Detection of organic dyes using Ag NPAs/SMP SERS substrate produced via sandpaper template-assisted lithography and liquid-liquid interface self-assembly.

Surface-enhanced Raman spectroscopy (SERS) is a highly sensitive and reliable fingerprinting technique. However, its analytical capability is closely related to the quality of a SERS substrate used for the analysis. In particular, conventional colloidal substrates possess disadvantages in terms of controllability, stability, and reproducibility, which limit their application. In order to address these issues, a simple, cost-effective, and efficient SERS substrate based on silver nanoparticle arrays (Ag NPAs) and sandpaper-molded polydimethylsiloxane (SMP) was proposed in this work. Successfully prepared via template lithography and liquid-liquid interface self-assembly (LLISA), the substrate can be applied to the specific detection of organic dyes in the environment. The substrate exhibited good SERS performance, and the limit of detection (LOD) of rhodamine 6G (R6G) was shown to be 10-7 M under the optimal conditions (1000 grit sandpaper) with a relative standard deviation (RSD) of 7.76%. Moreover, the SERS signal intensity was maintained at 60% of the initial intensity after the substrate was stored for 30 days. In addition, the Ag NPAs/SMP SERS substrate was also employed to detect crystal violet (CV) and methylene blue (MB) with the LODs of 10-6 M and 10-7 M, respectively. In summary, the Ag NPAs/SMP SERS substrate prepared in this study has great potential for the detection of organic dyes in ecological environments.

Fabrication of Micro-Cantilever Sensor Based on Clay Minerals for Humidity Detection.

In this paper, novel humidity sensors based on montmorillonite, kaolinite, and composite films coated on micro-cantilevers were prepared to measure the relative humidity (RH) values by the deflection of a micro-cantilever (MC) at room temperature. The humidity-sensing properties, such as response and recovery, sensitivity, repeatability, humidity hysteresis, and long-term stability, were investigated in the range of working humidity (10-80% RH). The humidity response in the close humidity range of 10% RH to 80% RH revealed a linear increase in water absorption of montmorillonite, kaolinite, and montmorillonite/kaolinite mixed dispersant (1:1) as a function of RH with linear correlation factors between the humidity change and deflection estimated to be 0.994, 0.991, and 0.946, respectively. Montmorillonite's sensitivity was better than kaolinite's, with the mixed-clay mineral film's response falling somewhere in between. This research provides a feasible and effective approach to constructing high-performance MC humidity sensors that can be operated at room temperature based on clay minerals.

A Carbonylated Terthiophene-Based Twisted Polymer for Efficient Ternary Polymer Solar Cells.

In polymer solar cells (PSCs), it is difficult for twisted conjugated polymers to achieve high power-conversion efficiency (PCE) as donors due to their low charge carrier mobilities and poor bulk heterojunction morphologies. In this work, a new twisted conjugated polymer (P3TCO-1) with excellent solubilities (above 30 mg mL-1 ) in common organic solvents at room temperature is reported. UV-visible absorption spectra and cyclic voltammetry indicate that P3TCO-1 has a wide optical bandgap of 1.90 eV and deep HOMO level of -5.39 eV. In binary PSCs, P3TCO-1:ITIC-based device shows a PCE of 10.11%, with JSC of 17.05 mA cm-2 and FF of 62.89%; P3TCO-1:PC71 BM-based device gives a PCE of 6.67% with JSC of 12.31 mA cm-2 and FF of 58.00%. When the two acceptors of ITIC and PC71 BM are combined, the twisted P3TCO-1-based ternary PSCs exhibit a significantly boosted PCE of up to 11.41%, with a simultaneously improved JSC of 18.16 mA cm-2 and FF of 66.78%. These results can guide the improvement of PCE for twisted conjugated polymer-based PSCs.

Electrodeposition Synthesis of Coral-like MnCo Selenide Binder-Free Electrodes for Aqueous Asymmetric Supercapacitors.

