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Zinc oxide (ZnO), a direct, wide band gap and n-type metal oxide semiconductor, is being anticipated as the next generation functional nano-material towards remarkably diversified sensing applications. ZnO and its composites have revealed a new era in the fabrication of sensors owing to their excellent opto-electronic, physicochemical, electrical properties such as low dielectric constant, plentiful Zn-O bonds, high luminous transmittance, good physicochemical stability, huge excitation binding energy, non-toxicity, biocompatibility, large surface area to volume ratio and so on. This comprehensive review summarizes the applications of ZnO nano-structures in the areas of environmental monitoring, biomedical, and optical sensing. Fundamental sensing mechanisms of the ZnO based sensors are examined to provide a better insight into the role of ZnO in each of these sensors. Wherever relevant, limitations of the existing approaches and future outlook have also been discussed. © 2022

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.

Most carbon electrode materials for supercapacitors (SCs) are prepared by the conventional KOH activation method that entails several steps at higher temperatures resulting in low-energy density. Herein, we report one-step facile carbonization and low-concentration-activation aided synthesis of activated carbon (AC) from Prunus dulcis (almond) peel (AP) by using three activating agents, namely (a) KOH (AC-K1); (b) KOH with K3[Fe(CN)6] (AC-K2); (c) KOH with K3[Fe(CN)6] and K4[Fe(CN)6] (AC-K3) for high-performance symmetric supercapacitor (SSCs) applications in 6 M KOH and 1 M TEABF4 electrolytes. Detailed structural and chemical characterization studies were performed on the as-prepared AC-K1/K2/K3 samples and optimization studies revealed that AC-K3 electrode delivers the highest performance due to the presence of trace amount of iron salts in the carbon network that acts as a catalyst and induces fast charge-transfer for electrochemical reactions. The BET surface area of AC-K1, AC-K2, and AC-K3 are found to be 408.89 m2 g−1, 819.79 m2 g−1, and 1061.6 m2 g−1, respectively. AC-K3 electrode delivers an outstanding half-cell specific capacitance of 320 F g−1 at 1 A g−1 in 6 M KOH. The SC device with AC-K3 electrode delivers full-cell specific capacitance of 290 F g−1 and 370.37 F g−1 in 6 M KOH and 1 M TEABF4, respectively. The highest energy density of 41.24 Wh kg−1 at 1349 W kg−1 power with the extended potential of ~2.7 V is delivered by the AC-K3 electrode in 1 M TEABF4, which is considerably higher and unprecedented compared to other reported carbon materials. After 10 000 cycles, there is a ~100% capacitance retention. As a result of this study, the abundant bio-derived AC-K3 is found to be a potential long-term electrode material for high-energy SC applications. © 2022 John Wiley & Sons Ltd.

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.

Photodetectors based on inorganic semiconductors demonstrate superior responsivity, but their high thermal budget fabrication process is a serious impediment for emerging applications. Hybrid photodetectors based on organic-inorganic heterojunctions synergistically offer the solution-processability and tunability of organic semiconductors, along with the superior absorption coefficient and transport properties of inorganic materials. In this work, a broadband photodetector based on a bulk-heterojunction of hybrid organic-PEDOT:PSS/inorganic-SnSe2 and a subsequent vertical junction on flexible ITO-coated-PET is demonstrated. SnSe2 nanoflakes, synthesized via a facile hydrothermal method, exhibit absorption in both the visible and NIR spectra, and are made into a bulk heterojunction (BHJ) with PEDOT:PSS. The ITO layer exhibits absorption in the UV spectra, onto which the SnSe2-PEDOT:PSS bulk-heterojunction composite is deposited to form a vertical junction. The broadband photodetector exhibits quick response times of 16 ms, 221 ms and 274 ms and superior responsivities of 0.72 A W-1, 0.67 A W-1 and 0.69 A W-1 in the UV, Vis and NIR spectra, respectively. This superior responsivity of the photodetector is related to the enhanced interfacial area between SnSe2-PEDOT:PSS in the bulk-heterojunction, which leads to efficient electron-hole pair separation. Furthermore, the device is subjected to multiple bending cycles (∼3000) and minimal deviation in responsivity is observed. The facile and low-cost approach demonstrated in this work finds potential applications in novel flexible opto-electronic devices. This journal is © the Partner Organisations.

