BIA-Pages

BIA-pages

Introduction

The BIApages are a roundup of the most common methods and techniques to investigate Biomolecular Interaction Analysis. Central are the methods which determine when and how biomolecules interact. You can think of the association and dissociation but also thermodynamics and conformational changes in molecules and complexes. The techniques are not necessarily label- or immobilization free.

Micro Scale Thermophoresis

MicroScale Thermophoresis (MST) measures the motion of molecules along microscopic temperature gradients and detects changes in their hydration shell, charge or size.

When performing a MicroScale Thermophoresis (MST) experiment, a microscopic temperature gradient is induced by an infrared laser, and the directed movement of molecules is detected and quantified using either covalently attached dyes, fluorescent fusion proteins or intrinsic tryptophan fluorescence.

By combining the precision of fluorescence detection with the flexibility ...
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Interaction kinetics

Interaction kinetics describes the interaction between one or more components. After the interaction the components leave each other unchanged as opposed to enzyme kinetics. The interaction kinetics can be subdivided in three distinct phases.

Association: two or more molecules bind to each other
Steady state: the amount of molecules that is binding is equal to the amount of bonds that is breaking
Dissociation: the breaking of the bounds between the molecules

Protein interaction

Each of the three phases contains information over the interaction between ...
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How low can you go?

In SPR experiments, low responses are preferred over high responses. This is because high responses in general are affected by mass transport and non 1:1 interactions (6), (8). But how low can you go? This depends in the first place on the instrument of choice. The signal should be above the noise level of the baseline. The curves should be easily recognisable and replicates should overlay (4), (7).

To determine the noise level of the instrument, first equilibrate the system to minimize drift. Then inject flow buffer several times and observe the average response. ...
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Label- or immobilization free?

There are only a few really label- and immobilization free techniques which are able to measure biomolecular interactions. One of the most used is Isothermal Titration Calorimetry (ITC). The technique is simple to perform but needs quite some sample. Other techniques require that at least one component is immobilized to a supporting structure or sensor surface.
Of this category, Surface Plasmon Resonance (SPR) and Bio Layer interferometry (BLI) are the most common used. The sample consumption with SPR type instruments vary on the design but are moderate to low. BLI however uses very low quantities of the sample which can be recovered after the experiment. For Micro Scale Thermophoresis (MST) one of the interactants must be labelled (although there is a complete label-free instrument). This method uses very low amounts of sample and is relatively fast compared to SPR and BLI.

There are many techniques to explore bio molecules and their interactions. Some are both label- and immobilization free, other require labelling or immobilization. In the table is a round-up of techniques used in the study of bio molecules with an indication of the main information that can be obtained.

Single surface referencing

Springer et al introduces single surface referencing. A single functionalized surface is split into the detection and reference channel to which complex sample (detection) and complex sample mixed with biomolecules binding to the analyte and thus inhibiting the binding of the analyte to the functionalized surface (reference) is introduced. Goto reference

Biomolecular techniques.
	Technique	Immob.	Label	Information
SPR	Surface Plasmon Resonance	yes	no	kinetic
BLI	Bio-Layer Interferometry	yes	no	kinetic
MST	Micro Scale Thermoforesis	no	yes/no*	equilibrium
ITC	Isothermal Titration Calorimetry	no	no	equilibrium
AUC	Analytical Ultra Centrifugation	no	no	equilibrium
	Microbalance / Cantilever	yes	no
AFM	Atomic Force Microscopy	yes	no
	High Performance capillary electrophoresis	no	?	equilibrium
LFII	Label-Free Intrinsic Imaging
NMR	Nuclear Magnetic Resonance			structural
	Electron Diffraction			structural
	Electron Microscopy			structural
FRET	Fluorescent Energy Transfer		yes	equilibrium
	Size exclusion chromatography	no	no	size / dimer
* _{Depending on the type of instrument.}

Label free techniques

Roundup of the websites and suppliers I found that do measurements in non invasive ways on non labelled molecules.

MicroCal	VP-ITC system which uses differential scanning calorimetry.
Axela Biosensors	Diffractive optics technology with grating-based light diffraction and immobilized capture surfaces.
Q-Sense	The quartz crystal microbalance consists of a thin quartz disc with electrodes on both sides. The resonance frequency depends on the attached mass that is oscillating. A viscoelastic film will dampen the oscillation.
BioForce Nanosciences	Atomic-force-microscopy-based platform for nanoarray analysis.
DeltaDot	High performance capillary electrophoresis with label-free intrinsic imaging using algorithms to identify biomolecules.