Bimetallic selenide compounds show great potential as supercapacitor electrode materials in energy storage and conversion applications. In this work, a coral-like MnCo selenide was grown on nickel foam using a facile electrodeposition method to prepare binder-free supercapacitor electrodes. The heating temperature was varied to tune the morphology and crystal phase of these electrodes. Excellent electrochemical performance was achieved due to the unique coral-like, dendritic- dispersed structure and a bimetallic synergistic effect, including high specific capacitance (509 C g-1 at 1 A g-1) and outstanding cycling stability (94.3% capacity retention after 5000 cycles). Furthermore, an asymmetric supercapacitor assembled with MnCo selenide as the anode and active carbon as the cathode achieved a high specific energy of 46.2 Wh kg-1 at 800 W kg-1. The work demonstrates that the prepared coral-like MnCo selenide is a highly promising energy storage material.

One-Step Hydrothermal Strategy for Preparation of a Self-Cleaning TiO2/SiO2 Fiber Membrane toward Oil-Water Separation in a Complex Environment.

Oil pollution caused by a large number of industrial activities and oil spill accidents has posed serious harm to the environment and human health. However, some challenges remain with the existing separation materials, such as poor stability and fouling resistance. Herein, a TiO2/SiO2 fiber membrane (TSFM) was prepared by a one-step hydrothermal method for oil-water separation in acid, alkali, and salt environments. The TiO2 nanoparticles were successfully grown on the fiber surface, endowing the membrane with superhydrophilicity/underwater superoleophobicity. The as-prepared TSFM exhibits high separation efficiency (above 98%) and separation fluxes (3016.38-3263.45 L·m-2·h-1) for various oil-water mixtures. Importantly, the membrane shows good corrosion resistance in acid, alkaline, and salt solutions and still maintains underwater superoleophobicity and high separation performance. The TSFM displays good performance after repeated separation, demonstrating its excellent antifouling ability. Importantly, the pollutants on the membrane surface can be effectively degraded under light radiation to restore its underwater superoleophobicity, showing the unique self-cleaning ability of the membrane. In view of its good self-cleaning ability and environmental stability, the membrane can be used for wastewater treatment and oil spill recovery and has a broad application prospect in water treatment in complex environments.

Stretchable and Flexible Micro-Nano Substrates for SERS Detection of Organic Dyes.

Surface-enhanced Raman spectroscopy (SERS) is a precise and noninvasive analytical technique to identify vibrational fingerprints of trace analytes with sensitivity down to the single-molecule level. However, substrates can influence this capability, and current SERS techniques lack uniform, reproducible, and stable substrates to control plasma hot spots over a wide spectral range. Herein, we demonstrate a flexible SERS substrate via longitudinal stretching of a polydimethylsiloxane (PDMS) film. This substrate, after stretching and shrinking, exhibits an irregular wrinkled structure with abundant gaps and grooves that function as hot spots, thereby improving the hydrophobic properties of the material. To investigate the enhancement effect of Raman signals, silver nanoparticles (AgNPs) were mixed with Rhodamine 6G (R6G) solution, and the obtained blend was dropped onto the PDMS film to form a coffee ring pattern. According to the results, the hydrophobicity of the substrate increases with the degree of PDMS stretching, achieving the optimal level at 150% stretching. Moreover, the increase in hydrophobicity makes the measured molecules more aggregated, which enhances the Raman signal. The stretching and shrinkage of the PDMS film lead to a much higher density of nanogaps among nanoparticles and nanogrooves, which serve as multiple hot spots. Being highly localized regions of intense local fields, these hot spots make a significant contribution to SERS performance, improving the sensitivity and reproducibility of the method. In particular, the relative standard deviation (RSD) was found to be 2.5544%, and the detection limit was 1 × 10-7 M. Therefore, SERS using stretchable and flexible micro-nano substrates is a promising way for detecting dyes in wastewater.

Ulothrix-Derived Sulfur-Doped Porous Carbon for High-Performance Symmetric Supercapacitors.

