Synergistic integration of Ni-metal organic framework/SnS2nanocomposite and nickel foam electrode for ultrasensitive and selective electrochemical detection of albumin in simulated human blood serum.

Albumin is a vital blood protein responsible for transporting metabolites and drugs throughout the body and serves as a potential biomarker for various medical conditions, including inflammatory, cardiovascular, and renal issues. This report details the fabrication of Ni-metal organic framework/SnS2nanocomposite modified nickel foam electrochemical sensor for highly sensitive and selective non enzymatic detection of albumin in simulated human blood serum samples. Ni-metal organic framework/SnS2nanocomposite was synthesized using solvothermal technique by combining Ni-metal-organic framework (MOF) with conductive SnS2leading to the formation of a highly porous material with reduced toxicity and excellent electrical conductivity. Detailed surface morphology and chemical bonding of the Ni-MOF/SnS2nanocomposite was studied using scanning electron microscopy, transmission electron microscopy, Fourier transform infra-red, and Raman analysis. The Ni-MOF/SnS2nanocomposite coated on Ni foam electrode demonstrated outstanding electrochemical performance, with a low limit of detection (0.44µM) and high sensitivity (1.3µA/pM/cm2) throughout a broad linear range (100 pM-10 mM). The remarkable sensor performance is achieved through the synthesis of a Ni-MOF/SnS2nanocomposite, enhancing electrocatalytic activity for efficient albumin redox reactions. The enhanced performance can be attributed due to the structural porosity of nickel foam and Ni-metal organic framework, which favours increased surface area for albumin interaction. The presence of SnS2shows stability in acidic and neutral solutions due to high surface to volume ratio which in turn improves sensitivity of the sensing material. The sensor exhibited commendable selectivity, maintaining its performance even when exposed to potential interfering substances like glucose, ascorbic acid, K+, Na+, uric acid, and urea. The sensor effectively demonstrates its accuracy in detecting albumin in real samples, showcasing substantial recovery percentages of 105.1%, 110.28%, and 91.16%.

Bismuth sulfide micro flowers decorated nickel foam as a promising electrochemical sensor for quantitative analysis of melamine in bottled milk samples.

Here, we demonstrate hydrothermally grown bismuth sulfide (Bi2S3) micro flowers decorated nickel foam (NF) for electrochemical detection of melamine in bottled milk samples. The orthorhombic phase of hydrothermally grown Bi2S3is confirmed by the detailed characterization of x-ray diffraction and its high surface area micro flowers-like morphology is investigated via field emission scanning electron microscope. Furthermore, the surface chemical oxidation state and binding energy of Bi2S3/NF micro flowers is analyzed by x-ray photoelectron spectroscopy studies. The sensor exhibits a wide linear range of detection from 10 ng l-1to 1 mg l-1and a superior sensitivity of 3.4 mA cm-2to melamine using differential pulse voltammetry technique, with a lower limit of detection (7.1 ng l-1). The as-fabricated sensor is highly selective against interfering species of p-phenylenediamine (PPDA), cyanuric acid (CA), aniline, ascorbic acid, glucose (Glu), and calcium ion (Ca2+). Real-time analysis done in milk by the standard addition method shows an excellent recovery percentage of Ì´ 98%. The sensor's electrochemical mechanism studies reveal that the high surface area bismuth sulfide micro flowers surface interacts strongly with melamine molecules through hydrogen bonding and van der Waals forces, resulting in a significant change in the sensor's electrical properties while 3D skeletal Nickel foam as a substrate provides stability, enhances its catalytic activity by providing a more number /of active sites and facilitates rapid electron transfer. The work presented here confirms Bi2S3/NF as a high-performance electrode that can be used for the detection of other biomolecules used in clinical diagnosis and biomedical research.

Nickel-cobalt metal-organic frameworks based flexible hydrogel as a wearable contact lens for electrochemical sensing of urea in tear samples.

