Double layered asymmetrical hydrogels enhanced by thermosensitive microgels for high-performance mechanosensors and actuators.

Thermosensitive hydrogels have found extensive applications in soft devices, but they often suffer from limited functionalities, low response rate and small response amplitude. In this work, double layered asymmetrical hydrogels composed of a thermosensitive layer and a non-thermosensitive layer are developed to simultaneously achieve high-performance mechanosensing and actuating properties in a single hydrogel. In thermosensitive layer, thermosensitive microgels are introduced to construct hierarchical structure, which accounts for the enhanced thermosensitive behaviors by cooperative responsiveness. In non-thermosensitive layer, poly(acrylamide-co-acrylic acid) (P(AM-co-AA)) hydrogel is constructed. KCl is introduced as conductive component. Mechanosensors for monitoring various mechanical stimuli in daily life have been fabricated utilizing such hydrogels and high gauge factors (GF) have been achieved, 0.38 for resistive strain sensors, 9.40 kPa-1 for piezoresistive pressure sensors and 3.92 kPa-1 for capacitive pressure sensors. Because of the asymmetrical structure, such hydrogels also exhibit outstanding actuating properties with a fast response rate of 863°/min and a bending amplitude about 360°. Interestingly, grasping-releasing of target objects utilizing an octopus-shaped hydrogel actuator and temperature alerting based on hydrogel actuator are also demonstrated. Overall, the double layered asymmetrical ionic hydrogels have provided a new clue to construct hydrogel devices with multiple functionalities and enhanced response properties.

Regenerable and Highly Stable Two-Dimensional Imine-Based Covalent Organic Framework for Simultaneous Rapid Detection and Adsorption of Cu2+ Ions.

The development of efficient fluorescent probes and adsorbents for detecting and removing Cu2+, which pose potential environmental and health risks, is a highly active area of research. However, achieving simultaneously improved fluorescence detection efficiency and enhanced adsorption capacity in a single porous probe remains a significant challenge. In this study, we successfully synthesized a two-dimensional imine-based TAP-COF using 2,4,6-triformylphloroglucinol and tri(4-aminophenyl)amine as raw materials. TAP-COF exhibited excellent properties, including a large specific surface area of 685.65 m2·g-1, exceptional thermal stability (>440 °C), chemical stability, temporal stability, and recyclability. Fluorescence testing revealed that TAP-COF exhibited remarkable specificity and high sensitivity for detecting Cu2+. The fluorescence mechanism, in which the excited state intramolecular proton transfer was impeded by the interaction of Cu2+ with C═O and C-N bonds on TAP-COF upon the addition of Cu2+, was further elucidated through experimental and theoretical methods. Furthermore, the adsorption capacity of TAP-COF toward Cu2+ was investigated, confirming the excellence of TAP-COF as a fluorescent probe and adsorbent for the specific detection and removal of Cu2+. This work holds significant implications for improving environmental and human health concerns associated with Cu2+ contamination.

Stable Flexible Electronic Devices under Harsh Conditions Enabled by Double-Network Hydrogels Containing Binary Cations.

Hydrogels are increasingly used in flexible electronic devices, but the mechanical and electrochemical stabilities of hydrogel devices are often limited under specific harsh conditions. Herein, chemically/physically cross-linked double-network (DN) hydrogels containing binary cations Zn2+ and Li+ are constructed in order to address the above challenges. Double networks of chemically cross-linked polyacrylamide (PAM) and physically cross-linked κ-Carrageenan (κ-CG) are designed to account for the mechanical robustness while binary cations endow the hydrogels with excellent ionic conductivity and outstanding environmental adaptability. Excellent mechanical robustness and ionic conductivity (25 °C, 2.26 S·m-1; -25 °C, 1.54 S·m-1) have been achieved. Utilizing the DN hydrogels containing binary cations as signal-converting materials, we fabricated flexible mechanosensors. High gauge factors (resistive strain sensors, 2.4; capacitive pressure sensors, 0.82 kPa-1) and highly stable sensing ability have been achieved. Interestingly, zinc-ion hybrid supercapacitors containing the DN hydrogels containing binary cations as electrolytes have achieved an initial capacity of 52.5 mAh·g-1 at a current density of 3 A·g-1 and a capacity retention rate of 82.9% after 19,000 cycles. Proper working of the zinc-ion hybrid supercapacitors at subzero conditions and stable charge-discharge for more than 19,000 cycles at -25 °C have been demonstrated. Overall, DN hydrogels containing binary cations have provided promising materials for high-performance flexible electronic devices under harsh conditions.

