Wearable electronics is expected to be one of the most active research areas in the next decade; therefore, nanomaterials possessing high carrier mobility, optical transparency, mechanical robustness and flexibility, lightweight, and environmental stability will be in immense demand. Graphene is one of the nanomaterials that fulfill all these requirements, along with other inherently unique properties and convenience to fabricate into different morphological nanostructures, from atomically thin single layers to nanoribbons. Graphene-based materials have also been investigated in sensor technologies, from chemical sensing to detection of cancer biomarkers. The progress of graphene-based flexible gas and chemical sensors in terms of material preparation, sensor fabrication, and their performance are reviewed here. The article provides a brief introduction to graphene-based materials and their potential applications in flexible and stretchable wearable electronic devices. The role of graphene in fabricating ...

Flexible Graphene-Based Wearable Gas and Chemical Sensors

Electrically–transduced sensors, with their simplicity and compatibility with standard electronic technologies, produce signals that can be efficiently acquired, processed, stored, and analyzed. Two dimensional (2D) nanomaterials, including graphene, phosphorene (BP), transition metal dichalcogenides (TMDCs), and others, have proven to be attractive for the fabrication of high–performance electrically-transduced chemical sensors due to their remarkable electronic and physical properties originating from their 2D structure. This review highlights the advances in electrically-transduced chemical sensing that rely on 2D materials. The structural components of such sensors are described, and the underlying operating principles for different types of architectures are discussed. The structural features, electronic properties, and surface chemistry of 2D nanostructures that dictate their sensing performance are reviewed. Key advances in the application of 2D materials, from both a historical and analytical pers...

Electrically-Transduced Chemical Sensors Based on Two-Dimensional Nanomaterials

Unraveling the role of surface oxide on affecting its native metal disulfide’s CO2 photoreduction remains a grand challenge. Herein, we initially construct metal disulfide atomic layers and hence deliberately create oxidized domains on their surfaces. As an example, SnS2 atomic layers with different oxidation degrees are successfully synthesized. In situ Fourier transform infrared spectroscopy spectra disclose the COOH* radical is the main intermediate, whereas density-functional-theory calculations reveal the COOH* formation is the rate-limiting step. The locally oxidized domains could serve as the highly catalytically active sites, which not only benefit for charge-carrier separation kinetics, verified by surface photovoltage spectra, but also result in electron localization on Sn atoms near the O atoms, thus lowering the activation energy barrier through stabilizing the COOH* intermediates. As a result, the mildly oxidized SnS2 atomic layers exhibit the carbon monoxide formation rate of 12.28 μmol g–1 ...

Partially Oxidized SnS2 Atomic Layers Achieving Efficient Visible-Light-Driven CO2 Reduction

The alarming rise of indoor pollution and the need to combat the associated negative effects have promoted increasing attention in modernizing the chemical sensing technologies by newly designed materials with rich and tunable functionalities at atomic or molecular levels. With the appealing physical, chemical, optical, and electronic properties for various potential applications, the state-of-art gas-sensing nanomaterials and their future perspectives are well-documented and summarized in this paper. Specifically, the key performance attributes are addressed in detail such as the sensitivity, selectivity, reversibility, operating temperature, response time, and detection limit. As such, this review provides both critical insights in exploring and understanding various gas sensing nanomaterials and points out limitations and opportunities for further developments, such as morphology control, doping and surface alteration, atomic-scale characterization, and applications in different fields. Finally, the challenges and outlooks are discussed on the basis of the current developments.

Functional gas sensing nanomaterials: A panoramic view

In this work, three-dimensional (3D) hierarchical In2O3@SnO2 core-shell nanofiber (In2O3@SnO2) was designed and successfully prepared via a facile electrospinning and further hydrothermal methods. Vertically aligned SnO2 nanosheets uniformly grown on the outside surface of In2O3 nanofibers were clearly observed by field emission scanning electron microscopy. Besides, hierarchical core-shell nanostructure of In2O3@SnO2 was characterized by elemental maps using scanning transmission electron microscopy. The formaldehyde (HCHO) sensing performances of pure In2O3 nanofibers, SnO2 nanosheets, and In2O3@SnO2 core-shell nanocomposite were compared, and the In2O3@SnO2 nanocomposite possessed highest response value, fast response/recovery speed, best selectivity, and lowest HCHO detection limit. Specifically, the response value (Ra/Rg) of the In2O3@SnO2 nanocomposite reached 180.1 toward 100 ppm of HCHO gas, which was near 9 and 6 times higher than that of the pure In2O3 nanofibers (Ra/Rg = 19.7) and pure SnO2 nanosheets (Ra/Rg = 33.2), respectively. In addition, the gas sensor showed instantaneous response/recovery time (3/3.6 s) toward 100 ppm of HCHO at the optimal operation temperature of 120 °C. More importantly, the detection limit toward HCHO gas was as low as 10 ppb (Ra/Rg = 1.9), which could be used for trace HCHO gas detection. The excellent sensing properties of the In2O3@SnO2 were attributed to the synergistic effect of large specific surface areas of SnO2 nanosheet arrays, abundant adsorbed oxygen species on the surface, unique electron transformation between core-shell heterogeneous materials, and long electronic transmission channel of SnO2 transition layer. This work provides an efficient route for the preparation of novel hierarchical sensitive materials.

