Nonspecific Physical Adsorption Research Articles

Liquid-solid heterojunction constructing bio-sensory floating-gate OECTs

The floating-gate organic electrochemical transistor (OECT) employs a distinct signal acquisition and amplification structure. This design offers two primary advantages: firstly, it mitigates the effects of non-specific physical adsorption during the sensing process and prevents contamination of the electrolyte solution by side reaction products, thereby enhancing detection accuracy. Secondly, it allows for an increased gate/electrolyte capacitance, optimizing the OECT’s signal amplification capability. Until now, optimizing the sensing electrode and control gate remains ambiguous. This current research uses a photosensitive liquid-solid heterojunction as the control gate. This choice is based on the observation that the photovoltage of −0.43 V remains unaffected by variations in electrode area, and any reduction in photocurrent due to area reduction can be offset by an increase in light intensity. Furthermore, given that the capacitance value of liquid-solid heterojunctions (4.386×10−2 F) significantly surpasses other components in equivalent circuits during light radiation, these heterojunctions can be considered self-driving and quasi-non-polarized. We confirmed the viability of this structural configuration through cortisol molecule detection. The potential application of this photosensitive liquid-solid heterojunction lies in constructing high-density and high-stability biosensors, a necessity in practical applications.

Electrostatic adsorption and removal mechanism of ochratoxin A in wine via a positively charged nano-MgO microporous ceramic membrane

Ochratoxin A (OTA) is a very important mycotoxin. However, there are few studies on the removal of OTA in wine because of the great influence on product quality and difficulty in practical application. A nano-MgO-modified diatomite ceramic membrane (MCM) with a high positive charge was prepared and applied to remove OTA in wine. The isotherm adsorption between the positively charged membrane and OTA was in accordance with the Langmuir model, with a maximum adsorption capacity of 806 ng/g at 25 °C. All of the changes in adsorption enthalpy (ΔH), adsorption free energy (ΔG) and adsorption entropy (ΔS) were negative, which indicated that the combination of nano-MgO MCM and OTA was a spontaneous exothermic and nonspecific physical adsorption process. The concentrations of OTA in adsorption-treated wines were lower than 2 μg/kg, and the removal rates exceeded 92%. After OTA removal, the composition of wines was preserved to some extent.

Silicon and hydrogenated amorphous silicon carbide as biofunctional platforms for immunosensors

In this work, we evaluate the performance of two biofunctionalization processes on silicon and hydrogenated amorphous silicon carbide (a-SiC:H). The biofunctionalization processes were designed to immobilize antibodies via non-specific physical adsorption or covalent attachment. The impact of the two surface types (crystalline and amorphous) on the resulting immunosensing layer is discussed in terms of the possible orientation, stability, and bioactivity of the immobilized antibodies. To evaluate the formation of active groups on the surface before and after the immobilization process, we used Fourier-transform infrared (FTIR) spectroscopy. On the other hand, to visualize the topography changes on the different surfaces with immobilized antibodies, we used atomic force microscopy (AFM). ELISA assay was conducted to obtain a quantitative parameter associated with the density of immobilized antibodies on the platforms. The results showed that the antibodies were immobilized on both platforms by any of the two immobilization mechanisms. The antigen capture did not show a direct relationship with the antibody estimation made by ELISA. According to the results, the a-SiC:H platforms by covalent attachment achieved the highest density of immobilized antibodies compared to silicon. However, its performance in the antigen detection assay was lower compared to silicon platforms. We concluded that the performance of the silicon platform was better in terms of its biofunctionalization and antigen detection. The orientation and structural integrity of the antibodies on the platforms was crucial to its performance on antigen detection.

Controlled hierarchical architecture in poly [oligo (ethylene glycol) methacrylate-b-glycidyl methacrylate] brushes for enhanced label-free biosensing

Surface-grafted polymer brushes have been long reported as a desired matrix for biosensing applications, owing to enhanced immobilization capacity and anti-fouling properties. However, simultaneous optimizing binding signal and minimizing non-specific adsorption using polymer matrix is still a challenge, due to the lack of systematic structural and composition optimization at molecular level. In this research, a series of block copolymer brushes with controlled hierarchical architectures, poly [oligo (ethylene glycol) methacrylate-b-glycidyl methacrylate] (POEMGA-b-PGMA) were prepared by two-stage surface-initiated polymerization. Surface plasmon resonance imaging (SPRi), as a real-time and label-free biosensing technology, was used as means to evaluate their detecting performances of bio-interactions. In contrast to one-layer poly (glycidyl methacrylate) (PGMA), 4.7-fold enhancement of signal-to-background (S/B) was achieved in bi-layer POEGMA-b-PGMA surface, by using rabbit IgG (R-IgG, in 10% serum) and a microarray of goat-anti-rabbit IgG (G-R-IgG) as the system of study. Interestingly, the binding signals and anti-fouling performances of the polymer brushes could be enhanced simultaneously by increasing the length of the monomer in the primary layer. Theoretically, it mainly owed to the formation of a densely packing protective primary layer against non-specific physical adsorption and a spatially optimized secondary layer of minimized steric hindrance that allowed optimum binding of analytes.

