Molecular imprinted polymer functionalized carbon nanotube sensors for detection of saccharides

In this work, we report the synthesis and fabrication of an enzyme-free sugar sensor based on molecularly imprinted polymer (MIP) on the surface of single walled carbon nanotubes (SWNTs). Electropolymerization of 3-aminophenylboronic acid (3-APBA) in the presence of 10 M d-fructose and fluoride at neutral pH conditions resulted in the formation of a self-doped, molecularly imprinted conducting polymer (MICP) via the formation of a stable anionic boronic ester complex between poly(aniline boronic acid) and d-fructose. Template removal generated binding sites on the polymer matrix that were complementary to d-fructose both in structure, i.e., shape, size, and positioning of functional groups, thus enabling sensing of d-fructose with enhanced affinity and specificity over non-MIP based sensors. Using carbon nanotubes along with MICPs helped to develop an efficient electrochemical sensor by enhancing analyte recognition and signal generation. These sensors could be regenerated and used multiple times unlike conventional affinity based biosensors which suffer from physical and chemical stability

Tungsten oxysulfide nanoparticles interspersed nylon based e-textile as a low cost, wearable multifunctional platform for ultra-sensitive tactile sensing and breath sensing applications

In this work, we report the hydrothermal synthesis of Tungsten Oxysulfide (WS2|O) nanoparticles interspersed onto porous, lightweight Nylon fabric as a clean-room-free, multifunctional sensor for detection of human breath, strain, and pressure. Morphological characterizations reveal the uniform dispersion of the conductive WS2|O nanosheets across the ultra-thin fibers of nylon. The fabricated WS2|O@nylon-based device as a breath sensor exhibits excellent sensitivity towards different breath patterns. The optimization studies resulted in a 4-layered high-performance piezoresistive wearable pressure sensor. It exhibited a sensitivity of 1.5 kPa−1, response time of 0.2 sec over a dynamic range of 50 Pa to 350 Pa. A Gauge factor of 24.2 and good mechanical stability across 10,000 cycles of compressive strain exhibited by the strain sensor makes it suitable for gesture recognition. The exceptional sensitivity, stability with good flexibility prove it as a promising device platform for the development of various wearable multifunctional sensor applications

Nickel MXene Nanosheet and Heteroatom Self-Doped Porous Carbon-Based Asymmetric Supercapacitors with Ultrahigh Energy Density

For high-energy-density supercapacitors, two-dimensional (2D) MXenes are being increasingly explored due to their inherent conductivity and excellent chemical properties. However, MXenes failed to achieve high power density and exceptional stability. Addressing this, we report the fabrication of an asymmetric supercapacitor with nickel MXene (cathode) and nitrogen (N), sulfur (S), and phosphorus (P) self-doped biomass-derived activated carbon (anode). Detailed structural and chemical characterization studies reveal layered nanosheets in NiMX caused due to solvothermal etching cum exfoliation and unique micro-mesopore distribution in the optimized Euphorbia milii plant leaf-derived heteroatom self-doped activated carbon (EMAC-700) because of KOH activation. NiMX and EMAC-700 delivered high capacitances of 474.3 and 575.8 F/g, respectively, at 1 A/g with a 6 M KOH electrolyte. This is attributed to the pseudonature of NiMX and the presence of heteroatoms and the large surface area (2349 m2/g) of EMAC-700, facilitating fast electrolytic ion transfer. Finally, an asymmetric device with NiMX//EMAC configuration in 6 M KOH delivered a 152.6 F/g cell capacitance at 0.5 A/g under 0-1.5 V. Additionally, an ultrahigh energy density of 47.6 W h/kg at a 375 W/kg power density was achieved along with an 81.7% capacitance retention after 30,000 cycles at 15 A/g, signifying its potential for next-generation energy storage applications

3D Printed SnS2/SnS-Based Nanocomposite Hydrogel as a Photoenhanced Triboelectric Nanogenerator

Recent advancements in printing technologies have led to new fabrication techniques for the development of various flexible, compact, wearable, and portable energy harvesters and self-powered devices. In particular, the three-dimensional printing (3DP) technology for a nanogenerator has become advantageous due to its low cost, simplicity, and high precision in fabricating complicated structures. Therefore, we report a 3DP-based photoinduced triboelectric nanogenerator (PTNG) fabrication, a hybrid version of a conventional triboelectric nanogenerator. Here, a 3D printed poly(vinyl alcohol) (PVA) nanocomposite hydrogel (3DPH) with photoactive SnS2/SnS nanoflakes is used as a tribo-positive material and copper foil as a tribo-negative material for PTNG application. Under light illumination, the as-fabricated PTNG with an optimized weight percentage of SnS2/SnS displays the open-circuit voltage (Voc) enhancement from 29 to 37.5 V and short-circuit current (Isc) enhancement from 1.23 to 1.58 μA. In addition, the power density of the device is observed at 5.4 μW/cm2 under illumination conditions at the external load of 60 MΩ. This enhanced performance of the as-fabricated PTNG is attributed to the mutual coupling effect and improved interfacial interactions between the SnS2/SnS nanoflakes and PVA under the influence of light illumination, leading to a charge-trapping mechanism. The outstanding performance and stability of the as-fabricated PTNG surpassing all similar recent reports, establish it as an effective hybrid platform for constructing multifunctional self-powered devices