A flexible, wearable, non-invasive contact lens sensor utilizing nickel-cobalt metal-organic framework (Ni-Co-MOF) based hydrogel is introduced for urea monitoring in tear samples. The synthesized Ni-Co-MOF hydrogel exhibits a porous structure with interconnected voids, as visualized by Scanning Electron Microscopy (SEM). Detailed structural and vibrational properties of the material were characterized using X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, and Raman spectroscopy. The developed Ni-Co-MOF hydrogel sensor showcases a detection limit of 0.445 mM for urea within a linear range of 0.5-70 mM. Notably, it demonstrates exceptional selectivity, effectively distinguishing against interfering species like UA, AA, glucose, dopamine, Cl-, K+, Na+, Ca2+, and IgG. The enhanced electrocatalytic performance of the Ni-Co-MOF hydrogel electrode is attributed to the presence of Ni and Co, fostering Ni2+ oxidation on the surface and forming a Co2+ complex that acts as a catalyst for urea oxidation. The fabricated sensor exhibits successful detection and retrieval of urea in simulated tear samples, showcasing promising potential for bioanalytical applications. The binder-free, non-toxic nature of the Ni-Co-MOF hydrogel sensor presents exciting avenues for future utilization in non-enzymatic electrochemical sensing, including applications in wearable devices, point-of-care diagnostics, and personalized healthcare monitoring.

A high performance lead-free flexible piezoelectric nanogenerator based on AlFeO3nanorods interspersed in PDMS matrix for biomechanical energy scavenging to sustainably power electronics.

Since lead-based piezoelectric nanogenerators (PENGs) possess serious health risks, environmental problems, proper disposal issues, and biocompatibility concerns, this work presents the fabrication of a flexible piezoelectric nanogenerator utilizing lead-free orthorhombic AlFeO3nanorods for biomechanical energy scavenging to sustainably power electronics. Hydrothermal technique is used to synthesize the AlFeO3nanorods and the PENG was fabricated on Indium tin oxide (ITO) coated Polyethylene terephthalate (PET) flexible film with AlFeO3nanorods interspersed in polydimethylsiloxane (PDMS). transmission electron microscopy proved that the AlFeO3nanoparticles are of nanorods shape. Through x-ray Diffraction, it is validated that AlFeO3nanorods have orthorhombic phase and crystalline structure. A high piezoelectric charge coefficient (d33) of 400 pm V-1is obtained from the piezoelectric force microscopy of AlFeO3nanorods. With optimized concentration of AlFeO3in the polymer matrix, an open circuit voltage (VOC) of 30.5 V, current density (JC) of 0.7888±0.0001µA cm-2and an instantaneous power density of 240.6 mW m-2are obtained under the application of a force of 1.25 kgf. To investigate the nanogenerator's practical utility, the PENG is used for lighting multiple LEDs, charging of a capacitor and as a pedometer via biomechanical energy harvesting. Hence, it can be employed for developing various self-powered wearable electronics such as flexible skin, artificial cutaneous sensors, etc.

Binary Ni-Fe layered double hydroxide on flexible nickel foam for the wide-range voltammetric detection of fibrinogen in simulated body fluid.

Fibrinogen, a circulating glycoprotein in the blood, is a potential biomarker of various health conditions. This work reports a flexible electrochemical sensor based on Ni-Fe layered double hydroxide (Ni-Fe LDH) coated on Nickel foam (Ni-Fe LDH/NF) to detect fibrinogen in simulated human body fluid (or blood plasma). The nanoflakes like morphology and hexagonal crystal structure of LDH, synthesized via urea hydrolysis assisted precipitation technique, are revealed by scanning electron microscopy (SEM) and powder x-ray diffraction (PXRD) techniques, respectively. The fabricated sensor exhibits linearity in a wide dynamic range covering the physiological concentration, from 1 ng ml-1to 10 mg ml-1, with a sensitivity of 0.0914 mA (ng/ml)-1(cm)-2. This LDH-based sensor is found to have a limit of detection (LOD) of 0.097 ng ml-1and a limit of quantification (LOQ) of 0.294 ng ml-1(S/N = 3.3). The higher selectivity of the sensor towards fibrinogen protein is verified in the presence of various interfering analytes such as dopamine, epinephrine, serotonin, glucose, potassium, chloride, and magnesium ions. The sensor is successful in the trace-level detection of fibrinogen in simulated body fluid with excellent recovery percentages ranging from 99.5% to 102.5%, proving the synergetic combination of 2D Ni-Fe layered double hydroxide and 3D nickel foam as a promising platform for electrochemical sensing that has immense potential in clinical applications.

