Curvature Sensor Research Articles

Curvature dependence of BAR protein membrane association and dissociation kinetics

BAR (Bin/Amphiphysin/Rvs) domain containing proteins function as lipid bilayer benders and curvature sensors, and they contribute to membrane shaping involved in cell signaling and metabolism. The mechanism for their membrane shape sensing has been investigated by both equilibrium binding and kinetic studies. In prior research, stopped-flow spectroscopy has been used to deduce a positive dependence on membrane curvature for the binding rate constant, kon, of a BAR protein called endophilin. However, the impact of bulk diffusion of endophilin, on the kinetic binding parameters has not been thoroughly considered. Employing similar methods, and using lipid vesicles of multiple sizes, we obtained a linear dependence of kon on vesicle curvature. However, we found that the observed relation can be explained without considering the local curvature sensing ability of endophilin in the membrane association process. In contrast, the diffusion-independent unbinding rate constant (koff) obtained from stopped-flow measurements shows a negative dependence on membrane curvature, which is controlled/mediated by endophilin-membrane interactions. This latter dependency, in addition to protein–protein interactions on the membrane, explains the selective binding of BAR proteins to highly curved membranes in equilibrium binding experiments.

Battery-Less Sensing of Body Movements Through Differential Backscattered RFID Signals

RFID tags not only can be used as identification devices, with antenna sensing techniques, they can also be used as low-cost and battery-less sensors. However, RFID antenna sensing relies on the impedance and/or gain modulation of the tag’s antenna, and extracts the sensing information through the RSSI variation of the backscattered signals. The sensing information is prone to the interferences and noises in the reader-tag communication channel, as well as the distance variations if the sensors are in constant motion. In this paper, we propose a sensor structure that is constructed from adjacently placed double tags to address these issues. The EM properties of the antennas of the double tags behave differently (or even oppositely) under the same sensing variation; therefore, the differential backscattered signals of the dual-tag sensor can eliminate the common-mode interferences while preserving the sensing information. We have constructed one curvature sensor and one deformation sensor with embroidered antennas (using conductive yarns) and all-fabric materials, and sewn the sensors on apparels to demonstrate their use in smart clothing applications. The experiments show that even when the human body is in constant motion, the curvature sensor sewn on the knee area can effectively monitor human’s body gesture, while the deformation sensor sewn on the chest area can precisely detect the respiration activities.

Insights into Membrane Curvature Sensing and Membrane Remodeling by Intrinsically Disordered Proteins and Protein Regions.

Cellular membranes are highly dynamic in shape. They can rapidly and precisely regulate their shape to perform various cellular functions. The protein’s ability to sense membrane curvature is essential in various biological events such as cell signaling and membrane trafficking. As they are bound, these curvature-sensing proteins may also change the local membrane shape by one or more curvature driving mechanisms. Established curvature-sensing/driving mechanisms rely on proteins with specific structural features such as amphipathic helices and intrinsically curved shapes. However, the recent discovery and characterization of many proteins have shattered the protein structure–function paradigm, believing that the protein functions require a unique structural feature. Typically, such structure-independent functions are carried either entirely by intrinsically disordered proteins or hybrid proteins containing disordered regions and structured domains. It is becoming more apparent that disordered proteins and regions can be potent sensors/inducers of membrane curvatures. In this article, we outline the basic features of disordered proteins and regions, the motifs in such proteins that encode the function, membrane remodeling by disordered proteins and regions, and assays that may be employed to investigate curvature sensing and generation by ordered/disordered proteins.Graphical

The curvature sensor based on fiber-optic spindle arrays

Three curvature optical fiber sensors inserted with different spindle arrays have been proposed and experimentally demonstrated. The spindle structure is fabricated by a fusion splicer after that prestress was applied to a complete single-mode-fiber (SMF) with coating peeled off, where cladding modes are excited and couple with the core mode. The experimental results show that the curvature sensitivities of these sensors are respectively 24.08 dB/m−1, 28.79 dB/m−1 and −38.40 dB/m−1. With inserted spindles in the array increasing in the same length, the curvature sensitivity is improved by 14.32 dB/m−1. In addition to the advantages of low cost and easy fabrication, the sensors have great value in improving curvature sensitivity.

