Biosensors with high sensitivity, selectivity and a low limit of detection, reaching nano/picomolar concentrations of biomolecules, are important to the medical sciences and healthcare industry for evaluating physiological and metabolic parameters. Over the last decade, different nanomaterials have been exploited to design highly efficient biosensors for the detection of analyte biomolecules. The discovery of graphene has spectacularly accelerated research on fabricating low-cost electrode materials because of its unique physical properties, including high specific surface area, high carrier mobility, high electrical conductivity, flexibility, and optical transparency. Graphene and its oxygenated derivatives, including graphene oxide (GO) and reduced graphene oxide (rGO), are becoming an important class of nanomaterials in the field of biosensors. The presence of oxygenated functional groups makes GO nanosheets strongly hydrophilic, facilitating chemical functionalization. Graphene, GO and rGO nanosheets can be easily combined with various types of inorganic nanoparticles, including metals, metal oxides, semiconducting nanoparticles, quantum dots, organic polymers and biomolecules, to create a diverse range of graphene-based nanocomposites with enhanced sensitivity for biosensor applications. This review summarizes the advances in two-dimensional (2D) and three-dimensional (3D) graphene-based nanocomposites as emerging electrochemical and fluorescent biosensing platforms for the detection of a wide range of biomolecules with enhanced sensitivity, selectivity and a low limit of detection. The biofunctionalization and nanocomposite formation processes of graphene-based materials and their unique properties, surface functionalization, enzyme immobilization strategies, covalent immobilization, physical adsorption, biointeractions and direct electron transfer (DET) processes are discussed in connection with the design and fabrication of biosensors. The enzymatic and nonenzymatic reactions on graphene-based nanocomposite surfaces for glucose- and cholesterol-related electrochemical biosensors are analyzed. This review covers a very broad range of graphene-based electrochemical and fluorescent biosensors for the detection of glucose, cholesterol, hydrogen peroxide (H2O2), nucleic acids (DNA/RNA), genes, enzymes, cofactors nicotinamide adenine dinucleotide (NADH) and adenosine triphosphate (ATP), dopamine (DA), ascorbic acid (AA), uric acid (UA), cancer biomarkers, pathogenic microorganisms, food toxins, toxic heavy metal ions, mycotoxins, and pesticides. The sensitivity and selectivity of graphene-based electrochemical and fluorescent biosensors are also examined with respect to interfering analytes present in biological systems. Finally, the future outlook for the development of graphene based biosensing technology is outlined.

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A review on graphene-based nanocomposites for electrochemical and fluorescent biosensors

The study of electrochemical behavior of bioactive molecules has become one of the most rapidly developing scientific fields. Biotechnology and biomedical engineering fields have a vested interest in constructing more precise and accurate voltammetric/amperometric biosensors. One rapidly growing area of biosensor design involves incorporation of carbon-based nanomaterials in working electrodes, such as one-dimensional carbon nanotubes, two-dimensional graphene, and graphene oxide. In this review article, we give a brief overview describing the voltammetric techniques and how these techniques are applied in biosensing, as well as the details surrounding important biosensing concepts of sensitivity and limits of detection. Building on these important concepts, we show how the sensitivity and limit of detection can be tuned by including carbon-based nanomaterials in the fabrication of biosensors. The sensing of biomolecules including glucose, dopamine, proteins, enzymes, uric acid, DNA, RNA, and H2O2 traditionally employs enzymes in detection; however, these enzymes denature easily, and as such, enzymeless methods are highly desired. Here we draw an important distinction between enzymeless and enzyme-containing carbon-nanomaterial-based biosensors. The review ends with an outlook of future concepts that can be employed in biosensor fabrication, as well as limitations of already proposed materials and how such sensing can be enhanced. As such, this review can act as a roadmap to guide researchers toward concepts that can be employed in the design of next generation biosensors, while also highlighting the current advancements in the field.