Visual detection of water content in liquor with near-infrared fluorescence sensor assisted by smartphone.

Water content was an essential indicator in organic solvents, and it was necessary to develop a facile, cheap and readily available tool for the real-time, specifical and sensitive detection of water content. In this work, two novel D-π-A type near-infrared fluorescence sensors (DCM-1 and DCM-2) were designed and synthesized for the detection of trace water in organic solvents. DCM-1 and DCM-2 with solvent-dependent effects and large Stokes shift (>120 nm) showed good linear "intensity-to-content" relationships in four commonly-used organic solvents, and accomplished the ultra-fast and high-accuracy detection of the trace water in organic solvents. More importantly, a portable, fast, and accurate smartphone-assisted visual assay was designed for visual quantitative detection of the water content in organic solvents with a detection limit as low as 1.028 % v/v (e.g. in ethanol) and a wide detection range (0-60 % v/v). The smartphone-based visual assay was further applied to estimate the water content in disinfection alcohol and commercial liquor, which furnished a new strategy and broad prospects to achieve the accurate onsite detection of water content.

An ESIPT-Based Fluorescent Probe for Aqueous Cu+ Detection through Strip, Nanofiber and Living Cells.

Constructed on the benzothiazole-oxanthracene structure, a fluorescent probe RBg for Cu+ was designed under the ESIPT mechanism and synthesized by incorporating amide bonds as the connecting group and glyoxal as the identifying group. Optical properties revealed a good sensitivity and a good linear relationship of the probe RBg with Cu+ in the concentration range of [Cu+] = 0-5.0 µmol L-1. Ion competition and fluorescence-pH/time stability experiments offered further possibilities for dynamic Cu+ detection in an aqueous environment. HRMS analysis revealed a possible 1:1 combination of RBg and Cu+. In addition, colorimetric Cu+ detection and lysosome-targeted properties of the probe RBg were analyzed through RBg-doped PVDF nanofiber/test strips and RBg-Mito/Lyso trackers that were co-stained in living HeLa cells, enabling the probe's future applications as real-time detection methods for dynamic Cu+ tracking in the lysosomes and Cu+ detection under diversified conditions.

A PET Fluorescent Probe for Dynamic Pd2+ Tracking with Imaging Applications in the Nanofiber and Living Cells.

Constructed on the moiety of a lactam screw ring, a near-infrared fluorescent probe RCya for Pd2+ was designed under the PET mechanism and synthesized by incorporating 2,4-dihydroxybenzaldehyde as the recognition group. Dynamic detection of aqueous Pd2+ by the probe RCya could be accomplished through ion competition, linear response, fluorescence-pH/time stabilities, and other optical tests. Moreover, the high selectivity, low cytotoxicity, cell permeability, and lysosome accumulation properties of RCya enabled the imaging applications on solid-state RCya-PAN composite nanofibers and in living cells. The recognition mechanism of probe RCya toward Pd2+ was further studied through simulation calculation and MS analysis.

High sensitivity for detecting trace Sn2+ in canned food using novel covalent organic frameworks.

