Novel Membrane Detector Based on Smart Nanogels for Ultrasensitive Detection of Trace Threat Substances

Designable Micro-/Nano-Structured Smart Polymeric Materials

Smart polymeric materials with dynamically tunable physico-chemical characteristics in response to changes of environmental stimuli, have received considerable attention in myriad fields. The diverse combination of their micro-/nano-structural and molecular designs creates promising and exciting opportunities for exploiting advanced smart polymeric materials. Engineering micro-/nano-structures into smart polymeric materials with elaborate molecular design enables intricate coordination between their structures and molecular-level response to cooperatively realize smart functions for practical applications. In this review, recent progresses of smart polymeric materials that combine micro-/nano-structures and molecular design to achieve designed advanced functions are highlighted. Smart hydrogels, gating membranes, gratings, milli-particles, micro-particles and microvalves are employed as typical examples to introduce their design and fabrication strategies. Meanwhile, the key roles of interplay between their micro-/nano-structures and responsive properties to realize the desired functions for their applications are emphasized. Finally, perspectives on the current challenges and opportunities of micro-/nano-structured smart polymeric materials for their future development are presented.

Natural and Engineered Nanomaterials for the Identification of Heavy Metal Ions—A Review

In recent years, there has been much interest in developing advanced and innovative approaches for sensing applications in various fields, including agriculture and environmental remediation. The development of novel sensors for detecting heavy metals using nanomaterials has emerged as a rapidly developing research area due to its high availability and sustainability. This review emphasized the naturally derived and engineered nanomaterials that have the potential to be applied as sensing reagents to interact with metal ions or as reducing and stabilizing agents to synthesize metallic nanoparticles for the detection of heavy metal ions. This review also focused on the recent advancement of nanotechnology-based detection methods using naturally derived and engineered materials, with a summary of their sensitivity and selectivity towards heavy metals. This review paper covers the pros and cons of sensing applications with recent research published from 2015 to 2022.

A novel AIEE active anti-B18H22derivative-based Cu2+and Fe3+fluorescence off-on-off sensor

A novel fluorescence sensor for successive detection of Cu²⁺and Fe³⁺based on anti-B₁₈H₂₂derivative which possesses 5-hydroxyisoquinoline as an ionophore was synthesized via a one-pot and its structure and photophysical properties were characterized by NMR, HRMS, FTIR, UV-vis, PL and theoretical calculation. The fluorophore displays two emission peaks at 460 nm and 670 nm in THF solution coming from the emission of the locally excited state and intramolecular charge transfer fluorescence, respectively. The complex exhibited obvious aggregation-induced emission enhancement (AIEE) characteristics in THF/H₂O solution by increasing the aqueous concentration from 70% to 95%. The AIEE molecules showed a high selectivity towards Cu²⁺over other metal ions by forming a 2:1 metal-to-ligand complex in THF/H₂O (fw = 20%) solution, the fluorescence intensity increased as a linear function of the Cu²⁺concentration at 460 nm due to the inhibition of PET effect. The fluorescent emission was quenched linearly by the addition of Fe³⁺, which provides a method for successive determination of Cu²⁺and Fe³⁺based on 'off-on-off' fluorescence of the fluorescent. The detection limit of Cu²⁺and Fe³⁺was 5.7 × 10^-6M and 7.2 × 10^-5M respectively. Morever, a rapid identification of Cu²⁺in the aqueous solution by naked eyes can be realized. In addition, the molecules were pH-sensitive, the fluorescence quenching can be observed in strongly alkaline environment. The method has been applied to the determination of copper ions in water samples with satisfactory results.

Electrochemical detection of heavy metal ions in water

Heavy metal ions are one of the main sources of water pollution. Most heavy metal ions are carcinogens that pose a threat to both ecological balance and human health. With the increasing demand for heavy metal detection, electrochemical detection is favorable due to its high sensitivity and efficiency. Here, after discussing the pollution sources and toxicities of Hg(ii), Cd(ii), As(iii), Pb(ii), UO₂(ii), Tl(i), Cr(vi), Ag(i), and Cu(ii), we review a variety of recent electrochemical methods for detecting heavy metal ions. Compared with traditional methods, electrochemical methods are portable, fast, and cost-effective, and they can be adapted to various on-site inspection sites. Our review shows that the electrochemical detection of heavy metal ions is a very promising strategy that has attracted widespread attention and can be applied in agriculture, life science, clinical diagnosis, and analysis.

One-Step Synthesis of Water-Soluble CdS Quantum Dots for Silver-Ion Detection

To realize fast synthesis of cadmium sulfide (CdS) quantum dots with a low-toxic material, a one-step synthesis method is investigated and conducted. Potato extract is used as a stabilizer and modifier, by which aqueous CdS quantum dots can be prepared at a lower temperature with a shorter time. Through systematic characterization and analysis, a green and fast synthesis mechanism is demonstrated in detail. And the nanoscale CdS quantum dots are uniform in size and dispersity. With low cost and high sensitivity, the prepared CdS quantum dots show promising application in silver-ion detection. This method shows great significance for an environmentally friendly and facile synthesis of CdS quantum dots.