http://pubs.acs.org/doi/pdf/10.1021/acsnano.5b05690

Engineered Carbon-Nanomaterial-Based Electrochemical Sensors for Biomolecules

Dopamine (DA) is an important neurotransmitter and its abnormal concentrations are associated with different diseases. Electrochemical detection of DA in real samples is challenging because of the presence of high concentrations of electroactive interferents such as uric acid (UA) and ascorbic acid (AA). Chemically modified electrodes have been widely used to counter the problems of poor sensitivity and selectivity faced at bare electrodes. We have briefly reviewed the materials that have been extensively used to fabricate modified electrode surfaces for detection of DA. The characteristics of the materials that improve the electrocatalytic activity of the modified surfaces are discussed. The boundary of search was limited to the electrochemical methods dealing with the simultaneous detection of DA, UA, and AA levels or detection of only DA in the presence of UA and AA. Challenges associated with the quantitative determination of dopamine in real samples are critically reviewed and the possible solutions are described.

Chemically modified electrodes for electrochemical detection of dopamine in the presence of uric acid and ascorbic acid: A review

Dopamine (DA) is an important catecholamine neurotransmitter in the mammalian central nervous system that influences several physiological functions. The impact of DA levels within the human body significantly affects the body functions. Maintaining DA level is essential and the electrochemical detection methods are often used to detect the DA level to regulate the body function. In this review, graphene (functionalized graphene and N-doped graphene) and its composites (metal, metal oxide, polymer, carbonaceous materials, clay, zeolite, and metal–organic framework based graphene composites) modified electrodes with their improved sensing performance towards DA along with several interfering species are described. Further, recent developments on the fabrication of various graphene based composite modified electrodes are also presented. Some important strategies to improve the selectivity and sensitivity towards DA with graphene based composite modified electrodes are also described.

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Graphene and its nanocomposite material based electrochemical sensor platform for dopamine

Herein, we report a multitasking Cu-MOF/rGO hybrid, fabricated by simple ultra-sonication of slow diffusion driven Cu-MOF crystals with chemically synthesized reduced graphene oxide (rGO). The molecular structure of the Cu-MOF was authenticated by single crystal X-ray studies. The prepared materials have been probed by various physicochemical characterization techniques. Due to the positive synergistic effects between Cu-MOF crystals and rGO nanosheets, the newly synthesized Cu-MOF/rGO hybrid delivers high charge storage efficiency (685.33 F g−1 at 1.6 A g−1), high energy (137.066 W h kg−1) and power density (4800.04 W kg−1) and excellent rate ability (retains 71.01% of its initial capacitance at 8 A g−1). Furthermore, the long cycle life (91.91% after 1000 cycles) of this hybrid indicates its high stability on the electrode surface. Additionally, the electrode modified with the Cu-MOF/rGO hybrid performs exceptionally towards the electrochemical detection of nitrite in a wide dynamic linear range of 3–40 000 μM (R2 = 0.99911), with a notable detection limit of 33 nm and a high sensitivity of 43.736 μA μM−1 cm−2. The versatility of the Cu-MOF/rGO modified electrode can be observed by distinguished selectivity in the presence of some common interfering species and also ability to detect nitrite in real samples.

A fascinating multitasking Cu-MOF/rGO hybrid for high performance supercapacitors and highly sensitive and selective electrochemical nitrite sensors

CTAB functionalized graphene oxide/multiwalled carbon nanotube composite modified electrode for the simultaneous determination of ascorbic acid, dopamine, uric acid and nitrite