Tin (Sn) element plays a vital role in the human body, and its detection is a mandatory inspection item for canned food. The application of covalent organic frameworks (COFs) in fluorescence detection has received extensive attentions. In this work, we designed a kind of novel COFs (COF-ETTA-DMTA) with high specific surface area (353.13 m2/g) by solvothermal synthesis using 2,5-dimethoxy-1,4-dialdehyde and tetra (4-aminophenyl) ethylene as precursors. It shows fast response time (about 50 s), low detection limit (228 nM) and good linearity (R2 = 0.9968) for the detection of Sn2+. Via coordination behavior, the recognition mechanism of COFs toward Sn2+ was simulated and verified by the small molecule with the same functional unit. More importantly, this COFs was successfully applied to identify Sn2+ in solid canned food (luncheon pork, canned fish, canned red kidney beans) with satisfactory results. This work provides a new approach for determining metal ions with COFs taking the advantage of their natural rich reaction set and specific surface area, improving the detection sensitivity and capacity.

A Highly Sensitive and Selective Fluorescein-Based Cu2+ Probe and Its Bioimaging in Cell.

Copper is a vital trace metal in human body, which plays the significant roles in amounts of physiological and pathological processes. The application of copper-selective probe has attracted great interests from environmental tests to life process research, yet a few of sensitive Cu2+ tests based on on-site analysis have been reported. In this paper, a novel fluorescein-based fluorescent probe N4 was designed, synthesized, and characterized, which exhibited high selectivity and sensitivity to Cu2+ comparing with other metal ions in ethanol-water (1/1, v/v) solution. The probe N4 bonded with Cu2+ to facilitate the ring-opening, and an obvious new band at 525 nm in the fluorescence spectroscopy appeared, which could be used for naked-eye detection of Cu2+ within a broad pH range of 6-9. Meanwhile, a good linearity between the fluorescence intensity and the concentrations of Cu2+ ranged 0.1-1.5 eq. was observed, and the limit of detection of N4 to Cu2+ was calculated to be as low as 1.20 µm. In addition, the interaction mode between N4 and Cu2+ was found to be 1:1 by the Job's plot and mass experiment. Biological experiments showed that the probe N4 exhibited low biological toxicity and could be applied for Cu2+ imaging in living cells. The significant color shift associated with the production of the N4-Cu2+ complex at low micromolar concentrations under UV light endows N4 with a promising probe for field testing of trace Cu2+ ions.

Electrospun Elastic Films Containing AgNW-Bridged MXene Networks as Capacitive Electronic Skins.

Electronic skins (e-skins) are increasingly investigated and applied in wearable devices, but the robustness and convenient production of traditional e-skins are restricted. In this work, electrospun sandwich-structured elastic films (ESEFs) are developed and utilized as capacitive e-skins. The ESEFs consist of two nanocomposite mats as the electrode layers and a sandwiched thermoplastic polyurethane (TPU) mat as the dielectric layer. The nanocomposite mats are composed of thermoplastic polyurethane (TPU) and AgNW-bridged MXene (AgNW, silver nanowire; MXene, Ti3C2Tx) conductive network. The resulting ESEFs achieve a tensile strength of 14.80 MPa, an elongation at break of 270%, and an outstanding antifatigue property. E-skins of such ESEFs have the ability to respond to both strain and pressure with a high gauge factor (GF) (strain: GF = 1.21; pressure: GF = 0.029 kPa-1), wide response range (strain: 0-150%; pressure: 0-70 kPa), low response time, and outstanding stability (2000 cycles). On the basis of integrated sensing performances, such e-skins are further applied in monitoring various mechanical stimuli in daily life, including bending of a plastic plate, joint bending, and swallowing.

Rational construction of deep-red fluorescent probe for rapid detection of HClO and its application in bioimaging and paper-based sensing.

Hypochlorous acid (HClO), the core bactericidal substance of the human immune system, plays a vital role in many physiological and pathological processes in the human body. In this work, we designed and synthesized a novel deep-red fluorescent probe TCF-ClO for the determination of hypochlorous acid through theoretical analysis. The results showed that probe TCF-ClO exhibited excellent characteristics of long-wavelength emission (635 nm), fast response (< 1 min), and low detection limit (24 nM). In addition, it had been successfully used for imaging of HClO in living HeLa cells. More importantly, the TCF-ClO composited paper-based sensing material was successfully constructed. The RGB/gray value was obtained from a mobile phone and computer, which could achieve the quantitative detection of HClO, with a linear detection range of 0-50 µM and a detection limit of 1.09 µM (RGB mode)/3.38 µM (gray mode). The function of the paper-based sensor extended from qualitative to quantitative detection of HClO, and it is expected to become a portable device widely used in the environmental area.