Nanometer-sized extracellular matrix coating on polymer-based scaffold for tissue engineering applications.

Surface modification can play a crucial role in enhancing cell adhesion to synthetic polymer-based scaffolds in tissue engineering applications. Here, we report a novel approach for layer-by-layer (LbL) fabrication of nanometer-size fibronectin and gelatin (FN-G) layers on electrospun fibrous poly(carbonate urethane)urea (PCUU) scaffolds. Alternate immersions into the solutions of fibronectin and gelatin provided thickness-controlled FN-G nano-layers (PCUU(FN-G) ) which maintained the scaffold's 3D structure and width of fibrous bundle of PCUU as evidenced by scanning electron miscroscopy. The PCUU(FN-G) scaffold improved cell adhesion and proliferation of bladder smooth muscles (BSMCs) when compared to uncoated PCUU. The high affinity of PCUU(FN-G) for cells was further demonstrated by migration of adherent BSMCs from culture plates to the scaffold. Moreover, the culture of UROtsa cells, human urothelium-derived cell line, on PCUU(FN-G) resulted in an 11-15 μm thick multilayered cell structure with cell-to-cell contacts although many UROtsa cells died without forming cell connections on PCUU. Together these results indicate that this approach will aid in advancing the technology for engineering bladder tissues in vitro. Because FN-G nano-layers formation is based on nonspecific physical adsorption of fibronectin onto polymer and its subsequent interactions with gelatin, this technique may be applicable to other polymer-based scaffold systems for various tissue engineering/regenerative medicine applications.

CNT loading into cationic cholesterol suspensions show improved DNA binding and serum stability and ability to internalize into cancer cells

Methods which disperse single-walled carbon nanotubes (SWNTs) in water as ‘debundled’, while maintaining their unique physical properties are highly useful. We present here a family of cationic cholesterol compounds (Chol+) {Cholest-5en-3β-oxyethyl pyridinium bromide (Chol-PB+), Cholest-5en-3β-oxyethyl N-methyl pyrrolidinium bromide (Chol-MPB+), Cholest-5en-3β-oxyethyl N-methyl morpholinium bromide (Chol-MMB+) and Cholest-5en-3β-oxyethyl diazabicyclo octanium bromide (Chol-DOB+)}. Each of these could be easily dispersed in water. The resulting cationic cholesterol (Chol+) suspensions solubilized single-walled carbon nanotubes (SWCNTs) by the non-specific physical adsorption of Chol+ to form stable, transparent, dark aqueous suspensions at room temperature. Electron microscopy reveals the existence of highly segregated CNTs in these samples. Zeta potential measurements showed an increase in potential of cationic cholesterol aggregates on addition of CNTs. The CNT–Chol+ suspensions were capable of forming stable complexes with genes (DNA) efficiently. The release of double-helical DNA from such CNT–Chol+ complexes could be induced upon the addition of anionic micellar solution of SDS. Furthermore, the CNT-based DNA complexes containing cationic cholesterol aggregates showed higher stability in fetal bovine serum media at physiological conditions. Confocal studies confirm that CNT–Chol+ formulations adhere to HeLa cell surfaces and get internalized more efficiently than the cationic cholesterol suspensions alone (devoid of any CNTs). These cationic cholesterol–CNT suspensions therefore appear to be a promising system for further use in biological applications.

Synthesis of highly magnetic graphite-encapsulated FeCo nanoparticles using ahydrothermal process

The graphite encapsulation of metal alloy magnetic nanoparticles has attracted attentionfor biological applications because of the high magnetization of the encapsulatedparticles. However, most of the synthetic methods have limitations in terms ofscalability and economics because of the demanding synthetic conditions and lowyields. Here, we show that well controlled graphite-encapsulated FeCo core–shellnanoparticles can be synthesized by a hydrothermal method, simply by mixingFe/Co with sucrose as acarbon source. Various Fe/Co metal ratios were used to determine the compositional dependence of the saturationmagnetization and relaxivity coefficient. Transmission electron microscopy indicated thatthe particle sizes were 7 nm. In order to test the capability of graphite-encapsulated FeConanoparticles as magnetic resonance imaging (MRI) contrast agents, these nanoparticleswere solubilized in water by the nonspecific physical adsorption of sodium dodecylbenzenesulfonate.

