Ultra-thin light-weight laser-induced-graphene (LIG) diffractive optics.

The realization of hybrid optics could be one of the best ways to fulfill the technological requirements of compact, light-weight, and multi-functional optical systems for modern industries. Planar diffractive lens (PDL) such as diffractive lenses, photonsieves, and metasurfaces can be patterned on ultra-thin flexible and stretchable substrates and be conformally attached on top of arbitrarily shaped surfaces. In this review, we introduce recent research works addressed to the design and manufacturing of ultra-thin graphene optics, which will open new markets in compact and light-weight optics for next-generation endoscopic brain imaging, space internet, real-time surface profilometry, and multi-functional mobile phones. To provide higher design flexibility, lower process complexity, and chemical-free process with reasonable investment cost, direct laser writing (DLW) of laser-induced-graphene (LIG) is actively being applied to the patterning of PDL. For realizing the best optical performances in DLW, photon-material interactions have been studied in detail with respect to different laser parameters; the resulting optical characteristics have been evaluated in terms of amplitude and phase. A series of exemplary laser-written 1D and 2D PDL structures have been actively demonstrated with different base materials, and then, the cases are being expanded to plasmonic and holographic structures. The combination of these ultra-thin and light-weight PDL with conventional bulk refractive or reflective optical elements could bring together the advantages of each optical element. By integrating these suggestions, we suggest a way to realize the hybrid PDL to be used in the future micro-electronics surface inspection, biomedical, outer space, and extended reality (XR) industries.

GMM-Based Adaptive Extended Kalman Filter Design for Satellite Attitude Estimation under Thruster-Induced Disturbances.

Star images from star trackers are usually defocused to capture stars over an exposure time for better centroid measurements. While a satellite is maneuvering, the star point on the screen of the camera is affected by the satellite, which results in the degradation of centroid measurement accuracy. Additionally, this could result in a worse star vector outcome. For geostationary satellites, onboard thrusters are used to maintain or change orbit parameters under orbit disturbances. Since there is misalignment in the thruster and torque is generated by an impulsive shape signal from the torque command, it is difficult to generate target torque; in addition, it also impacts the star image because the impulsive torque creates a sudden change in the angular velocity in the satellite dynamics. This makes the noise of the star image non-Gaussian, which may require introducing a method for dealing with non-Gaussian measurement noise. To meet this goal, in this study, an adaptive extended Kalman filter is implemented to predict measurement vectors with predicted states. The GMM (Gaussian mixture model) is connected in this sequence, giving weighting parameters to each Gaussian density and resulting in the better prediction of measurement vectors. Simulation results show that the GMM-EKF exhibits a better performance than the EKF for attitude estimation, with 30% improvement in performance. Therefore, the GMM-EKF could be a more attractive approach for use with geostationary satellites during station-keeping maneuvers.

Hysteresis-Free Double-Network Hydrogel-Based Strain Sensor for Wearable Smart Bioelectronics.

Hydrogel-based electronics have attracted substantial attention in the field of biological engineering, energy storage devices, and soft actuators due to their resemblance to living tissues, biocompatibility, tunable softness, and consolidated structures. However, combining the properties of quick resilience, hysteresis-free, and robust mechanical properties in physically cross-linked hydrogels is still a great challenge. Herein, we present a vinyl hybrid silica nanoparticle (VSNPs)/polyacrylamide (PAAm)/alginate double-network hydrogel-based strain sensor with the characteristics of quick resilience, hysteresis-free, and a low limit of detection (LOD). The physical cross-linking among PAAm chains and covalent cross-linking between PAAm, alginate, and N,N-methylenebisacrylamide chains promotes excellent mechanical properties. Moreover, the incorporation of VSNPs reinforces the mechanical strength by the dynamic cross-linking of the PAAm network to maintain the integrity of the hydrogel and works as a stress buffer to dissipate energy. The as-prepared hydrogel-based sensor exhibits a strain sensitivity (i.e., gauge factor) of 1.73 (up to 100% strain), a response time of 0.16 s, an ultra-low electrical hysteresis of 2.43%, and a low LOD of 0.4%. The outstanding properties of the hydrogel are further used to illustrate the utility of the sensor in e-skin, ranging from low-strain applications, such as carotid pulse and artificial sound detection, to large bending applications, such as sign language translations. In addition, an efficient and cost-effective synthesis of double-network hydrogel that can overcome the bottleneck of the electromechanical properties of single network hydrogel has potential prospects in soft actuators, tissue engineering, and various biomedical applications.

