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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 Fe 2 O 3 nanoparticles is fabricated. NiO nanofibers were synthesized via economical and scalable electro-spinning technique and made composite with Fe 2 O 3 nanoclusters for hetero-structure fabrication. The optical absorption spectra of NiO nanofibers and Fe 2 O 3 nanoparticles 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-Fe 2 O 3 device also exhibits excellent detectivity in the order of 10 12 jones. The superior performance of the device is ascribed to the type-II heterojunction between NiO-Fe 2 O 3 nanostructures, 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., (© 2022 IOP Publishing Ltd.)

Obtaining sustainable, high output power supply from triboelectric nanogenerators still remains a major issue that restricts their widespread use in self-powered electronic applications. In this work, an ultra-high performance, non-toxic, flexible triboelectric nanogenerator based on bismuth tungstate (Bi 2 WO 6 ):polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) is fabricated. A hydrothermal technique is used to synthesize highly crystalline Bi 2 WO 6 nanoparticles that are then incorporated inside the P(VDF-TrFE) matrix nanofiber mat using electrospinning over an aluminum-coated PET substrate to yield a nanogenerator with a device configuration of Cu-coated PET/(Bi 2 WO 6 :P(PVDF-TrFE)) nanofiber mat/Al-coated PET. The highly crystalline nature of the biconcave shaped Bi 2 WO 6 nanoparticles and β - P(VDF-TrFE) is confirmed by X-ray powder diffraction (XRD) and Raman spectroscopic techniques. The dielectric constant of the Bi 2 WO 6 :P(PVDF-TrFE) nanofiber mat was studied and a high dielectric constant of 44 was observed. The as-fabricated nanogenerator delivers a very high output voltage (open circuit) of 205 V and current density (short circuit) of 11.91 mA m -2 at ∼0.15 kgf without any electric poling, which is higher than all the prior reports in this field. The fabricated nanogenerator possesses very high output stability and ultra-sensitivity with a swift response time of 60 ms. This outstanding performance of the nanogenerator can be ascribed to the synergistic combination of the β-phase P(VDF-TrFE) polymer and non-centrosymmetric nature of Bi 2 WO 6 nanoparticles. Furthermore, a Bi 2 WO 6 -based pH sensor is driven by the energy obtained from the as-fabricated nanogenerator and the real time demonstration of the nanogenerator powering a calculator is also demonstrated. The strategy outlined here presents a cost-effective, high performance alternative for driving various portable bio-compatible self-powered electronic devices.

Flexible nanofiber-based composites have been widely explored because of their light weight, high surface area, scalability, and tunable physical and mechanical properties. In this work, we report electrospun 2D-Bi 2 S 3 incorporated PVDF/PPy nanofibers as a versatile platform for ultrasensitive pressure, strain, and temperature sensing. Detailed characterization studies revealed the formation of ultrathin nanofibers and characteristic Raman and IR vibration modes of PPy, 2D-Bi 2 S 3 , β-phased PVDF. The fabricated pressure sensor exhibited a sensitivity of 1.51 kPa -1 in the wide linear range of 1-50 kPa and a response time of 0.04 s. The practical ability of pressure sensor was tested by successfully detecting pulse rate of human radial arteries. Further, the BS- PVDF/PPy composite was employed as a strain sensor in the range of 3.1-61.5%, displayed a gauge factor (GF) of 45.45 and a response time of 0.1 s. The wearable sensor was capable of detecting minute changes in hand gestures by recognizing the microstrains applied to the device. The sensing mechanism can be attributed to the excellent piezoelectric property of β- phase PVDF, electron transport property of PPy nanoparticles and tensile strength of the BS nanoparticles embedded in the polymer matrix. When used as a wearable temperature sensor, the versatile device demonstrated a linear range of detection 24- 48 °C with a response time of 0.33 s and Temperature coefficient of resistance (TCR) of -0.1117 °C -1 that can be attributed to the phonon-assisted hoping mechanism. The nanofiber composite dissolved in volatile organic solvent acetone in 5 days with the least impact on the surrounding environment thus making this a promising strategy to develop transient technologies aimed at zero-waste, green electronics.

In this work we report for the first time surface functionalization of 2D MoS2 with X (metals: Al, Cu, Sn, Ti) to develop a low-cost, ultra-selective biosensor array based Electronic Tongue (E-Tongue) for the detection of 4 vital neurological drugs in human saliva. The hydrothermally grown surface functionalized X-MoS2 was integrated onto a single 1 × 1 cm aluminium foil and contacts were defined using Cr electrodes. Detailed characterization revealed the formation of 2-H MoS2 and metal-X (Al, Cu, Sn, Ti)-functionalized MoS2 nanoflower like morphology decorated with nanoflake, nanorod, nanocube and nanostick structures, respectively. The response of the sensor array was recorded for aspirin, nicotine, caffeine and tramadol. Principal Component Analysis (PCA) was performed to reduce the dimension of numerous response data sets from all sensors and predict the likely possible response from various neurological drugs towards each sensor. Pattern-recognition analysis confirmed a definite pattern in response to respective functionalization and could efficiently differentiate neurological drugs from one another. Real-time analysis was performed using saliva samples for monitoring the therapeutic neurological drug concentration in the human body. Furthermore, the biosensor array was exposed to respective neurological drugs to study their sensitivity, selectivity, stability, reproducibility and adhesion onto the device. The strategy outlined can be used to develop lab-on-a-chip devices for the real-time detection of numerous bioanalytes in body fluids.