Mussel-inspired self-adhesive hydrogels by conducting free radical polymerization in both aqueous phase and micelle phase and their applications in flexible sensors.

Polydopamine (PDA)-based self-adhesive hydrogel sensors are extensively explored but it is still a challenge to construct PDA-based hydrogels by free radical polymerization. Herein, a new approach to construct self-adhesive hydrogels by conducting free radical polymerization in both aqueous phase and micelle phase is developed. The following two-phase polymerization processes account for the formation of the self-adhesive hydrogels. The first one is the polymerization of acrylamide (AM) and dopamine (DA) in aqueous phase to form adhesive component PAM-PDA (PAM, polyacrylamide; PDA, polydopamine). The second one is the polymerization of hydrophobic monomer 2-methoxyethyl acrylate (MEA) in micelles of an amphiphilic block copolymer Pluronic F127 diacrylate (F127DA). The poly(2-methoxyethyl acrylate) (PMEA) networks help to maintain the high robustness of the hydrogel. Because PMEA and PDA form in relatively separated phases, the inhibition effect of PDA on the free radical polymerization process of PMEA is weakened. Based on this mechanism, mechanically strong and adhesive hydrogels are achieved. The introduced ions during preparation process, such as Na+, OH- and K+, endow the resulting hydrogels ionic conductivity. Resistive strain sensor of the hydrogel achieves a high gauge factor (GF) of 5.26, a response time of 0.25 s and high sensing stability. Because of the adhesiveness, such hydrogel sensor can be applied as wearable sensors in monitoring various human motions. To further address the freezing and drying problems of the hydrogels, organohydrogels are constructed in glycerol-water mixed solvent. The organohydrogels exhibit outstanding anti-freezing property and moisture retention ability, and their adhesiveness is well maintained in subzero conditions. Capacitive pressure sensors of the organohydrogels possessing a GF of 2.05 kPa-1, high sensing stability and reversibility, are demonstrated and explored in monitoring diverse human motions.

Green synthesis of orange emissive carbon dots for the detection of Ag+and their application via solid-phase sensing and security ink.

Fluorescent carbon dots (CDs) have attracted considerable interest due to their superior optical properties and facile preparation. In this work, O-phenylenediamine and melamine were used as precursors for the one-step hydrothermal synthesis of novel orange emissive CDs (O-CDs) in an aqueous solution. The fluorescence intensity (580 nm) of the O-CDs exhibited a good linear relationship with Ag+in the range of 0.0-50.0µM with the detection limit of 0.289µM. Moreover, the O-CDs were successfully used to determine Ag+in biological samples (Hela cells) because of their low cytotoxicity, and good biocompatibility. Besides, the O-CDs-doped solid-phase detection materials (test paper and hydrogel) were employed to monitor Ag+qualitatively and quantitatively, indicated that the O-CDs had a great capacity for the detection of Ag+in biological and environmental areas. Based on their extraordinary fluorescence property, the O-CDs could also be used as security ink. Overall, based on their excellent fluorescent performance, the CDs in this study have significant potential for practical application toward solid-phase sensing and security ink.

Fabrication of carbon dots for sequential on-off-on determination of Fe3+ and S2- in solid-phase sensing and anti-counterfeit printing.

Glutathione and 2-aminopyridine are used as carbon sources to prepare carbon dots (CDs) by a one-step hydrothermal reaction. The results show that the average particle diameter of CDs is 8.64 nm with uniform size distribution and the fluorescence quantum yield is 13.62%. We further demonstrate that novel CDs possess highly selective sensing of Fe3+ from 0.2 to 200 µM with a low detection limit (0.194 µM). Meanwhile, the fluorescence of CDs can be repeated many times by the addition of S2-. Moreover, the CDs are used for biological imaging of living cells with well cell penetrability and low toxicity. Furthermore, it is successfully applied for anti-counterfeiting and information encryption. More interestingly, it can be doped with hydrogel and filter paper to prepare solid-phase sensors exhibiting high sensitivity and fast response, demonstrating their tremendous potential for the simple, rapid, and low-cost monitoring of Fe3+ and S2-.

