Synthesis of photoluminescent Au ND-PNIPAM hybrid microgel for the detection of Hg2+

Recent progress in nanomaterial-functionalized membranes for removal of pollutants

Membrane technology has gained tremendous attention for removing pollutants from wastewater, mainly due to their affordable capital cost, miniature equipment size, low energy consumption, and high efficiency even for the pollutants present in lower concentrations. In this paper, we review the literature to summarize the progress of nanomaterial-modified membranes for wastewater treatment applications. Introduction of nanomaterial in the polymeric matrix influences membrane properties such as surface roughness, hydrophobicity, porosity, and fouling resistance. This review also covers the importance of functionalization strategies to prepare thin-film nanocomposite hybrid membranes and their effect on eliminating pollutants. Systematic discussion regarding the impact of the nanomaterials incorporated within membrane, toward the recovery of various pollutants such as metal ions, organic compounds, dyes, and microbes. Successful examples are provided to show the potential of nanomaterial-functionalized membranes for regeneration of wastewater. In the end, future prospects are discussed to develop nanomaterial-based membrane technology.

Encapsulation of gold nanoclusters: stabilization and more

Gold nanoparticles with only a few atoms, known as gold nanoclusters (AuNCs), have dimensions below 2 nm and feature singular properties such as size dependent luminescence. AuNCs are also highly photostable and have catalytic activity, low toxicity and good biocompatibility. With these properties, they are extremely promising candidates for application in bioimaging, sensing and catalysis. However, when stabilized only with small capping ligands, their use is hindered by lack of colloidal stability. Encapsulation of the AuNCs can contribute to provide a more robust protection and even to improve their properties. Here, we review the encapsulation of AuNCs in polymers, silica and metal organic frameworks (MOFs) for applications in bioimaging, sensing and catalysis.

Stimuli-responsive Ca-alginate-based photothermal system with enhanced foliar adhesion for controlled pesticide release

For minimizing volatilization and leaching of pesticides, and enhancing their residence time on crop surfaces, we synthesized and characterized a novel intelligent pesticide delivery system. Therein, imidacloprid (IMI) was adsorbed by polydopamine modified kaolin (PK) with high adsorption property through hydrogen bonds. Ca-alginate was used as a structural matrix of the system and a protective shell to hinder the pesticide burst release from PK, and endowed the system with unique pH-sensitive property for IMI release. The amino silicone oil (ASO) coating could bind with the waxy layer of crop leaves by the theory of "similarity-intermiscibility", which increased the adhesion of composite on crop leaves. Moreover, by the excellent light-sensitive property of detonation nanodiamond (DND) and temperature-responsive performance of poly(N-isopropylacrylamide) (PNIPAm), the release of IMI from the functional system could be adjusted by sunlight. Besides, the composite displayed high control efficacy. This novel composite can promote the targeting ability and utilization efficiency of pesticides, thus having a huge potential application prospect in agriculture.

Stimuli-responsive polymer/nanomaterial hybrids for sensing applications

Chemical and biological/biochemical sensors are capable of generating readout signals that are proportional to the concentration of specific analytes of interest. Signal sensitivity and limit of detection/quantitation can be enhanced through the use of polymers, nanomaterials, and their hybrids. Of particular interest are stimuli-responsive polymers and nanomaterials due to their ability to change their physical and/or chemical characteristics in response to their environment, and/or in the presence of molecular/biomolecular species of interest. Their individual use for sensing applications have many benefits, although this review focuses on the utility of stimuli-responsive polymer and nanomaterial hybrids. We discuss three main topics: stimuli-responsive nanogels, stimuli-responsive network polymers doped with nanomaterials, and nanoparticles modified with stimuli-responsive polymers.

Synthesis and characterization of dopamine-modified Ca-alginate/poly(N-isopropylacrylamide) microspheres for water retention and multi-responsive controlled release of agrochemicals

The multi-responsive controlled-release system could enhance crop yield while improving utilization efficiency of agrochemicals, and minimize environmental pollution caused by agrochemicals overuse. This work reports a novel Ca-alginate/Poly(N-isopropylacrylamide)@polydopamine (Ca-alginate/PNIPAm@PDA) microsphere to control the agrochemicals release. Microsphere with a semi-interpenetrating network, which contained pH-sensitive Ca-alginate, temperature-sensitive poly(N-isopropylacrylamide) (PNIPAm), and sunlight-sensitive polydopamine (PDA), was characterized by thermogravimetric analysis, zeta potential, Fourier transform infrared spectroscopy, and scanning electron microscopy to prove the successful synthesis. Moreover, the comprehensive performances, including photothermal conversion, water absorbency, water retention, and controlled-release agrochemicals behaviors, were systematically investigated. The results indicated that the composite microsphere was a prosperous water and agrochemicals manager to effectively retain water and control the release of agrochemicals by external stimulation. Consequently, the Ca-alginate/PNIPAm@PDA microsphere with outstanding water-retention and controlled-release capacities is economical and eco-friendly and thus is promising for utilization as water and agrochemicals controlled-release carrier material in agriculture applications.

