Ken Kojio

Bovine serum albumin adsorption onto immobilized organotrichlorosilane surface: Influence of the phase separation on protein adsorption patterns

Octadecyltrichlorosilane (OTS) and [2-(perfluorooctyl)ethyl]trichlorosilane (FOETS) monolayers and their mixed monolayer were polymerized on a water subphase and subsequently immobilized onto a silicon wafer surface by covalent bonding. Atomic force microscopic (AFM) observation of the mixed (OTS/FOETS) monolayer revealed the formation of a phase-separated structure. Protein-adsorption behavior onto the monolayers was investigated in situ on the basis of an attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopic flow cell method and the morphology of the monolayer surface-adsorbed bovine serum albumin (BSA) was observed by AFM. Protein adsorption behavior observed by ATR-FT-IR flow cell method revealed that the amount of BSA adsorption onto the OTS and FOETS monolayers increased remarkably at an initial experimental stage and attained a steady state within a few minutes at pH 7.5. The amount of steady state adsorption was c. 0.18-0.2 microgcm(-2). AFM observation of the monolayer after exposure to BSA solution suggested that BSA adsorbed in the end-on adsorption state on OTS monolayer and side-on one in the FOETS monolayer, respectively. However, in the case of the mixed (OTS/FOETS) monolayer, ATR-FT-IR flow cell experiment revealed that the amount of steady state adsorption of BSA was suppressed. Also, AFM observation revealed that at pH 7.5, BSA preferentially adsorbed onto the FOETS phase of the mixed (OTS/FOETS) monolayer, which had a higher interfacial free energy against water. On the other hand, BSA adsorbed homogeneously onto the OTS and FOETS phases at the isoelectric point of BSA (pH 4.7). These results indicate that the preferential adsorption of BSA onto the FOETS phase in the mixed (OTS/FOETS) monolayer system is due to: (1) the minimization of the interfacial free energy between a monolayer surface and an aqueous solution; and (2) the electrostatic repulsion between BSA molecules bearing negative charges.

Scanning force microscopic studies of surface structure and protein adsorption behavior of organosilane monolayers

Alkyltrichlorosilanes, [2‐(perfluorooctyl)ethyl]trichlorosilane (FOETS) and their mixed monolayers were polymerized on the water subphase and were subsequently immobilized onto the silicon wafer surface by covalent bonding. Atomic force microscopic (AFM) observation of the [n‐octadecyltrichlorosilane(OTS)/FOETS] mixed monolayer revealed that the crystalline OTS formed circular domains of ∼1–2 μm in diameter that were surrounded by an amorphous FOETS matrix. Lateral force microscopic (LFM) and scanning viscoelasticity microscopic (SVM) observations of the (OTS/FOETS) mixed monolayer could also distinguish the difference in the physical and mechanical properties between domain and matrix. The (alkylsilane/FOETS) mixed monolayers with a shorter alkyl chain such as n‐dodecyltrichlorosilane (DDTS) did not show the phase‐separated structure maybe due to the lack in crystallinity of DDTS component. AFM observation of the [crystalline fatty acid (nonreactive)/FOETS (reactive)] mixed monolayer also revealed the ph...

Control of Mechanical Properties of Thermoplastic Polyurethane Elastomers by Restriction of Crystallization of Soft Segment

Mechanical properties of thermoplastic polyurethane elastomers based on either polyether or polycarbonate (PC)-glycols, 4,4’-dipheylmethane diisocyanate (1,1’-methylenebis(4-isocyanatobenzene)), 1,4-butanediol, were controlled by restriction of crystallization of polymer glycols. For the polyether glycol based-polyurethane elastomers (PUEs), poly(oxytetramethylene) glycol (PTMG), and PTMG incorporating dimethyl groups (PTG-X) and methyl side groups (PTG-L) were employed as a polymer glycol. For the PC-glycol, the randomly copolymerized PC-glycols with hexamethylene (C6) and tetramethylene (C4) units between carbonate groups with various composition ratios (C4/C6 = 0/100, 50/50, 70/30 and 90/10) were employed. The degree of microphase separation and mechanical properties of both the PUEs were investigated using differential scanning calorimetry, dynamic viscoelastic property measurements and tensile testing. Mechanical properties could be controlled by changing the molar ratio of two different monomer components.