Curvature sensor based on femtosecond laser-inscribed straight waveguide in FMF

We propose an ingenious method for higher-order mode excitation in few-mode fiber (FMF), in which a femtosecond laser is utilized to inscribe a straight waveguide in FMF. Based on this method, a new-type in-fiber Mach-Zehnder interferometer (MZI) for bending sensing is proposed. The in-fiber MZI is achieved through femtosecond laser directly writing a straight waveguide in a very short section of FMF between two standard single mode fibers. The MZI is caused by the interference between the fundamental mode and the higher-order mode excited in the modified FMF. When the device is bent in specific four orthogonal orientations, the direction of its spectrum shift is different. The device has a large curvature measurement range of 0–10 m−1. The curvature sensitivity can reach 2 nm/m−1 and the temperature sensitivity is as low as 2.34 pm/°C. Moreover, the device has the superiorities of miniature size, simple manufacturing, high reproducibility, low insertion loss and high spectral contrast.

Coarse-Grained Simulations Suggest Potential Competing Roles of Phosphoinositides and Amphipathic Helix Structures in Membrane Curvature Sensing of the AP180 N-Terminal Homology Domain.

The generation and sensing of membrane curvature by proteins has become of increasing interest to researchers with multiple mechanisms, from hydrophobic insertion to protein crowding, being identified. However, the role of charged lipids in the membrane curvature-sensing process is still far from understood. Many proteins involved in endocytosis bind phosphatidylinositol 4,5-bisphosphate (PIP2) lipids, allowing these proteins to accumulate at regions of local curvature. Here, using coarse-grained molecular dynamics simulations, we study the curvature-sensing behavior of the ANTH domain, a protein crucial for endocytosis. We selected three ANTH crystal structures containing either an intact, split, or truncated terminal amphipathic helix. On neutral membranes, the ANTH domain has innate curvature-sensing ability. In the presence of PIP2, however, only the domain with an intact helix senses curvature. Our work sheds light on the role of PIP2 and its modulation of membrane curvature sensing by proteins.

Self-Assembled Vector Curvature Sensor Based on Vernier Effect

A novel fiber Fabry-Perot interferometer (FPI) vector curvature sensor based on Vernier effect is proposed and demonstrated. The triangular-distributed sensing structure is fabricated by self-assembly of FPI and single-mode fiber (SMF). When the device is bent in any orientation, a direction-dependent wavelength shift of the interference pattern is produced because the sensing fiber always deviates from the neutral plane. In order to overcome the trade-off between high sensitivity and large dynamic range, we connect the reference fiber and the sensing fiber to produce the Vernier effect. Without affecting the measurement range of the sensing structure, the sensitivity of the self-assembled sensor based on Vernier effect is amplified by 5 times and 3.6 times respectively by using different FPIs as sensing arm. The experimental results show that the sensing structure has good stability and repeatability. Compared with the substrate packaging, the fiber FPI sensing structure based on self-assembly can realize miniaturization, which is conducive to the application of the sensor in medical detection and artificial intelligence.

Quantification of Curvature Sensing Behavior of Curvature-Inducing Proteins on Model Wavy Substrates.

Curvature-inducing proteins are involved in a variety of membrane remodeling processes in the cell. Several in vitro experiments have quantified the curvature sensing behavior of these proteins in model lipid systems. One such system consists of a membrane bilayer laid atop a wavy substrate (Hsieh in Langmuir 28:12838-12843, 2012). In these experiments, the bilayer conforms to the wavy substrate, and curvature-inducing proteins show preferential segregation on the wavy membrane. Using a mesoscale computational membrane model based on the Helfrich Hamiltonian, here we present a study which analyzes the curvature sensing characteristics of this membrane-protein system, and elucidates key physical principles governing protein segregation on thewavy substrate and other in vitro systems. In this article we compute the local protein densities from the free energy landscape associated with membrane remodeling by curvature-inducing proteins. In specific, we use the Widom insertion technique to compute the free energy landscape for an inhomogeneous system with spatially varying density and the results obtained with this minimal model show excellent agreement with experimental studies that demonstrate the association between membrane curvature and local protein density. The free energy-based framework employed in this study can be used for different membrane morphologies and varied protein characteristics to gain mechanistic insights into protein sorting on membranes.