Thermoresponsive Diblock Copolymer Films with a Linear Shrinkage Behavior and Its Potential Application in Temperature Sensors

The linear shrinkage behavior in thermoresponsive diblock copolymer films and its potential application in temperature sensors are investigated. The copolymer is composed of two thermoresponsive blocks with different transition temperatures (TTs): di(ethylene glycol) methyl ether methacrylate (MEO₂MA; TT₁ = 25 °C) and poly(ethylene glycol) methyl ether methacrylate (OEGMA₃₀₀; TT₂ = 60 °C) with a molar ratio of 1:1. Aqueous solutions of PMEO₂MA-b-POEGMA₃₀₀ show a three-stage transition upon heating as seen with optical transmittance and small-angle X-ray scattering: dissolution (T < TT₁), self-assembled micelles with core-shell structure (TT₁ < T < TT₂), and aggregation of collapsed micelles (T > TT₂). Due to the restrictions in the polymer chain arrangement introduced by the solid Si substrate, spin-coated PMEO₂MA-b-POEGMA₃₀₀ films exhibit an entirely different internal structure and transition behavior. Neutron reflectivity shows the absence of an ordered structure normal to the Si substrate in as-prepared PMEO₂MA-b-POEGMA₃₀₀ films. After exposure to D₂O vapor for 3 h and then increasing the temperature above its TT₁ and TT₂, the ordered structure is still not observed. Only a D₂O enrichment layer is formed close to the hydrophilic Si substrate. Such PMEO₂MA-b-POEGMA₃₀₀ films show a linear shrinkage between TT₁ and TT₂ in a D₂O vapor atmosphere. This special behavior can be attributed to the synergistic effect between the restrained collapse of the PMEO₂MA blocks by the still swollen POEGMA₃₀₀ blocks and the impedance of chain arrangement by the Si substrate. Based on this unique behavior, spin-coated PMEO₂MA-b-POEGMA₃₀₀ films are further prepared into a temperature sensor by implementing Ag electrodes. Its resistance decreases linearly with temperature between TT₁ and TT₂.

Synthesis and characterization of thermoresponsive ZIF-8@PNIPAm-co-MAA microgel composites with enhanced performance as an adsorption/release platform

Composite materials featuring a synergic combination of interesting properties such as stimuli responsiveness and tailored porosity are highly appealing due to their multiple possible applications. We hereby present an example which brings together such features by using poly(N-isopropyl-acrylamide)-derived thermo-responsive microgels and Zn-based Metal Organic Framework (MOF) ZIF-8, capable of selective adsorption. Such a composite was obtained by including methacrylic acid as a co-monomer in the microgel, in order to position carboxylic acid moieties within the polymeric matrix, which via preconcentration of MOF precursors would trigger confined heterogeneous nucleation. The highly integrated composite obtained features thermoresponsivity and permanent porosity. Methylene blue adsorption/desorption experiments were performed, revealing a dramatic enhancement of its cargo capacity together with an increased release efficiency.

We hereby present a composite material which combines porosity (ZIF-8 MOF) and stimuli-responsiveness (PNIPAm-co-MAA microgel) in a synergistic way thus opening the path for its use in adsorption and sensing applications.

Hybrid Microgels for Catalytic and Photocatalytic Removal of Nitroarenes and Organic Dyes From Aqueous Medium: A Review

Polymer microgels loaded with inorganic nanoparticles have gained much attention as catalytic systems for reduction of toxic chemicals. Enhanced catalytic properties of hybrid microgels are related to the stimuli responsive nature of microgels and extraordinary stability of nanoparticles within network of polymer microgels. Catalytic properties of hybrid microgels can be tuned very easily by slight variation in environmental conditions. Herein we have reviewed catalytic reduction of toxic chemicals such as nitroarenes and organic dyes in the presence of appropriate hybrid microgel catalytic systems under different operating conditions of reaction. Recent advancements in catalytic behavior of hybrid microgels with special emphasis on their ability to catalytically degrade various toxic chemicals has been presented in this review.

