Adsorption Behavior of Glucose Oxidase on a Dipalmitoylphosphatic Acid Monolayer and the Characteristics of the Mixed Monolayer at Air/Liquid Interfaces

Abstract

A dipalmitoylphosphatic acid (DPPA) monolayer at the air/liquid interface is used as a binding layer to incorporate glucose oxidase (GOx) from the subphase. The effects of the adsorption time of GOx on the behavior of the mixed DPPA/GOx monolayer and the relevant structure of the mixed LB film were studied using the characteristics of the pressure-area (pi-A) isotherm, Brewster angle microscopy (BAM), and atomic force microscopy (AFM). The experimental results show that two equilibrium states of GOx adsorption exist in the presence of a DPPA monolayer. The first equilibrium stage occurs at tens of minutes after spreading of DPPA, and a surface pressure of ca. 7.5 mN/m is obtained. The second equilibrium stage approaches slowly, and a higher equilibrium surface pressure (ca. 16 mN/m) was obtained at ca. 8 h after the first stage. The BAM and AFM images show that, after the second equilibrium stage is reached, a more condensed phase and rough morphology are obtained on the mixed DPPA/GOx monolayer, indicating a higher amount of GOx incorporated into the mixed film. For the first equilibrium stage of GOx adsorption, DPPA molecules can still pack regularly and closely under compression, suggesting that GOx molecules are mainly located beneath the DPPA monolayer at the compressed state. A more uniform phase was detected on a film prepared after the first equilibrium stage was reached. The present result indicates that distinct structures and properties of mixed DPPA/GOx films can be prepared from the various stages of GOx adsorption.

Using phospholipid Langmuir and Langmuir–Blodgett films as matrix for urease immobilization

“…8 mN m −1 in Fig. 2A is analogous to that observed for proteins such as glucose oxidase [8], which may be ascribed either to changes in orientation of urease or to expelling of urease upon compression. Fig.…”

“…In order to achieve robust LB films, the properties of materials interacting at the air-water interface need to be investigated. For some enzymes, their conformation and orientation change at the air-water interface [6][7][8], and their surface activity may be modified with the incorporation of other amphiphilic materials, such as lipids [9][10][11], which also serve as a protecting matrix for the enzyme. Furthermore, the properties of the material in an ultrathin film normally differ from those in the bulk state, and depend strongly on the molecular arrangements.…”

Manipulation ordered and close-packed nanoparticle monolayers at air/liquid interface coupling Langmuir-Blodgett and self-assembly techniques

“…In general, an incorporation of a foreign material into a monolayer will cause a rise of surface pressure. 37 However, the constant surface pressure obtained in the present case does not mean that no AuNPs were adsorbed into the monolayer because TEM observation confirmed the incorporation of AuNPs. Several possible reasons are proposed for this result.…”

Cation effects on phosphatidic acid monolayers at various pH conditions

“…Phospholipids from the marine biota such as dipalmitoylphosphatidic acid (DPPA) and dipalmitoylphosphatidylcholine (DPPC) are believed to be important sources of saturated fatty acids found in the sea surface microlayer (SSML) and at the surface of marine aerosols (Lee et al, 2007;Marty et al, 1979;Tervahattu et al, 2002). In particular, saturated fatty acids with 16 (palmitic acid) and 18 (stearic acid) carbon alkyl chains are known to be the most abundant.…”