Vector curvature sensor based on asymmetrically polished long-period fiber grating

In this paper, we experimentally propose and theoretically investigate a two-dimensional vector curvature sensor based on asymmetrically polished long period fiber grating (AP-LPFG). This sensor is fabricated by a high-frequency CO2 laser in order to polish periodic asymmetrical V-shaped grooves on a single mode fiber (SMF). Such grooves efficiently enhances the bending sensitivity of sensor and shorten the length of the structure to 7.39 mm. Experimental results show that the sensitivity of AP-LPFG reaches 30.85 nm/m−1 in the direction of the X-axis and −0.97 nm/m−1 in the direction of the Y-axis. Meanwhile, the temperature response of AP-LPFG is carried out, which is 76 pm/℃ in range of 30-160℃. Moreover, the AP-LPFG has the features of compact length and simple structure, which shows the potential in curvature sensing.

Experimental demonstration of optical Vernier effect by cascading tapered single-mode optical fibres

An experimental demonstration of the optical Vernier effect (OVE) achieved by cascading tapered single-mode optical fibres (SMF28) is presented. The tapered optical fibres conform to a pair of Mach–Zehnder fibre interferometers (MZFIs) with slightly different free spectral ranges. Three different experiments with MZFIs in tandem were carried out to evaluate the OVE characteristics such as the magnification and free spectral range of the envelope. The displacement/curvature sensor exhibited a sensitivity of 0.069 nm/µm (∼84.2 nm/m−1) in the displacement/curvature range of 250–500 µm (∼0.12–0.24 m−1) with a magnification of 8.84. A brief comparison to other OVE-based curvature sensors is presented.

One dimensional vector curvature sensor based on 2-core fiber offset structure

In this paper, a curvature sensor based on 2-core fiber offset structure is proposed. Firstly, the curvature sensing principle of this sensor is qualitatively analyzed. It is concluded that this sensor has the ability to identify one-dimensional bending direction. This is proved by the following experiments. Considering that there can be two offset modes, experiments are carried out on sensors with different offset modes. Through experiments, it is concluded that the sensor in positive offset mode has better sensing performance. The sensors with different offset value are also tested. It is found that the sensor has better curvature sensing performance when its offset value is + 6 μm. The experiments show that the sensitivity of this sensor bending along different directions can reach −14.19 nm/m−1 and + 16.58 nm/m−1. Meanwhile, it has a large measurement range and good linearity. The sensor is also insensitive to strain and twist. This sensor has a wide application prospect in the fields of industry, architecture and structural health monitoring.

High Sensitivity Temperature and Curvature Sensor Based on Mach-Zehnder Interferometer With Tapered Two Peanut-Shaped Structures

A high-sensitivity temperature and curvature microfiber Mach-Zehnder interferometer (MMZI) with two peanut-shaped structures is proposed and demonstrated for the first time. The interferometer consists of a section of microfiber and two peanut-shaped structures. The microfiber can be easily affected by the external environment due to its strong evanescent field on the surface and the peanut-shaped structure is conducive to excite fundamental mode to high-order mode, which is beneficial to realize high-sensitivity sensing detection. The experimental results show that the maximum temperature sensitivity of &#x2212;678.67 pm<inline-formula> <tex-math notation="LaTeX">$/$ </tex-math></inline-formula>&#x00B0;C is obtained in the range of 30 &#x00B0;C to 42 &#x00B0;C, which is the highest temperature sensitivity we have known in the peanut-shaped structure sensor. Furthermore, the sensor is also used for curvature measurements. The curvature sensitivity can be up to &#x2212;79.09 nm<inline-formula> <tex-math notation="LaTeX">$/\text{m}$ </tex-math></inline-formula>^&#x2212;1 from 0.10188 m^&#x2212;1 to 0.20374 m^&#x2212;1. Therefore, the proposed sensor will have good application prospects in the field of biological detection and environment monitoring due to the advantage of high temperature sensitivity.

