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1.
Front Mol Biosci ; 8: 651232, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-33869287

RESUMO

We report on the fabrication and characterisation of graphene field-effect transistor (GFET) biosensors for the detection of Clusterin, a prominent protein biomarker of Alzheimer's disease (AD). The GFET sensors were fabricated on Si/SiO2 substrate using photolithographic patterning and metal lift-off techniques with evaporated chromium and sputtered gold contacts. Raman Spectroscopy was performed on the devices to determine the quality of the graphene. The GFETs were annealed to improve their performance before the channels were functionalized by immobilising the graphene surface with linker molecules and anti-Clusterin antibodies. Concentration of linker molecules was also independently verified by absorption spectroscopy using the highly collimated micro-beam light of Diamond B23 beamline. The detection was achieved through the binding reaction between the antibody and varying concentrations of Clusterin antigen from 1 to 100 pg/mL, as well as specificity tests using human chorionic gonadotropin (hCG), a glycoprotein risk biomarker of certain cancers. The GFETs were characterized using direct current (DC) 4-probe electrical resistance (4-PER) measurements, which demonstrated a limit of detection of the biosensors to be ∼ 300 fg/mL (4 fM). Comparison with back-gated Dirac voltage shifts with varying concentration of Clusterin show 4-PER measurements to be more accurate, at present, and point to a requirement for further optimisation of the fabrication processes for our next generation of GFET sensors. Thus, we have successfully fabricated a promising set of GFET biosensors for the detection of Clusterin protein biomarker. The developed GFET biosensors are entirely generic and also have the potential to be applied to a variety of other disease detection applications such as Parkinson's, cancer, and cardiovascular.

2.
Food Chem ; 355: 129547, 2021 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-33773454

RESUMO

The detection of food adulterants and toxicants can prevent a large variety of adverse health conditions for the global population. Through the process of rapid sensing enabled by deploying novel and robust sensors, the food industry can assist in the detection of adulterants and toxicants at trace levels. Sensor platforms which exploit graphene-based nanomaterials satisfy this requirement due to outstanding electrical, optical and thermal properties. The materials' facile conjugation with linkers and biomolecules along with the option for further enhancement using nanoparticles results in highly sensitive and selective sensing characteristics. This review highlights novel applications of graphene derivatives for detection covering three important approaches; optical, electrical (field-effect) and electrochemical sensing. Suitable graphene-based sensors for portable devices as point-of-need platforms are also presented. The future scope of these sensors is discussed to showcase how these emerging techniques will disrupt the food detection sector for years to come.


Assuntos
Análise de Alimentos/métodos , Contaminação de Alimentos/análise , Grafite/química , Eletricidade , Nanotecnologia
3.
Langmuir ; 30(33): 9991-10001, 2014 Aug 26.
Artigo em Inglês | MEDLINE | ID: mdl-25084476

RESUMO

Here we show that transport-generated phase separation at the air-liquid interface in systems containing self-assembling amphiphilic molecules and polymers can be controlled by the relative humidity (RH) of the air. We also show that our observations can be described quantitatively with a theoretical model describing interfacial phase separation in a water gradient that we published previously. These phenomena arises from the fact that the water chemical potential corresponding to the ambient RH will, in general, not match the water chemical potential in the open aqueous solution. This implies nonequilibrium conditions at the air-water interface, which in turn can have consequences on the molecular organization in this layer. The experimental setup is such that we can control the boundary conditions in RH and thereby verify the predictions from the theoretical model. The polymer-surfactant systems studied here are composed of polyethylenimine (PEI) and hexadecyltrimethylammonium bromide (CTAB) or didecyldimethylammonium bromide (DDAB). Grazing-incidence small-angle X-ray scattering results show that interfacial phases with hexagonal or lamellar structure form at the interface of dilute polymer-surfactant micellar solutions. From spectroscopic ellipsometry data we conclude that variations in RH can be used to control the growth of micrometer-thick interfacial films and that reducing RH leads to thicker films. For the CTAB-PEI system, we compare the phase behavior of the interfacial phase to the equilibrium bulk phase behavior. The interfacial film resembles the bulk phases formed at high surfactant to polymer ratio and reduced water contents, and this can be used to predict the composition of interfacial phase. We also show that convection in the vapor phase strongly reduces film formation, likely due to reduction of the unstirred layer, where diffusive transport is dominating.

