Multi-Sensing Platform Based on 2D Monoelement Germanane.

Covalently functionalized germanane is a novel type of fluorescent probe that can be employed in material science and analytical sensing. Here, a fluorometric sensing platform based on methyl-functionalized germanane (CH3 Ge) is developed for gas (humidity and ammonia) sensing, pH (1-9) sensing, and anti-counterfeiting. Luminescence (red-orange) is seen when a gas molecule intercalates into the interlayer space of CH3 Ge and the luminescence disappears upon deintercalation. This allows for direct detection of gas absorption via fluorometric measurements of the CH3 Ge. Structural and optical properties of CH3 Ge with intercalated gas molecules are investigated by density functional theory (DFT). To demonstrate real-time and on-the-spot testing, absorbed gas molecules are first precisely quantified by CH3 Ge using a smartphone camera with an installed color intensity processing application (APP). Further, CH3 Ge-paper-based sensor is integrated into real food packets (e.g., fish and milk) to monitor the shelf life of perishable foods. Finally, CH3 Ge-based rewritable paper is applied in water jet printing to illustrate the potential for secret communication with quick coloration and good reversibility by water evaporation.

Wearable sensors for telehealth based on emerging materials and nanoarchitectonics.

Wearable sensors have made significant progress in sensing physiological and biochemical markers for telehealth. By monitoring vital signs like body temperature, arterial oxygen saturation, and breath rate, wearable sensors provide enormous potential for the early detection of diseases. In recent years, significant advancements have been achieved in the development of wearable sensors based on two-dimensional (2D) materials with flexibility, excellent mechanical stability, high sensitivity, and accuracy introducing a new approach to remote and real-time health monitoring. In this review, we outline 2D materials-based wearable sensors and biosensors for a remote health monitoring system. The review focused on five types of wearable sensors, which were classified according to their sensing mechanism, such as pressure, strain, electrochemical, optoelectronic, and temperature sensors. 2D material capabilities and their impact on the performance and operation of the wearable sensor are outlined. The fundamental sensing principles and mechanism of wearable sensors, as well as their applications are explored. This review concludes by discussing the remaining obstacles and future opportunities for this emerging telehealth field. We hope that this report will be useful to individuals who want to design new wearable sensors based on 2D materials and it will generate new ideas.

Black phosphorous-based human-machine communication interface.

Assistive technology involving auditory feedback is generally utilized by those who are visually impaired or have speech and language difficulties. Therefore, here we concentrate on an auditory human-machine interface that uses audio as a platform for conveying information between visually or speech-disabled users and society. We develop a piezoresistive tactile sensor based on a black phosphorous and polyaniline (BP@PANI) composite by the facile chemical oxidative polymerization of aniline on cotton fabric. Taking advantage of BP's puckered honeycomb lattice structure and superior electrical properties as well as the vast wavy fabric surface, this BP@PANI-based tactile sensor exhibits excellent sensitivity, low-pressure sensitivity, reasonable response time, and good cycle stability. For a real-world application, a prototype device employs six BP@PANI tactile sensors that correspond to braille characters and can convert pressed text into audio on reading or typing to assist visually or speech-disabled persons. Overall, this research offers promising insight into the material candidates and strategies for the development of auditory feedback devices based on layered and 2D materials for human-machine interfaces.

Telemedicine platform for health assessment remotely by an integrated nanoarchitectonics FePS3/rGO and Ti3C2-based wearable device.

Due to the emergence of various new infectious (viral/bacteria) diseases, the remote surveillance of infected persons has become most important, especially if hospitals need to isolate infected patients to prevent the spreading of pathogens to health care personnel. Therefore, we develop a remote health monitoring system by integrating a stretchable asymmetric supercapacitor (SASC) as a portable power source with sensors that can monitor the human physical health condition in real-time and remotely. An abnormal body temperature and breathing rate could indicate a person's sickness/infection status. Here we integrated FePS3@graphene-based strain sensor and SASC into an all-in-one textile system and wrapped it around the abdomen to continuously monitor the breathing cycle of the person. The real body temperature was recorded by integrating the temperature sensor with the SASC. The proposed system recorded physiological parameters in real-time and when monitored remotely could be employed as a screening tool for monitoring pathogen infection status.

3D-Printed SARS-CoV-2 RNA Genosensing Microfluidic System.