Multifunctional hybrid skin patch for wearable smart healthcare applications.

Recent advances in wearable patches have included various sensors to monitor either physiological signs, such as the heart rate and respiration rate, or metabolites. Nevertheless, most of these have focused only on a single physiological measurement at a time, which significantly inhibits the calibration of various biological signals and diagnostic facilities. In this study, a novel multifunctional hybrid skin patch was developed for the electrochemical analysis of sweat glucose levels and simultaneous monitoring of electrocardiograms (ECGs). Furthermore, pH and temperature sensors were co-integrated onto the same patch for the calibration of the glucose biosensor to prevent inevitable inhibition and weakening of enzyme activity due to changes in the sweat pH and temperature levels. The fabricated electrochemical glucose biosensor exhibited excellent linearity (R2 = 0.9986) and sensitivity (29.10 µA mM-1 cm-2), covering the normal range of human sweat. The potentiometric pH sensor displayed a good response with an excellent sensitivity of -77.81 mV/pH and high linearity (R2 = 0.991), indicating that it can distinguish variations in the typical pH range for human sweat. Furthermore, the P, QRS complex, and T peaks in the measured ECG waveforms could be clearly distinguished, indicating the reliability of the fabricated flexible dry electrodes for continuous monitoring. The fabricated skin patch overcomes the inconvenience of the mandatory attachment of multiple patches on the human body by fully integrating all the electrochemical and electrophysiological sensors on a single patch, thus facilitating advanced glycemic control and continuous ECG monitoring for smart management of chronic diseases and healthcare applications.

A highly selective and stable cationic polyelectrolyte encapsulated black phosphorene based impedimetric immunosensor for Interleukin-6 biomarker detection.

Due to the insufficiency of binding sites for the immobilized recognition biomolecules on the immunosensing platform, cancer detection becomes challenging. Whereas, the degradation of black phosphorene (BP) in the presence of the environmental factors becomes a concerning issue for use in electrochemical sensing. In this study, BP is successfully encapsulated by polyallylamine (PAMI) to increase its stability as well as to enhance its electrochemical performance. The successful encapsulation of BP is ensured through X-ray Photoelectron spectroscopy and Raman spectroscopy, whereas the stability of black phosphorus is ensured by Zeta potential measurements and cyclic voltammetry tests. The developed BP-PAMI composite showed high stability in the ambient environment and exhibited improved electrochemical performances. The impedimetric immunosensor was developed on a BP-PAMI modified laser burned graphene (LBG) to detect interleukin-6 biomarkers using electrochemical impedance spectroscopy (EIS). Under the optimized parameters, the fabricated immunosensor demonstrated a wide linear range of 0.003-75 ng/mL, limit of detection (LOD) of 1 pg/mL. Based on the experimental analysis, the developed sensing strategy can be employed as an easy, disposable, cost-effective and highly selective point-of-care cancer detection. In addition, the developed technique can be applied broadly for detecting other biomarkers after treating with suitable biomolecules.

A rime ice-inspired bismuth-based flexible sensor for zinc ion detection in human perspiration.

A nature-inspired special structure of bismuth is newly presented as Zn ion sensing layer for high-performance electrochemical heavy metal detection sensor applications. The rime ice-like bismuth (RIBi) has been synthesized using an easy ex situ electrodeposition method on the surface of a flexible graphene-based electrode. The flexible graphene-based electrode was fabricated via simple laser-writing and substrate-transfer techniques. The Zn ion sensing performance of the proposed heavy metal sensor was evaluated by square wave anodic stripping voltammetry after investigating the effects of several parameters, such as preconcentration potential, preconcentration time, and pH of acetate buffer. The proposed RIBi-based heavy metal sensor demonstrated a good linear relationship between concentration and current in the range 100-1600 ppb Zn ions with an acceptable sensitivity of 106 nA/ppb·cm2. The result met the requirements in terms of common human perspiration levels (the average Zn ion concentration in perspiration is 800 ppb). In addition, the heavy metal sensor response to Zn ions was successfully performed in human perspiration samples as well, and the results were consistent with those measured by atomic absorption spectroscopy. Besides, the fabricated Zn ion sensor exhibited excellent selectivity, repeatability, and flexibility. Finally, a PANI-LIG-based pH sensor (measurement range: pH 4-7) was also integrated with the Zn ion sensor to form a single chip hybrid sensor. These results may provide a great possibility for the use of the proposed flexible sensor to realize wearable perspiration-based healthcare systems. Graphical abstract.

