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Whispering gallery mode resonators for rapid label-free biosensing in small volume droplets.

Wildgen SM, Dunn RC - Biosensors (Basel) (2015)

Bottom Line: WGM resonances are sensitive to the effective refractive index, which changes upon analyte binding to recognition sites on functionalized resonators.Droplet evaporation leads to potentially useful convective mixing, but also limits the time over which analysis can be completed.We show that active droplet mixing combined with initial binding rate measurements is required for accurate nanomolar protein quantification within the first minute following injection.

View Article: PubMed Central - PubMed

Affiliation: Ralph N. Adams Institute for Bioanalytical Chemistry, University of Kansas, 2030 Becker Drive, Lawrence, KS 66047, USA. swildgen@ku.edu.

ABSTRACT
Rapid biosensing requires fast mass transport of the analyte to the surface of the sensing element. To optimize analysis times, both mass transport in solution and the geometry and size of the sensing element need to be considered. Small dielectric spheres, tens of microns in diameter, can act as label-free biosensors using whispering gallery mode (WGM) resonances. WGM resonances are sensitive to the effective refractive index, which changes upon analyte binding to recognition sites on functionalized resonators. The spherical geometry and tens of microns diameter of these resonators provides an efficient target for sensing while their compact size enables detection in limited volumes. Here, we explore conditions leading to rapid analyte detection using WGM resonators as label-free sensors in 10 μL sample droplets. Droplet evaporation leads to potentially useful convective mixing, but also limits the time over which analysis can be completed. We show that active droplet mixing combined with initial binding rate measurements is required for accurate nanomolar protein quantification within the first minute following injection.

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Related in: MedlinePlus

Comparison of the WGM response in unstirred 100 μL (A) and 10 μL (B) water droplets following a saline injection to raise the refractive index 0.002 RIU. The same WGM resonator was used in both experiments. Convective mixing in the droplets equilibrates the solution in minutes, with the smaller droplet requiring less time.
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biosensors-05-00118-f004: Comparison of the WGM response in unstirred 100 μL (A) and 10 μL (B) water droplets following a saline injection to raise the refractive index 0.002 RIU. The same WGM resonator was used in both experiments. Convective mixing in the droplets equilibrates the solution in minutes, with the smaller droplet requiring less time.

Mentions: To characterize resonator response in small sessile droplets, Figure 4 compares representative WGM shifts with time for two different droplet volumes. Figure 4A,B compare the response of the same WGM resonator in a 100 μL and a 10 μL droplet, respectively, upon injection of salt solution to increase droplet refractive index 0.002 RIU. Both time traces show an initial maximum shift in the WGM resonance as the injected high index solution interacts with the resonator. These shifts relax towards an equilibrium value as convective currents in the sessile droplets mix the solution.


Whispering gallery mode resonators for rapid label-free biosensing in small volume droplets.

Wildgen SM, Dunn RC - Biosensors (Basel) (2015)

Comparison of the WGM response in unstirred 100 μL (A) and 10 μL (B) water droplets following a saline injection to raise the refractive index 0.002 RIU. The same WGM resonator was used in both experiments. Convective mixing in the droplets equilibrates the solution in minutes, with the smaller droplet requiring less time.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4384086&req=5

biosensors-05-00118-f004: Comparison of the WGM response in unstirred 100 μL (A) and 10 μL (B) water droplets following a saline injection to raise the refractive index 0.002 RIU. The same WGM resonator was used in both experiments. Convective mixing in the droplets equilibrates the solution in minutes, with the smaller droplet requiring less time.
Mentions: To characterize resonator response in small sessile droplets, Figure 4 compares representative WGM shifts with time for two different droplet volumes. Figure 4A,B compare the response of the same WGM resonator in a 100 μL and a 10 μL droplet, respectively, upon injection of salt solution to increase droplet refractive index 0.002 RIU. Both time traces show an initial maximum shift in the WGM resonance as the injected high index solution interacts with the resonator. These shifts relax towards an equilibrium value as convective currents in the sessile droplets mix the solution.

Bottom Line: WGM resonances are sensitive to the effective refractive index, which changes upon analyte binding to recognition sites on functionalized resonators.Droplet evaporation leads to potentially useful convective mixing, but also limits the time over which analysis can be completed.We show that active droplet mixing combined with initial binding rate measurements is required for accurate nanomolar protein quantification within the first minute following injection.

View Article: PubMed Central - PubMed

Affiliation: Ralph N. Adams Institute for Bioanalytical Chemistry, University of Kansas, 2030 Becker Drive, Lawrence, KS 66047, USA. swildgen@ku.edu.

ABSTRACT
Rapid biosensing requires fast mass transport of the analyte to the surface of the sensing element. To optimize analysis times, both mass transport in solution and the geometry and size of the sensing element need to be considered. Small dielectric spheres, tens of microns in diameter, can act as label-free biosensors using whispering gallery mode (WGM) resonances. WGM resonances are sensitive to the effective refractive index, which changes upon analyte binding to recognition sites on functionalized resonators. The spherical geometry and tens of microns diameter of these resonators provides an efficient target for sensing while their compact size enables detection in limited volumes. Here, we explore conditions leading to rapid analyte detection using WGM resonators as label-free sensors in 10 μL sample droplets. Droplet evaporation leads to potentially useful convective mixing, but also limits the time over which analysis can be completed. We show that active droplet mixing combined with initial binding rate measurements is required for accurate nanomolar protein quantification within the first minute following injection.

Show MeSH
Related in: MedlinePlus