Fluorogenic Polydiacetylene Supramolecules: Immobilization, Micropatterning, and Application to Label-Free Chemosensors

This Account describes a new strategy for the preparation of label-free sensor systems based on the fluorogenic properties of the conjugated polymer, polydiacetylene (PDA). PDA has been extensively investigated as a sensor matrix, owing to a brilliant blue-to-red color transition that takes place in response to environmental perturbations. It has been known for some time that "blue-phase" PDAs are nonfluorescent while their "red-phase" counterparts fluoresce. For the most part, however, the significance of the different fluorogenic properties of PDAs has been ignored in the context of sensor applications. In the course of developing PDA-based sensors, we discovered that PDA vesicles can be readily immobilized on solid substrates. This is an attractive property of PDAs since it leads to the combined advantages of the vesicle sensors (which have three-dimensional interactions between sensor and target molecules) and film sensors (which are applicable to a two-dimensional array or chip format). Stable blue-phase immobilized PDAs can be prepared by employing one of three strategies involving the formation of covalent adducts, biotin-avidin complexes, or complexes formed through nonspecific physical adsorption. A procedure for generating well-patterned fluorescence images is necessary for the immobilized PDAs to function in chip-based sensor systems. Patterned fluorescence images are readily constructed by employing (1) the photolithographic technique, (2) the micromolding in capillaries (MIMIC) method, or (3) an array spotting system. Heat treatment of the patterned "blue-phase" PDA vesicles transforms the nonfluorescent images into their fluorescent red forms. The observation that finely resolved fluorescence patterns can be generated by heat treatment of microarrayed PDAs is highly significant in that it indicates that fluorescence signals might be produced by specific molecular recognition events. Indeed, red fluorescence emission is observed when immobilized PDAs are subjected to specific molecular recognition events, such as ligand--cyclodextrin or protein-protein interactions. The facile immobilization of PDA vesicles on solid substrates and the affinity-induced fluorescence emission combine to make this system applicable to the fabrication of label-free PDA sensors. Since in theory any molecular recognition event that promotes the blue-to-red color transition of PDAs should result in the generation of fluorescence, it should be possible to reformat a variety of previously described colorimetric PDA sensors into fluorescence-based sensor systems. The fluorescence properties of PDAs, when combined with modern methods for the fabrication of microarrays, should stimulate the development of a number of new label-free chemosensor systems.

Recent developments in the site‐specific immobilization of proteins onto solid supports

Immobilization of proteins onto surfaces is of great importance in numerous applications, including protein analysis, drug screening, and medical diagnostics, among others. The success of all these technologies relies on the immobilization technique employed to attach a protein to the corresponding surface. Non-specific physical adsorption or chemical cross-linking with appropriate surfaces results in the immobilization of the protein in random orientations. Site-specific covalent attachment, on the other hand, leads to molecules being arranged in a definite, orderly fashion and allows the use of spacers and linkers to help minimize steric hindrances between the protein and the surface. The present work reviews the latest chemical and biochemical developments for the site-specific covalent attachment of proteins onto solid supports.

Determination of the Concentration of Single-Walled Carbon Nanotubes in Aqueous Dispersions Using UV−Visible Absorption Spectroscopy

Stable, homogeneous, aqueous dispersions of single-walled carbon nanotubes (SWNTs) are prepared by nonspecific physical adsorption of surfactants enhanced by sonication. Upon centrifugation, supernatant and precipitate phases are obtained. The initial weights of the SWNTs and the surfactant are divided between these two phases, and the respective SWNT concentration in each phase is unknown. The focus of this work is on the determination of the true concentration of raw, exfoliated HiPCO SWNTs in the supernatant phase. A UV-visible absorption-based approach is suggested for a direct measurement of the SWNT and the surfactant concentration in the supernatant. UV-visible absorbance spectra of SWNTs-surfactant dispersions and surfactants alone reveal that the intensity of a certain peak, attributed to the pi-plasmon resonance absorption, is unaffected by the presence of most surfactants. A calibration plot is then made by monitoring the intensity of the peak as a function of the true concentration of the exfoliated SWNTs. Thus, we are able to determine the unknown concentration of surfactant-dispersed HiPCO SWNTs in the supernatant solution, simply by measuring its optical absorbance. Moreover, we can now calculate the surfactant efficiency in dispersing SWNTs. Cryogenic-transmission electron microscopy and thermogravimetric analysis techniques are used for the characterization of these dispersions and to complement the UV-visible measurements.