Hierarchical In2O3@SnO2 Core-Shell Nanofiber for High Efficiency Formaldehyde Detection.

We report a one step facile hydrothermal synthesis of layered SnS2 nanoflakes The as-synthesized nanosheets are characterized using X-ray diffraction, Raman spectroscopy and Transmission Electron Microscopy (TEM) The humidity sensing behavior of SnS2 nanoflake sensor device were investigated in the range of 11–97% of relative humidity (RH) at room temperature The response time of ∼85 s and recovery time of ∼6 s were observed for the SnS2 nanoflake based humidity sensor A maximum sensitivity of 11 300% is recorded We also investigate the SnS2 nanoflake based alcohol sensing properties towards methanol, ethanol and iso-propyl alcohol An exclusive selectivity towards methanol with a response of 1580 is shown as compared to other analytes The response time of ∼67 s and recovery time of just 5 s were observed for the SnS2 nanoflake based methanol sensor

SnS2 nanoflakes for efficient humidity and alcohol sensing at room temperature

Impedimetric detection of Pseudomonas aeruginosa attachment on flexible ITO-coated polyethylene terephthalate substrates

Ultrasound-enhanced drug delivery has shown great promise in providing targeted burst release of drug at the site of the disease. Yet current solid ultrasound-responsive particles are non-degradable with limited potential for drug-loading. Here, we report on an ultrasound-responsive multi-cavity poly(lactic-co-glycolic acid) microparticle (mcPLGA MP) loaded with rhodamine B (RhB) with or without 4′,6-diamidino-2-phenylindole (DAPI) to represent small molecule therapeutics. After exposure to high intensity focused ultrasound (HIFU), these delivery vehicles were remotely implanted into gel and porcine tissue models, where the particles rapidly released their payload within the first day and sustained release for at least seven days. RhB-mcPLGA MPs were implanted with HIFU into and beyond the sub-endothelial space of porcine arteries without observable damage to the artery. HIFU also guided the location of implantation; RhB-mcPLGA MPs were only observed at the focus of the HIFU away from the direction of ultrasound. Once implanted, DAPI co-loaded RhB-mcPLGA MPs released DAPI into the arterial wall, staining the nucleus of the cells. Our work shows the potential for HIFU-guided implantation of drug-loaded particles as a strategy to improve the local and sustained delivery of a therapeutic for up to two weeks.

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Remote targeted implantation of sound-sensitive biodegradable multi-cavity microparticles with focused ultrasound

Bacterial biofilms are typically more tolerant to antimicrobials compared to bacteria in the planktonic phase and therefore require alternative treatment approaches. Mechanical biofilm disruption from ultrasound may be such an alternative by circumventing rapid biofilm adaptation to antimicrobial agents. Although ultrasound facilitates biofilm dispersal and may enhance the effectiveness of antimicrobial agents, the resulting biological response of bacteria within the biofilms remains poorly understood. To address this question, we investigated the microstructural effects of Pseudomonas aeruginosa biofilms exposed to high intensity focused ultrasound (HIFU) at different acoustic pressures and the subsequent biological response. Confocal microscopy images indicated a clear microstructural response at peak negative pressures equal to or greater than 3.5 MPa. In this pressure amplitude range, HIFU partially reduced the biomass of cells and eroded exopolysaccharides from the biofilm. These pressures also elicited a biological response; we observed an increase in a biomarker for biofilm development (cyclic-di-GMP) proportional to ultrasound induced biofilm removal. Cyclic-di-GMP overproducing mutant strains were also more resilient to disruption from HIFU at these pressures. The biological response was further evidenced by an increase in the relative abundance of cyclic-di-GMP overproducing variants present in the biofilm after exposure to HIFU. Our results, therefore, suggest that both physical and biological effects of ultrasound on bacterial biofilms must be considered in future studies.

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Lakshmi Deepika Bharatula

Papers

SnS2 nanoflakes for efficient humidity and alcohol sensing at room temperature

Impedimetric detection of Pseudomonas aeruginosa attachment on flexible ITO-coated polyethylene terephthalate substrates

Remote targeted implantation of sound-sensitive biodegradable multi-cavity microparticles with focused ultrasound

Influence of High Intensity Focused Ultrasound on the Microstructure and c-di-GMP Signaling of Pseudomonas aeruginosa Biofilms.

Unsupported gold nanocones as sonocatalytic agents with enhanced catalytic properties.