4.
Langmuir ; 29(31): 9874-80, 2013 Aug 06.
Artigo em Inglês | MEDLINE | ID: mdl-23837868

RESUMO

Lipid cubic phases are complex nanostructures that form naturally in a variety of biological systems, with applications including drug delivery and nanotemplating. Most X-ray scattering studies on lipid cubic phases have used unoriented polydomain samples as either bulk gels or suspensions of micrometer-sized cubosomes. We present a method of investigating cubic phases in a new form, as supported thin films that can be analyzed using grazing incidence small-angle X-ray scattering (GISAXS). We present GISAXS data on three lipid systems: phytantriol and two grades of monoolein (research and industrial). The use of thin films brings a number of advantages. First, the samples exhibit a high degree of uniaxial orientation about the substrate normal. Second, the new morphology allows precise control of the substrate mesophase geometry and lattice parameter using a controlled temperature and humidity environment, and we demonstrate the controllable formation of oriented diamond and gyroid inverse bicontinuous cubic along with lamellar phases. Finally, the thin film morphology allows the induction of reversible phase transitions between these mesophase structures by changes in humidity on subminute time scales, and we present time-resolved GISAXS data monitoring these transformations.


Assuntos
Lipídeos/química , Tamanho da Partícula , Espalhamento a Baixo Ângulo , Propriedades de Superfície , Difração de Raios X
5.
Langmuir ; 25(7): 4047-55, 2009 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-19714828

RESUMO

We have investigated the spontaneous self-assembly of solid, mesostructured films that form at the air-solution interface on solutions containing a neutral water-soluble polymer and catanionic surfactant mixtures of hexadecyl-trimethylammonium bromide (CTAB) and sodium dodecylsulphate (SDS). The formation processes and structures were probed using neutron reflectivity, X-ray reflectivity, off-specular time-resolved scattering, and grazing incidence diffraction. The mesostructures of films prepared with polyethylene oxide, polyethylenimine, and polyacrylamide at various cationic/anionic surfactant molar ratios are compared. The results suggest that polymers having a weak interaction with the surfactants cause a depletion aggregation process that results in a lamellar phase, whereas polymers having a stronger interaction with the surfactants produce more complex mesostructures in the films.

6.
Langmuir ; 25(24): 13776-83, 2009 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-19572512

RESUMO

Gel diagrams based on tube inversion and oscillatory rheometry are reported for Pluronic copolymers F127 (E(98)P(67)E(98)) and P123 (E(21)P(67)E(21)) in mixtures with anionic surfactant sodium dodecyl sulfate (SDS). Total concentrations (c, SDS+copolymer) were as high as 50 wt % with mole ratios SDS/copolymer (mr) in the ranges 1-5 (F127) and 1-7 (P123). Temperatures were as high as 90 degrees C. Determination of the temperature dependences of the dynamic moduli served to confirm the gel boundaries from tube inversion and to reveal the high elastic moduli of the gels, e.g., compared at comparable positions in the gel phase, a 50 wt % SDS/P123 with mr = 7 had G' three times that of a corresponding gel of P123 alone. Small-angle X-ray scattering (SAXS) was used to show that the structures of all the SDS/F127 gels were bcc and that the structures of the SDS/P123 gels with mr = 1 were either fcc (c = 30 wt %) or hex (c = 40 wt %). Assignment of structures to SDS/P123 gels with values of mr in the range 3-7 was more difficult, as high-order scattering peaks could be very weak, and at the higher values of c and mr, the SAXS peaks included multiple reflections.

7.
J Colloid Interface Sci ; 317(2): 585-92, 2008 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-17964590

RESUMO

Recently we have investigated the formation of novel thick, solid, mesostructured films of polymer/surfactant mixtures which form spontaneously at the air-solution interface. Here we report studies of the effect of adding a series of sparingly soluble species to the precursor solution, to alter the mesostructure of cetyltrimethylammonium bromide/polyethylenimine films and to investigate the incorporation of small molecules within the films. Small-angle neutron scattering confirmed that cyclohexane and decane evenly swell the micelles in film forming solutions, while cyclohexanol extends the prolate micelles along their long axis. Although the presence of these additives in solution did not greatly affect the formation of the film, it was observed that they did influence the structure of the films. Films produced with decane consisted of a cubic phase rather the conventional 2-D hexagonal phase, whilst both cyclohexane and cyclohexanol enhance the level of ordering in low MW polymer films. Benzene was found to have no significant effect on the film.