Detection of Cu2+ and S2- with fluorescent polymer nanoparticles and bioimaging in HeLa cells.

Novel spherical polymer nanoparticles were synthesized by hyperbranched polyethylenimine (hPEI) and 6-hydroxy-2-naphthaldehyde (HNA) via Schiff base reaction (one-pot reaction), which had great advantages in water solubility and green synthesis. Meanwhile, probe PEI-HNA could quickly detect Cu2+ in the range of 0-60 µM in 30 s with the detection limit of 243 nM. The fluorescence of PEI-HNA-Cu2+ could be recovered by the addition of S2- in 50 s with the detection limit of 227 nM. Based on the excellent optical properties, PEI-HNA has been used in the bioimaging of living cells with excellent cell penetrability and low toxicity. More importantly, PEI-HNA has been doped into filter paper, hydrogel, and nanofibrous film to prepare solid-phase sensors, displaying rapid response and excellent sensitivity. Moreover, the low-cost and simple preparation of these sensors offers great potential and possibilities for industrialization, which could help accelerate the development of sensors in environmental and biological fields.

Construction of DCM-based NIR fluorescent probe for visualization detection of H2S in solution and nanofibrous film.

Hydrogen sulfide (H2S) played crucial roles in biological processes and daily life, and the abnormal level of H2S was associated with many physiological processes. In this paper, we designed and developed a dicyanomethylene-4H-chromene (DCM)-based near-infrared (NIR) fluorescent probe DCM-NO guided by theoretical calculation. The probe displayed excellent selectivity towards H2S with a fast response time (3 min) and low detection limit (fluorescence 25.3 nM/absorption 6.61 nM) in Hela cells and real water samples. Furthermore, the probe-doped solid sensing materials (test strips and nanofibrous films) exhibited specific visualization of H2S under ambient light or hand-held UV lamp, providing great potential for on-site and real-time application in environmental and biological systems.

Capacitive Pressure Sensors Containing Reliefs on Solution-Processable Hydrogel Electrodes.

Highly sensitive capacitive-type pressure sensor has been achieved by fabricating reliefs on solution-processable hydrogel electrodes. Hybrid PVA/PANI hydrogels (PVA, poly(vinyl alcohol); PANI, polyaniline) with a fully physically cross-linked binary network are selected as the electrodes of the pressure sensors. On the basis of the solution processability, reliefs are fabricated on the surface of PVA/PANI hydrogel electrodes by a template method. The gauge factor (GF) is enhanced by introducing reliefs and regulated by controlling the composition and relief dimension of hydrogel electrodes. The optimized pressure sensor containing reliefs achieves the highest GF of 7.70 kPa-1 and a sensing range of 0-7.4 kPa. Furthermore, the freezing and drying problems of the hydrogel sensors are overcome by introducing a binary solvent of water/glycerol and the pressure sensing ability at -18 °C has been achieved. Finally, monitoring of various pressures in daily life, such as joint bending, blowing, and brush writing, is demonstrated using such pressure sensors.

Oxidized nanoscale zero-valent iron changed the bioaccumulation and distribution of chromium in zebrafish.