Chicken Egg White-stabilized Au Nanoclusters for Selective and Sensitive Detection of Hg(II)

In this paper, chicken egg white purchased from a local market without further purification was directly used to prepare fluorescent gold nanoclusters through a one-step, simple, fast and green synthesis approach for analytical purposes. The as-prepared chicken egg white stabilized gold nanocluster probe has strong red fluorescence emission, which can be quenched by mercury ions and copper ions sensitively. By using an ethylenediaminetetraacetate (EDTA) masking method, mercury ions in the range from 0.60 to 10 μM can be linearly detected with the limit of detection (LOD, 3σ) of 0.510 μM in the presence of equivalent copper ions. Since the preparation of a chicken egg white stabilized gold nanocluster probe is fast, easy and cheap, this selective analytical method for mercury pollution monitoring in environmental waters may be widely used in daily life by ordinary people.

Functional Stimuli-Responsive Gels: Hydrogels and Microgels

One strategy that has gained much attention in the last decades is the understanding and further mimicking of structures and behaviours found in nature, as inspiration to develop materials with additional functionalities. This review presents recent advances in stimuli-responsive gels with emphasis on functional hydrogels and microgels. The first part of the review highlights the high impact of stimuli-responsive hydrogels in materials science. From macro to micro scale, the review also collects the most recent studies on the preparation of hybrid polymeric microgels composed of a nanoparticle (able to respond to external stimuli), encapsulated or grown into a stimuli-responsive matrix (microgel). This combination gave rise to interesting multi-responsive functional microgels and paved a new path for the preparation of multi-stimuli "smart" systems. Finally, special attention is focused on a new generation of functional stimuli-responsive polymer hydrogels able to self-shape (shape-memory) and/or self-repair. This last functionality could be considered as the closing loop for smart polymeric gels.

Smart app-based on-field colorimetric quantification of mercury via analyte-induced enhancement of the photocatalytic activity of TiO2-Au nanospheres

We have devised a unique strategy for highly sensitive, selective, and colorimetric detection of mercury based on analyte-induced enhancement of the photocatalytic activity of TiO₂-Au nanospheres (TiO₂-Au NSs) toward degradation of methylene blue (MB). Through electrostatic interactions, Au nanoparticles are attached to poly-(sodium 4-styreneulfonate)/poly(diallyldimethylammonium chloride) modified TiO₂ nanoparticles, which then form an Au shell on each TiO₂ core through reduction of Au³⁺ with ascorbic acid. Notably, the deposition of Hg species (Hg²⁺/CH₃Hg⁺) onto TiO₂-Au NSs through strong Au-Hg aurophilic interactions speeds up catalytic degradation of MB. The first-order degradation rates of MB by TiO₂-Au NSs and TiO₂-Au-Hg NSs are 1.4 × 10^-2 min^-1 and 2.1 × 10^-2 min^-1, respectively. Using a commercial absorption spectrometer, the TiO₂-Au NSs/MB approach provides linearity (R² = 0.98) for Hg²⁺ over a concentration range of 10.0 to 100.0 nM, with a limit of detection (LOD) of 1.5 nM. On the other hand, using a low-cost smartphone app that records the color changes (ΔRGB) of MB solution based on the red-blue-green (RGB) component values, the TiO₂-Au NSs/MB approach provides an LOD of 2.0 nM for Hg²⁺ and 5.0 nM for CH₃Hg⁺, respectively. Furthermore, the smartphone app sensing system has been validated for the analyses of various samples, including tap water, lake water, soil, and Dorm II, showing its great potential for on-line analysis of environmental and biological samples. Graphical Abstract ᅟ.

Synthesis, Optical Properties, and Sensing Applications of Gold Nanodots

In this Personal Account, we briefly address our journey in developing photoluminescent nanomaterials for sensing purposes, with a focus on gold nanodots (Au NDs). Their synthetic strategies, optical properties, and sensing applications are emphasized. The Au NDs can be simply prepared from the etching of small-sized Au nanoparticles (<3 nm in diameter) by thiol compounds such as 11-mercaptoundecanoic acid under alkaline conditions. This simple approach allows the preparation of various functional Au NDs by choosing different thiol compounds as etching agents. Since the optical properties of Au NDs are highly dependent on the core and shell of each Au ND, the selection of etching reagents is important. Over the years we have developed various sensing systems using Au NDs for the detection of metal ions, anions, and proteins, based on analyte-induced photoluminescence quenching/enhancement of Au NDs as a result of changes in their oxidation state, shell composition, and structure.

