Nano-enabled smart and functional materials toward human well-being and sustainable developments.

Fabrication and operation on increasingly smaller dimensions have been highly integrated with the development of smart and functional materials, which are key to many technological innovations to meet economic and societal needs. Along with researchers worldwide, the Waterloo Institute for Nanotechnology (WIN) has long realized the synergetic interplays between nanotechnology and functional materials and designated 'Smart & Functional Materials' as one of its four major research themes. Thus far, WIN researchers have utilized the properties of smart polymers, nanoparticles, and nanocomposites to develop active materials, membranes, films, adhesives, coatings, and devices with novel and improved properties and capabilities. In this review article, we aim to highlight some of the recent developments on the subject, including our own research and key research literature, in the context of the UN Sustainability development goals.

Paper-Based Screen-Printed Ionic-Liquid/Graphene Electrode Integrated with Prussian Blue/MXene Nanocomposites Enabled Electrochemical Detection for Glucose Sensing.

As glucose biosensors play an important role in glycemic control, which can prevent the diabetic complications, the development of a glucose sensing platform is still in needed. Herein, the first proposal on the in-house fabricated paper-based screen-printed ionic liquid/graphene electrode (SPIL-GE) modified with MXene (Ti3C2Tx), prussian blue (PB), glucose oxidase (GOx), and Nafion is reported. The concentration of PB/Ti3C2Tx was optimized and the optimal detection potential of PB/Ti3C2Tx/GOx/Nafion/SPIL-GE is -0.05 V. The performance of PB/Ti3C2Tx/GOx/Nafion modified SPIL-GE was characterized by cyclic voltammetry and chronoamperometry technique. This paper-based platform integrated with nanomaterial composites were realized for glucose in the range of 0.0-15.0 mM with the correlation coefficient R2 = 0.9937. The limit of detection method and limit of quantification were 24.5 µM and 81.7 µM, respectively. In the method comparison, this PB/Ti3C2Tx/GOx/Nafion/SPIL-GE exhibits a good correlation with the reference hexokinase method. This novel glucose sensing platform can potentially be used for the good practice to enhance the sensitivity and open the opportunity to develop paper-based electroanalytical devices.

Synergistic Behavior of Polyethyleneimine and Epoxy Monomers Loaded in Mesoporous Silica as a Corrosion-Resistant Self-Healing Epoxy Coating.

Corrosion is a significant problem and is, to a large extent, responsible for the degradation of metallic parts. In this direction, mesoporous silica particles (MSPs) were synthesized by a sol-gel technique and had an average pore diameter of ∼6.82 nm. The MSPs were loaded with polyethyleneimine (PEI) and epoxy monomers and, after that, carefully mixed into the epoxy matrix to formulate new modified polymeric coatings. The microstructural, compositional, structural, and thermal properties were investigated using various characterizing tools [Transmission electron microscopy, Fourier transform infrared spectroscopy, hermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy]. TGA confirms the loading of mesoporous silica with a corrosion inhibitor, and its estimated loading amount is ∼8%. The electrochemical impedance spectroscopy properties of the reference and modified coated samples confirm the promising anti-corrosive performance of the synthesized polymeric smart coatings. Localized electrochemical tests (scanning vibrating electrode technique and scanning ion-selective electrode technique) evidence the corrosion inhibition ability of the coating, and its self-healing was also observed during 24 h of immersion. The decent anti-corrosion performance of the modified coatings can be credited to the efficient synergistic effect of the PEI and epoxy monomer.

A comprehensive review on electrochemical and optical aptasensors for organophosphorus pesticides.

There has been a rise in pesticide use as a result of the growing industrialization of agriculture. Organophosphorus pesticides have been widely applied as agricultural and domestic pest control agents for nearly five decades, and they remain as health and environmental hazards in water supplies, vegetables, fruits, and processed foods causing serious foodborne illness. Thus, the rapid and reliable detection of these harmful organophosphorus toxins with excellent sensitivity and selectivity is of utmost importance. Aptasensors are biosensors based on aptamers, which exhibit exceptional recognition capability for a variety of targets. Aptasensors offer numerous advantages over conventional approaches, including increased sensitivity, selectivity, design flexibility, and cost-effectiveness. As a result, interest in developing aptasensors continues to expand. This paper discusses the historical and modern advancements of aptasensors through the use of nanotechnology to enhance the signal, resulting in high sensitivity and detection accuracy. More importantly, this review summarizes the principles and strategies underlying different organophosphorus aptasensors, including electrochemical, electrochemiluminescent, fluorescent, and colorimetric ones.

Paper-Based Competitive Immunochromatography Coupled with an Enzyme-Modified Electrode to Enable the Wireless Monitoring and Electrochemical Sensing of Cotinine in Urine.