Plasma protein adsorption behavior onto the surface of phase-separated organosilane monolayers on the basis of scanning force microscopy

Abstract The n -octadecyltrichlorosilane (OTS, CH 3 (CH 2 ) 17 SiCl 3 ), 18-nonadecenyltrichlorosilane (NTS, CH 2 CH(CH 2 ) 17 SiCl 3 ), [2-(perfluorooctyl)ethyl]trichlorosilane (FOETS, CF 3 (CF 2 ) 7 CH 2 CH 2 SiCl 3 ) monolayers, and their mixed monolayers were used as model surfaces for the study of protein adsorption mechanism. Surface plasmon resonance (SPR) spectroscopy was applied to analyze the protein adsorption behavior onto the monolayer surfaces. The surfaces after exposure of these monolayers to bovine serum albumin (BSA) and γ-globulin(IgG) solutions were observed with atomic force microscope(AFM). AFM observation revealed that the charged protein either below or above pI was preferentially adsorbed onto the FOETS phase of the phase-separated (OTS/FOETS) mixed monolayer. in situ AFM observation of monolayer surfaces in BSA solution also revealed the preferential adsorption of BSA onto the hydrophobic FOETS surface. SPR clarified that the amount of adsorbed protein in the charged state was lower than that in the neutral state. Adhesion force was not detected in the force–distance curve measurement between negatively-charged HOOC(CH 2 ) 9 SH chemisorbed cantilever tip and the OTS phase in the presence of adsorbed BSA on FOETS phase of mixed monolayer. These results indicate that the preferential adsorption of protein onto the FOETS phase for the mixed monolayer systems at either below or above pI is due to, (1) the minimization of interfacial free energy between the monolayer surface and the buffer solution; and (2) the electrostatic repulsion among protein molecules bearing charges.

Formation mechanism of n-octadecyltrichlorosilane monolayer prepared at the air/water interface

Abstract The n-octadecyltrichlorosilane (OTS) monolayer was prepared by the Langmuir–Blodgett method. The formation mechanism of the OTS monolayer on the water subphase was investigated on the basis of electron diffraction (ED) study, Fourier transform infrared external reflection spectroscopic (FT-IR/ERS) measurement and high-resolution atomic force microscopic (AFM) observation. Morphological changes in the monolayer in a compression process were observed by AFM. FT-IR/ERS measurement was performed for the monolayer at the air/water interface, and that the ED and AFM observations were done for the monolayer transferred onto substrate. ED study and high-resolution AFM observation revealed that the OTS monolayer was in a crystalline state at 293 K. Also, FT-IR/ERS measurement and AFM observation showed that the OTS molecules crystallize and polymerize spontaneously right after spreading a toluene solution of OTS on the water subphase. Then, during a monolayer compression, the crystalline OTS monolayer domain did not form the larger ones by sintering at the crystalline domain interface at 293 K. Also, AFM and ED observations revealed that the defect-diminished OTS monolayer could be successfully prepared by using the multi-step creep method.

In situ atomic force microscopic observation of albumin adsorption onto phase-separated organosilane monolayer surface

A mixed (n-octadecyltrichlorosilane (OTS)/[2-(perfluorooctyl)ethyl]trichlorosilane (FOETS)) monolayer was prepared on the water subphase and was subsequently immobilized onto the silicon wafer surface by chemical bonds. Atomic force microscopic (AFM) observation of the mixed (OTS/FOETS) monolayer revealed the formation of a phase-separated structure. In situ AFM observation of the adsorption behavior of bovine serum albumin (BSA) onto the mixed (OTS/FOETS) monolayers, successfully showed the adsorption behavior of BSA onto the phase-separated surface. It also revealed that in the case of pH 7.5, BSA was preferentially adsorbed onto the lower surface free energy FOETS phase of the mixed (OTS/FOETS) monolayer. On the other hand, BSA was adsorbed homogeneously onto the OTS and FOETS phases at the isoelectric point of BSA (pI 4.7). These results indicate that the preferential adsorption of BSA onto the FOETS phase in the mixed (OTS/FOETS) monolayer system may be due to: (1) the minimization of interfacial free energy between a monolayer surface and an aqueous solution; and (2) the electrostatic repulsion among BSA molecules bearing negative charges.

Scanning force microscopic study of surface structure and properties of (alkylsilane/ fluoroalkylsilane) mixed monolayers