Temperature compensated curvature sensor with insensitive axial strain based on tapered ring core fiber interferometer

An all fiber temperature compensated curvature sensor with insensitive axial strain is proposed and experimentally demonstrated. The sensor is fabricated by a 2 cm ring core fiber (RCF) which is spliced between single mode fibers (SMFs) with two up-tapers, and a Mach–Zehnder Interferometer (MZI) is formed. The simulation results show that the first up-taper scatters a portion of the input light that should be in the ring core into the outer cladding, and then the ring core modes interfere with the cladding modes distributed in both inner cladding and outer cladding. The interference dips of this structure respond differently to curvature and temperature, so a calibration matrix can be established to implement temperature compensation. Experimental results show that this structure offers a maximum curvature sensitivity of −3.504 nm/m−1 in the range from 1.316 m−1 to 2.372 m−1 with a high linear regression coefficient value of 0.9971, and a maximum temperature sensitivity of 59.42 pm/°C is obtained in the range from 25 °C to 60 °C. We also test the axial strain characteristics of this structure and the results imply a minimum cross sensitivity of 8.086 × 10−5 m−1/με which is extremely low. This indicates that our sensor has axial strain insensitivity which will improve its measurement accuracy.

Low-cost wearable device based D-shaped single mode fiber curvature sensor for vital signs monitoring

A low-cost wearable pulse and respiratory monitoring system based on D-shaped single mode fiber (SMF) curvature sensor is proposed and investigated. The curvature sensing performance of D-shaped SMFs with different transmission loss are tested and analyzed, and the sensitivity up to − 7.208%/m−1. The D-shaped optical fiber structure is encapsulated by polydimethylsiloxane (PDMS) and implanted in a wrist strap, which realizes good wearability and comfort in the process of human pulse monitoring. The system adopts laser source module and signal acquisition module for integrated and miniaturized design, and real time signal acquisition using Field-Programmable Gate Array (FPGA). The real-time monitoring of pulse signal intensity and frequency before and after exercise was realized. The results show that pulse intensity increased after exercise, with a 10%− 30% increase in pulse frequency, which is consistent with the results in medical theory. In addition, the D-shaped SMF encapsulated by PDMS also was implanted into the belt, which also successfully applied to the monitoring of respiratory signals under quiet and walking conditions.

Optical curvature sensor with high resolution based on in-line fiber Mach-Zehnder interferometer and microwave photonic filter.

Curvature measurement plays an important role in structural health monitoring, robot-pose measuring, etc. High-resolution curvature measurement is highly demanded. In this paper, an optical curvature sensor with high resolution based on in-fiber Mach-Zehnder interferometer (MZI) and microwave photonic filter (MPF) is proposed and experimentally demonstrated. The in-fiber MZI is constructed with a ring-core fiber (RCF) which is fusion spliced between two coreless fibers (CLFs). The structure of CLF-RCF-CLF is then sandwiched between two segments of single-mode fiber (SMF), making the whole interferometer structure of SMF-CLF-RCF-CLF-SMF. The operating principle is that different curvatures will cause the variations of the interference spectrum of MZI due to elastic-optic effect, and then the variations are converted into the frequency-shift of the MPF. The factors affecting the visibility of the interference spectrum are researched. A preliminary exploration of the multiplexing demodulation for the in-fiber-MZIs is also investigated and discussed, which is for the first time to the best of our knowledge, holding great potential to pave the way for constructing the sensing network composed of interferometric sensors. The curvature measurement sensitivity is -147.634 MHz/m-1, and the resolution is 6.774 × 10-6 m-1 which is the highest value up to now.