ZnO nanoparticles-copper metal-organic framework composite on 3D porous nickel foam: a novel electrochemical sensing platform to detect serotonin in blood serum.

Herein, we report a simple non-enzymatic electrochemical sensor for the detection of serotonin (5-HT) in blood serum using ZnO oxide nanoparticles-copper metal-organic framework (MOF) composite on 3D porous nickel foam, namely, ZnO-Cu MOF/NF. The x-ray diffraction analysis reveals the crystalline nature of synthesized Cu MOF and Wurtzite structure of ZnO nanoparticles, whereas SEM characterization confirms the high surface area of the composite nanostructures. Differential pulse voltammetry analysis under optimal conditions yields a wide linear detection range of 1 ng ml-1to 1 mg ml-1to 5-HT concentrations and a LOD (signal to noise ratio = 3.3) of 0.49 ng ml-1, which is well below the lowest physiological concentration of 5-HT. The sensitivity of the fabricated sensor is found to be 0.0606 mA ng-1ml-1.cm2,and it exhibited remarkable selectivity towards serotonin in the presence of various interferants, including dopamine and AA, which coexist in the real biological matrix. Further, successful determination of 5-HT is achieved in the simulated blood serum sample with a good recovery percentage from ∼102.5% to ∼99.25%. The synergistic combination of the excellent electrocatalytic properties and surface area of the constituent nanomaterials proves the overall efficacy of this novel platform and shows immense potential to be used in developing versatile electrochemical sensors.

Tin oxide-polyaniline nanocomposite modified nickel foam for highly selective and sensitive detection of cholesterol in simulated blood serum samples.

Cholesterol (CH) is a vital diagnostic marker for a variety of diseases, making its detection crucial in biological applications including clinical practice. In this work, we report the synthesis of tin oxide-polyaniline nanocomposite-modified nickel foam (SnO2-PANI/NF) for non-enzymatic detection of CH in simulated human blood serum. SnO2was synthesized via the hydrothermal method, followed by the synthesis of SnO2-PANI nanocomposite throughin situchemical polymerization of aniline using ammonium persulfate as the oxidizing agent. Morphological studies display agglomerated SnO2-PANI, which possess diameters ranging from an average particle size of ∼50 to ∼500 nm, and the XRD analysis revealed the tetragonal structure of the SnO2-PANI nanocomposite. Optimization studies demonstrating the effect of pH and weight percentage are performed to improve the electrocatalytic performance of the sensor. The non-enzymatic SnO2-PANI/NF sensor exhibits a linear range of 1-100µM with a sensitivity of 300µAµM-1/cm-2towards CH sensing and a low limit of detection of 0.25µM (=3 S m-1). SnO2-PANI/NF facilitates the electrooxidation of CH to form cholestenone by accepting electrons generated during the reaction and transferring them to the nickel foam electrode via Fe (III)/Fe (IV) conversion, resulting in an increased electrochemical current response. The SnO2-PANI/NF sensor demonstrated excellent selectivity against interfering species such as Na+, Cl-, K+, glucose, ascorbic acid, and SO42-. The sensor successfully determined the concentration of CH in simulated blood serum samples, demonstrating SnO2-PANI as a potential platform for a variety of electrochemical-based bioanalytical applications.