8.
Langmuir ; 23(8): 4589-98, 2007 Apr 10.
Artigo em Inglês | MEDLINE | ID: mdl-17371057

RESUMO

Mesostructured films of alkyltrimethylammonium bromides or cetylpyridinium bromide and polyethylenimines that spontaneously self-assemble at the air/water interface have been examined using a range of surface sensitive techniques. These films are unusual in that they can be micrometers thick and are relatively robust. Here we show that the films can be cross-linked and thus removed from the liquid surface where they form, as solid, mesostructured polymer-surfactant membranes. Cross-linking causes little change in the structure of the films but freezes in the metastable mesostructures, enhancing the potential of these films for future applications. Cross-linked films, dried after removal from the solution surface, retain the ordered nanoscale structure within the film. We also report grazing incidence X-ray diffraction (GID), which shows that most films display scattering consistent with 2D-hexagonal phase crystallites of rodlike surfactant micelles encased in polymer. Polymer branching makes little difference to the film structures; however, polymer molecular weight has a significant effect. Films with lower polymer MW are generally thinner and more ordered, while higher polymer MW films were thicker and less ordered. Increased pH causes formation of thicker films and improves the ordering in low MW films, while high MW films lose order. To rationalize these results, we propose a model for the film formation process that relates the kinetic and thermodynamic limits of phase separation and mesophase ordering to the structures observed.


Assuntos
Polímeros/química , Tensoativos/química , Cátions , Físico-Química/métodos , Reagentes para Ligações Cruzadas/química , Reagentes para Ligações Cruzadas/farmacologia , Concentração de Íons de Hidrogênio , Cinética , Micelas , Modelos Químicos , Estrutura Molecular , Nêutrons , Polietilenoimina/química , Hidróxido de Sódio/química , Propriedades de Superfície , Termodinâmica
9.
Chem Commun (Camb) ; (10): 1068-70, 2007 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-17325808

RESUMO

A new type of surfactant templated polymer film, which spontaneously forms at the air/water interface into micron-thick structures, was prepared from a water-soluble polymer and a catanionic surfactant mixture; the film is stable, highly ordered and robust, requiring no cross-linking agents to fix the structure.


Assuntos
Ânions , Cátions , Membranas/química , Nanoestruturas , Polímeros/química , Tensoativos/química , Cetrimônio , Compostos de Cetrimônio/química , Iminas/química , Polietilenoglicóis/química , Propriedades de Superfície
10.
J Phys Chem B ; 110(11): 5330-6, 2006 Mar 23.
Artigo em Inglês | MEDLINE | ID: mdl-16539465

RESUMO

Surfactant-templated polymer films prepared from polyethylenimine (PEI), cetyltrimethylammonium bromide (CTAB), and octaethylene glycol monohexadecyl ether (C(16)E(8)) were examined and the effect of increasing the percentage of nonionic surfactant in the micelles measured using both surface and bulk-sensitive techniques. It was found that there is a strong interaction between CTAB and C(16)E(8), although no interaction between the C(16)E(8) and PEI was observed. Generally, increasing the percentage of C(16)E(8) in the micelles decreases both the thickness and degree of order in the films; however, it was observed, depending on the conditions, that films could still be formed with as little as 20% cationic surfactant. Experiments on the CTAB/Brij56/PEI system were also performed and these indicate that it is similar to the CTAB/C(16)E(8)/PEI system.

11.
Langmuir ; 20(15): 6246-51, 2004 Jul 20.
Artigo em Inglês | MEDLINE | ID: mdl-15248709

RESUMO

Langmuir and Langmuir-Blodgett (LB) films of a cationic amphiphilic porphyrin mixed with n-alkanes octadecane and hexatriacontane were prepared and characterized, to examine the influence of the alkanes on film structure and stability. While the structure present in these films was controlled primarily by the porphyrin, the addition of the alkanes resulted in significant changes to both the phase behavior of the Langmuir films and the molecular arrangement of the LB films. These changes, as well as the observed chain length effects, are explained in terms of the intermolecular interactions present in the films.

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