces the leakage current and increases the charge-transfer efficiency at the CSCO/CsFAMA interface and therefore improves the PCE of the PSCs. However, for a thicker CSCO film with a thickness >42 nm, the ultraviolet–visible absorption intensity of CSCO increases, which is harmful to light absorption of the perovskite layer and therefore decreases the short-circuit current density of PSCs. Furthermore, a thicker CSCO film (>42 nm) leads to a sharply decreased shunt resistance, lowering the fill factor and open-circuit voltage. As a consequence, the maximum PCE of 20.42% is achieved by the PSCs based on the CSCO film with a thickness of 42 nm. In addition, the optimal PSC without encapsulation shows remarkable stability, retaining more than 85% of its initial conversion efficiency after 3000 h of storage in an ambient environment.