With the demand for carbon dioxide emission reduction, the sustainable conversion of useless biomass into high-value energy storage devices has received excellent scientific and technological attention. The high synthesis cost and low specific capacitance limited the supercapacitor application. Therefore, biomass-derived sulfur-doping porous carbon (SPC) has been synthesized from ulothrix using simple pyrolysis and chemical activation methods. The unique activated carbon material exhibits a high specific surface area (2490 m2 g-1), and the effect of the activator addition ratio was systematically investigated. The optimized SPC-2 displayed a high specific capacitance (324 F g-1 at 1 A g-1) and excellent cycling stability (90.6% retention after 50 000 cycles). Furthermore, a symmetric supercapacitor (SSC) based on SPC-2 demonstrated a high energy density (12.9 Wh kg-1) at an 800 W kg-1 power density. This work offers a simple, economical, and ecofriendly synthetic strategy of converting widespread, useless biomass waste into high-performance supercapacitor applications.

Multi-responsive and conductive bilayer hydrogel and its application in flexible devices.

Multi-stimuli-responsive hydrogels are intelligent materials that present advantages for application in soft devices compared with conventional machines. In this paper, we prepared a bilayer hydrogel consisting of a poly(2-(dimethylamino)ethyl methacrylate) layer and a poly(N-isopropylacrylamide) layer. The hydrogel responded to temperature, pH, NaCl, and ethanol by undergoing bending deformation. At 40 °C, it only took 23 s for the hydrogel to bend nearly 300°. Carbon black was also introduced into the hydrogel network to render it conductive. Based on its multi-stimuli-responsive properties and conductivity, the hydrogel was used to construct a 4-arm gripper, thermistor, and finger movement monitor. The time required to grip and release an object was 141 s. The resistance changed with temperature, which affected the brightness of an LED. Finger motions were monitored, and the bending angle could be distinguished.

Dual-ZIF-derived "reassembling strategy" to hollow MnCoS nanospheres for aqueous asymmetric supercapacitors.

Construction of delicate nanostructures with a facile, mild-condition and economical method is a key issue for building high-performance electrode materials. We demonstrate a facile and novel "reassembling strategy" to hollow MnCoS nanospheres derived from dual-ZIF for supercapacitors. The spherical shell's surface structure, thickness and Mn distribution were controlled by regulating the solvothermal reaction time. The chemical composition, phases, specific surface areas and microstructure were studied and the electrochemical performances were systematically estimated. As the unique low-crystalline and optimized hollow nanosphere structure contributes to increasing active sites, MnCoS nanospheres exhibit excellent electrochemical performance. The test results show that the specific capacitance increases with increasing solvothermal time, and the MCS with a 5 h reaction time exhibits optimal electrochemical properties with a high specific capacity of 957 C g-1 (1 A g-1). Furthermore, an MCS-5//AC asymmetric supercapacitor device delivers a specific energy as high as 36.9 W h kg-1 at a specific power of 750 W kg-1.

Green and Rapid Preparation of Fluorosilicone Rubber Foam Materials with Tunable Chemical Resistance for Efficient Oil-Water Separation.

Polydimethylsiloxane (PDMS) foam materials with lightweight, excellent oil resistance and mechanical flexibility are highly needed for various practical applications in aerospace, transportation, and oil/water separation. However, traditional PDMS foam materials usually present poor chemical resistance and easily swell in various solvents, which greatly limits their potential application. Herein, novel fluorosilicone rubber foam (FSiRF) materials with different contents of trifluoropropyl lateral groups were designed and fabricated by a green (no solvents used) and rapid (<10 min foaming process) foaming/crosslinking approach at ambient temperature. Typically, vinyl-terminated poly(dimethyl-co-methyltrifluoropropyl) siloxanes with different fluorine contents of 0−50 mol% were obtained through ring-opening polymerization to effectively adjust the chemical resistance of the FSiRFs. Notably, the optimized FSiRF samples exhibit lightweight (~0.25 g/cm−3), excellent hydrophobicity/oleophilicity (WCA > 120°), reliable mechanical flexibility (complete recovery ability after stretching of 130% strain or compressing of >60%), and improved chemical resistance and structural stability in various solvents, making them promising candidates for efficient and continuous oil−water separation. This work provides an innovative concept to design and prepare advanced fluorosilicone rubber foam materials with excellent chemical resistance for potential oil−water separation application.

A Sulfhydryl Azobenzene-Modified Polyaniline/Silver Electrode and Its Photoswitching Electrochemical Performance.