ZnO decorated with organic nanoparticles based sensor for the ratiometric selective determination of mercury ions

Fully characterized organic nanoparticles (R1) decorated on the surface of ZnO (N1), used for selective nanomolar determination of mercury ions.

Real-time selective visual monitoring of Hg(2+) detection at ppt level: An approach to lighting electrospun nanofibers using gold nanoclusters

In this work, fluorescent gold nanocluster (AuNC) decorated polycaprolactone (PCL) nanofibers (AuNC*PCL-NF) for real time visual monitoring of Hg(2+) detection at ppt level in water is demonstrated. The resultant AuNC*PCL-NF exhibiting remarkable stability more than four months at ambient environment and facilitates increased accessibility to active sites resulting in improved sensing performance with rapid response time. The fluorescence changes of AuNC*PCL-NF and their corresponding time dependent spectra, upon introduction of Hg(2+), led to the visual identification of the sensor performance. It is observed that the effective removal of excess ligand (bovine serum albumin (BSA) greatly enhances the surface exposure of AuNC and therefore their selective sensing performance is achieved over competent metal ions such as Cu(2+), Ni(2+), Mn(2+), Zn(2+), Cd(2+), and Pb(2+) present in the water. An exceptional interaction is observed between AuNC and Hg(2+), wherein the absence of excess interrupting ligand makes AuNC more selective towards Hg(2+). The underlying mechanism is found to be due to the formation of Au-Hg amalgam, which was further investigated with XPS, TEM and elemental mapping studies. In short, our findings may lead to develop very efficient fluorescent-based nanofibrous mercury sensor, keeping in view of its stability, simplicity, reproducibility, and low cost.

Engineering noble metal nanomaterials for environmental applications

Besides being valuable assets in our daily lives, noble metals (namely, gold, silver, and platinum) also feature many intriguing physical and chemical properties when their sizes are reduced to the nano- or even subnano-scale; such assets may significantly increase the values of the noble metals as functional materials for tackling important societal issues related to human health and the environment. Among which, designing/engineering of noble metal nanomaterials (NMNs) to address challenging issues in the environment has attracted recent interest in the community. In general, the use of NMNs for environmental applications is highly dependent on the physical and chemical properties of NMNs. Such properties can be readily controlled by tailoring the attributes of NMNs, including their size, shape, composition, and surface. In this feature article, we discuss recent progress in the rational design and engineering of NMNs with particular focus on their applications in the field of environmental sensing and catalysis. The development of functional NMNs for environmental applications is highly interdisciplinary, which requires concerted efforts from the communities of materials science, chemistry, engineering, and environmental science.

Sensitive detection of mercury and copper ions by fluorescent DNA/Ag nanoclusters in guanine-rich DNA hybridization

In this work, we designed a new fluorescent oligonucleotides-stabilized silver nanoclusters (DNA/AgNCs) probe for sensitive detection of mercury and copper ions. This probe contains two tailored DNA sequence. One is a signal probe contains a cytosine-rich sequence template for AgNCs synthesis and link sequence at both ends. The other is a guanine-rich sequence for signal enhancement and link sequence complementary to the link sequence of the signal probe. After hybridization, the fluorescence of hybridized double-strand DNA/AgNCs is 200-fold enhanced based on the fluorescence enhancement effect of DNA/AgNCs in proximity of guanine-rich DNA sequence. The double-strand DNA/AgNCs probe is brighter and stable than that of single-strand DNA/AgNCs, and more importantly, can be used as novel fluorescent probes for detecting mercury and copper ions. Mercury and copper ions in the range of 6.0-160.0 and 6-240 nM, can be linearly detected with the detection limits of 2.1 and 3.4 nM, respectively. Our results indicated that the analytical parameters of the method for mercury and copper ions detection are much better than which using a single-strand DNA/AgNCs.

Fluorescent and colorimetric sensors for environmental mercury detection

The development of fluorescent and colorimetric sensing strategies for environmental mercury is described.