This paper proposes a combined strategy of using paper-based competitive immunochromatography and a near field communication (NFC) tag for wireless cotinine determination. The glucose oxidase labeled cotinine antibody specifically binds free cotinine in a sample, whereas the unoccupied antibody attached to BSA-cotinine at the test line on a lateral flow strip. The glucose oxidase on the strip and an assistant pad in the presence of glucose generated H2O2 and imposed the Ag oxidation on the modified electrode. This enabled monitoring of immunoreaction by either electrochemical measurement or wireless detection. Wireless sensing was realized for cotinine in the range of 100-1000 ng/mL (R2 = 0.96) in PBS medium. Undiluted urine samples from non-smokers exhibited an Ag-oxidation rate three times higher than the smoker's urine samples. For 1:8 diluted urine samples (smokers), the proposed paper-based competitive immunochromatography coupled with an enzyme-modified electrode differentiated positive and negative samples and exhibited cotinine discrimination at levels higher than 12 ng/mL. This novel sensing platform can potentially be combined with a smartphone as a reader unit.

An electrochemical sensor for ifosfamide, acetaminophen, domperidone, and sumatriptan based on self-assembled MXene/MWCNT/chitosan nanocomposite thin film.

New multi-walled carbon nanotubes supported on Ti3C2-MXene and chitosan (chit) composite film-based electrochemical sensor for ifosfamide (IFO), acetaminophen (ACOP), domperidone (DOM), and sumatriptan (SUM) have been developed. Ti3C2-MXene was synthesized by a fluoride method. Structural and chemical characterizations suggested the successful preparation of Ti3C2-MXene with clearly seen layered morphology, defined 0 0 2 diffraction peak at 7.5° and complete absence of 1 0 4 plane at 39°. The electrochemical performance of the sensor was investigated by cyclic voltammetry and adsorptive stripping differential pulse voltammetry. The Ti3C2/MWCNT/Chit modified glassy carbon electrode exhibits enhanced electrocatalytic activities toward the oxidation of target analytes. Excellent conductivity, large surface area, and high catalytic properties of the Ti3C2-MXene showed synergistic effects with MWCNTs and helped in achieving low detection limits of targets with high selectivity and reproducibility. The assay allows determination of IFO, ACOP, DOM, and SUM in the concentration ranges 0.0011-1.0, 0.0042-7.1, 0.0046-7.3, and 0.0033-61 µM with low detection limits of 0.00031, 0.00028, 0.00034, and 0.00042 µM, respectively. The sensor was successfully applied for voltammetric screening of target analytes in urine and blood serum samples with recoveries > 95.21%. Schematic illustration of the synthesis of self-assembled MXene/MWCNT/chitosan nanocomposite is given and its application to the voltammetric determination of ifosfamide, acetaminophen, domperidone, and sumatriptan described. Graphical abstract.

Electrochemical (bio) sensors go green.

Electrochemical (bio) sensors are now widely acknowledged as a sensitive detection tool for disease diagnosis as well as the detection of numerous species of pharmaceutical, clinical, industrial, food, and environmental origin. The term 'green' demonstrates the development of electrochemical (bio) sensing platforms utilizing biodegradable and sustainable materials. Development of green sensing platforms is one of the most active areas of research minimizing the use of toxic/hazardous reagents and solvent systems, thereby further reducing the production of chemical wastes in sensor fabrication. The present review includes green electrochemical (bio) sensors which are based on firstly, green sensors comprising natural and non-hazardous materials (e.g., paper/clay/zeolites/biowastes), secondly sensors based on nanomaterials synthesized by green methods and lastly sensors constituting green solvents (e.g., ionic liquids/deep eutectic solvents). Electrochemical performances of such green sensors and their benefits such as biodegradability, non-toxicity, sustainability, low-cost, sensitive surfaces, etc. Have been discussed for quantification of various target analytes. Associated challenges, possible solutions, and opportunities towards fabricating green electrochemical sensors and biosensors have been provided in the conclusion section.

Biomimetic Root-like TiN/C@S Nanofiber as a Freestanding Cathode with High Sulfur Loading for Lithium-Sulfur Batteries.

It is a tough issue to achieve high electrochemical performance and high sulfur loading simultaneously, which is of important significance for practical Li-S batteries applications. Inspired by the transportation system of the plant root in nature, a biomimetic root-like carbon/titanium nitride (TiN/C) composite nanofiber is designed as a freestanding current collector for the high sulfur loading cathode. Like the plant root which absorbs water and oxygen from soil and transfers them to the trunk and branches, the root-like TiN/C matrix provides high-efficiency polysulfide, electron, and electrolyte transfer for the redox reactions via its three-dimensional-porous interconnected structure. In the meantime, TiN can not only anchor the polysulfides via the polar Ti-S and N-S bond but also further facilitate the redox reaction because of its high catalytic effect. With 4 mg cm-2 sulfur loading, the TiN/C@S cathode delivers a high initial discharge capacity of 983 mA h g-1 at 0.2 C current density; after 300 charge/discharge cycles, the discharge capacity remains 685 mA h g-1, corresponding to a capacity decay rate of ∼0.1%. Even when the sulfur loading is increased to 10.5 mg cm-2, the cell still delivers a high capacity of 790 mA h g-1 and a decent cycle life. We believe that this novel biomimetic root-like structure can provide some inspiration for the rational structure design of the high-energy lithium-sulfur batteries and other composite electrode materials.