Recycling of aluminum metal from scrap materials demands a high processing temperature, which releases several toxic gases to the environment. In contrast, aluminum metal is known as the cleanest and cheapest source for hydrogen production because of its 3+ oxidation state and spontaneous exothermic reaction with water molecules. In this work, we report the hydrothermal synthesis of hybrid Cu2S decorated on nickel foam (NF) for direct aluminum fuel cell application. The hybrid structure of the Cu2S nanoflake- and nanosphere-based catalyst distributed on the three-dimensional (3D) skeletal NF is revealed via detailed structural analysis. The Cu2S/NF-8 catalyst electrode exhibits a maximum mass activity of 106.7 mA/mg at an overpotential of 0.8 V (vs Hg/HgO) for a 40 mg Al source. The high mass activity of the optimized Cu2S/NF-8 catalyst electrode is attributed to the hybrid Cu2S structure, which facilitates improved electrocatalytic activity via its point defects and metallic edges. Likewise, the high electrical conductivity, chemical stability, and rapid charge transfer at the electrode with a short diffusion path are because of the arrangements of the hybrid Cu2S on the NF substrate. The stability and real-time performance of the Cu2S/NF-8 catalyst electrode is successfully studied via chronoamperometry in the presence of an Al ball and a scrap aluminum source. The electrode exhibits a capacity retention of ∼60% (for 7000 s; Al ball) and ∼35% (for 100000 s; scrap Al). This proves the Cu2S/NF-8 catalyst electrode as a promising platform for aluminum source-based fuel cell applications.

This work demonstrates the single-step solvothermal synthesis of marcasite FeS2 as a low-cost electrochemical platform for the separation-less sensing of four nucleobases of DNA. FESEM micrographs reveal high surface area micro-flowers like morphology of the marcasite FeS2 wherein each micro-flower comprises vertically grown interwoven 2D nanosheets. XRD and Raman spectra further confirm the successful synthesis of the marcasite FeS2. A detailed optimization study on the impact of electrolytic pH values on the simultaneous determination of four DNA bases (adenine (A), thymine (T), guanine (G) and cytosine (C)) is performed. Under optimal pH conditions, the marcasite FeS2 based electrode is capable of identifying DNA bases altogether over the linear range of 500-2000 µM with excellent reproducibility and stability. The superior electrochemical sensing properties of the marcasite FeS2 towards simultaneous detection of four bases can be ascribed to high electro-active surface area and conductivity from the active sites of this unique 2D nanosheets-like structure. Besides, to establish its efficacy in real-time applications, the sensor is successfully utilized for the detection of nucleobases of denatured DNA of calf-thymus, and the obtained value of is found to be 0.77. These results establish that the marcasite FeS2 has enormous potential to be used as a promising low-cost, functional transition metal di-chalcogenide (TMD) nanomaterial for bio-analytical and sensing applications. IEEE

Flexible and compressible sensors have been widely used for various wearable applications; however, the devices are typically planar, expensive and with limited compressibility. In this work, carbon-doped polypyrrole nanoparticles interfaced in a 3D-macroporous melamine foam (C-PPy@MF) composite are used as a low-cost multifunctional sensor for breath monitoring, pressure-, and strain-sensing applications. The C-PPy nanostructures were grown on MF using an ultrasonic irradiation technique to achieve a firm loading of C-PPy on the MF surface and interface. Detailed morphological characterization studies reveal the discrete distribution of C-PPy nanoparticles in the MF matrix. Structural analysis revealed a broad amorphous phase corresponding to the carbon polymer chains. The fabricated C-PPy@MF-based breath sensor displayed a fast response time of 0.9 s and a recovery time of 1.3 s upon continuous exhalation and inhalation cycles. In addition, the breath sensor was used for the monitoring of human breath per minute (bpm) and dehydration of the lungs. The superior response of the breath sensor can be attributed to the surface engineering of MF with the C-PPy nanostructures, which enables an excellent surface reactivity due to their large relative surface area. The C-PPy@MF-based piezoresistive pressure sensor exhibits a sensitivity of 2 kPa-1 in the pressure range of 1-90 kPa and a rapid response time of 160 ms. A 3 × 3 pressure sensor array was developed for precise spatial mapping to demonstrate the practicability of the pressure sensor. The fabricated C-PPy@MF-based strain sensor recorded a maximum gauge factor (GF) of 23.47 and can withstand a maximum strain of 80%, which is higher than most of the previously reported similar yet sophisticated devices. In addition, a constant response was obtained for 1000 bending cycles, demonstrating the excellent mechanical stability of the fabricated C-PPy@MF device. The fabricated C-PPy@MF-based flexible breath, pressure, and