Coaxial SnS2/SnS Nanostructures on the Ag Fiber Substrate for Flexible Self-Powered Photodetectors

Sustainable and stable photodetectors with self-powering nature and superior performance are necessary to address the growing demand for flexible and wearable optoelectronic devices. This work demonstrates a flexible, self-powered, coaxial p-n heterojunction photodetector using SnS2/SnS on an Ag fiber substrate by coupling the photoexcitation property, semiconductor nature, and piezoelectric effect. Detailed characterization studies confirm the formation of hexagonal and orthorhombic crystal planes of SnS2 and SnS nanoflakes, respectively, with a piezoelectric coefficient (d33) of 175 pm/V for SnS2. The photoabsorption is maximum in the visible region with a direct band gap of 2.1 eV. The electrical studies display a tunable photoresponse under zero-bias conditions. Upon compressive strain of 0.43%, the photoresponse increases by 36%. The Ion/Ioff ratio of the fabricated photodetector was 102 at a zero bias, and the rise and decay times shorter than 1 s were obtained. The maximum external quantum efficiency of the fabricated photodetector was found to be 54.2%, owing to the superior piezo-phototronic properties. The band diagram and the charge transfer mechanism are studied to investigate the piezo-phototronic effect. The uniform strain on the Ag fiber substrate and the piezo-potential distribution upon compressive and tensile strain promotes carrier separation in the coaxial interfaces of the p-n junction. The demonstrated strategy provides a direction for developing fiber-based photodetectors with self-powering behavior and enhanced photoresponsivity for next-generation smart wearable textile-based applications

Ti@MoS2 incorporated Polypropylene/Nylon fabric-based porous, breathable triboelectric nanogenerator as respiration sensor and ammonia gas sensor applications

High output and non-interrupted power supply from fabric-based nanogenerators still remain a major challenge in developing self-powered wearable electronic applications. Addressing this, we demonstrate a low-cost, lead-free triboelectric nanogenerator based on hydrothermally grown Titanium (Ti) functionalized Molybdenum Disulfide (MoS2) interspersed polypropylene (PP) cloth and sandwiched with Nylon cloth for a highly sensitive respiration sensor and self-powered ammonia gas sensor. The nanogenerator with the device configuration Cu/Ti@MoS2/PP: Nylon /Ag is attached to a respiratory mask, and the open-circuit voltage (Voc) and short-circuit current density (JSC) during respiration cycles were obtained as 29.3 V and 42.7 µA/cm2 respectively. A significant difference in the breath pattern of human respiration cycles. Further, a fully self-powered ammonia gas sensor was demonstrated by integrating the triboelectric nanogenerator with Ti@MoS2/PP ammonia sensor. The self-powered Ti- MoS2 on PP cloth-based gas sensor driven by TENG displays an excellent response with a wide dynamic sensing range of ammonia gas from 200 ppb to 2600 ppb at room temperature, with a high sensitivity, selectivity and a rapid response time. This study explores the bifunctional nature of Ti@MoS2 nanoparticles as a respiratory mask and a self-powered ammonia gas sensor fabricated with excellent potential for self-powered health diagnostic applications

FeS2-based aerogel as a flexible low-cost substrate for rapid SERS detection of histamine in biofluids

Histamine is an organic nitrogenous compound released from mast cells, often as part of an instant immune response. Life-threatening anaphylaxis can occur with significant histamine intolerance, which is also referred to as histaminosis caused by overproduction of histamine in the body. Herein, we demonstrate the synthesis of FeS2-incorporated rGO aerogel (FeS2-AG) by lyophilization, as an active SERS substrate for the detection of histamine in blood serum. The morphological characterization revealed the nanoflower structure of FeS2 and uniform porosity of the aerogel, in which the nanoflower structure of FeS2 was homogenously distributed on the surface of the porous aerogel. The cubic structure of FeS2 nanoflowers was revealed by X-ray diffraction and Fourier transform infrared spectroscopy demonstrated the characteristic peak at ∼1176 cm−1 which is related to pyrite surface chemistry of FeS2 nanoparticles. The as-fabricated sensor exhibited an enhancement factor of 1.61 × 107 with a limit of detection of 0.08 ng mL−1. The substrate exhibited a good selectivity and linear range of detection towards histamine in the presence of 2-fold concentration of ascorbic acid, glucose, urea, and uric acid. This excellent performance of the sensor can be ascribed to the chemical enhancement occurring via the interaction of oxy functional groups of aerogel and multiple coordination sites (ferrous ions (Fe2+)) of FeS2 with histamine molecules causing reconstruction of the band gap. This newly formed energy band further leads to the occurrence of the Raman resonance effect, providing an enhancement in the SERS signal over that of the Raman signal obtained from bulk histamine. The sensor showed good recovery percentage of 97.25% from real samples, highlighting the efficiency of the as-fabricated sensor towards histamine detection