Fabrication of high-performance triboelectric nanogenerator based on Ni3C nanosheets to self-power thermal patch for pain relief.

In this work, we report a vertical contact-separation mode triboelectric nanogenerators (TENG) comprising of Ni3C/PDMS composite and Nylon Nanofibers for self-powering a nichrome wire-based thermal patch for muscular/joint relaxation. An optimised composition of Ni3C (25 wt%) and PDMS as a tribo-negative material and Nylon Nanofibers synthesised via electrospinning on copper electrode foil as a tribo-positive material were used to fabricate the TENG. The fabricated TENG exhibits outstanding output generating an average open circuit voltage of ∼252 V, an average short circuit current of ∼40.87µA and a peak power of ∼562.35µW cm-2at a matching resistance of 20 MΩ by manual tapping. Enhancement in contact area due to electrospun nylon and micro capacitive Ni3C flakes in dielectric PDMS contribute to the exceptional performance of the TENG. The optimised TENG is then connected to a full bridge rectifier with a 100 nF filtering capacitor to convert the AC voltage to a DC output with a peak voltage of ∼5.4 V and a ripple voltage of ∼1.04 V to recharge an ICR 18650 Li-ion battery, which functions as a medium to improve electrical energy flow to the heat patch. The electrical energy is converted into heat energy by a wounded nichrome wire placed inside the heat patch. The nichrome wire of length 3 cm with appropriate number of windings was employed in the heat patch. An increment of 45 °F can be observed by switching the charged Li-ion battery-based circuit ON for just 30 s. The strategy of self-powering a heat patch using this TENG finds enormous applications in physiotherapy and sports to relieve muscle and joint pains.

1D NiO-3D Fe2O3mixed dimensional heterostructure for fast response flexible broadband photodetector.

Conventional heterojunction photodetectors rely on planar junction architecture which suffer from low interfacial contact area, inferior light absorption characteristics and complex fabrication schemes. Heterojunctions based on mixed dimensional nanostructures such as 0D-1D, 1D-2D, 1D-3D etc have recently garnered exceptional research interest owing to their atomically sharp interfaces, tunable junction properties such as enhanced light absorption cross-section. In this work, a flexible broadband UV-vis photodetector employing mixed dimensional heterostructure of 1D NiO nanofibers and 3D Fe2O3nanoparticles is fabricated. NiO nanofibers were synthesized via economical and scalable electro-spinning technique and made composite with Fe2O3nanoclusters for hetero-structure fabrication. The optical absorption spectra of NiO nanofibers and Fe2O3nanoparticles exhibit peak absorption in UV and visible spectra, respectively. The as-fabricated photodetector displays quick response times of 0.09 s and 0.18 s and responsivities of 5.7 mA W-1(0.03 mW cm-2) and 5.2 mA W-1(0.01 mW cm-2) for UV and visible spectra, respectively. The fabricated NiO-Fe2O3device also exhibits excellent detectivity in the order of 1012jones. The superior performance of the device is ascribed to the type-II heterojunction between NiO-Fe2O3nanostructures, which results in the localized built-in potential at their interface, that aids in the effective carrier separation and transportation. Further, the flexible photodetector displays excellent robustness when bent over ∼1000 cycles thereby proving its potential towards developing reliable, diverse functional opto-electronic devices.

3D, large-area NiCo2O4 microflowers as a highly stable substrate for rapid and trace level detection of flutamide in biofluids via surface-enhanced Raman scattering (SERS).