Visual detection of trace lead(II) using a forward osmosis-driven device loaded with ion-responsive nanogels

A simple and portable thermometer-type device based on forward osmosis-driven liquid column rising is developed for visual detection of trace Pb²⁺. The device consists of a top indicator tube, a chamber loaded with Pb²⁺-responsive poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) (PNB) smart nanogels and a bottom semipermeable membrane. Upon the recognition of Pb²⁺, PNB smart nanogels undergo a Pb²⁺-induced hydrophobic to hydrophilic transition, which simultaneously causes the increase of osmotic pressure inside the device. Driven by this osmotic pressure difference, more Pb²⁺ solution flows into the device, causing the rise of the liquid column in the indicator tube, which can be directly observed by naked eyes. The relationship between the change of liquid column height and the Pb²⁺ concentration is investigated for the quantitative detection of Pb²⁺. With the proposed forward osmosis-driven device, trace Pb²⁺ as low as 10^-10 M in aqueous solutions can be detected. This method provides a novel and simple strategy for the visual detection of trace Pb²⁺.

Zwitterionic Nanohydrogels-Decorated Microporous Membrane with Ultrasensitive Salt Responsiveness for Controlled Water Transport

Highly sensitive responsiveness is vital for stimuli-responsive membranes. However, it is a great challenge to fabricate stimuli-responsive membranes with ultrahigh gating ratio (the ratio of the salt solution permeating flux to the pure water permeating flux) and high response speed simultaneously. In this work, a salt-responsive membrane with an ultrahigh gating ratio is fabricated via a facile strategy by grafting zwitterionic nanohydrogels onto a poly(acrylic acid)-grafting-poly(vinylidene fluoride) (PAA-g-PVDF) microporous membrane. Due to the synergistic effect of two functional materials, PAA chains and zwitterionic nanohydrogels tethered on PAA chains, this stimuli-responsive membrane exhibits an ultrasensitive salt responsiveness with a gating ratio of up to 8.76 times for Na⁺ ions, 89.6 times for Mg²⁺ ions, and 89.3 times for Ca²⁺ ions. In addition, such zwitterionic nanohydrogels-grafted PAA-g-PVDF (ZNG-g-PVDF) membranes exhibit very rapid responses to stimuli. The permeating flux changes swiftly while altering the feed solution in a continuous filtration process. The excellent salt-responsive characteristics endow such a ZNG-g-PVDF membrane with great potential for applications like drug delivery, water treatment, and sensors.

Aggregation-induced emission supramolecular organic framework (AIE SOF) gels constructed from tri-pillar[5]arene-based foldamer for ultrasensitive detection and separation of multi-analytes

In this study, a novel aggregation-induced emission supramolecular organic framework (AIE SOF) with ultrasensitive response, termed FSOF, was constructed using a tri-pillar[5]arene-based foldamer. Interestingly, benefiting from the noise signal shielding properties of FSOF as well as the competition between the cationπ and ππ interactions, the FSOF shows an ultrasensitive response for multi-analytes, such as Fe3+, Hg2+ and Cr3+. The limits of detection (LODs) of the FSOF for Fe3+, Hg2+ and Cr3+ are in the range of 9.40 × 10-10-1.86 × 10-9. More importantly, the xerogel of FSOF exhibits porous mesh structures, which could effect high-efficiency separation above metal ions from their aqueous solution, with adsorption percentages in the range 92.39-99.99%. In addition, by introducing metal ions into the FSOF, a series of metal ions coordinated supramolecular organic frameworks (MSOFs) were successfully constructed. Moreover, MSOFs show selective fluorescence "turn on" ultrasensitive detection CN- (LOD = 2.12 × 10-9) and H2PO4- (LOD = 1.78 × 10-9). This is a novel approach to construct SOFs through a tri-pillar[5]arene-based foldamer, and also provides a new way to achieve ultrasensitive detection and high-efficiency separation.

Nanostructured Thermoresponsive Surfaces Engineered via Stable Immobilization of Smart Nanogels with Assistance of Polydopamine

Thermoresponsive surfaces featured with nanostructures have found wide potential applications in biological and chemical fields. Herein, we report nanostructured thermoresponsive surfaces engineered via stable immobilization of thermoresponsive nanogels with the assistance of polydopamine. The results show that the thin layer of polydopamine on the poly( N-isopropylacrylamide) (PNIPAM) nanogels nearly does not affect the thermoresponsive property of the nanogels. The stability of the thermoresponsive nanogels on the substrate surfaces immobilized under different pH conditions of dopamine solutions are quatitively studied by fluid shearing experiments inside capillaries, and the characterization results show that the strong interaction forces between the polydopamine layer on the substrate surfaces and the thermoresponsive nanogels are heavily dependent on the oxidation state of the dopamine molecules. With the proposed strategy, thermoresponsive nanostructured surfaces immobilized with PNIPAM nanogels on two-dimensional and three-dimensional substrate surfaces are generated to achieve smart cell culture plates and smart gating membranes, respectively, which demonstrate versatile applications of the nanostructured thermoresponsive surfaces.