Langmuir–Blodgett Procedure to Precisely Control the Coverage of Functionalized AFM Cantilevers for SMFS Measurements: Application with Cellulose Nanocrystals

Abstract

Atomic force microscopy (AFM) experiments with functionalized tips are currently one of the most powerful tools to locally measure adhesion forces via single-molecule force spectroscopy (SMFS) measurements. The main difficulty is to precisely control the attachment of biomolecules to the cantilever. Different chemistry procedures have been developed including the use of spacer molecules. Even if a process works well for small biomolecules such as antibodies, issues remain regarding nanoparticles or larger objects such as cellulose nanocrystals because it is difficult to precisely control their coverage and homogeneity. In this work, an original procedure based on the Langmuir-Blodgett (LB) technique was implemented for lever functionalization with cellulose nanocrystals and compared with classical chemical strategies. LB shows to be almost 6.0-fold more efficient than chemical procedure in terms of cellulose nanocrystals coverage attachment. Moreover, the LB technology provides advantage of not requiring linker molecules, which could have detrimental effects such as overestimation of the interaction force. The structural characterization and SMFS measurements of lignocellulosic polymers show that this strategy enables the precise control of the lever coverage, which improves the accuracy of the adhesion measurements. Such methodology is expected to strongly impact the AFM tip/tipless functionalization and SMFS measurements in different fields.

Influence of the polarity of the matrix on the breakage mechanisms of lignocellulosic fibers during twin‐screw extrusion

“…The aspect ratio of the nanocrystalline cellulose is 30, being in the same range as the aspect ratio of hemp and flax fibers (Table ). As the interactions between two surfaces strongly depend on their load contact area, a high coverage of the probes with nanocrystalline cellulose (55.8 ± 2.6%) and a surface of low roughness for the matrices (PP, PP/PP‐g‐MA, and PBS) were chosen to ensure the comparison between each surface. Thus, areas of similar roughness were selected for SMFS measurements to ensure that the interaction between the nanocrystalline cellulose and the section of interest was determined over similar contact areas (roughness parameter R a of PP, PP/PP‐g‐MA, and PBS surfaces was 53.8 nm, 51.8 nm, and 49.1 nm, respectively.…”

“…To investigate the adhesion forces between the fibers and the different matrices, single molecule force spectroscopy (SMFS) measurements were performed using a Multimode‐8 atomic force microscope (Santa Barbara, California). Tip‐less AFM levers were functionalized with nanocrystalline cellulose using a protocol described elsewhere to accurately control the cellulose nanorods density on the lever . Briefly, a Langmuir‐Blodgett procedure was used to deposit the nanocrystalline cellulose extracted from bleached ramie fibers on a tipless AFM lever (NP‐O levers from Bruker Nano, Santa Barbara).…”

“…Tip-less AFM levers were functionalized with nanocrystalline cellulose using a protocol described elsewhere to accurately control the cellulose nanorods density on the lever. [32] Briefly, a Langmuir-Blodgett procedure was used to deposit the nanocrystalline cellulose extracted from bleached ramie fibers on a tipless AFM lever (NP-O levers from Bruker Nano, Santa Barbara). By controlling the surface pressure during the transfer, it is possible to obtain a known density of cellulose nanorods on the AFM lever.…”

“…Therefore, in the present study, single molecule force microscopy (SFMS) was used to address the intermolecular adhesion forces between the cellulose functionalized AFM tipless levers and the polymer surface. Based on a previously developed methodology, AFM tipless levers were functionalized with nanocrystalline cellulose to mimic the high cellulose content in flax and hemp fibers. Then, the adhesion forces were measured on smooth surfaces of the different polymer matrices.…”

Cellulose Nanocrystals as a Sustainable Raw Material: Cytotoxicity and Applications on Healthcare Technology

“…Transmission electronic microscopy (TEM) and atomic force microscopy (AFM) analysis are valuable tools to crimp the morphological nanostructure of CNCs: the acicular shape of the crystals and their nanosized characteristics . The relationship between CNC nanosizes and mammalian cell interactions are discussed in Section 3.…”