A one-pot hydrothermal synthesis of three-dimensional (3D), large-area, bimetallic oxide NiCo2O4 (NCO) microflowers has been developed as a novel substrate for surface-enhanced Raman scattering (SERS) detection of flutamide in biological fluids. The 3D flower-like morphology of the NCO is observed via FESEM micrographs, while the orthorhombic phase formation is confirmed through XRD spectra. Due to the presence of multiple coordination cations of the 3D NCO microflowers (such as Ni2+ and Co2+), the high surface area and surface roughness, the NCO-modified indium tin oxide (NCO/ITO) SERS substrate exhibits a linear detection range from 0.5-500 nM with a low limit of detection (LOD) of 0.1 nM. The SERS substrate provides a high enhancement factor of 1.864 × 106 with an accumulation time of 30 s using a laser source of λ = 532 nm, which can be ascribed to the excellent and rapid interaction between the flutamide molecule and the NCO microflower substrate that leads to photoinduced charge transfer (PICT) resonance. The NCO/ITO substrate exhibits excellent homogeneity and high chemical stability. Besides, the substrate displays an excellent selectivity to flutamide molecules in the existence of other metabolites such as urea, ascorbic acid (AA), glucose, NaCl, KCl, CaCl2, and hydroxyflutamide. The NCO/ITO substrate is successful in the trace-level detection of flutamide in simulated blood serum samples. The strategy outlined here presents a novel strategy for the efficacy of transition metal oxides (TMOs) based electrodes useful for a wide variety of bioanalytical applications.

Recent advancements in fabrication of nanomaterial based biosensors for diagnosis of ovarian cancer: a comprehensive review.

Ovarian cancer is commonly diagnosed via determination of biomarkers like CA125, Mucin 1, HE4, and prostasin that can be present in the blood. However, there is a substantial need for less expensive, simpler, and portable diagnostic tools, both for timely diagnosis and management of ovarian cancer. This review (with 101 refs.) discusses various kinds of nanomaterial-based biosensors for tumor markers. Following an introduction into the field, a first section covers different kinds of biomarkers for ovarian cancer including CA125 (MUC16), mucin 1 (MUC1), human epididymis protein 4 (HE4), and prostasin. This is followed by a short overview on conventional diagnostic approaches. A large section is then presented on biosensors for determination of ovarian cancer, with subsections on optical biosensors (fluorimetric, colorimetric, surface plasmon resonance, chemiluminescence, electrochemiluminescence), on electrochemical sensors, molecularly imprinted sensors, paper-based biosensors, microfluidic (lab-on-a-chip) assays, chemiresistive and field effect transistor-based sensors, and giant magnetoresistive sensors. Tables are presented that give an overview on the wealth of methods and materials. A concluding section summarizes the current status, addresses current challenges, and gives an outlook on potential future trends. Graphical abstract Schematic representation of the review covering the advancements in the fabrication of various nanomaterial based biosensors for diagnosis of ovarian cancer.

Few layered MoS2 grown on pencil graphite: a unique single-step approach to fabricate economical, binder-free electrode for supercapacitor applications.

While all reports on supercapacitors are based on electrodes that are fabricated either using expensive, complex fabrication techniques or multiple steps based synthesis routes, the current work is the first report of one-step hydrothermally grown MoS2 on pencil graphite electrode (PGE) for ultra-high performance supercapacitor application. Field emission scanning electron microscope images revealed MoS2 micro-flower like structure containing interwoven nanosheets whereas chemical characterizations data confirmed the successful growth of few layered (>4 layers) MoS2 on PGE. The performance of the electrode was optimized using various grades of pencil, and it was found that the areal capacitance of the MoS2 grown on 1H PGE(7178.8 mF cm-2) was about 3.4 and 4.1 folds greater than those of the MoS2 grown on 2B, 6H PGE at the same current density respectively. This low cost, binder-free MoS2 based PGE paves a novel way towards the advancement of affordable electrodes for energy storage-conversion and bioanalytical applications.

Large area, one step synthesis of NiSe2 films on cellulose paper for glucose monitoring in bio-mimicking samples for clinical diagnostics.