Despite the low cost of paper substrates, the lack of appropriate device fabrication techniques has hampered the overall efficacy of paper-based sensors. Addressing this issue, in this work, we develop a multi-walled carbon nanotube (MWCNTs) coated paper substrate-based biosensor using a novel method of wax deposition followed by vacuum filtration to design dedicated hydrophobic and hydrophilic channels for label-free, highly selective, and sensitive detection of cholesterol. Detailed morphological characterization studies reveal the uniform deposition of MWCNTs on the paper substrate (∼15–20 nm average diameter). Upon exposure to cholesterol, an excellent dynamic range of response over three orders of magnitude from 10 nM −75 µM and 100 µM–8 mM concentration range with a limit of detection of 3.2 nM (3 S/m) was obtained. The Michaelis–Menten constant (Km) was found to be 0.0093 µM. In addition, the fabricated biosensor exhibited excellent reproducibility, stability and high specificity to cholesterol with negligible response from interfering analytes. The excellent response of the fabricated biosensor can be attributed to the modulation of electrical properties due to electrostatic gating effect and direct electron transfer between MWCNTs and cholesterol due to the bioconjugation of Cholesterol oxidase (ChOx). The strategy employed here addresses some major challenges faced by the current methods of using rigid substrates and liquid electrolyte based analytical methods for detection of cholesterol. Furthermore, the sensor could successfully measure concentrations of cholesterol in saliva. This work provides a promising platform for developing low cost, interference free, disposable paper-based biosensors for point of care diagnostics. © 2022 The Korean Society of Industrial and Engineering Chemistry

The multicomponent electrocatalyst is a low-cost composite material exhibiting excellent catalytic activity suitable for methanol oxidation reactions (MOR). In this work, we report a glassy carbon electrode modified nickel oxide nanospheres (NiO) decorated biomass-derived activated carbon (AC) nanosheets and polypyrrole (PPy) nanowire, electrocatalyst (NiO_AC@PPy/GCE) for direct methanol oxidation fuel cell (DMFC) application. The SEM micrographs reveal the nanosheets and nanowire-like morphology of AC and PPy decorated with NiO nanospheres which provide a high surface area with electrocatalytic activity, and stability for MOR. The NiO_AC@PPy/GCE exhibits a high current density of 551 mA/mg at a low onset potential of 0.5 V (vs Ag|AgCl) towards electro-oxidation of 0.5 M methanol (MeOH) in an alkaline medium. This superior performance of the NiO_AC@PPy/GCE over other reported metal-oxides based electrocatalysts is attributed to the synergistic effect of the NiO_AC@PPy electrocatalyst, wherein NiO provides electrocatalytic active sites for MOR via Ni2+/Ni3+ redox couple while the PPy and AC contribute towards the chemical stability and electrical conductivity of the electrode, respectively. The electrode shows 79% of capacity retention after 10,000 s of chronoamperometry displaying excellent chemical stability with reduced effect of CO intermediate poisoning at the electrode surface. This excellent stability and overall performance of the NiO_AC@PPy proves it as an ideal, low-cost non-noble electrocatalyst for DMFCs. © 2021 Hydrogen Energy Publications LLC

