Optimizing multiple beam interferometry in the surface forces apparatus: Novel optics, reflection mode modeling, metal layer thicknesses, birefringence, and rotation of anisotropic layers

Schwenzfeier, Kai Alexander; Erbe, Andreas; Bilotto, Pierluigi; Lengauer, Maximilian; Merola, Claudia; Cheng, Hsiu‐Wei; Mears, Laura L. E.; Valtiner, Markus

doi:10.1063/1.5085210

Cited by 28 publications

(37 citation statements)

References 48 publications

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“…The PEG brush is approached by a mica surface at a decreasing distance z and the force is measured. The separation between the surfaces is measured optically based on multiple beam interference fringes of equal chromatic order 48 (FECO). (B) Semilogarithm plot of the force–distance curve profile during the approach of a mica surface to a PEG brush in pH 4.5 PBS (black markers), after PMAA bound to the PEG brush (red markers), and after increase of pH to 7.5 PBS (blue markers).…”

Section: Resultsmentioning

confidence: 99%

Control of Polymer Brush Morphology, Rheology, and Protein Repulsion by Hydrogen Bond Complexation

et al. 2021

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Polymer brushes are widely used to alter the properties of interfaces. In particular, poly(ethylene glycol) (PEG) and similar polymers can make surfaces inert toward biomolecular adsorption. Neutral hydrophilic brushes are normally considered to have static properties at a given temperature. As an example, PEG is not responsive to pH or ionic strength. Here we show that, by simply introducing a polymeric acid such as poly(methacrylic acid) (PMAA), the highly hydrated brush barrier can change its properties entirely. This is caused by multivalent hydrogen bonds in an extremely pH-sensitive process. Remarkably, it is sufficient to reduce the pH to 5 for complexation to occur at the interface, which is two units higher than in the corresponding bulk systems. Below this critical pH, PMAA starts to bind to PEG in large amounts (comparable to the PEG amount), causing the brush to gradually compact and dehydrate. The brush also undergoes major rheology changes, from viscoelastic to rigid. Furthermore, the protein repelling ability of PEG is lost after reaching a threshold in the amount of PMAA bound. The changes in brush properties are tunable and become more pronounced when more PMAA is bound. The initial brush state is fully recovered when releasing PMAA by returning to physiological pH. Our findings are relevant for many applications involving functional interfaces, such as capture–release of biomolecules.

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Section: Resultsmentioning

confidence: 99%

Control of Polymer Brush Morphology, Rheology, and Protein Repulsion by Hydrogen Bond Complexation

et al. 2021

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“…It introduces advantages in terms of the optics, alignment and sample handling during the experiment. 21 Mica sheets used in these experiments were hand-cleaved to provide sheets with an area of 5-10 cm 2 and uniform thickness raging from 3-5 µm. The edges of these sheets were melt-cut with a hot platinum wire.…”

Section: Surface Forces Apparatusmentioning

confidence: 99%

Interaction Profiles and Stability of Rigid and Polymer-Tethered Lipid Bilayer Models at Highly Charged and Highly Adhesive Contacts

et al. 2019

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Understanding interaction force versus distance profiles of supported lipid bilayers (SLBs) is relevant to a number of areas which rely on these model systems, including e.g. characterization of ligand/receptor interactions or bacterial adhesion. Here, the stability of 4 different SLB architectures was compared using the surface forces apparatus (SFA) and atomic force microscopy (AFM). Specifically, the outer envelope of the bilayer systems remained constant as 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). The inner layer was varied between DPPC and 1,2-dipalmitoyl-3-trimethylammonium-propane (DPTAP), both on mica and self-assembled monolayers (SAMs) of hexadecanethiol and the polymer tethered di-phytanylglycerol-tetraethyleneglycollipoid acid (DPhyTL) on smooth gold surfaces. In that same order these gave an increasing strength of interaction between the inner layer and the supporting substrate and hence improved stability under highly adhesive conditions. Detachment profiles from highly charged and highly adhesive contacts were characterized and approach characteristics were fitted to DLVO models. We find increasing stability under highly adhesive loads, approaching the hydrophobic limit of the adhesive energy between the inner and outer layers for the SAM based systems. For all four SLBs we further compare AFM surface topographies, which strongly depend on preparation conditions, and the DLVO fitting of the SFA approach curves find a strong charge regulation behaviour during interaction, dependent on the particular model system. In addition, we find undulation characteristics during approach and separation. The increased stability of the complex architectures on a gold support make these model systems an ideal starting point for studying more complex strongly adhesive/interacting systems, including for example ligand/receptor interactions, bio-sensing interactions or cell/surface interactions.

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“…The absolute separation distance (as well as the separation distance profile along a line through the contact region) between the mica surfaces can be calculated from the FECO fringes. [22][23][24][25][26][27] To measure a force-distance profile a piezo drive or a motorized micrometer drives the surfaces together (with a known distance displacement ΔD over a short time interval) from a region of no inter-surface force into a separation distance at which the surfaces interact, after which they are separated again. Over the same time interval, the actual distance displacement ΔDa is calculated from the FECO.…”

Section: Surface Forces Apparatus (Sfa) Technique the Surface Forcesmentioning

confidence: 99%

Multimodal Miniature Surface Forces Apparatus (μSFA) for Interfacial Science Measurements

et al. 2019

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Advances in the research of intermolecular and surface interactions result from the development of new and improved measurement techniques and combinations of existing techniques. Here, we present a new miniature version of the Surface Force Apparatus -the µSFA -that has been designed for ease of use and multi-modal capabilities with retention of the capabilities of other SFA models including accurate measurement of surface separation distance and physical characterization of dynamic and static physical forces (i.e., normal, shear, and friction) andinteractions (e.g., van der Waals, electrostatic, hydrophobic, steric, bio-specific). The small physical size of the µSFA, compared to previous SFA models, makes it portable and suitable for integration into commercially available optical and fluorescence light microscopes, as demonstrated here. The large optical path entry and exit ports make it ideal for concurrent force measurements and spectroscopy studies. Examples of the use of the µSFA in combination with surface plasmon resonance (SPR) and Raman spectroscopy measurements are presented. Due to the short working distance constraints associated with Raman spectroscopy, an interferometric technique was developed and applied for calculating the inter-surface separation distance based on Newton's rings. The introduction of the µSFA will mark a transition in SFA usage from primarily physical characterization to concurrent physical characterization with in situ chemical and biological characterization to study interfacial phenomena, including (but not limited to) molecular adsorption, fluid flow dynamics, determination of surface species and morphology, and (bio-)molecular binding kinetics.

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Optimizing multiple beam interferometry in the surface forces apparatus: Novel optics, reflection mode modeling, metal layer thicknesses, birefringence, and rotation of anisotropic layers

Cited by 28 publications

References 48 publications

Control of Polymer Brush Morphology, Rheology, and Protein Repulsion by Hydrogen Bond Complexation

Control of Polymer Brush Morphology, Rheology, and Protein Repulsion by Hydrogen Bond Complexation

Interaction Profiles and Stability of Rigid and Polymer-Tethered Lipid Bilayer Models at Highly Charged and Highly Adhesive Contacts

Multimodal Miniature Surface Forces Apparatus (μSFA) for Interfacial Science Measurements

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