Temperature and Curvature Measurement Based on Low Cavity Loss FLRD Technology

In this study, we proposed a fiber loop ring-down (FLRD) based method for simultaneous temperature and curvature measurements. A tapered single-mode fiber (TSMF) and a TSMF covered with polydimethylsiloxane (PDMS-TSMF) were used as curvature and temperature sensors, respectively. Owing to the low insertion loss of these sensors, erbium-doped fiber amplifiers were not required to compensate for the intensity of the pulsed light in the FLRD. The insertion loss of PDMS-TSMF decreased as the ambient temperature increased, which decreased the slope of the peak envelope of the ring-down pulse. The results show that the linear relationship between the pulse envelope slope and temperature varied from 1.237 dB/(km °C) to 0.397 dB/(km °C) in the temperature range of 40–70 °C. The insertion loss of TSMF increased with the increase in curvature. The slope-curvature relationship was 51.013 dB/(km m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ) from 2.706 to 4.364 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> . The proposed quasi-distributed sensing system has the advantages of low cavity loss, high sensitivity, low cost, and independent measurement of two variables simultaneously. It has potential value in practical engineering applications, especially in building structural health detection, disaster warning.

Reconstitution of membrane curvature sensing by the autophagy initiation machinery

Several membrane curvature sensors have been identified among autophagy initiation proteins, but their ability to work together to sense curvature remains an open question. Here, we reconstituted the interaction of autophagy initiator complexes with curved membranes in vitro to quantify how curvature sensitivity could regulate autophagosome biogenesis. Using membrane nanotubes pulled from giant unilamellar vesicles (GUVs), we assayed the curvature sensing activity of autophagy initiating proteins, including PI3KC3-C1, ATG3, and ATG12-5-16.

Deep learning based optical curvature sensor through specklegram detection of multimode fiber

An optical fiber curvature sensor based on the detection of specklegrams from the facet of multimode fiber (MMF) is realized by using a deep learning regression model. Since the specklegrams result from mode interference in the MMF, they can be used to characterize the status of the MMF. In the experiment, light from a semiconductor laser source was injected into a section of 10-cm-long step-indexed MMF with a core diameter of 50 μm. A large number of specklegrams at the facet of the MMF were automatically detected when different curvatures were introduced for the MMF by a controllable moving translation stage. The output specklegrams of the MMF under different curvatures were then fed into a convolutional neural network (CNN) for training, validation and testing. Experimental results demonstrate that after the CNN was well-trained by the specklegrams with specified curvatures, the CNN can effectively predict the curvature from any of the specklegrams obtained from the MMF with a curvature in the trained range. In the experiment, the CNN trained by specklegrams with 20 curvatures successfully predicted the curvatures corresponding to the specklegrams from the MMF under 57 curvatures in the range of 1.55–6.93 m−1. The prediction error for 94.7% of the specklegrams is within an error range of ±0.3m-1, confirming the feasibility of curvature sensing based on the analysis of specklegrams by CNN.

Two-dimensional vector bending sensor based on Fabry-Pérot cavities in a multicore fiber.

In this work we demonstrate the fabrication and characterization of a temperature insensitive, two-dimensional curvature sensor using a resin based Fabry-Pérot interferometer, constructed using a multicore fiber (MCF). The fabrication simplicity makes this fiber device very attractive compared to the already reported technologies. Furthermore, the sensitivity reached (>400 pm/m-1), 7 times higher than the one reported for fiber Bragg gratings written on a similar MCF. The reconstruction of the amplitude and curvature has been performed for, showing errors lower than 4%. A numerical study has also been developed, allowing us to understand the sensor response at different fiber sensor geometries.

High-Sensitive and Temperature-Immune Curvature Sensor Based on Bitaper Sandwiching in Sms Fiber Structure

High-Sensitive and Temperature-Immune Curvature Sensor Based on Bitaper Sandwiching in Sms Fiber Structure