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Using complementary acoustic and optical techniques for quantitative monitoring of biomolecular adsorption at interfaces.

Konradi R, Textor M, Reimhult E - Biosensors (Basel) (2012)

Bottom Line: In this tutorial review, different optical and acoustic evanescent techniques are used to illustrate how an understanding of the transducer principle of each technique can be exploited for further interpretation of hydrated and extended polymer and biological films.The case studies deal with representative examples of adsorption of protein films, polymer brushes and lipid membranes, and describe e.g., how to deal with strongly vs. weakly hydrated films, large conformational changes and ordered layers of biomolecules.The presented systems and methods are compared to other representative examples from the increasing literature on the subject.

View Article: PubMed Central - PubMed

Affiliation: BASF SE, Advanced Materials and Systems Research, D-67056 Ludwigshafen, Germany. rupert.konradi@basf.com.

ABSTRACT
The great wealth of different surface sensitive techniques used in biosensing, most of which claim to measure adsorbed mass, can at first glance look unnecessary. However, with each technique relying on a different transducer principle there is something to be gained from a comparison. In this tutorial review, different optical and acoustic evanescent techniques are used to illustrate how an understanding of the transducer principle of each technique can be exploited for further interpretation of hydrated and extended polymer and biological films. Some of the most commonly used surface sensitive biosensor techniques (quartz crystal microbalance, optical waveguide spectroscopy and surface plasmon resonance) are briefly described and five case studies are presented to illustrate how different biosensing techniques can and often should be combined. The case studies deal with representative examples of adsorption of protein films, polymer brushes and lipid membranes, and describe e.g., how to deal with strongly vs. weakly hydrated films, large conformational changes and ordered layers of biomolecules. The presented systems and methods are compared to other representative examples from the increasing literature on the subject.

No MeSH data available.


Schematic of a surface plasmon resonance (SPR) measurement in the Kretschmann configuration. The laser beam, totally internally reflected from the back-side of the sensor surface, creates a plasmon coupled to an evanescent field in the solution.
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biosensors-02-00341-f001: Schematic of a surface plasmon resonance (SPR) measurement in the Kretschmann configuration. The laser beam, totally internally reflected from the back-side of the sensor surface, creates a plasmon coupled to an evanescent field in the solution.

Mentions: SPR can sense changes in the effective refractive index smaller than 10−5 with a time resolution of a few seconds [8]. At lower resolution for changes in the refractive index, the time step is only limited by the temporal resolution of the intensity detector. In the Kretschmann configuration (see Figure 1) [9], the laser excites an electron density wave, called a plasmon, at the surface of a noble metal film (typically gold) through total internal reflection from the back of the sensor surface. The exponentially decaying evanescent electromagnetic field extending from the plasmon into solution concentrates the sensitivity to a volume within ~70–150 nm from the surface [10]. For the plasmon to be excited the momentum of the incoming photons must match the momentum of the surface plasmon. Matching occurs only for p-polarized light when [10](1)where εg is the dielectric constant of the prism or glass slide on which the gold film with dielectric constant εr,Au is evaporated, and εr,m is the dielectric constant of the medium on the other side of the gold film. For this to occur, it follows that εg must be higher than εr,m. When Equation (1) is fulfilled, the energy transfer to the plasmon creates a minimum in the reflected intensity of the reflected laser beam. The angle at which this condition occurs depends on the refractive index of the medium for the evanescent wave. Thus, it is possible to sense changes in the medium within the evanescent field caused by adsorption of biomolecules, which changes εr,m, by monitoring the change in angle of the incoming light at which the resonance occurs for monochromatic laser light.


Using complementary acoustic and optical techniques for quantitative monitoring of biomolecular adsorption at interfaces.

Konradi R, Textor M, Reimhult E - Biosensors (Basel) (2012)

Schematic of a surface plasmon resonance (SPR) measurement in the Kretschmann configuration. The laser beam, totally internally reflected from the back-side of the sensor surface, creates a plasmon coupled to an evanescent field in the solution.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4263558&req=5

biosensors-02-00341-f001: Schematic of a surface plasmon resonance (SPR) measurement in the Kretschmann configuration. The laser beam, totally internally reflected from the back-side of the sensor surface, creates a plasmon coupled to an evanescent field in the solution.
Mentions: SPR can sense changes in the effective refractive index smaller than 10−5 with a time resolution of a few seconds [8]. At lower resolution for changes in the refractive index, the time step is only limited by the temporal resolution of the intensity detector. In the Kretschmann configuration (see Figure 1) [9], the laser excites an electron density wave, called a plasmon, at the surface of a noble metal film (typically gold) through total internal reflection from the back of the sensor surface. The exponentially decaying evanescent electromagnetic field extending from the plasmon into solution concentrates the sensitivity to a volume within ~70–150 nm from the surface [10]. For the plasmon to be excited the momentum of the incoming photons must match the momentum of the surface plasmon. Matching occurs only for p-polarized light when [10](1)where εg is the dielectric constant of the prism or glass slide on which the gold film with dielectric constant εr,Au is evaporated, and εr,m is the dielectric constant of the medium on the other side of the gold film. For this to occur, it follows that εg must be higher than εr,m. When Equation (1) is fulfilled, the energy transfer to the plasmon creates a minimum in the reflected intensity of the reflected laser beam. The angle at which this condition occurs depends on the refractive index of the medium for the evanescent wave. Thus, it is possible to sense changes in the medium within the evanescent field caused by adsorption of biomolecules, which changes εr,m, by monitoring the change in angle of the incoming light at which the resonance occurs for monochromatic laser light.

Bottom Line: In this tutorial review, different optical and acoustic evanescent techniques are used to illustrate how an understanding of the transducer principle of each technique can be exploited for further interpretation of hydrated and extended polymer and biological films.The case studies deal with representative examples of adsorption of protein films, polymer brushes and lipid membranes, and describe e.g., how to deal with strongly vs. weakly hydrated films, large conformational changes and ordered layers of biomolecules.The presented systems and methods are compared to other representative examples from the increasing literature on the subject.

View Article: PubMed Central - PubMed

Affiliation: BASF SE, Advanced Materials and Systems Research, D-67056 Ludwigshafen, Germany. rupert.konradi@basf.com.

ABSTRACT
The great wealth of different surface sensitive techniques used in biosensing, most of which claim to measure adsorbed mass, can at first glance look unnecessary. However, with each technique relying on a different transducer principle there is something to be gained from a comparison. In this tutorial review, different optical and acoustic evanescent techniques are used to illustrate how an understanding of the transducer principle of each technique can be exploited for further interpretation of hydrated and extended polymer and biological films. Some of the most commonly used surface sensitive biosensor techniques (quartz crystal microbalance, optical waveguide spectroscopy and surface plasmon resonance) are briefly described and five case studies are presented to illustrate how different biosensing techniques can and often should be combined. The case studies deal with representative examples of adsorption of protein films, polymer brushes and lipid membranes, and describe e.g., how to deal with strongly vs. weakly hydrated films, large conformational changes and ordered layers of biomolecules. The presented systems and methods are compared to other representative examples from the increasing literature on the subject.

No MeSH data available.