Spiral-wound modules have been the most common configuration of packing flat-sheet membranes since the early development of polyamide (PA) membranes for water treatment applications. Conventional spiral-wound modules (SWMs) for desalination applications typically consist of several leaf sets, with each leaf set comprising feed spacers, membranes, and a permeate carrier (PC) wrapped around a permeate-collecting tube. The membrane area that can be packed into a given module diameter is limited by the overall leaf set thickness, restricting module productivity for a given membrane permeability. We describe here a novel industrial-scale method for successfully coating the polysulfone (PSf) ultrafiltration (UF) support layer directly onto a permeate carrier, instead of conventional non-woven fabric, as a precursor to the polyamide TFC coating, resulting in twofold benefits: (a) drastically simplifying the membrane fabrication process by eliminating the use of non-woven fabric and (b) increasing the throughput of each membrane module by facilitating the packing of a larger membrane area in a standard module housing. By combining the permeate carrier and membrane into a single sheet, the need for the non-woven support layer was eliminated, leading to a significantly reduced leaf set thickness, enabling a much larger membrane area to be packed in a given volume, leading to lower energy consumption per cubic meter of produced water. Molecular-weight cutoff (MWCO) values in the range of 36–96 kDa were found to be dependent on PC thickness and material. Nevertheless, the reinforced membranes were successfully fabricated with a ~9% reduction in membrane leaf thickness compared to a conventional membrane. Preliminary trials of coating a thin-film composite PA layer resulted in defect-free reverse osmosis (RO) membranes with a salt rejection of 94% and a flux of 40 L m−2 h−1 when tested against a 2000 mg/L NaCl feed solution at an operating pressure of 15 bar. Results from the testing of the 1812 and 2514 elements validated the novel concept and paved the way for further improvements towards full-scale RO membranes with the potential to be the next low-energy workhorse of the water industry.

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Development and Industrial-Scale Fabrication of Next-Generation Low-Energy Membranes for Desalination

Abstract The growth of NiCo-LDH/CoNi2S4/rGO composite on Ni foam was achieved with a simple one-step hydrothermal method. The obtained binder-free electrode (NiCo-LDH/CoNi2S4/rGO/Ni foam) was characterized with X-ray diffraction (XRD), field emission microscopy (FE-SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and galvanostastic charge/discharge (GCD). NiCo-LDH/CoNi2S4/rGO/Ni foam demonstrates a unique morphology with nanoparticles and nanowires mingled together, which endows the electrode large surface area as verified by the Brunauer–Emmett–Teller gas sorptometry measurement (BET). NiCo-LDH/CoNi2S4/rGO/Ni foam possesses excellent charge storage capabilities such as high areal capacitance, long cycling life and good rate performance. The asymmetric supercapacitor (ASC) with NiCo-LDH/CoNi2S4/rGO/Ni foam and activated carbon (AC) as positive and negative electrodes was assembled, characterized and successfully applied in practical applications, further confirming the great prospect of NiCo-LDH/CoNi2S4/rGO/Ni foam in energy storage.

One step synthesis of NiCo-LDH/CoNi2S4/rGO composite on Ni foam for asymmetric supercapacitor

Herein, interpenetrating network (IPN) hydrogels were successfully prepared for the first time through integrating two cross-linking reactions in water in one pot, including amine-anhydride reaction and subsequent photopolymerization. First, the polymer containing anhydride groups was prepared via free radical copolymerization of maleic anhydride and acrylamide. Second, the as-prepared polymer was dissolved in water with polyacrylamine hydrochloride, N-isopropylacrylamide, polyethylene glycol dimethacrylate, 2-acrylamido-2-methylpropanesulfonic acid, and photoinitiator to obtain a homogeneous transparent solution. Third, the mixed solution was put in water bath of 50°C for 1 h to obtain the first network via the amine-anhydride click reaction. Afterward, the second network was formed by photopolymerization. Finally, the swelling and drug release behavior of the hydrogels were studied with isoniazid as a model drug. The results show the IPN hydrogel possesses pH and temperature sensitivity and their controlled-release behavior can be tuned via adjusting pH and temperature. In view of the advantages of amine-anhydride reaction and photopolymerization, the strategy described here is of significance for the preparation of IPN hydrogel. 

Weikun Li

Papers

CTAB functionalized graphene oxide/multiwalled carbon nanotube composite modified electrode for the simultaneous determination of ascorbic acid, dopamine, uric acid and nitrite

Development and Industrial-Scale Fabrication of Next-Generation Low-Energy Membranes for Desalination

One step synthesis of NiCo-LDH/CoNi2S4/rGO composite on Ni foam for asymmetric supercapacitor

Fabrication and characterization of interpenetrating network hydrogels based on sequential amine‐anhydride reaction and photopolymerization in water

Magnetic-driving Giant Multilayer Polyelectrolyte Microcapsules for Intelligent Enhanced Oil Recovery