Hydrogen-Bond-Triggered Hybrid Nanofibrous Membrane-Based Wearable Pressure Sensor with Ultrahigh Sensitivity over a Broad Pressure Range.

Recently, flexible capacitive pressure sensors have received significant attention in the field of wearable electronics. The high sensitivity over a wide linear range combined with long-term durability is a critical requirement for the fabrication of reliable pressure sensors for versatile applications. Herein, we propose a special approach to enhance the sensitivity and linearity range of a capacitive pressure sensor by fabricating a hybrid ionic nanofibrous membrane as a sensing layer composed of Ti3C2Tx MXene and an ionic salt of lithium sulfonamides in a poly(vinyl alcohol) elastomer matrix. The reversible ion pumping triggered by a hydrogen bond in the hybrid sensing layer leads to high sensitivities of 5.5 and 1.5 kPa-1 in the wide linear ranges of 0-30 and 30-250 kPa, respectively, and a fast response time of 70.4 ms. In addition, the fabricated sensor exhibits a minimum detection limit of 2 Pa and high durability over 20 000 continuous cycles even under a high pressure of 45 kPa. These results indicate that the proposed sensor can be potentially used in mobile medical monitoring devices and next-generation artificial e-skin.

Smart bandage with integrated multifunctional sensors based on MXene-functionalized porous graphene scaffold for chronic wound care management.

Three-dimensional (3D) porous laser-guided graphene (LGG) electrodes on elastomeric substrates are of great significance for developing flexible functional electronics. However, the high sheet resistance and poor mechanical properties of LGG sheets obstruct their full exploitation as electrode materials. Herein, we applied 2D MXene nanosheets to functionalize 3D LGG sheets via a C-O-Ti covalent crosslink to obtain an LGG-MXene hybrid scaffold exhibited high conductivity and improved electrochemistry with fast heterogeneous electron transfer (HET) rate due to the synergistic effect between LGG and MXene. Then we transferred the obtained hybrid scaffold onto PDMS to engineer a smart, flexible, and stretchable multifunctional sensors-integrated wound bandage capable of assessing uric acid (UA), pH, and temperature at the wound site. The integrated UA sensor exhibited a rapid response toward UA in an extended wide range of 50-1200 µM with a high sensitivity of 422.5 µA mM-1 cm-2 and an ultralow detection limit of 50 µM. Additionally, the pH sensor demonstrated a linear Nernstian response (R2 = 0.998) with a high sensitivity of -57.03 mV pH-1 in the wound relevant pH range of 4-9. The temperature sensor exhibited a fast and stable linear resistive response to the temperature variations in the physiological range of 25-50 °C with an excellent sensitivity and correlation coefficient of 0.09% °C-1 and 0.999, respectively. We anticipate that this stretchable and flexible smart bandage could revolutionize wound care management and have profound impacts on the therapeutic outcomes.

An Electrodeposited MXene-Ti3C2Tx Nanosheets Functionalized by Task-Specific Ionic Liquid for Simultaneous and Multiplexed Detection of Bladder Cancer Biomarkers.