Additive manufacturing technology, referred as 3D printing technology, is a growing research field with broad applications from nanosensors fabrication to 3D printing of buildings. Nowadays, the world is dealing with a pandemic and requires the use of simple sensing systems. Here, the strengths of fast screening by a lab-on-a-chip device through electrochemical detection using 3D printing technology for SARS-CoV-2 sensing are combined. This system comprises a PDMS microfluidic channel integrated with an electrochemical cell fully 3D-printed by a 3D printing pen (3D-PP). The 3D-PP genosensor is modified with an ssDNA probe that targeted the N gene sequence of SARS-CoV-2. The sensing mechanism relies on the electro-oxidation of adenines present in ssDNA when in contact with SARS-CoV-2 RNA. The hybridization between ssDNA and target RNA takes a place and ssDNA is desorbed from the genosensor surface, causing a decrease of the sensor signal. The developed SARS-CoV-2/3D-PP genosensor shows high sensitivity and fast response.

Synergistic 2D MoSe2@WSe2 nanohybrid heterostructure toward superior hydrogen evolution and flexible supercapacitor.

Two-dimensional (2D) transition metal dichalcogenide (TMDC) heterostructure is a new age strategy to achieve high electrocatalytic activity and ion storage capacity. The less complex and cost-effective applicability of the large-area TMDC heterostructure (HS) for energy applications require more research. Herein, we report the MoSe2@WSe2 nanohybrid HS electrocatalyst prepared using liquid exfoliated nanocrystals, followed by direct electrophoretic deposition (EPD). The improved catalytic activity is attributed to the exposure of catalytic active sites on the edge of nanocrystals after liquid exfoliation and the synergistic effect arises at HS interfaces between the MoSe2 and WSe2 nanocrystals. As predicted, the HS catalyst achieves a lower overpotential of 158 mV, a smaller Tafel slope of 46 mV dec-1 for a current density of 10 mA cm-2, and is stable for a long time. The flexible symmetric supercapacitor (FSSC) based on the HS catalyst demonstrates the excellent specific capacitance (Csp) of 401 F g-1 at 1 A g-1, 97.20% capacitance retention after 5000 cycles and high flexible stability over 1000 bending cycles. This work presents a less complex and solution-processed efficient catalyst for future electrochemical energy applications.

Pick up and dispose of pollutants from water via temperature-responsive micellar copolymers on magnetite nanorobots.

Nano/micromotor technology is evolving as an effective method for water treatment applications in comparison to existing static mechanisms. The dynamic nature of the nano/micromotor particles enable faster mass transport and a uniform mixing ensuring an improved pollutant degradation and removal. Here we develop thermosensitive magnetic nanorobots (TM nanorobots) consisting of a pluronic tri-block copolymer (PTBC) that functions as hands for pollutant removal. These TM nanorobots are incorporated with iron oxide (Fe3O4) nanoparticles as an active material to enable magnetic propulsion. The pickup and disposal of toxic pollutants are monitored by intermicellar agglomeration and separation of PTBC at different temperatures. The as-prepared TM nanorobots show excellent arsenic and atrazine removal efficiency. Furthermore, the adsorbed toxic contaminants on the TM nanorobots can be disposed by a simple cooling process and exhibit good recovery retention after multiple reuse cycles. This combination of temperature sensitive aggregation/separation coupled with magnetic propulsion opens a plethora of opportunities in the applicability of nanorobots in water treatment and targeted pollutant removal approaches.

Flexible wearable MXene Ti3C2-Based power patch running on sweat.

Flexible supercapacitors (FSCs) have received a lot of interest as portable power sources for wearable electronics. The biocompatibility of electrodes and electrolytes in wearable FSCs is important to consider although research into these topics is still in its early stages. In this work, we developed a wearable FSC that uses MXene Ti3C2 nanosheets and polypyrrole-carboxymethylcellulose nanospheres composite (Ti3C2@PPy-CMC) as the active electrode material and sweat as the electrolyte. The electrochemical performances of Ti3C2@PPy-CMC FSC were analyzed using an artificial sweat solution and exhibited excellent specific capacitance, power density, cycling stability, and bending stability. To demonstrate a real application of Ti3C2@PPy-CMC FSC, a sweat-chargeable FSC patch has been developed that can be applied directly to human clothing and skin to power a portable electronic gadget when the wearer is exercising. A comprehensive electrochemical study of the FSC patch was also conducted in various sweat secretion body regions such as the finger, foot sole, and wrist. Ti3C2@PPy-CMC composite's outstanding electrochemical performance indicates its potential capabilities and biocompatibility in wearable energy storage devices.

Real-Time Biomonitoring Device Based on 2D Black Phosphorus and Polyaniline Nanocomposite Flexible Supercapacitors.