In this work, a sulfhydryl-functionalized azobenzene derivative (Azo) was synthesized and polyaniline/silver was modified (PANI/Ag) to make a nanocomposite (PANI/Ag/Azo). A series of characterization techniques like1HNMR, UV-vis absorption spectra, Raman spectra, FT-IR, XRD, SEM, TEM, and TGA was employed to study Azo, PANI/Ag, and PANI/Ag/Azo. Electrochemical properties were measured by cyclic voltammetry (CV) and galvanostatic charging/discharging (GCD). CV showed that UV and blue light had hardly any effect on PANI/Ag. However, with the prolonged exposure time of UV light, the maximum CV current density of PANI/Ag/Azo rose from 1.24 to 2.72 A g-1. Then, after 20 min of blue light irradiation, the maximum current density gradually recovered (from 2.72 to 1.26 A g-1). The GCD also obtained similar results. After formula calculation, the specific capacitance of PANI/Ag/Azo also presented a reversible trend under the alternating irradiation of UV light and blue light. All the results show that PANI/Ag/Azo has a good photoelectric response, and its electrochemical performance can be reversibly adjusted by light. This result provides a new design idea for developing electrode materials with real-time electrochemical properties.

Development of protein A functionalized microcantilever immunosensors for the analyses of small molecules at parts per trillion levels.

Development of microcantilever biosensors for small molecules was exemplified with the beta-adrenergic agonist clenbuterol and the antibiotic chloramphenicol. In this paper, antibody sulfhydrylation and protein A were used to modify the microcantilever Au surface, and the antibody activities on the microcantilever were evaluated with direct competitive enzyme-linked immunosorbent assay (dcELISA). The activity of the antibodies immobilized on the microcantilever via protein A was 1.7-fold of that via the sulfhydrylation reagent 2-iminothiolane hydrochloride. A microcantilever immunosensor method with protein A as the functionalization reagent was established to detect the residues of clenbuterol and chloramphenicol at limits of detection (LOD) of approximately 0.1 and 0.2 ng/mL, respectively. Such LODs were better than that of the corresponding dcELISAs. The concentration of clenbuterol in a fortified feed sample detected with the microcantilever immunosensor after thorough extraction and purification agreed well with that detected with the dcELISA. Protein A showed to be simple and reproducible for functionalization of the antibodies on the Au surface and, thus, has common application values in microcantilever immunosensor development. The results suggest that microcantilever immunosensors be suitable for detection of small molecules, and the assay sensitivity is mainly related to the quality and activities of the antibodies.

Synthesis of EDTA-bridged CdS/g-C3N4 heterostructure photocatalyst with enhanced performance for photoredox reactions.

Photocatalytic reactions represent a kind of green and sustainable chemical processes for organic transformations, but the efficiency is limited by the severe recombination and/or inadequate redox potentials of photoinduced charge carriers in photocatalysts. To address these issues, herein, the CdS-EDTA/g-C3N4 heterostructures were designed according to Z-scheme photocatalytic mechanism and synthesized by the hydrothermal growth of CdS on g-C3N4 nanoflakes with assistance of EDTA chelating agent. EDTA played multiple roles in the formation of CdS-EDTA/g-C3N4 heterostructure photocatalysts, such as controlling the morphology of CdS nanostructures, linking CdS and g-C3N4 together, and boosting the charge transfer between two semiconductors. The optimized CdS-EDTA/g-C3N4(10%) photocatalyst exhibited much higher activities toward the selective reduction of nitrophenol and the selective oxidation of benzyl alcohol, than those of CdS/g-C3N4 heterostructures without EDTA. The enhanced photocatalysis of CdS-EDTA/g-C3N4 can be ascribed to the efficient separation and suitable photoredox potentials of photoexcited charge carriers in the EDTA-bridged Z-scheme system. This work provides the inspiration for exploring inexpensive organic electron mediators for constructing all-solid-state Z-scheme photocatalysts and demonstrates the enhanced performance of Z-scheme photocatalysts for photoredox reactions of organic transformations.

Nanomechanical sensors for direct and rapid characterization of sperm motility based on nanoscale vibrations.

