Marine oil spills have induced severe water pollution and threatened sea ecosystems, which also result in a loss of energy resources. To deal with this problem, much work has been done for using superhydrophobic or superhydrophilic mesh for oil–water separation. Nevertheless, there are still great challenges in the rapid fabrication of extremely durable mesh with superwetting properties, particularly considering the highly efficient oil–water separation. In this study, we present a simple, efficient method to fabricate superhydrophilic and underwater superoleophobic stainless steel mesh surfaces with one-step femtosecond laser induced periodic nanoripple structures. The as-prepared mesh shows high separation efficiency, which is higher than 99% for various oil–water mixtures. More importantly, the wettability and the separation efficiency of the fabricated mesh show no obvious change after the abrasion tests and corrosion tests, indicating that the as-prepared samples possess robust stability. This study provides an efficient route for constructing durable and highly efficient separation mesh, which can be applied in the cleanup of large-scale oil spills in the near future.

Femtosecond laser induced robust periodic nanoripple structured mesh for highly efficient oil–water separation

DOI: 10.1002/adom.201801433 Scientific American selects plasmonic sensing as the top 10 emerging technologies of 2018.[15] Almost every single new plasmonic or photonic structure would be explored to test its sensing ability.[16–29] These works tend to report the sensing performance of their own structure. Some declare that their sensitivity breaks the world record. However, there is still a missing literature on what the world record really is, the gap between the experiments and the theoretical limit, as well as the differences between metal-based plasmonic sensors and dielectric-based photonic sensors. To push plasmonic and photonic sensors into industrial applications, an optical sensing technology map is absolutely necessary. This review aims to cover a wide range of most representative plasmonic and photonic sensors, and place them into a single map. The sensor performances of different structures will be distinctly illustrated. Future researchers could plot the sensing ability of their new sensors into this technology map and gauge their performances in this field. In this review, we focus on optical refractive index (RI) sensors with no fluorescent labeling required. We will utilize two parameters to characterize and compare the performance of optical RI sensors: sensitivity to RI change (denoted by symbol SRI) and figure of merit (in short, FoM). For simplicity, we restrict our discussions to bulk RI change, where the change in RI occurs within the whole sample. There is another case where the RI variation occurs only within a very small volume close to the sensor surface. This surface RI sensitivity is proportional to the bulk RI sensitivity, the ratio of the thickness of the layer within which the surface RI variation occurs, and the penetration depth of the optical mode.[6] The bulk RI sensitivity defines the ratio of the change in sensor output (e.g., resonance angle, intensity, or resonant wavelength) to the bulk RI variations. Here, we limit our discussions to the spectral interrogations and the bulk RI sensitivity SRI is given by[3,5–7,30]

Optical Refractive Index Sensors with Plasmonic and Photonic Structures: Promising and Inconvenient Truth

This is the first comprehensive review on methods and materials for use in optical sensing of pH values and on applications of such sensors. The Review starts with an introduction that contains subsections on the definition of the pH value, a brief look back on optical methods for sensing of pH, on the effects of ionic strength on pH values and pKa values, on the selectivity, sensitivity, precision, dynamic ranges, and temperature dependence of such sensors. Commonly used optical sensing schemes are covered in a next main chapter, with subsections on methods based on absorptiometry, reflectometry, luminescence, refractive index, surface plasmon resonance, photonic crystals, turbidity, mechanical displacement, interferometry, and solvatochromism. This is followed by sections on absorptiometric and luminescent molecular probes for use pH in sensors. Further large sections cover polymeric hosts and supports, and methods for immobilization of indicator dyes. Further and more specific sections summarize the state of the art in materials with dual functionality (indicator and host), nanomaterials, sensors based on upconversion and 2-photon absorption, multiparameter sensors, imaging, and sensors for extreme pH values. A chapter on the many sensing formats has subsections on planar, fiber optic, evanescent wave, refractive index, surface plasmon resonance and holography based sensor designs, and on distributed sensing. Another section summarizes selected applications in areas, such as medicine, biology, oceanography, bioprocess monitoring, corrosion studies, on the use of pH sensors as transducers in biosensors and chemical sensors, and their integration into flow-injection analyzers, microfluidic devices, and lab-on-a-chip systems. An extra section is devoted to current challenges, with subsections on challenges of general nature and those of specific nature. A concluding section gives an outlook on potential future trends and perspectives.

Optical Sensing and Imaging of pH Values: Spectroscopies, Materials, and Applications

Fog collection is receiving increasing attention for providing water in semi-arid deserts and inland areas. Inspired by the fog harvesting ability of the hydrophobic-hydrophilic surface of Namib desert beetles, we present a simple, low-cost method to prepare a hybrid superhydrophobic-hydrophilic surface. The surface contains micro/nanopatterns, and is prepared by incorporating femtosecond-laser fabricated polytetrafluoroethylene nanoparticles deposited on superhydrophobic copper mesh with a pristine hydrophilic copper sheet. The as-prepared surface exhibits enhanced fog collection efficiency compared with uniform (super)hydrophobic or (super)hydrophilic surfaces. This enhancement can be tuned by controlling the mesh number, inclination angle, and fabrication structure. Moreover, the surface shows excellent anti-corrosion ability after immersing in 1 M HCl, 1 M NaOH, and 10 wt% NaCl solutions for 2 hours. This work may provide insight into fabricating hybrid superhydrophobic-hydrophilic surfaces for efficient atmospheric water collection.