Flexible energy storage devices are becoming significantly important to power wearable and portable devices that monitor physiological parameters for many biomedical applications. Many hybrid nanomaterials based on 2D materials are used in order to improve the performance of flexible energy storage devices. Here, a hybrid nanocomposite is synthesized through in situ polymerization of aniline in the presence of black phosphorus (BP) nanoflakes. This nanocomposite, polyaniline (PANI)@BP, is employed to fabricate flexible supercapacitor (FSC) electrodes. PANI@BP FSCs can provide a power source for biometric devices. The generated signal can be transmitted to a smartphone in real time via wireless communication. Such a compact and lightweight integrated device has been used to track a human heart beat while powered by PANI@BP FSC. These findings are providing a promising example of a flexible energy storage device that can be integrated with different real-time health monitoring devices.

MXene-Based Flexible Supercapacitors: Influence of an Organic Ionic Conductor Electrolyte on the Performance.

Owing to the rise of miniaturized wearable electronic devices in the last decade, significant demands have arisen to obtain high-performance flexible supercapacitors (FSCs). Recently, a lot of research has been focused on developing smart components of FSCs and integrating them into new device configurations. In this work, FSCs based on a Ti3C2 nanosheet (NS) and an organic ionic conductor (OIC)-induced hydrogel as the electrode and the electrolyte, respectively, were used. The FSCs fabricated have three different configurations (sandwich, twisted fiber, and interdigitated) and a comparative study of their electrochemical performance was investigated in terms of cycle stability, bending stability, power density, and energy density. Finally, the experimental validation of practical application was conducted, which suggested excellent electrochemical stability of Ti3C2 NS FSCs for driven commercial electronic gadgets. This study presents mechanically robust, lightweight, high-performance FSCs, which can be assembled in different configurations for powering wearable electronic devices.

Flexible energy generation and storage devices: focus on key role of heterocyclic solid-state organic ionic conductors.

An evolving trend toward the ever-growing market of portable and wearable electronics has accelerated development in the construction of multifunctional energy generation and storage systems that can be twisted and folded to multiple deformations while retaining their electrochemical performance. The latest advances and well developed approaches for the design of heterocyclic solid-state organic ionic conductors (SOICs) in flexible energy generation and storage devices are discussed here. The development of SOICs with improved physical, optical, and electrochemical properties provides new prospects for flexible photoelectrochemical cells and supercapacitors. Equipped with a better knowledge of SOICs' multifunctional properties, researchers have made considerable progress in their development that allows modification according to the requirements of different types of flexible energy devices. Within this review, we highlight the design of efficient SOICs and their incorporation into flexible energy generation and storage devices, and address exciting instances that profile the multifunctionality of SOICs such as three-dimensional (3D) ionic channels, excellent thermal stability, dual functionality (hole/ions transportation), one-dimensional (1D) lamellar network, light-harvesting, and non-toxicity to mention a few. It is expected that innovative and customizable properties utilized in the development of multifunctional SOICs will provide a forum for future advancement in flexible and wearable energy generation and storage devices.

Self-powered all weather sensory systems powered by Rhodobacter sphaeroides protein solar cells.

Natural photosynthetic proteins can convert solar energy into electrical energy with close to 100% quantum efficiency, and there is increasing interest in their use for sustainable photoelectrochemical devices. The primary processes of photosynthesis remain operational and efficient down to extremely low temperatures, and natural photosystems exhibit a variety of self-healing mechanisms. Herein we demonstrate the use of an amphiphilic triblock copolymer, Pluronic F127, to fabricate a self-healing photosynthetic protein photoelectrochemical cell that operates optimally at sub-zero temperatures. A concentration of 30% (w/w) Pluronic F127 depressed the freezing point of an electrolyte comprising 50 mM ubiquinone-0 in aqueous buffer such that optimal device solar energy conversion was seen at -12 °C rather than at room temperature. Fabrication of the protein photoelectrochemical cells with flexible electrodes enabled the demonstration of self-healing of damage caused by repeated mechanical deformation. Multiple bending cycles caused a marked deterioration of the photocurrent response to around a third of initial levels due to damage to the gel phase of the electrolyte, but this could be restored to ~95% by simply cooling and rewarming the device. This self-recoverability of the electrolyte extended the operational life of the protein cell through a process that increased its photoelectrochemical output during the repair. Utility of the cells as components of a touch sensor operational across a wide temperature range, including freezing conditions, is demonstrated.

A Smart Flexible Solid State Photovoltaic Device with Interfacial Cooling Recovery Feature through Thermoreversible Polymer Gel Electrolyte.

