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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.


Related in: MedlinePlus

Illustration of the step-by-step procedure (a–f described in the text) used to separate the contribution to the change in SPR angle, Θ, and coupled mass, mtotal, originating from adsorbed vesicles (ΔΘvesicle, mvesicle) and supported bilayer islands (ΔΘSPB, mSPB), respectively. Also shown in (f) is the expected mass adsorption from diffusion limited transport of lipid material in liposomes. Adapted with permission from Reimhult et al. [14]. Anal. Chem. 2004, 76, 7211–7220. Copyright 2004 American Chemical Society.
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biosensors-02-00341-f009: Illustration of the step-by-step procedure (a–f described in the text) used to separate the contribution to the change in SPR angle, Θ, and coupled mass, mtotal, originating from adsorbed vesicles (ΔΘvesicle, mvesicle) and supported bilayer islands (ΔΘSPB, mSPB), respectively. Also shown in (f) is the expected mass adsorption from diffusion limited transport of lipid material in liposomes. Adapted with permission from Reimhult et al. [14]. Anal. Chem. 2004, 76, 7211–7220. Copyright 2004 American Chemical Society.

Mentions: Figure 9 details a step-wise procedure allowing the separation of ΔΘtotal(t) into its two components: ΔΘvesicle(t) and ΔΘSPB(t) (Figure 8(a–d)). Since the surface is occupied only by vesicles until the critical coverage is reached [15,94], the temporal variations in D and Θ (Figure 9(a)) up to the critical coverage (maximum in ΔD) are used to produce a calibration curve relating changes in Θ to changes in D: ΔΘcalibration(Dt <peak), as shown in Figure 9(b). Under the reasonable assumption that a given ΔD value reflects a unique state of adsorbed vesicles, the fraction of ΔΘ originating from adsorbed vesicles after the critical coverage/maximum in D was then given by ΔΘvesicle(t > peak)= ΔΘcalibration(Dt > peak), as shown in Figure 9(c). By then simply subtracting ΔΘvesicle(t) in Figure 9(c) from ΔΘtotal(t), the response of the lipids in the SLB, ΔΘSPB(t), is obtained, as shown together with ΔΘvesicles(t) in Figure 9(d). With the SPR-signals of liposomes and SLB islands separated, it is possible to apply for example Equation (5) with the appropriate choices of d and dc/dn to each signal respectively. While dc/dn can often be found in the literature, there is still some confusion about the actual value of dc/dn for liposomes and SLB, since it is difficult to determine directly (see also Section 7.5 and [93,95] for the influence of anisotropy on the interpretation of dc/dn). It can also be calculated from theory (see e.g., Cuypers et al. [96]) or approximated from waveguide spectroscopy measurements where the optical anisotropy has been taken into account [93]. The effective film thickness can be obtained by visco-elastic modeling of the thickness at the peak in ΔD through an iterative approach [14,52,61] or by independent measurements using, e.g., AFM [15]. The result of the mass calculations is shown in Figure 9(e) (see Reimhult et al. [14,15] for further details on the calculations) and the sum of the total mass lipid mass—both liposomes and SLB—in Figure 9(f).


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

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

Illustration of the step-by-step procedure (a–f described in the text) used to separate the contribution to the change in SPR angle, Θ, and coupled mass, mtotal, originating from adsorbed vesicles (ΔΘvesicle, mvesicle) and supported bilayer islands (ΔΘSPB, mSPB), respectively. Also shown in (f) is the expected mass adsorption from diffusion limited transport of lipid material in liposomes. Adapted with permission from Reimhult et al. [14]. Anal. Chem. 2004, 76, 7211–7220. Copyright 2004 American Chemical Society.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

biosensors-02-00341-f009: Illustration of the step-by-step procedure (a–f described in the text) used to separate the contribution to the change in SPR angle, Θ, and coupled mass, mtotal, originating from adsorbed vesicles (ΔΘvesicle, mvesicle) and supported bilayer islands (ΔΘSPB, mSPB), respectively. Also shown in (f) is the expected mass adsorption from diffusion limited transport of lipid material in liposomes. Adapted with permission from Reimhult et al. [14]. Anal. Chem. 2004, 76, 7211–7220. Copyright 2004 American Chemical Society.
Mentions: Figure 9 details a step-wise procedure allowing the separation of ΔΘtotal(t) into its two components: ΔΘvesicle(t) and ΔΘSPB(t) (Figure 8(a–d)). Since the surface is occupied only by vesicles until the critical coverage is reached [15,94], the temporal variations in D and Θ (Figure 9(a)) up to the critical coverage (maximum in ΔD) are used to produce a calibration curve relating changes in Θ to changes in D: ΔΘcalibration(Dt <peak), as shown in Figure 9(b). Under the reasonable assumption that a given ΔD value reflects a unique state of adsorbed vesicles, the fraction of ΔΘ originating from adsorbed vesicles after the critical coverage/maximum in D was then given by ΔΘvesicle(t > peak)= ΔΘcalibration(Dt > peak), as shown in Figure 9(c). By then simply subtracting ΔΘvesicle(t) in Figure 9(c) from ΔΘtotal(t), the response of the lipids in the SLB, ΔΘSPB(t), is obtained, as shown together with ΔΘvesicles(t) in Figure 9(d). With the SPR-signals of liposomes and SLB islands separated, it is possible to apply for example Equation (5) with the appropriate choices of d and dc/dn to each signal respectively. While dc/dn can often be found in the literature, there is still some confusion about the actual value of dc/dn for liposomes and SLB, since it is difficult to determine directly (see also Section 7.5 and [93,95] for the influence of anisotropy on the interpretation of dc/dn). It can also be calculated from theory (see e.g., Cuypers et al. [96]) or approximated from waveguide spectroscopy measurements where the optical anisotropy has been taken into account [93]. The effective film thickness can be obtained by visco-elastic modeling of the thickness at the peak in ΔD through an iterative approach [14,52,61] or by independent measurements using, e.g., AFM [15]. The result of the mass calculations is shown in Figure 9(e) (see Reimhult et al. [14,15] for further details on the calculations) and the sum of the total mass lipid mass—both liposomes and SLB—in Figure 9(f).

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.


Related in: MedlinePlus