Here we report a low-cost, flexible amperometric sensing platform for highly selective and sensitive detection of carbamazepine (CBZ) in human sweat samples. Detailed morphological characterization of the two-dimensional transition metal dichalcogenide NiSe 2 , synthesized using one-step hydrothermal method, confirms the formation of dense NiSe 2 nanoclusters in the range of 500-650 nm, whereas X-ray diffraction and X-ray photoelectron spectroscopy studies reveal a stable and pure cubic crystalline phase of NiSe 2 . The sensor device is fabricated by uniformly depositing an optimized weight percentage of as-synthesized NiSe 2 onto flexible and biocompatible polyimide substrate using spin coating, and metal contacts are established using thermal evaporation technique. The sensor exhibits a remarkable sensitivity of 65.65 μA/nM over a wide linear range of 50 nM to 10 μM CBZ concentrations and a low limit of detection of 18.2 nM. The sensing mechanism and excellent response of NiSe 2 toward CBZ can be attributed to the highly conductive metallic NiSe 2 , large electroactive surface area of its nanoclusters, and highly interactive Ni 2+ /Ni 3+ oxidation states. Furthermore, the presence of 10-fold excess of capable interferents, such as lactic acid, glucose, uric acid, and ascorbic acid, does not affect the accurate determination of CBZ, thus demonstrating excellent selectivity. The real-time detection of CBZ is evaluated in human sweat samples using standard addition method, which yields reliable results. Furthermore, the sensor shows excellent robustness when subject to bending cycles and fast response time of 2 s. The strategy outlined here is useful in developing sensing platforms at low potential without the use of enzymes or redox binders for applications in healthcare., (Copyright © 2020 Veeralingam and Badhulika.)

Pristine ZnO has been widely explored for its use in UV photodetectors; however, the utility of ZnO in broadband photodetectors is still a challenge as it absorbs in the UV region only with low quantum efficiency and responsivity that can be accredited to the high recombination rate of photo-generated charge carriers. To address this issue, we report an Fe-doped 2D ZnO thin film, obtained through band gap engineering, and a 1D electrospun mixed-inorganic monoclinic BiVO 4 nanofiber heterostructure on an ITO-coated PET substrate-based broadband photodetector (PD) with ultra-high responsivity and EQE values in comparison to PDs fabricated using expensive cleanroom techniques. BiVO 4 plays the dual role of absorbing photons in the visible and NIR regions and creating local electric fields at the interface of the Fe-doped ZnO (FZO)-BiVO 4 heterostructure, which helps in the separation of electron-hole pairs. The robustness of the flexible PD was further examined under the conditions of repeated bending cycles (up to 500), yielding a stable response. The responsivity values obtained for UV, visible and NIR irradiation are 7.35 A W -1 , 3.8 A W -1 and 0.18 A W -1 with very high EQE values of 2501.7%, 851.2% and 28.3%, respectively. The facile and cost-effective fabrication of the device with high performance provides a new approach for developing flexible electronics and high-performance optoelectronic devices.

In this work, we demonstrate a simple, low-cost biocompatible 1D-WO 3 electrospun nanofibers based strain-induced high-performance chemiresistive catechol sensor. WO 3 nanofibers were synthesized using e-spinning, annealed and drop-casted on to flexible PET substrate. X-Ray Diffraction (XRD) studies confirm the formation of Hexagonal phase-WO 3 and Raman spectroscopy proved the presence of O-W-O bending modes. Field emission scanning electron microscopy (FESEM) images displayed the random orientation of dense WO 3 nanofibers on PET substrate. Hall measurements confirmed the formation of n-type WO 3 nanofibers with carrier density of 10 19  cm -3 . The sensor responded to a broad dynamic range of catechol concentrations from 1 μM to 100 μM with sensitivity of 51.29 μM -1  cm -2 and limit of detection of 0.52 μM which are better than previously reported catechol sensors. Interestingly, upon application of compressive strain to the flexible sensor, a remarkable increase in sensitivity to 88.34 μM -1  cm -2 was observed with further reduction of the limit of detection to 42 nM. Upon subjecting the sensor to strain ranging from 3.14% to 47.6%, an increase in sensitivity to catechol was observed due to the increase in the exposed surface area of interconnected WO 3 nanofibers which enhances the active sites for catechol oxidation by enhancing the tunneling current. The sensor could detect catechol in simulated blood samples with excellent selectivity against AA, UA, Na + , Ca + , hydroquinone and glucose., (Copyright © 2019 Elsevier B.V. All rights reserved.)