Influences of colloidal stabilities of nanoparticles (NPs) on the bioaccumulation of co-existing pollutants remains largely unknown. In this study, two oxidation products of nanoscale zero-valent iron (nZVI) with totally varied colloidal stabilities, termed highly oxidized nZVI (HO-nZVI) and lowly oxidized nZVI (LO-nZVI), were exposed to zebrafish with chromium (Cr); this approach was used to investigate the impacts of colloidal stability of oxidized nZVI on the bioaccumulation of Cr in zebrafish. A significant increase in the Cr and NP content in the viscera of fish in the presence of the oxidized nZVI after 20 days of exposure was confirmed, which indicated that Cr was consumed by fish through the uptake of the NPs. Furthermore, a significantly higher level of the HO-nZVI accumulated in the viscera in contrast to LO-nZVI, which suggested that the colloidal stability of NP is a crucial factor when evaluating the accessibility of NPs to zebrafish. Thus, HO-nZVI induced a significantly stronger enhancement of Cr content in fish than LO-nZVI. Our results suggest that oxidized nZVI will act as the carrier of co-existing heavy metals and change the transportation and distribution of heavy metals in zebrafish; moreover, the colloidal stability of NP will have a significant influence on the bioaccumulation of coexisting Cr.

Fluorescent sensing film decorated with ratiometric probe for visual and recyclable monitoring of Cu2.

Specifically, visually, and quantitatively monitor copper ion (Cu2+) is critical in the area of biological and environmental detection. Herein, a ratiometric fluorescent probe with benzoxazole appended xanthenes skeleton was constructed and further employed to monitor Cu2+ in Hela cells, real water samples, and test strips. An easily distinguishable colorimetric (colorless to red) and fluorescence (green to red) change could be observed by naked eye under the portable UV lamp (365 nm) and the changes could be recovered by adding S2-. Furthermore, electrospinning technique was employed to fabricate a probe composited fluorescent sensing film (PMMA) for realizing the visual and recyclable monitoring of Cu2+, indicating that the probe-composited fluorescent sensing film has great potential for on-site and naked-eye detection of Cu2+ in practical.

Predicting the aggregation tendency of oxidized nanoscale zero-valent iron in aquatic environments.

Predicting the aggregation tendency of nanoscale zero-valent iron (nZVI), oxidized nZVI, in particular, is crucial for the risk assessment of nZVI in aquatic environments. In this study, the comprehensive effects of the pH and ionic strength (IS) on the aggregation behaviors of two highly oxidized nZVIs (HO-nZVI) were examined. Compared with hematite nanoparticles, HO-nZVI presented a sudden acceleration in aggregation under critical conditions; moreover, the morphology of the HO-nZVI aggregates at pH and IS values higher or lower than the critical conditions was significantly different. Furthermore, owing to the differences in magnetization between the two prepared HO-nZVI samples, their critical coagulation conditions were significantly different. The significant changes in the aggregation behavior of the HO-nZVI samples were analyzed using colloidal theories, and the aggregation tendency of HO-nZVI under specific conditions could be simulated by calculating the theoretical critical conditions of aggregation via a method that takes into account the hydrochemical properties, magnetization, and surface charge of HO-nZVI. To examine the correctness of the method, we compared the experimentally determined colloidal stability of HO-nZVI in water samples collected from nearby rivers with the theoretically predicted value. The results indicated that the method was adequate for most situations, except for those in which the hydrochemical properties of the water samples were close to the critical coagulation conditions. Our study proposes a theoretical approach that is viable for simulating the colloidal stability of magnetic nanoparticles in aquatic environments; we anticipate that it will further facilitate the risk assessment of nanoparticles.

Rhodol-based fluorescent probes for the detection of fluoride ion and its application in water, tea and live animal imaging.

Herein, we presented two novel turn-on colorimetric and fluorescent probes based on a F- triggered SiO bond cleavage reaction, which displayed several desired properties for the quantitative detection for F-, such as high specificity, rapid response time (within 3 min) and naked-eye visualization. The fluorescence intensity at 574 nm (absorbance at 544 nm) of the solution was found to increase linearly with the concentration of F- (0.00-30.0 µM) with the detection limit was estimated to be 0.47 µM/0.48 µM. Based on these excellent optical properties, the probes were employed to monitor F- in real water samples and tea samples with satisfactory. Furthermore, it was successfully applied for fluorescent imaging of F- in living nude mice, suggesting that it could be used as a powerful tool to predict and explore the biological functions of F- in physiological and pathological processes.