There is an urgent need to develop low cost electrochemical sensors wherein the sensor can be disposed after recording data, thereby eliminating the issue of inaccuracy arising from repeated sensing measurements, which plagues most conventional electrochemical sensors. This work is the first demonstration of a NiSe2 based disposable, one time use electrochemical glucose sensor in bio-mimicking real samples wherein NiSe2 was hydrothermally grown NiSe2 on a biodegradable cellulose paper. Both physicochemical (x-ray diffraction, x-ray photoelectron spectroscopy, field emission scanning electron microscope) and electrochemical (impedance spectroscopy and cyclic voltammetry (CV)) characterization techniques confirmed the growth and presence of NiSe2 on a cellulose paper. Electrochemical techniques like CV and amperometric (i-t) were utilized for the selective and sensitive oxidation of glucose. The results suggests that the proposed NiSe2 sensor is effective in a linear range of 0.1-1 mM with fast response time (3.9 s), low detection limit (24.8 ± 0.1 µM) and high sensitivity (0.25 A M-1 cm-2) at a potential applied (E app = 0.55 V versus Ag∣AgCl). Prior to the real sample analyses i.e. glucose detection in human urine, the fabricated NiSe2 sensor was tested for selectivity towards glucose in co-existing interferences (dopamine, ascorbic acid, uric acid, urea, sodium chloride, fructose, lactose and cysteine). Finally, glucose in artificial blood serum and urine samples was demonstrated with the fabricated NiSe2 sensor and the results are comparable to the conventional laboratory methods. The present methodology presents a novel possibility towards the design of next generation, affordable point-of-care devices for a broad range of clinical diagnostics.

A ruthenium(IV) disulfide based non-enzymatic sensor for selective and sensitive amperometric determination of dopamine.

An electrochemical dopamine (DA) sensor has been fabricated by modifying a glassy carbon electrode (GCE) with ruthenium disulfide (RuS2) nanoparticles (NPs). FESEM and TEM micrographs show the NPs to have an average size of ~45 nm. XRD, Raman and EDS, in turn, confirm the successful formation of cubic phased RuS2 NPs. The modified GCE displays has attractive features of merit that include (a) an ultra-low detection limit (73.8 nM), (b) fast response time (< 4 s), (c) a low oxidation potential (0.25 V vs. Ag|AgCl), (d) excellent reproducibility and stability, (e) an electrochemical sensitivity of 18.4 µA µM-1 cm-2 and 1.8 µA.µM-1.cm-2 in the linear ranges from 0.1-10 µM of DA (R2 = 0.97) and 10-80 µM of DA (R2 = 0.99), respectively. The sensor exhibits excellent specificity over potential interferents like ascorbic acid, glucose and uric acid. The superior performance of the sensor is attributed to its high electrical conductivity, large electro-active surface, and large numbers of exposed catalytically active sites resulting from the presence of unreacted sulfur atoms. Graphical abstract A ruthenium disulfide modified electrochemical sensor material was obtained by single-step hydrothermal synthesis. Sensitive and highly selective detection of dopamine is demonstrated.

Pyro-phototronic nanogenerator based on flexible 2D ZnO/graphene heterojunction and its application in self-powered near infrared photodetector and active analog frequency modulation.

Even though 2D ZnO has been utilized for enhanced self-powered sensing by strain modulation due to its piezoelectric property, study on utilizing the pyroelectric property of ZnO remains unexplored. The piezoelectric property of 2D ZnO works on mechanical strain, which disrupts the structure of ZnO leading to the failure of the device. For a pyroelectric nanogenerator, the temperature difference can be triggered by an external light source, which does not disrupt the ZnO structure and also avoids the need for physical bending/pressing, as in the case of a piezoelectric nanogenerator. This work represents the first demonstration of the fabrication of a flexible 2D ZnO/Gr pyro-phototronic diode where the pyro-potential generated in the 2D ZnO due to the near infrared (NIR) illumination adds to or subtracts from the built-in electric field of the heterojunction and modulates the depletion region of the heterojunction thereby enabling bias-free operation. Furthermore, the variation in the depletion width of the heterojunction was utilized as a variable capacitor in the frequency modulator, wherein, with the increasing intensity, the frequency of oscillations increased from 9.8 to 10.42 MHz. The work presented provides an alternative approach for a self-powered NIR photodetector and the utilization of the same at circuit level, having potential applications in the fields of optothermal detection, electronic tuning circuits, etc.