Rotating-disk electrode analysis of the oxidation behavior of dissolved Li2O2 in Li-O2 batteries.

The development of the rechargeable Li-O2 battery (LOB) has encountered several bottlenecks till date. One of the biggest challenges is to lower the oxidation potential of Li2O2, which is the insulating and insoluble discharge product. A possible solution to this problem is to use high acceptor number (AN) or donor number (DN) solvents to increase the solubility of Li2O2, so that the dissolved Li2O2 can diffuse to the cathode surface and get oxidized at a relatively low potential. Herein, we explored the efficiency and side-reactions in the LOB charge process with different Li2O2 soluble electrolytes. The relationship between the solubility of Li2O2 and charging rate was analyzed quantitatively with ultraviolet-visible (UV-Vis) spectroscopy and rotating disk electrode experiments. As a result, electrolytes with high AN usually have higher solubility for Li2O2 than electrolytes with high DN, and thus exhibit higher Li2O2 oxidation rates. Nevertheless, higher Li2O2 solubility in high AN electrolytes also induces more severe side reactions and easily passivates the electrode surface. The trade-off between charging reaction rate and electrolyte stability is a key issue to be considered when designing high performance LOB electrolytes.

Highly sensitive and selective determination of methylergometrine maleate using carbon nanofibers/silver nanoparticles composite modified carbon paste electrode.

A highly sensitive and selective voltammetric method for determination of Methylergometrine maleate (MM) in pharmaceutical formulations, urine and blood serum samples has been developed based on enhanced electrochemical response of MM at carbon nanofibers and silver nanoparticles modified carbon paste electrode (CNF-AgNP-CPE). The electrode material was characterized by various techniques viz., X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. The electrocatalytic response of MM at CNF-AgNP-CPE was studied by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). Under optimized conditions, the proposed sensor exhibits excellent electrochemical response towards MM. The DPV study shows greatly enhanced electrochemical signal for MM at CNF-AgNP-CPE lending high sensitivity to the proposed sensor for MM detection. The peak (Ip) current for MM is found to be rectilinear in the range 4.0×10(-8)-2.0×10(-5)M with a detection limit of 7.1×10(-9)M using DPV. The feasibility of the proposed sensor in analytical applications was investigated by conducting experiments on commercial pharmaceutical formulations, human urine and blood serum samples, which yielded satisfactory recoveries of MM. The proposed electrochemical sensor offers high sensitivity, selectivity, reproducibility and practical utility. We recommend it as an authentic and productive electrochemical sensor for successful determination of MM.

Voltammetric determination of sumatriptan based on a graphene/gold nanoparticles/Nafion composite modified glassy carbon electrode.

A mixture of graphene oxide and tetrachloroauric acid was electrochemically co-reduced directly on a glassy carbon electrode (GCE) surface via cyclic voltammetry so as to form a graphene (Gr)-gold nanoparticles (AuNP) composite. This nanocomposite was then coated with nafion (NAF) film so as to form Gr/AuNP/NAF/GCE. Sumatriptan (SUM) is a drug belonging to the triptan class, used for the treatment of migraine headaches. In this work, an electrochemical method based on the adsorptive stripping differential pulse voltammetry (AdSDPV) employing Gr/AuNP/NAF/GCE has been proposed for the subnanomolar determination of SUM. Characterization of the electrode material has been carried out by UV-visible spectrophotometry, X-ray diffraction and scanning electron microscopy. Also the electrode surface has been characterized by means of cyclic voltammetry, electrochemical impedance spectroscopy, chronocoulometry. By employing Gr/AuNP/NAF/GCE at pH 7.0 phosphate buffer, a 20-fold enhancement in the AdSDPV signal was observed as compared to GCE. Under the optimized conditions, Ip (µA) was proportional to the SUM concentration in the range of 1.0×10(-6)-4.12×10(-5) M (R(2)=0.9991) and 2.14×10(-9)-1.0×10(-6) M (R(2)=0.9954) with a detection limit (3×SD/s) of 7.03×10(-10) M. The practical analytical utilities of the modified electrode were demonstrated by the determination of SUM in pharmaceutical formulations, human urine and blood serum samples. This proposed method was validated by HPLC and the results are in agreement at the 95% confidence level.