Piezo/Triboelectric Nanogenerator from Lithium-Modified Zinc Titanium Oxide Nanofibers to Monitor Contact in Sports

The need for technological innovation in competitive sports is crucial for self-monitoring and smart decision making. In this work, we demonstrate how intelligent sports and smart decision making can be achieved in cricket and boxing using lithium-modified zinc titanium oxide (LZTO) nanofibers based on piezoelectric nanogenerators (PENGs) and triboelectric nanogenerators (TENGs). Zinc titanium oxide (ZTO) nanofibers synthesized using electrospinning followed by a calcination technique are modified with lithium to increase the output of the nanogenerator. An optimized PENG is fabricated using 25 wt % loading of LZTO (d33 = 214 pm/V) in a poly(vinylidene fluoride) (PVDF) matrix as a double-layered structure and yields an open-circuit voltage (Voc) of 35 V and a short-circuit current (Isc) of 1.6 μA by manual tapping. To fabricate the TENG, Kapton and LZTO are used as negative and positive tribolayers, while Cu and adhesive polymer tape are used as the electrode and spacer, respectively. Furthermore, a hybrid nanogenerator (HNG) is fabricated by combining the PENG and TENG to produce a rectified voltage, current, and power density of up to 75 V, 3.2 μA, and 240 μW/cm2, respectively. These HNGs are integrated with a punching bag and demonstrated to differentiate among the six types of punches in boxing. Furthermore, PENGs are used in cricket to monitor the number of balls middled on the bat during practice and the contact of the ball with the bat and stumps for smart decision making. All kinds of lab-scale testing are done for these applications, which pave a way for exploring the frontiers in nanogenerator applications in sports as maintenance-free and self-powered sensing technology

Current Challenges and Developments in Perovskite-Based Electrochemical Biosensors for Effective Theragnostics of Neurological Disorders

Early-stage diagnosis of neurological disease and effective therapeutics play a significant role in improving the chances of saving lives through suitable and personalized courses of treatment. Biomolecules are potential indicators of any kind of disorder in a biological system, and they are recognized as a critical quantitative parameter in disease diagnosis and therapeutics, collectively known as theragnostics. The effective diagnosis of neurological disorders solely depends on the detection of the imbalance in the concentration of neurological biomarkers such as nucleic acids, proteins, and small metabolites in bodily fluids such as blood serum, plasma, urine, etc. This process of neurological biomarker detection can lead to an effective prognosis with a prediction of the treatment efficiency and recurrence. While review papers on electrochemical, spectral, and electronic biosensors for the detection of a wide variety of biomarkers related to neurological disorders are available in the literature, the prevailing challenges and developments in perovskite-based biosensors for effective theragnostics of neurological disorders have received scant attention. In this Mini-Review, we discuss the topical advancements in design strategies of perovskite-based electrochemical biosensors with detailed insight into the detection of neurological disease or disorder-specific biomarkers and their trace-level detection in biological fluids with high specificity and sensitivity. The tables in this Review give the performance analysis of recently developed perovskite-based electrochemical biosensors for effective theragnostics of neurological disorders. To conclude, the current challenges in biosensing technology for early diagnosis and therapeutics of neurological disorders are discussed along with a forecast of their anticipated developments

Editorial for a showcase issue for India

Dear Readers, It gives us immense pleasure to present this special issue that aims to highlight the ongoing research being carried out in the area of sensors and actuators in India. The issue comprises of both original research as well as review articles. A review article on ZnO nano-structured devices for chemical and optical sensing applications provides a systematic and comprehensive guide to the readers on the use of one of the most explored functional metal oxides (ZnO) in remarkably diversified applications such as biomedical, environmental, and optical sensing. Further, this issue contains an article on perovskites for chemometric assisted simultaneous detection of trace amounts of heavy metal ions in biological samples. Apart from reporting well-established and emerging nanomaterials in the field of sensing, there are articles on various analytical detection techniques that are optical, and fluorescence based. An article on TiO2 nanoparticles based non-enzymatic label-free optical sensor for the rapid detection of L-lactate in apple juice would be of great interest to the scientific community working in the area of food quality and safety. Other works include a research paper on the colorimetric detection of zinc sulfate ions using a tetra-(4-pyridylphenyl) ethylene as an active sensing material and an article on electrochemical immunosensor for detection of cardiac troponin-I