Bimetallic Pt-Pd nanostructures supported on MoS2 as an ultra-high performance electrocatalyst for methanol oxidation and nonenzymatic determination of hydrogen peroxide.

The authors report on a composite based electrocatalyst for methanol oxidation and H2O2 sensing. The composite consists of Pt nanoparticles (NPs), Pd nanoflakes, and MoS2. It was synthesized by chemical reduction followed by template-free electro-deposition of Pt NPs. FESEM images of the Pd nanoflakes on the MoS2 reveal nanorod-like morphology of the Pd NPs on the MoS2 support, whilst FESEM images of the Pt-Pd/MoS2 composite show Pt NPs in high density and with the average size of ~15 nm, all homogeneously electrodeposited on the Pd-MoS2 composite. A glassy carbon electrode (GCE) was modified with the composite to obtain an electrode for methanol oxidation and H2O2 detection. The modified GCE exhibits excellent durability with good catalytic efficiency (the ratio of forward and backward peak current density, If/Ib, is 3.23) for methanol oxidation in acidic medium. It was also used to sense H2O2 at an applied potential of -0.35 V vs. Ag|AgCl which can be detected with a 3.4 µM lower limit of detection. The sensitivity is 7.64 µA µM-1 cm-2 and the dynamic range extends from 10 to 80 µM. This enhanced performance can be explained in terms of the presence of higher percentage of metallic 1T phase rather than a semiconducting 2H phase in MoS2. In addition, this is a result of the high surface area of MoS2 with interwoven nanosheets, the uniform distribution of the Pt NPs without any agglomeration on MoS2 support, and the synergistic effect of Pt NPs, Pd nanoflakes and MoS2 nanosheets. In our perception, this binder-free nano-composite has promising applications in next generation energy conversion and in chemical sensing. Graphical abstract A composite consisting of palladium nanoflakes and molybdenum disulfide was decorated with platinum nanoparticles and then placed on a glassy carbon electrode which is shown to be a viable electrocatalyst for both methanol oxidation and detection of hydrogen peroxide.

Strain-modulation-assisted enhanced broadband photodetector based on large-area, flexible, few-layered Gr/MoS2 on cellulose paper.

Electronic structure and carrier behavior in semiconductor junctions can be effectively modulated on the application of strain. This work represents the first demonstration of a large-area, flexible, paper-based graphene-molybdenum disulfide (Gr/MoS2) broadband photodetector using a low-cost solution-processed hydrothermal method and enhancement in photodetection through strain modulation by assembling the device on polydimethylsiloxane. Optimization, in terms of process parameters, was carried out to obtain trilayer MoS2 over Gr-cellulose paper. Under strain, potential barrier variation and piezopotential induced in MoS2 leads to 79.41% enhancement in photodetection in the visible region. Piezopotential induced in MoS2 lowers the conduction-band energy thereby increasing the effective electric field favoring easy electron-hole separation. The advantage of vertically stacked Gr/MoS2 for the photodetector is the utilization of the entire area as a junction where effective separation of electron-hole pairs occurs. Detailed studies of the mechanism in terms of potential barrier variation in Gr/MoS2 and an energy-band diagram are presented to help understand the proposed phenomenon. The present work demonstrates the significance of few-layer MoS2 or Gr in relation to strain-modulated photosensing in comparison to their counterparts grown via chemical vapor deposition. The results provide an excellent approach for the fabrication of low-cost heterojunctions for improved optoelectronic performance, which can be further extended to similar 2D-material heterojunctions for analog, digital and optoelectronic applications.

Eraser-based eco-friendly fabrication of a skin-like large-area matrix of flexible carbon nanotube strain and pressure sensors.