High Weight Fraction Surfactant Solubilization of Single-Wall Carbon Nanotubes in Water

We report a simple process to solubilize high weight fraction single-wall carbon nanotubes in water by the nonspecific physical adsorption of sodium dodecylbenzene sulfonate. The diameter distribution of nanotubes in the dispersion, measured by atomic force microscopy, showed that even at 20 mg/mL ∼63 ± 5% of single-wall carbon nanotube bundles exfoliated into single tubes. A measure of the length distribution of the nanotubes showed that our dispersion technique reduced nanotube fragmentation.

Stereospecific and Structure Specific Recognition of Two- and Three- Dimensionally Organized Surfacesby Biological Macromolecules

The interactions between proteins and crystal surfaces can range from totally non-specific physical adsorption of the macromolecule on the surface to the most highly specific complementarity. Among proteins, antibodies are the tool that nature evolved to recognize foreign invaders. Recognition occurs through complementarity of their binding sites with the surface of the invader. Recognition in antibody-antigen interactions was studied using crystals and monolayers of cholesterol and its structural isomers as well as crystals of dinitrobenzene. Sequencing and modeling of specific antibodies show an impressive degree of complementarity between the antibodies and the organized surfaces they recognize. In the cholesterol system, one antibody binds to monolayers of cholesterol and entcholesterol with affinity in the range of 10 m 12 M and high stereoselectivity, but no enantioselectivity. We conclude that the low level of chirality exposed at the monolayer surface limits the chiral discrimination.

Diffuse reflectance IR study of molecular hydrogen and deuterium adsorbed at 77 K on NaA zeolite Part 1.—Fundamentals, combination and vibrational–rotational modes

V. B. Kazansky, V. Yu. Borovkov and H. G. Karge, J. Chem. Soc., Faraday Trans., 1997, 93, 1843 DOI: 10.1039/A700079K

Biomolecular Recognition at Phospholipid-Covered Polystyrene Microspheres

Cholera toxin and its receptor (the monosialoganglioside GM1) are used as a model pair to evaluate phospholipid-covered polystyrene microspheres regarding their suitability as a matrix to promote biomolecular recognition. Toxin binding to GM1/phosphatidylcholine-covered polystyrene microspheres occurs in a molar proportion of 1:1 (toxin/GM1) and is strictly dependent on GM1 incorporation in the phospholipid-covered latex. Phospholipid coverage on latex offers a proper environment to GM1/toxin recognition. Phospholipid assembly on the latex surface depends on the physical state of the bilayer. A dipalmitoylphosphatidylcholine (DPPC) monolayer coverage on latex at room temperature can be obtained by incubating latex and DPPC vesicles in buffer solution for 1 h at 65 °C. Nonspecific physical adsorption of cholera antitoxin on latex surfaces can be controlled by covering latex with phospholipids. Upon increasing dipalmitoylphosphatidylcholine (DPPC) concentration in latex dispersions, nonspecific cholera antitoxin adsorption on latex decreases. This provides a way of modulating protein adsorption on the DPPC-covered latex. Changing the hydrophobic−hydrophilic character of the antitoxin itself by covalent attachment of an N-acyl residue increases physical adsorption on bare latex and decreases it on phospholipid-covered latex. The results may be of importance in development of immunoassays and biosensors for amplification of biomolecular recognition.

Adsorption of paraffin hydrocarbons on nonirradiated and ?-irradiated chromium oxide

1. On Cr2O3 containing Cr2+ ions, C2-C6 paraffin hydrocarbons are adsorbed rapidly and reversibly at temperatures below 100°. The heats of adsorption at low degrees of surface coverage are 1.5–2 times as great as the heat of nonspecific physical adsorption of paraffins on other oxides. As the surface of Cr2O3 is covered, the heat of adsorption decreases. 2. At temperatures above 100° on the investigated sample of Cr2O3, against a background of equilibrium adsorption, there is an activated irreversible chemisorption. 3. Equilibrium adsorption of paraffins with increased heats and irreversible chemisorption occur on Cr2+ions. 4. It was hypothesized that the increase in the adsorption of n-C6H14 after γ irradiation of Gr2O3is associated with the formation of supplementary amounts of Cr2+ions after the capture of electrons by Cr3+ ions.