A simple way to achieve bioinspired hybrid wettability surface with micro/nanopatterns for efficient fog collection.

Ambipolar or bipolar transistors are transistors in which both holes and electrons are mobile inside the conducting channel. This device allows switching among several states: the hole-dominated on-state, the off-state, and the electron-dominated on-state. In the past year, it has attracted great interest in exotic semiconductors, such as organic semiconductors, nanostructured materials, and carbon nanotubes. The ability to utilize both holes and electrons inside one device opens new possibilities for the development of more compact complementary metal-oxide semiconductor (CMOS) circuits, and new kinds of optoelectronic device, namely, ambipolar light-emitting transistors. This progress report highlights the recent progresses in the field of ambipolar transistors, both from the fundamental physics and application viewpoints. Attention is devoted to the challenges that should be faced for the realization of ambipolar transistors with different material systems, beginning with the understanding of the importance of interface modification, which heavily affects injections and trapping of both holes and electrons. The recent development of advanced gating applications, including ionic liquid gating, that open up more possibility to realize ambipolar transport in materials in which one type of charge carrier is highly dominant is highlighted. Between the possible applications of ambipolar field-effect transistors, we focus on ambipolar light-emitting transistors. We put this new device in the framework of its prospective for general lightings, embedded displays, current-driven laser, as well as for photonics-electronics interconnection.

Outlook and emerging semiconducting materials for ambipolar transistors.

A fiber Mach–Zehnder interferometer (MZI) sensor, novel to our knowledge, based on a single “S”-like fiber taper has been fabricated via applying nonaxial pull in fiber tapering by a fusion splicer. The typical feature size of the structure has a length of 660 μm and the axial offset of 96 μm. This S fiber taper MZI has a refractive index (RI) sensitivity of 1590 nm/refractive index unit in the RI range of 1.409–1.425 and a strain sensitivity of about −60 pm/microstrain, which is 30 times higher than that of the normal two-taper-based MZI sensors.

Single S-tapered fiber Mach-Zehnder interferometers.

An S-tapered fiber sensor has been realized on the common single-mode fiber by a fusion splicer. The S fiber taper (SFT) can be considered as a compact fiber Mach-Zehnder interferometer with the total length of hundreds of microns. The spectral characteristics of the SFTs with different structure parameters including axial offsets and taper waist diameters have been studied. Sensing experiments have also been carried out to test their response to refractive index (RI) and axial strain. The SFT with an axial offset of 114 μm and a taper waist diameter of 54.6 μm exhibits the best combination property. Its RI sensitivity reaches as high as 2066 nm/RI unit in the RI range of 1.407-1.421 and the average strain sensitivity is -183.4 pm/μe, which is the highest strain sensitivity, to the best of our knowledge, with one or two orders of magnitude larger than the existing fiber strain sensors.

S-Tapered Fiber Sensors for Highly Sensitive Measurement of Refractive Index and Axial Strain

Organic crystals have great potential for the applications in laser devices. This article presents an effective approach for fabrication of distributed feedback single crystal lasers. With the laser interference ablation method, high quality grating structures have been fabricated on the organic single-crystalline thin film materials. The relationship between the depth, periodicity, and laser fluence is discussed. The optical properties, such as photoluminescence, and diffractive properties are studied in detail. With the appropriate period, strong laser emission has been observed from these devices. Distributed feedback lasing is demonstrated from the laser interference ablated organic single crystals for the first time.

Distributed Feedback Lasers Based on Thiophene/Phenylene Co-Oligomer Single Crystals

We demonstrate an ultrasensitive temperature sensor based on an isopropanol-sealed optical microfiber taper (OMT) in a capillary. The OMT is highly sensitive to ambient refractive index (RI) with a maximum sensitivity of 18989  nm/RI unit in the range of 1.3955–1.4008. The thermo-optic effect of isopropanol and the thermal expansions of the sealant and sealed liquid turn the OMT into an ultrasensitive temperature sensor with the maximum sensitivity of −3.88  nm/°C in the range of 20°C–50°C. The temperature sensitivity contributions from different mechanisms are also investigated theoretically and experimentally.

Ultrasensitive temperature sensor based on an isopropanol-sealed optical microfiber taper.

We have demonstrated an end-of-fiber polydimethylsiloxane (PDMS) cap based fiber Fabry-Perot interferometer in this letter, which could be used for simultaneous measurement of refractive index (RI) and temperature with extremely low cross sensitivity. The RI and temperature sensitivities of the interferometer are -240.425 dB/RI unit based on extinction ratio measurement in the RI range of 1.3625-1.4150 and 385.46 pm/°C in the temperature range of 25°C-60°C, respectively. Not only does the interferometer have the characteristics of high sensitivity and low cost, but also PDMS has a good biocompatibility, so that the sensor can be used as a cell culture or bacteria growth detection probe.

Rui Yang

Papers

Single S-tapered fiber Mach-Zehnder interferometers.

S-Tapered Fiber Sensors for Highly Sensitive Measurement of Refractive Index and Axial Strain

Distributed Feedback Lasers Based on Thiophene/Phenylene Co-Oligomer Single Crystals

Ultrasensitive temperature sensor based on an isopropanol-sealed optical microfiber taper.

Miniature End-Capped Fiber Sensor for Refractive Index and Temperature Measurement