Solution processed photodetectors with high responsivities and simple fabrication schemes are high on demand for variety of emerging opto-electronic applications. However, these devices suffer from sluggish response and recovery times. In this work, we demonstrate the simultaneous enhancement of the responsivity, response time and spectral range of detection in a solution-processed device based on organic/inorganic hybrid junction. A solution-processed flexible CdS photodetector is fabricated using a facile and economical chemical bath deposition technique. The fabricated pristine-CdS device exhibits responsivity and response time of 50 mA/W and 5.4 s. The resultant device exhibits enhanced responsivity and response time of around 740 mA/W and 0.6 s, respectively, upon modification with the PEDOT:PSS conducting polymer. These values of PEDOT-modified device are one order larger than pristine-CdS detector. Further, PEDOT:PSS modification also extends the responsivity of the device from UV-Vis to NIR spectra. NIR responsivity in the hybrid device, is imputed to the photothermal property of the PEDOT:PSS layer. Thus, the overall device spectral response is accredited to the simultaneous existence of photoelectric and photo-thermal phenomena. The observed responsivity and faster response time is ascribed primarily to the built-in potential at interface of CdS-PEDOT:PSS, which not only facilitates efficient separation of photo carriers but also leads to a reduction in the recombination of excitons. Given the simple approach and excellent enhancement in the device performance, the idea demonstrated here could be useful to design high performance opto-electronic device based on solution-processed techniques. © 2022 Elsevier B.V.

Self-powered biocompatible electronic devices to detect vital physiological signals of the human body are in great demand in wearable applications. In this work, a low-cost polydimethylsiloxane/polypyrrole composite polymer film-based piezoelectric nanogenerator is fabricated and utilized as a self-powered arterial pulse pressure sensor. XRD and Raman analysis are used to confirm the crystal structural orientation and chemical composition of composite polymer, respectively. Uniform and crack-free morphology of PDMS/PPy composite polymer film is confirmed via Field Emission Scanning Electron Microscopy, while Energy Dispersive X-Ray is used to study the elemental analysis of composite polymer film, which confirms that there is no extra impurity present in the system. A flexible and robust piezoelectric nanogenerator with device configuration of Al coated PET/(PDMS: PPy)/ ITO coated PET is fabricated that gives an output voltage of 12 V and current density of 0.11 µA/cm2 when 1.47 N/cm2 pressure is applied. The biocompatible nanogenerator as a self-powered pulse sensor is demonstrated, thus proving its potential for developing versatile self-powered systems useful in biomedical applications. © 2022

Enhanced carrier separation and inbuilt electric field are recommended to demonstrate self-powered, high-performance photodetectors. Traditionally, planar, bulk, and vertical heterojunctions are used for fabrication of photodetectors.In this work, we demonstrate a self-powered piezo-phototronic photodetector using a unique coaxial n-n heterojunction i.e., ZnSnO3/In2O3 core-shell nanofibers synthesized using electrospinning. The detailed morphological characterization reveals the formation of ZnSnO3 core and In2O3 shell nanofiber while structural studies confirm the non-centrosymmetric cubic In2O3, with a space group of I213 and rhombohedral ZnSnO3 with R3c space group. The Piezo force microscopy (PFM studies displayed a piezoelectric coefficient (d33) value of the ZnSnO3/In2O3 nanofibers was obtained as 254 pm/V. The fabricated piezo-phototronic device displays a superior photo-response upon illumination of UV light at zero bias owing to the built-in electric potential. The optimized UV photodetector displayed a large Ion/Ioff ratio of 102. Upon application of a compressive strain of 4.3%, the device exhibits an increase in photocurrent up to 58% and upon the tensile strain of 3.2%, the device shows a decrease in photocurrent up to 24%. The obtained results can be attributed to the enhanced carrier separation in the coaxial interfaces of ZnSnO3/In2O3 junctions, thus improving the ability to detect UV light. The fabricated device exhibits a maximum responsivity and detectivity of 0.7 mA/W and 8.3 × 109 Jones respectively which are far superior to the existing class of similar devices fabricated using sophisticated cleanroom techniques Further, a stable photo-response even after 1000 bending cycles proves its mechanical robustness. This work provides a promising strategy for improving the responsivity and detectivity of photodetectors as well as a unique coaxial nanostructure for self-powered, UV light detection for optoelectronic applications. © 2022 Elsevier Ltd