Controlled deposition of 2D multilayered nanomaterials onto different electrodes to design a highly sensitive biosensing platform utilizing their active inherent electrochemistry is extremely challenging. Herein, a green, facile, and cost-effective one-pot deposition mechanism of 2D MXene-Ti3C2Tx nanosheets (MXNSs) onto conductive electrodes within few minutes via electroplating (termed electroMXenition) is reported for the first time. The redox reaction in the colloidal MXNS solution under the effect of a constant applied potential generates an electric field, which drives the nanoparticles toward a specific electrode interface such that they are cathodically electroplated. A task-specific ionic liquid, that is, 4-amino-1-(4-formyl-benzyl) pyridinium bromide (AFBPB), is exploited as a multiplex host arena for the substantial immobilization of MXNSs and covalent binding of antibodies. A miniaturized, single-masked gold dual interdigitated microelectrode (DIDµE) is microfabricated and presented by investigating the benefit of AFBPB coated on MXNSs. The resulting MXNSs-AFBPB-film-modified DIDµE biosensor exhibited a 7× higher redox current than bare electrodes owing to the uniform deposition. Using Apo-A1 and NMP 22 as model bladder cancer analytes, this newly developed dual immunosensor demonstrated precise and large linear ranges over five orders of significance with limit of detection values as low as 0.3 and 0.7 pg mL-1, respectively.

Wearable Capacitive Pressure Sensor Based on MXene Composite Nanofibrous Scaffolds for Reliable Human Physiological Signal Acquisition.

In recent years, highly sensitive pressure sensors that are flexible, biocompatible, and stretchable have attracted significant research attention in the fields of wearable electronics and smart skin. However, there has been a considerable challenge to simultaneously achieve highly sensitive, low-cost sensors coupled with optimum mechanical stability and an ultralow detection limit for subtle physiological signal monitoring devices. Targeting aforementioned issues, herein, we report the facile fabrication of a highly sensitive and reliable capacitive pressure sensor for ultralow-pressure measurement by sandwiching MXene (Ti3C2Tx)/poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) composite nanofibrous scaffolds as a dielectric layer between biocompatible poly-(3,4-ethylenedioxythiophene) polystyrene sulfonate /polydimethylsiloxane electrodes. The fabricated sensor exhibits a high sensitivity of 0.51 kPa-1 and a minimum detection limit of 1.5 Pa. In addition, it also enables linear sensing over a broad pressure range (0-400 kPa) and high reliability over 10,000 cycles even at extremely high pressure (>167 kPa). The sensitivity of the nanofiber-based sensor is enhanced by MXene loading, thereby increasing the dielectric constant up to 40 and reducing the compression modulus to 58% compared with pristine PVDF-TrFE nanofiber scaffolds. The proposed sensor can be used to determine the health condition of patients by monitoring physiological signals (pulse rate, respiration, muscle movements, and eye twitching) and also represents a good candidate for a next generation human-machine interfacing device.

MoS2-Decorated Laser-Induced Graphene for a Highly Sensitive, Hysteresis-free, and Reliable Piezoresistive Strain Sensor.

Advancement of sensing systems, soft robotics, and point-of-care testing requires the development of highly efficient, scalable, and cost-effective physical sensors with competitive and attractive features such as high sensitivity, reliability, and preferably reversible sensing behaviors. This study reports a highly sensitive and reliable piezoresistive strain sensor fabricated by one-step carbonization of the MoS2-coated polyimide film to obtain MoS2-decorated laser-induced graphene. The resulting three-dimensional porous graphene nanoflakes decorated with MoS2 exhibit stable electrical properties yielding a reliable output for longer strain/release cycles. The sensor demonstrates high sensitivity (i.e., gauge factor, GF ≈1242), is hysteresis-free (∼2.75%), and has a wide working range (up to 37.5%), ultralow detection limit (0.025%), fast relaxation time (∼0.17 s), and a highly stable and reproducible response over multiple test cycles (>12 000) with excellent switching response. Owing to the outstanding performances of the sensor, it is possible to successfully detect various subtle movements ranging from phonation, eye-blinking, and wrist pulse to large human-motion-induced deformations.

Ultrasensitive Interfacial Capacitive Pressure Sensor Based on a Randomly Distributed Microstructured Iontronic Film for Wearable Applications.