This paper reports a new type of electronic, recoverable skin-like pressure and strain sensor, produced on a flexible, biodegradable pencil-eraser substrate and fabricated using a solvent-free, low-cost and energy efficient process. Multi-walled carbon nanotube (MWCNT) film, the strain sensing element, was patterned on pencil eraser with a rolling pin and a pre-compaction mechanical press. This induces high interfacial bonding between the MWCNTs and the eraser substrate, which enables the sensor to achieve recoverability under ambient conditions. The eraser serves as a substrate for strain sensing, as well as acting as a dielectric for capacitive pressure sensing, thereby eliminating the dielectric deposition step, which is crucial in capacitive-based pressure sensors. The strain sensing transduction mechanism is attributed to the tunneling effect, caused by the elastic behavior of the MWCNTs and the strong mechanical interlock between MWCNTs and the eraser substrate, which restricts slippage of MWCNTs on the eraser thereby minimizing hysteresis. The gauge factor of the strain sensor was calculated to be 2.4, which is comparable to and even better than most of the strain and pressure sensors fabricated with more complex designs and architectures. The sensitivity of the capacitive pressure sensor was found to be 0.135 MPa-1.To demonstrate the applicability of the sensor as artificial electronic skin, the sensor was assembled on various parts of the human body and corresponding movements and touch sensation were monitored. The entire fabrication process is scalable and can be integrated into large areas to map spatial pressure distributions. This low-cost, easily scalable MWCNT pin-rolled eraser-based pressure and strain sensor has huge potential in applications such as artificial e-skin in flexible electronics and medical diagnostics, in particular in surgery as it provides high spatial resolution without a complex nanostructure architecture.

Eco-friendly all-carbon paper electronics fabricated by a solvent-free drawing method.

Here we report the fabrication of high-performance all-carbon temperature and infrared (IR) sensors with a solvent-free multiwalled carbon nanotube (MWCNT) trace as the sensing element and commercial graphite pencil trace as the electrical contact on recyclable and biodegradable cellulose filter paper without using any toxic materials or complex procedures. The temperature sensor shows a large negative temperature coefficient of resistance (TCR) in the range of -3100 ppm K(-1) to -4900 ppm K(-1), which is comparable to available commercial temperature sensors, and an activation energy of 34.85 meV. The IR sensor shows a high responsivity of 58.5 V W(-1), which is greater than reported IR sensors with similar dimensions. A detailed study of the conduction mechanism in MWCNTs with temperature and the photo response with IR illumination was done and it was found that the conduction is due to thermally assisted hopping in band tails and the photo response is bolometric in nature. The successful fabrication of these sensors on cellulose filter paper with a comparable performance to existing components indicates that it is possible to fabricate high-performance electronics using low-cost, eco-friendly materials without the need for expensive clean-room processing techniques or harmful chemicals.

Poly(3-aminophenylboronic acid)-functionalized carbon nanotubes-based chemiresistive sensors for detection of sugars.

The poly(aniline boronic acid) (PABA)-functionalized single-walled carbon nanotube (SWNT) non-enzymatic sensor was developed for the detection of saccharides. The work involved the electrochemical polymerization of 3-aminophenylboronic acid (3-APBA) in the presence of fluoride on the surface of SWNTs and their subsequent evaluation as chemiresistive sensors towards the detection of d-fructose and d-glucose. By varying the sensor's synthesis conditions by charge-controlled electropolymerization, the sensing performance was systematically optimized. Through electrical characterization in terms of change in resistance, cyclic voltammetry confirmed the electrochemical deposition of the PABA coating on the SWNTs. The optimized sensors showed sensing response over a wide dynamic range of concentrations and a limit of detection of 2.92 mM for D-fructose and 3.46 mM for D-glucose. The hybrid sensors could be regenerated on the basis of the reversible nature of the binding between PABA and 1,2- or 1,3-diols at lower values of pH.