Sweat is one of the non-invasive diagnostic biofluids that provides critical information about human health. In this work, a wearable sweat sensor integrated with a polymer-based fluid absorption layer modified with titanium oxide (TiO2) nanoparticles decorated sodium niobate (NaNbO3) nanoflakes in porous polyvinyl alcohol (PVA) film matrix is demonstrated for the detection of vital metabolites (such as glucose and urea) and biomolecules (ascorbic acid (AA) and uric acid (UA)) in human sweat samples via surface-enhanced Raman scattering (SERS). The TiO2@NaNbO3/PVA (SERS patch) exhibits a low limit of detection (LOD) of 0.50, 0.80, 1.00, and 100 mm towards AA, glucose, UA, and urea, respectively. The SERS patch displays a high enhancement factor with a low accumulation time of 20s which can be ascribed to the surface coordination between the TiO2@NaNbO3 and the analytes leading to interfacial charge-transfer transition (ICTT). Besides, the photo-induced charge transfer (PICT) resonance significantly amplifies the SERS signal. The SERS patch is successful in the simultaneous determination of AA, glucose, UA, and urea in simulated sweat samples with minimal mutual interference. The high efficacy of the SERS patch proves it as an ideal platform for a wide range of wearable healthcare monitoring applications. © 2022 Wiley-VCH GmbH.

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 Fe2O3 nanoparticles is fabricated. NiO nanofibers were synthesized via economical and scalable electro-spinning technique and made composite with Fe2O3 nanoclusters for hetero-structure fabrication. The optical absorption spectra of NiO nanofibers and Fe2O3 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-Fe2O3 device also exhibits excellent detectivity in the order of 1012 jones. The superior performance of the device is ascribed to the type-II heterojunction between NiO-Fe2O3 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.

Piezoelectric materials are used to degrade organic pollutants in water under ultrasonic vibration. However, in particulate form, it limits recyclability and reuse. On the other hand, a polymer-based device suffers from low piezo-catalytic performance. This work reports a free-standing, non-toxic, retrievable and reusable polyvinylidene fluoride (PVDF)-[0.67BiFeO3–0.33BaTiO3] (BF33BT) composite mold for fast degradation of complex organic dyes. BF33BT nanoparticles and PVDF-BF33BT composite mold were synthesized using the sol-gel and solvent casting methods. The optimized composite mold degrades 5 mg.L−1 of methylene blue, rhodamine B, and crystal violet up to 98 %, 91 %, and 88 %, respectively, in 40 min. The superior performance is attributed to the combined piezoelectric property of PVDF and BF33BT, which enhances the production of reactive oxygen species. The mold can be used up to 10 times with negligible loss in efficiency, hence presenting a low-cost strategy for the degradation of complex dyes found in industrial effluents for remediation. © 2022 Elsevier Ltd

Textile-based energy storage devices help realize the full potential of flexible electronics as they combine the functionality of wearable devices with the inherent high-power density and fast charging/discharging capability of supercapacitors. In this work, Nickel di-selenide (NiSe2) is grown on carbon cloth (CC) via a facile one-pot hydrothermal technique and is used for supercapacitor and pressure sensor to demonstrate a textile-based fully integrated system. In a three-electrode configuration, the NiSe2 electrode produces a half-cell specific capacitance of 980 Fg−1 at 1 Ag−1, indicating its high-rate capability. Further, the NiSe2 electrode is combined with activated carbon (AC) electrodes generated from biomass to construct an asymmetric supercapacitor device (ASC) with a 1.6 V of output voltage. The ASC device delivers maximum specific energy of 50 Whkg−1 at a current density of 1 Ag−1 and a maximum specific power of 900 Wkg−1 at 10 Ag−1. An ultra-sensitive pressure sensor is fabricated by sandwiching the NiSe2 grown carbon cloth between thin layers of PDMS, which exhibits a sensitivity of 0.91 kPa−1 in the wide dynamic pressure range of 1– 80 kPa−1. An exceptional mechanical stability is obtained for an unloading/loading of 1 kPa of pressure for 5000 cycles. Further, it is powered using the NiSe2/CC || AC/CC AFSC for steady and reliable detection of radial pulse pressure on the human wrist in real-time. This work paves a new path in exploring the potential of textiles when combined with nanomaterials to develop low-cost, self-powered healthcare systems for real-time monitoring of health parameters. © 2022 Elsevier Ltd