Quasi-solid-state dye-sensitized solar cells (DSSCs) fabricated with lightweight flexible substrates have a great potential in wearable electronic devices for in situ powering. However, the poor lifespan of these DSSCs limits their practical application. Strong mechanical stresses involved in practical applications cause breakage of the electrode/electrolyte interface in the DSSCs greatly affecting their performance and lifetime. Here, a mechanically robust, low-cost, long-lasting, and environment-friendly quasi-solid-state DSSC using a smart thermoreversible water-based polymer gel electrolyte with self-healing characteristics at a low temperature (below 0 °C) is demonstrated. When the performance of the flexible DSSC is hindered by strong mechanical stresses (i.e., from multiple bending/twisting/shrinking actions), a simple cooling treatment can regenerate the electrode/electrolyte interface and recover the performance close to the initial level. A performance recovery as high as 94% is proven possible even after 300 cycles of 90° bending. To the best of our knowledge, this is the first aqueous DSSC device with self-healing behavior, using a smart thermoreversible polymer gel electrolyte, which provides a new perspective in flexible wearable solid-state photovoltaic devices.

Iodine induced 1-D lamellar self assembly in organic ionic crystals for solid state dye sensitized solar cells.

A novel saturated heterocyclic organic ionic crystal, piperidinium iodide (PiHI), is synthesized by a facile route and applied as a solid electrolyte in Dye Sensitized Solar Cells (ss-DSSCs). Upon addition of a small quantity of iodine, PiHI self-assembles into a 1D lamellar micro crystalline structure that shows anisotropic conductivity. The two-component PiHI was characterized by using electrochemical impedance spectroscopy, cyclic voltammetry, steady state voltammetry, FT-IR, and Raman spectroscopy. Wide angle X-ray diffraction (XRD) measurement confirms the presence of long range 1D lamellar channels that pave the way for the diffusion of the redox couple I-/I3- and exhibit high anisotropic conductivity. The ionic conductivity of 1D PiHI (with I2) aligned perpendicular to the electrode, σ⊥ (15.46 mS cm-1), is 1.5 times higher than that aligned parallel to the electrode σ∥ = 10.32 mS cm-1. The ss-DSSC devices with these self-assembled ordered ionic crystals with a carbazole based sensitizer (SK1) achieved a power conversion efficiency (PCE) of 4.2% and 5.2% for ∥al and ⊥ar arrangement, respectively. The reported PCEs are better than that obtained from a classical liquid electrolyte with SK1 sensitizers. The electron kinetics at various interfaces of ss-DSSC devices was evaluated using Electrochemical Impedance Spectroscopy (EIS) measurements. The presence of a saturated cyclic structure promotes close packing through H-bonding and electrostatic interactions, which make ss-DSSC devices more stable up to 600 h under illumination of 1 sun.

Design, synthesis and DSSC performance of o-fluorine substituted phenylene spacer sensitizers: effect of TiO2 thickness variation.

The influence of TiO2 film thickness on the performance of DSSCs with a new series of dyes having ortho-fluorine substituted phenyl spacers and different donor moieties is reported. Optical, electrochemical, molecular orbital and photovoltaic properties were studied by varying the TiO2 thickness (9 and 12 µm) using these dyes. The thickness variation of TiO2 films had a significant effect on the open circuit voltage (Voc), short circuit current (Jsc) and efficiency. The Jsc and Voc of dye 1b with a TiO2 film thickness of 12 µm (8.91 mA cm-2 and 0.63 V) were larger than those of the 9 µm film thickness device (8.40 mA cm-2 and 0.57 V). This could be due to the variation in the thickness of the TiO2 film. However, at an optimized thickness of the TiO2 film (12 µm), 1b exhibited the highest power conversion efficiency (η) of 4.0% (average 3.6%). This highest efficiency value for 1b from 3.3% to 4.0% without using any co-absorbents was solely based on changing the thickness of the TiO2 film. In addition 1b had a planar structure, whereas dyes 2b and 3b had three and two dimensional structures. The optimized geometry calculation of o-fluoro phenyl π-spacer dyes was ascertained by density functional theory (DFT) using the B3LYP/631G(d,p) basis set. These results reveal that dye 1b has higher efficiency due to the deeper HOMO level and it exhibited better charge transfer from donor to acceptor, compared to the other dyes.

Humic Acid as a Sensitizer in Highly Stable Dye Solar Cells: Energy from an Abundant Natural Polymer Soil Component.

