Shift of Whispering Gallery Modes in Microspheres by Protein Adsorption

The Rockefeller University, New York, New York, United States
Optics Letters (Impact Factor: 3.29). 03/2003; 28(4):272-4. DOI: 10.1364/OL.28.000272
Source: PubMed


Biosensors based on the shift of whispering-gallery modes in microspheres accompanying protein adsorption are described by use of a perturbation theory. For random spatial adsorption, theory predicts that the shift should be inversely proportional to microsphere radius R and proportional to protein surface density and excess polarizability. Measurements are found to be consistent with the theory, and the correspondence enables the average surface area occupied by a single protein to be estimated. These results are consistent with crystallographic data for bovine serum albumin. The theoretical shift for adsorption of a single protein is found to be extremely sensitive to the target region, with adsorption in the most sensitive region varying as 1/R(5/2). Specific parameters for single protein or virus particle detection are predicted.

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    • "The nanoparticle shifts the frequency of a mode by moving into the evanescent field of the mode. The degree of the shift is proportional to local field intensity [44]. Besides, the evanescent field of a mode decays (decay factor α) exponentially along with the distance d. "
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    ABSTRACT: A transient and high sensitivity sensor based on high-Q microcavity is proposed and studied theoretically. There are two ways to realize the transient sensor: monitor the spectrum by fast scanning of probe laser frequency or monitor the transmitted light with fixed laser frequency. For both methods, the non-equilibrium response not only tells the ultrafast environment variance, but also enable higher sensitivity. As examples of application, the transient sensor for nanoparticles adhering and passing by the microcavity is studied. It's demonstrated that the transient sensor can sense coupling region, external linear variation together with the speed and the size of a nanoparticle. We believe that our researches will open a door to the fast dynamic sensing by microcavity.
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    • "While this approach has allowed for unprecedented sensing performance and Q factors [5] , it is limited in practice because any variation of the distance between the tapered fiber and resonator results not only in changes in the coupling efficiency but also in fluctuation of the resonance positions [6] [7] . Furthermore, using small optical resonators, which would enable improved performance, since the refractive index sensitivity is inversely proportional to the resonator diameter [8] , is challenging from a practical point of view using this approach. The alternative approach involves using resonators that contain a gain medium. "
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    ABSTRACT: Whispering-gallery modes have been studied extensively for biosensing applications. Whilst the vast majority of work undertaken has focused on high Q factor resonators, with the main improvement being a reduction of the resonator size to improve sensitivity, we have chosen a different pathway by starting with resonators that exhibit extremely high refractive index sensitivity but low Q factor. A way forward to overcome this limitation is to introduce a gain medium and operate the resonator above its lasing threshold. This has been shown to result on average in a 5 fold increase in the Q factor. With the lasing threshold itself being dependent on the Q factor, amongst other parameters, the Q factor enhancement can be exploited to either reduce the lasing threshold or alternatively enable smaller resonators to be operated above their lasing threshold. As a demonstration we present a 10 μm diameter polystyrene microsphere lasing in aqueous solution for refractive index sensing applications, which to the best of our knowledge is the smallest polystyrene microsphere laser ever demonstrated in these conditions.
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    • "Any drift in the baseline data was corrected by subtracting a linear function from the data. The surface density (mass per unit area) was calculated from the resonance shift [34] [36] using the equation: "
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    ABSTRACT: a b s t r a c t Understanding protein adsorption and resultant conformation changes on modified and unmodified silicon dioxide surfaces is a subject of keen interest in biosensors, microfluidic systems and for medical diagnostics. However, it has been proven difficult to investigate the kinetics of the adsorption process on these surfaces as well as understand the topic of the denaturation of proteins and its effect on enzyme activity. A highly sensitive optical whispering gallery mode (WGM) resonator was used to study a cat-alytic enzyme's adsorption processes on different silane modified glass substrates (plain glass control, DETA, 13F, and SiPEG). The WGM sensor was able to obtain high resolution kinetic data of glucose oxidase (GO) adsorption with sensitivity of adsorption better than that possible with SPR. The kinetic data, in combination with a functional assay of the enzyme activity, was used to test hypotheses on adsorption mechanisms. By fitting numerical models to the WGM sensograms for protein adsorption, and by con-firming numerical predictions of enzyme activity in a separate assay, we were able to identify mecha-nisms for GO adsorption on different alkylsilanes and infer information about the adsorption of protein on nanostructured surfaces.
    Biomaterials 10/2014; 38. DOI:10.1016/j.biomaterials.2014.10.002 · 8.56 Impact Factor
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