Most inorganic photodetectors are rigid and have narrow intrinsic bandgap, which severely limits their application in next generation flexible electronics. To overcome this issue, this work reports a flexible, biocompatible, organic-photodetector based on solution processed Ppy nanospheres deposited over 3D-hierarchical macro-porous Ni foam substrate using ultrasonic irradiation technique. The Ni foam substrate is used as buffering layer to bond with organic polypyrrole which has outstanding flexible photoelectric character. Morphological studies reveal the uniform growth of Ppy nanospheres over the porous Ni foam substrate that provides a large surface to volume ratio for efficient interaction of photons. Optical studies show excellent absorption in the UV region and a soret peak in the visible region while structural studies confirm the formation of polypyrrole with C=C stretching and C=N stretching modes. The Ppy/Ni foam-based photodetector displays excellent response with responsivity of 6.5 A/W, 5.4 A/W and 17.3 A/W in the UV, visible and NIR region of the spectrum, respectively for a minimum bias voltage of 1 mV. The spectral detectivity of the device was obtained as 1011 Jones demonstrating a least noise equivalent power. The acquired performance can be attributed to the synergistic effect of photon excitation as well as molecular-phonon vibration upon illumination of light. A maximum EQE of 27.56 was achieved for NIR light owing to the trap-assisted charge carrier tunneling injection from the Ppy/Ni interface. The solution processed Ppy/Ni foam photodetector proves to be a better alternative for broad band photodetection over previously reported organic photodetectors fabricated using sophisticated techniques. The strategy employed here paves new path for synthesis and fabrication of organic photodetectors towards optoelectronic applications. © 2021

Supercapacitors are generally high-power devices, yet their energy is low in contrast to batteries. In the present study, the N-doped porous carbon optimized from brinjal bio-mass waste (solanum melongena) using KOH+ Urea activation confirms its ability as a supercapacitor electrode in presence of an aqueous (1 M H2SO4), ionic liquid (1-ethyl-3-methylimidazolium-tetrafluoroborate-EMIMBF4) and an improved redox additive (0.01 M Hydroquinone-HQ) electrolytes. The hierarchical porous nature of the activated brinjal bio-mass waste carbon with desired compositions and structure is analyzed using FE-SEM and HR-TEM analysis. In a two electrodes symmetric configuration, brinjal waste-derived activated carbon (BC-700) delivers a high specific capacitance of 460 F/g at 1 A/g in 1 M H2SO4 aqueous electrolyte. In ionic liquid, it delivers 133 F/g high specific capacitance with an energy of 41 Wh/kg. This outstanding electrochemical performance is due to the electrolyte-ion movement of heteroatoms into the carbon matrix resulting in high specific surface area (850 m2 g−1) and effective microporosity. The energy density of the supercapacitor device is further enriched using the novel redox additive 0.01 M Hydroquinone in H2SO4 electrolyte with a specific capacity of 888 C/g and a maximum energy density of 61 Wh/kg, which is very high compared to batteries. Outstanding cyclic stability of 77 % capacitance retention after 5000 cycles is achieved in HQ-added aqueous electrolyte. Hence, the bio-mass waste-derived activated carbon performs as an excellent low-cost material for various electrochemical applications. © 2022 Elsevier Ltd