Infertility, whether of male or female origin, is a critical challenge facing the low birth rate and aging population throughout the world, and semen analysis is a cornerstone of the diagnostic evaluation of the male contribution to infertility. This means that tools which can characterize sperm properties in an effective manner are very much needed. The conventional approaches are essentially image-based, which have a limited value for analyzing sperm properties. Here, we show that an assay using nanomechanical sensors can detect sperm motility based on nanomotion. We use microcantilever sensors to directly characterize the mechanical response of the sperm based on the fluctuations of microcantilevers. We applied this methodology to sperms exposed to different chemical or physical agents. Real-time nanomechanical fluctuations showed that living sperms produced smaller fluctuations after treatment with inhibitory chemicals, and larger fluctuations after treatment with stimulatory chemicals. Our preliminary experiments suggest that the frequency of fluctuation is associated with sperm motility. This technique offers a brand-new perspective in the characterization of the sperm. By combining conventional measurements, reproductive medicine doctors and researchers should now be able to achieve unprecedented depth in the sperm properties.

Photoswitching of glass transition temperatures of azobenzene-containing polymers induces reversible solid-to-liquid transitions.

The development of polymers with switchable glass transition temperatures (Tg) can address scientific challenges such as the healing of cracks in high-Tg polymers and the processing of hard polymers at room temperature without using plasticizing solvents. Here, we demonstrate that light can switch the Tg of azobenzene-containing polymers (azopolymers) and induce reversible solid-to-liquid transitions of the polymers. The azobenzene groups in the polymers exhibit reversible cis-trans photoisomerization abilities. Trans azopolymers are solids with Tg above room temperature, whereas cis azopolymers are liquids with Tg below room temperature. Because of the photoinduced solid-to-liquid transitions of these polymers, light can reduce the surface roughness of azopolymer films by almost 600%, repeatedly heal cracks in azopolymers, and control the adhesion of azopolymers for transfer printing. The photoswitching of Tg provides a new strategy for designing healable polymers with high Tg and allows for control over the mechanical properties of polymers with high spatiotemporal resolution.

Mechanism and enhancement of the surface stress caused by a small-molecule antigen and antibody binding.

Generation of microcantilever bending from biochemical interactions can have wide applications, ranging from high-throughput molecular detection to bioactuation. However, the origin of the biochemically induced surface stress causing the bending is a subject of much scientific debate and interest. Unlike a compressive surface stress caused by biomacromolecule antigen and antibody binding, here we show that a small molecule antigen and antibody binding on the surface gives rise to a tensile stress. We propose that the tensile stress is induced by antibody conformational change which manifests itself as Fab arm motion that exposes the C1q binding site of the antibody due to antigen binding. A microcantilever immunosensor was developed for the detection of Chlorimuron-ethyl (CE). We found that antibodies with oriented immobilization induce a greater resultant surface stress than those with random immobilization. The length of linker between the surface and the antibody plays an important role on the stress transmission. The shorter the length, the greater the surface stress. These mechanism and principles will underpin the design of devices and coatings to significantly lower the small molecule detection limit and may also have an impact on our understanding of antigen and antibody binding.

Detection of copper ions using microcantilever immunosensors and enzyme-linked immunosorbent assay.

A sensitive and specific monoclonal antibody (designated as mAb6A9) recognizing a Cu(II)-ethylenediamine-N,N,N',N'-tetraacetic acid (EDTA) complex but not metal-free EDTA was obtained by using an 1-(4-aminobenzyl)-EDTA-Cu(II) complex covalently coupled to a carrier protein as an immunogen to immunize the Balb/c mice. A mAb6A9-modified microcantilever sensor (MCS) was developed. A bending response was found to occur at or below 1 ng mL(-1) of Cu(II)-EDTA complex. An indirect competitive enzyme-linked immunosorbent assay (icELISA) was developed with mAb6A9. The icELISA had a half maximum inhibition concentration and working range of approximately 1.8 and 0.2-17 ng mL(-1), respectively. The icELISA showed cross-reactivity of 18.8%, 1.1% and less than 1% with bivalent cobalt, mercury and other metals, respectively. The icELISA and functionalized MCSs were utilized to analyze the content of copper in spiked tap water samples. The assay conditions were optimized. The results of icELISA and MCS correlated well with those obtained by graphite furnace atomic absorption spectrometry.