Humic acid (HA), a natural polymer and soil component, was explored as a photosensitizer in dye-sensitized solar cells (DSSCs). Photophysical and electrochemical properties show that HA covers a broad visible range of the electromagnetic spectrum and exhibits a quasi-reversible nature in cyclic voltammetry (CV). Because of its abundant functionalities, HA was able to bind onto the nano-titania surface and possessed good thermal stability. HA was employed as a sensitizer in DSSCs and characterized by various photovoltaic techniques such as I-V, incident-photo-to-current conversion efficiency (IPCE), electrochemical impedance spectroscopy (EIS), and Tafel polarization. The HA-based device shows a power conversion efficiency (PCE) of 1.4% under 1 sun illumination. The device performance was enhanced when a coadsorbent, chenodeoxycholic acid (CDCA), along with HA was used and displayed 2.4% PCE under 0.5 sun illumination. The DSSCs employing HA with CDCA showed excellent stability up to 1000 h. The reported efficiency of devices with HA is better than that of devices with all natural sensitizers reported so far.

Microbial Selenium Nanoparticles (SeNPs) and Their Application as a Sensitive Hydrogen Peroxide Biosensor.

The cell-free extract, a crude enzyme (cytosolic and membrane fraction) obtained from an environmental isolate, Bacillus pumilus sp. BAB-3706 worked as excellent in reducing as well as stabilizing agent and facilitated the formation of stable colloidal selenium nanoparticles (SeNPs). Resulting nanoparticles were characterized using UV-vis spectrophotometer, TEM, EDAX, FT-IR and XRD, respectively. A working electrode was modified by coating the surface of indium tin oxide (ITO) with colloidal SeNPs. Successive additions of H2O2 (100 to 600 µM) in conventional three electrodes system, cyclic voltammeter with potential scan rate 25.0 mV/s, in 0.1 M phosphate buffer solution (PBS) yielded increase in current. A perpetual amperometric response at fixed potential (-1.0 V) and at selected time interval of 100 s showed different magnitude of current at every addition of H2O2. The linear range of detection of H2O2 was from 5 to 600 mM (R(2) = 0.9965), while the calculated limit of detection was found to be 3.00 µM. The current study suggested that microbial SeNPs can be used for fabrication of low cost, sensitive H2O2 biosensor.

Highly efficient one-dimensional ZnO nanowire-based dye-sensitized solar cell using a metal-free, D-π-A-type, carbazole derivative with more than 5% power conversion.

Hydrothermally grown one-dimensional ZnO nanowire (1D ZnO NW) and a newly synthesized metal-free, D-π-A type, carbazole dye (SK1) sensitizer-based photovoltaic device with a power conversion efficiency (PCE) of more than 5% have been demonstrated by employing the cobalt tris(2,2'-bipyridyl) redox shuttle. A short-circuit current density (Jsc) of ∼12.0 mA/cm(2), an open-circuit voltage (Voc) of ∼719 mV, and a fill factor (FF) of ∼65% have been afforded by the 1D ZnO NW-based dye-sensitized solar cell (DSSC) incorporating [Co(bpy)3](3+/2+) complex as the one-electron redox mediator. In contrast, the identical DSSC with traditional I3(-)/I(-) electrolyte has shown a Jsc ≈ 12.2 mA/cm(2), a Voc ≈ 629 mV, and a FF ≈ 62%, yielding a PCE of ∼4.7%. The persuasive role of the inherent superior electron transport property of 1D ZnO NWs in enhancing the device efficiency is evidenced from the impoverished performance of the DSSCs with photoanodes fabricated using ZnO nanoparticles (NPs). The DSSCs having ZnO NP-based photoanodes have achieved the PCEs of ∼3.6% and ∼3.2% using cobalt- and iodine-based redox electrolytes, respectively. The electronic interactions between the SK1 sensitizer and ZnO (NWs and NPs) to induce the photogenerated charge transfer from SK1 to the conduction band (CB) of ZnO are evidenced from the significant quenching of photoluminescence and exciton lifetime decay of SK1, when it is anchored onto the ZnO architectures. The energetics of the SK1 dye molecule are estimated by combining the spectroscopic and electrochemical techniques. The electronic distributions of SK1 dye molecule in its HOMO and LUMO energy levels are interpreted using density functional theory (DFT)-based calculations. The electron donor-π linker-acceptor (D-π-A) configuration of SK1 dye provides an intramolecular charge transfer within the molecule, prompting the electron migration from the carbazole donor to cyanoacrylic acceptor moiety via the oligo-phenylenevinylene linker group. The D-π-A-mediated electron movement witnesses the favorable photoexcited electron transfer from the LUMO of SK1 dye to the CB of ZnO through the carboxyl anchoring group.