Hybrid organic-inorganic composites offer solution processability and ease to construct opto-electronic devices with diverse functionalities, which are desirable for applications like flexible and printed electronics. Trigonal Selenium (t-Se) has been recently investigated for photodetector application, owing to its inherent superior optical properties such as high absorption coefficient and photoconductivity. However, most of the reported Selenium photodetectors use vapor transport based device fabrication techniques which require controlled environments and face scalability issues. In this work, high-performance photodetector based on Selenium-PEDOT:PSS hybrid junction is demonstrated using a facile sonication assisted mechanical mixing and drop-casting technique. XRD and Raman analysis reveals the existence of Selenium in trigonal crystal structure and FE-SEM images show clustered nanoparticles. Selenium is mixed with PEDOT:PSS to form bulk heterojunction, which enhances the electron-hole pair separation efficiency and results in improved device responsivity. Also, due to the favorable band offset between Selenium and PEDOT:PSS which results in built-in field, the photodetector operates in self-biased mode. The device exhibits broad spectral response in UV–Vis–NIR range with responsivities of 0.56 A/W, 66 mA/W and 1.363 A/W at 315 nm, 620 nm and 820 nm, respectively. Response times of 7.7 s, 9.4 s and 6.4 s and external quantum efficiencies (EQE) of 192.58%, 13.25% and 206.55% are obtained for UV, Vis and NIR spectra respectively. Further to validate the robustness, the device is subjected to multiple bending cycles (∼2500) and minimal degradation in performance is observed. Given the simple device architecture and facile device fabrication scheme, this work would enable promising approach for high performance flexible photodetectors. © 2022 Elsevier B.V.

Traditionally, two different techniques have been used to enhance the spectral operating range of a photodetector, i.e., either combining materials of different bandgaps or combining semiconductor materials to form tertiary alloys. However, these methods involve multiple synthesis/processing steps and complex clean room-based fabrication. Addressing this, a simple and novel step in device architecture is demonstrated by surface engineering of Cu buffer layer in between a paper substrate and Cu2S to develop a highly responsive photodetector with tunable operating range. Cu2S nanoparticles were grown directly on the surface of Cu pre-deposited paper substrate using facile hydrothermal technique to obtain Ag/Cu2S/Ag - metal semiconductor metal (MSM) configuration on Cu/paper substrate. The morphological characterization revealed the uniform distribution of Cu2S nanoparticles on the surface of cellulose microfibers and the structural studies confirmed the formation of highly crystalline cubic - Cu2S with Cu-S stretching vibrations. In comparison to the pristine Ag/Cu2S/Ag on paper photodetector, the buffer-based Ag/Cu/Cu2S/Ag photodetector displayed excellent response from visible to NIR region. A superior responsivity and detectivity of 27 mA/W and 2.5 ×108 Jones respectively are observed for Cu buffer/Cu2S photodetector. The obtained response of the paper/Cu/Cu2S device can be attributed to the synergistic combination of Cu buffer layer induced reduction of defect sites and LSPR induced transfer of electrons from the Cu metal to Cu2S. The paper-based photodetector displayed a fast response time of 0.09 sec, and excellent mechanical stability and durability for 1000 bending cycles. The surface engineering of a buffer layer in the photodetector architecture certainly bridges a technological gap and presents a new strategy for development of high-performance optoelectronic devices. © 2022 Elsevier B.V.

We present a one-step, solid-state synthesis of Al2NiCoO5 nanoflakes (ANC) modified glassy carbon electrode (GCE) for ultra-selective and trace level simultaneous detection of HMIs like copper (Cu2+), mercury (Hg2+), cadmium (Cd2+), and lead (Pb2+) ions in aqua and simulated blood serum samples. ANC/GCE sensor exhibits a low limit of detection (LOD = 3S/m) of 0.00154 ppb, 0.00232 ppb, 0.00261 ppb and 0.00114 ppb towards Pb2+, Hg2+ Cu2+ and Cd2+ ions, correspondingly that are far lower than the perilous limits of HMI concentration reported for blood serum and water samples. The quantitative study and multiple response analysis of the sensor towards each metal ions are accomplished via principal component analysis (PCA) which verifies the selectivity of the ANC/GCE sensor with satisfactory recovery percentages. The superior performance, reproducibility and stability of the sensor are attributed to the electrocatalytic active sites of ANC nanoflakes facilitated by the Ni2+/Ni3+ and Co2+/Co3+ redox couple along with the oxy-functional groups. The sensor was efficacious in detecting the trace level concentrations of HMIs in samples like simulated blood serum, drinking water and tap water with good recovery percentages. This efficiency of the sensor demonstrates it as a promising platform for a broad-spectrum of environmental and bioanalytical applications. © 2022 The Author(s)