Functional microgels assisted tryptic digestion and quantification of cytochrome c through internal standard mass spectrometry

Quantitation of cytochrome c (Cyt c) in cell lysates through surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) using gold nanoparticles (Au NPs) as the matrix and GR-10 peptide as an internal standard has been demonstrated. To shorten digestion time, temperature sensitive microgels containing trypsin (TR) and Au NPs have been employed. As-prepared functional microgels (TR/Au NPs/MGs) allow digestion of Cyt c within 15 s under microwave irradiation. The internal standard SALDI-MS approach provides linearity (R(2) = 0.98) of MS signal ratio (I 1168.6/I 1067.6) of the tryptic digested peptide (m/z 1168.6) to GR-10 peptide (m/z 1067.6) against the concentration of Cyt c ranging from 25 to 200 nM, with a limit of detection (at a signal-to-noise ratio of 3) of 10 nM. This approach has been validated by the analysis of the lysates of HeLa cells, with an average concentration of 13.7 ± 3.5 μM for cytoplasmic Cyt c. Increased concentrations of Cyt c in the HeLa cells treated with etoposide (a commercial drug) or carbon dots (potential drug) have been revealed through this simple, sensitive, and rapid SALDI-MS approach, supporting the drugs induced Cyt c-mediated apoptosis of the cells. This study has shown that this internal standard SALDI-MS approach holds great potential for cell study.

Self-assembly of hybridized ligands on gold nanodots: tunable photoluminescence and sensing of nitrite

Highly photoluminescent gold nanodots (Au NDs) via etching and co-deposition of hybridized ligands [11-mercaptoundecanol (11-MU) and its complexes with amphiphilic ligands] on gold nanoparticles (∼3 nm) have been prepared and employed for the detection of nitrite based on the analyte-induced photoluminescence quenching.

Interfacing a tetraphenylethene derivative and a smart hydrogel for temperature-dependent photoluminescence with sensitive thermoresponse

We report, for the first time, the design and synthesis of thermoresponsive (TR) photoluminescent (PL) hydrogel nanoparticles, with a core consisting of poly[styrene-co-(N-isopropylacrylamide)] (PS-co-PNIPAM) and a PNIPAM-co-PAA shell. PAA represents polyacrylic acid which interacts with our emitting molecule 1,2-bis[4-(2-triethylammonioethoxy)phenyl]-1,2-diphenylethene dibromide (d-TPE). The electrostatic interaction between each water-soluble d-TPE molecule and two AA repeat units activates these d-TPE molecules to exhibit strong PL. Our d-TPE doped PS-co-PNIPAM/PNIPAM-co-PAA particles in water display remarkable TR PL: the emission intensity decreased in the course of heating from 2 to 80 °C and recovered during cooling from 80 to 2 °C. Such linear, reversible, and sensitive TR PL is achieved by the use of both PAA and PNIPAM as the shell polymeric chain and by careful optimization of the d-TPE to AA feed molar ratio. Thus, the emission of the d-TPE molecule is affected sensitively by temperature. In addition to such an exceptionally temperature-dependent PL, the presence of CrO4(2-) resulted in the decrease of the emission intensity, which was also temperature-dependent. The present study provides a unified conceptual methodology to engineer functional water-dispersible hydrogel nanoparticles that are stimuli-responsive with the potential to advance various PL-based applications.

Synthesis of fluorescent gold nanodot-liposome hybrids for detection of phospholipase C and its inhibitor

We report the synthesis of fluorescent 11-mercaptoundecanoic acid-gold nanodot-liposome (11-MUA-Au ND/Lip) hybrids by incorporation of gold nanoparticles (∼3 nm) and 11-MUA molecules in hydrophobic phospholipid membranes that self-assemble to form small unilamellar vesicles. A simple and homogeneous fluorescence assay for phospholipase C (PLC) was developed on the basis of the fluorescence quenching of 11-MUA-Au ND/Lip hybrids in aqueous solution. The fluorescence of the 11-MUA-Au ND/Lip hybrids is quenched by oxygen (O2) molecules in solution, and quenching is reduced in the presence of PLC. PLC catalyzes the hydrolysis of phosphatidylcholine units from Lip to yield diacylglycerol (DAG) and phosphocholine (PC) products, leading to the decomposition of Lip. The diacylglycerol further interacts with 11-MUA-Au NDs via hydrophobic interactions, leading to inhibition of O2 quenching. The 11-MUA-Au ND/Lip probe provides a limit of detection (at a signal-to-noise ratio of 3) of 0.21 nM for PLC, with high selectivity over other proteins, enzymes, and phospholipases. We have validated the practicality of using this probe for the determination of PLC concentrations in breast cancer cells (MCF-7 and MDA-MB-231 cell lines) and nontumor cells (MCF-10A cell line), revealing that the PLC activity in the first two is at least 1.5-fold higher than that in the third. An inhibitor assay using 11-MUA-Au ND/Lip hybrids demonstrated that tricyclodecan-9-yl potassium xanthate (D609) inhibits PLC (10 nM) with an IC50 value of 3.81 ± 0.22 μM. This simple, sensitive, and selective approach holds great potential for detection of PLC in cancer cells and for the screening of anti-PLC drugs.