The rapid development of pressure sensors with distinct functionalities, notably, with increased sensitivity, fast response time, conformability, and a high degree of deformability, has increased the demand for wearable electronics. In particular, pressure sensors with an excellent sensitivity in the low-pressure range (<2 kPa) and a large working range simultaneously are strongly demanded for practical applications in wearable electronics. Here, we demonstrate an emerging class of solid polymer electrolyte obtained by incorporating a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide with poly(vinylidene fluoride- co-hexafluoropropylene) as a high-capacitance dielectric layer for interfacial capacitive pressure sensing applications. The solid polymer electrolyte exhibits a very high interfacial capacitance by virtue of mobile ions that serve as an electrical double layer in response to an electric field. The randomly distributed microstructures created on the solid electrolyte help the material to elastically deform under pressure. Moreover, the interfacial capacitance is improved by utilizing a highly conductive porous percolated network of silver nanowires reinforced with poly(dimethylsiloxane) as the electrodes. An ultrahigh-pressure sensitivity of 131.5 kPa-1, a low dynamic response time of ∼43 ms, a low limit of detection of 1.12 Pa, and a high stability for over 7000 cycles are achieved. Finally, we demonstrate the application of the sensor for international Morse code detection, artery pulse detection, and eye blinking. Owing to the ultrahigh sensitivity, the as-fabricated sensor will have great potential for wearable devices in health status monitoring, motion detection, and electronic skin.

Wearable, robust, non-enzymatic continuous glucose monitoring system and its in vivo investigation.

Electroplating of nanoporous Pt (nPt) induces an extremely strong tensile stress, which results in the exfoliation of nPt on flexible polymer substrate despite plasma treatment to improve adhesion. Here, we overcame this challenge by modifying flexible stainless-steel, and developed wearable, robust, flexible, and non-enzymatic continuous glucose monitoring system. The flexible stainless-steel was highly effective in improving the adhesion between the metal layer and substrate. The developed wireless system included electrochemical analysis circuits, a microcontroller unit, and a wireless communication module. Finally, we evaluated the continuous glucose monitoring system through two animal testing, by implanting into subcutaneous tissue and measuring interstitial fluid (ISF) glucose values at 5-15-min intervals. Comparison of the measured ISF glucose with blood glucose determined by the Clarke error grid analysis showed that 82.76% of the measured glucose was within zone A. Furthermore, the wearable glucose sensor exhibited bio-compatible to implant through various bio-compatibility tests.

Trimetallic Pd@Au@Pt nanocomposites platform on -COOH terminated reduced graphene oxide for highly sensitive CEA and PSA biomarkers detection.

In this paper, a trimetallic Pd@Au@Pt nanocomposites platform on -COOH terminated reduced graphene oxide (COOH-rGO) was newly developed for sensing carcinoembryonic antigen (CEA) and prostate specific antigen (PSA) biomarkers. Trimetallic electro-catalytic surfaces were prepared by the electrodeposition of noble metals (Pd@Au@Pt) nanoparticles on COOH- rGO. After EDC/NHS treatment, the anti-CEA and anti-PSA were immobilized separately on two different platforms. Under optimized conditions, the platforms were analyzed by cyclic voltammetry and differential pulse voltammetry (DPV). The platform shows good electro catalytic activity, high sensitivity, and acceptable stability for sensing CEA and PSA biomarkers. For CEA, we obtained sensitivity of 0.099 ± 0.007µAng-1ml, wide linear range from 12pgml-1 to 85ngml-1 and a limit of detection (LOD) of 8pgml-1, while for PSA sensitivity is 0.267 ± 0.02µAng -1 ml, wide linear range from 3pgml-1 to 60ngml-1 and LOD of 2pgml-1. The validation of the platform was observed through standard addition method. Thus, the sensing platform could be used for the point of care detection of CEA and PSA.

N719 dye-sensitized organophotocatalysis: enantioselective tandem Michael addition/oxyamination of aldehydes.

A remarkably efficient photosensitizer, N719 dye, was used in asymmetric tandem Michael addition/oxyamination of aldehydes, rendering α,ß-substituted aldehydes in good yields with excellent levels of enantioselectivity and diastereoselectivity. This is the first report of a multiorganocatalytic reaction involving iminium catalysis and photoinduced singly occupied molecular orbital (SOMO) catalysis. This reaction is expected to expand the scope of tandem organocatalytic reactions.