(Alkylsilane/fluoroalkylsilane) mixed monolayers were immobilized covalently on a silicon wafer surface with stable surface structure. Atomic force microscopic observation of the n-octadecyltrichlorosilane (OTS)/[2-(perfluorooctyl)ethyl]trichlorosilane (FOETS) mixed monolayer revealed that the crystalline OTS circular domains of ca. 1–2μm in diameter were surrounded by a sealike amorphous FOETS matrix, even though the molar fraction of OTS was above 75%. Also, the phaseseparated monolayer can be prepared from FOETS, and a non-polymerizable and crystallizable amphiphile such as lignoceric acid (LA). The phase separation of the (alkylsilane/fluoroalkylsilane) mixed monolayer might be attributed to both faster spreading of FOETS molecules on the water surface and the crystallizable characteristics of alkylsilane molecules. The mixed monolayer of crystalline alkylsilane (OTS) and amorphous alkylsilane (n-dodecyltrichlorosilane, DDTS) formed a phase-separated structure on the water surface because of the crystallizable characteristics of OTS. Lateral force microscopic (LFM) observation revealed that the order of the magnitude of lateral force generated against the silicon nitride tip was: n-triacontyltrichlorosilane (TATS) domain with longer alkyl chain > amorphous FOETS matrix > crystalline OTS domain. On the other hand, scanning viscoelasticity microscopic observation revealed that the order of the magnitude of modulus was: Si substrate > crystalline OTS domain > amorphous FOETS matrix.

Effect of aggregation state on nanotribological behaviors of organosilane monolayers

Nanotribological behaviors of organosilane monolayers prepared by the Langmuir-Blodgett (LB) and chemisorption methods are discussed in terms of their aggregation states. Aggregation structure of the LB n-octadecyltrichlorosilane (OTS-C18) monolayers changed from a rectangular to an amorphous phase via a hexagonal phase with increasing temperature. A distinct lateral force decrease accompanies the phase transition. The LB alkyltrichlorosilane monolayers with longer alkyl chains were in a crystalline state at 293 K. The lateral force of the LB alkyltrichlorosilane monolayers at 293 K increased with increasing chain length. The n-triacontyltrichlorosilane LB monolayer (TATS-C30) in a rectangular phase showed higher lateral force than that of the alkyltrichlorosilane with shorter alkyl chains in a hexagonal phase. The lateral force of the OTS-C18 monolayer prepared by the LB method was higher than that of the chemisorbed one because of the higher packing density of alkyl chain for the LB monolayer, though both monolayers are in a hexagonal phase at 293 K. A large increase in lateral force was observed for the 18-nonadecenyltrichlorosilane (NTS) after oxidation of vinyl end groups.

pH-Responsive and selective protein adsorption on an amino acid-based zwitterionic polymer surface

The synergistic interactions between the α-amine and the carboxylic acid in an amino acid have recently been studied as bio-based zwitterions. Here, we report a new amphiphilic polymer containing glutamic acid grafted to the end of a dodecyl polymer side chain, which contains the α-amine and the γ-carboxylic acid of the glutamic acid moiety. The polymer self-assembled into a multilayered structure in the thin film, and the glutamic acid moieties in the polymer side chains were exposed to the polymer film/water interface. Annealing the sample enhanced the formation of a well-oriented lamellar structure in the films. Due to the presence of the glutamic acid moieties at the interface, the surface charge was controllable by pH in buffer solutions, resulting in zwitterionic character at neutral pH. It has been widely accepted that zwitterionic surfaces can exhibit non-fouling for proteins. Interestingly enough, the polymer film showed charge-selective protein adsorption since the synergistic interaction between the α-amine and the γ-carboxylic acid was weaker than conventional amino acid-based zwitterionic systems. This is due to the separated state of the functional groups by a three carbon spacer.

Scanning force microscopic study of protein adsorption on the surface of organosilane monolayers prepared by the Langmuir-Blodgett method

The n-octadecyltrichlorosilane (OTS, CH 3 (CH 2 ) 17 SiCl 3 ), 18-nonadecenyltrichlorosilane (NTS, CH 2 =CH(CH 2 ) 17 SiCl 3 ), [2-(perfluorooctyl)ethyl] trichlorosilane (FOETS, CF 3 (CF 2 ) 7 CH 2 CH 2 SiCl 3 ) monolayers, and their mixed monolayers were used as the model substrates for the study of protein adsorption mechanism. Surface plasmon resonance (SPR) spectroscopy was applied to analyze the protein adsorption behavior onto the surface of the monolayers. Atomic force microscope (AFM) was used to observe the monolayer surfaces after exposure of these monolayers to bovine serum albumin (BSA) and γ-globulin(IgG) solution. AFM observation revealed that the charged protein either below or above the isoelectric point was preferentially adsorbed onto the FOETS phase of the (OTS/FOETS) mixed monolayer. SPR revealed that the amount of adsorbed protein in the charged state was lower than that in the neutral state. These results indicate that the preferential adsorption of protein onto the FOETS phase for the mixed monolayer systems at either below or above pI is due to (1) the minimization of interfacial free energy between the monolayer surface and the buffer solution, and (2) the electrostatic repulsion among protein molecules bearing charges.