Wetting Adsorption

The common methods for the multi-site adsorption of DNA on carbonaceous-based material can be classified into physical (dry and wet) adsorption and electrostatic adsorption. 

Besides thick-layer DNA/GEC surface, a thin-layer DNA/GEC could be achieved by wet-adsorption of ss- and dsDNA and ODN onto a GEC transducer under static conditions [99,100]. In this case, the hydrated B-DNA form was stabilized over the GEC surface by weaker forces. Unlike the GEC surface modified by the thick DNA layer —produced in dry conditions—the thin-layer DNA/GEC surface required blocking treatment to avoid nonspecific... 

Fig. 21.1. Schematic representation of the manipulation of DNA biosensors using different strategies. (A) DNA biosensors modified with DNA by (Al) dry-adsorption and (A2) wet-adsorption on GEC platform. (B) DNA biosensors based on the single-point immobilization of biotinylated DNA on Av-GEB universal affinity platform. (C) Immobilization of DNA on magnetic beads followed by (Cl) the capture of the modified beads on m-GEC electrode (more details in Pividori and Alegret [58]).

Electrochemical genosensing of food pathogens based on DNA wet-adsorption on GEC as electrochemical transducer... 

Wet adsorption relies on leaving DNA to interact with the carbonaceous surface through physical forces in the presence of water. During wet adsorption, the stabilization of B-DNA is expected to occur on the carbonaceous surface, by keeping the hydration water of the DNA molecule. In this case, the hydrated B-DNA form is stabilized over the GEC surface by weaker forces as the water is kept on the DNA adsorbed molecule, it can be easily desorbed from the GEC surface if soaked in aqueous solutions. 

DNA can be easily immobilized on GEC by simple wet-adsorption onto GEC surface (Fig. 21.1(A2)). A small drop of DNA probe in acetate saline solution pH 4.8 [58] is put onto the surface of a GEC electrode in upright position. The immobilization of the probe was allowed to proceed for 15 min without applying any potential under static conditions. After the inosine-modified DNA probe immobilization, the DNA target was detected by the intrinsic DNA oxidation signal coming from the guanine moieties. Briefly, the procedure consists of the following... 

Wetting Adsorption at the interface Intimate contact with surface Displacement of air at interface... 

Energy conditions Wetting Adsorption on the solid Examples of adsorption isotherms of Figure 1.35 Example... 

Adsorbates Partial pressure of hydrocarbon (kPa) Water RH (%) Dry adsorption capacity (moles/kg) Wet adsorption capacity (moles/kg)... 

Adsorption and wetting Adsorption of gases and vapors, combined with IR spectroscopy, microcalorimetry, and so forth Temperature-programmed desorption of absorbed substances (ammonia, pyridine, and so forth, coupled with mass spectrometry and IR spectroscopy Heats of adsorption, specific surface area, pore size distribution, average pore diameter, and fractal dimension Acidic functional groups, relative acid strength ... 

PVT data for polymers are important both from the academic and practical points of view. On the scientific side, PVT data are frequently needed for model considerations on polymer solutions and melts. On the industrial side, these data are needed for process design. An equally important thermodynamic quantity is the surface tension of polymer melts, due to their relevance in wetting, adsorption, and adhesion. It may strongly govern such surface processes as film formation or coating. Here we report on PVT data and surface tensions of different random copolymers. We also relate thermodynamic quantities describing bulk properties to surface tension of polymer melts. 

Adsorption is an easy way to attach nucleic acids to solid surfaces, since no reagents or modified-DNA are required, as shown in Fig. 3.3. These features have promoted extensive use of adsorption as immobilization methodology in genetic analysis. The mainly claimed disadvantages of adsorption with respect to covalent immobilization are (i) nucleic acids may be readily desorbed from the substrate and (ii) base moieties may be unavailable for hybridization if they are bonded to the substrate in multiple sites [76]. However, the electrochemical detection strategy based on the intrinsic oxidation of DNA requires the DNA to be adsorbed in close contact with the electrochemical substrate by multisite attachment, as schematically shown in Fig. 3.4. This multisite attachment of DNA can be thus detrimental for its hybridization but is crucial for the detection based on its oxidation signals. The common method for the multisite physical adsorption of DNA on carbonaceous-based materials can be classified into dry or wet adsorptions. 

The "irreversible" behavior of the dry adsorbed DNA layer has been previously reported on glassy carbon electrodes [77]. DNA can be tightly and irreversibly immobilized on GEC by both dry and wet adsorption procedures under static conditions [78]. The dual nature... 

Electrochemical Genosensing Based on DNA Wet Adsorption on GEC as Electrochemical Transducer... 

DNA can be easily immobilized on GEC by simple wet adsorption onto GEC surface. A small drop of DNA probe in acetate saline... 

The adsorption method at controlled potential or without potential application called "wet adsorption" [16, 17] is the easiest way to immobilize DNA (or probes) onto carbon transducers [2, 18, 19]. There is no need of special reagents, expensive labeled nucleic acids, or long experimental steps in adsorption-based immobilization technique. Hovewer, random immobilization of DNA were obtained with this technique and nucleic acids bound weakly to the surface as parallel layers. Additionally, it is possible to aglomerate DNA onto the surface and when the electrode is rinsed stringently, noncovalently bound DNA can be removed from the transducer surface. 

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