Evanescent field response to immunoassay layer thickness on planar waveguides

Department of Electrical and Computer Engineering, Colorado State University, Fort Collins, Colorado 80523, USA
Applied Physics Letters (Impact Factor: 3.3). 10/2008; 93(10):101110. DOI: 10.1063/1.2981212
Source: PubMed


The response of a compact photonic immunoassay biosensor based on a planar waveguide to variation in antigen (C-reactive protein) concentration as well as waveguide ridge height has been investigated. Near-field scanning optical microscope measurements indicate 1.7%nm and 3.3%nm top surface optical intensity modulation due to changes in effective adlayer thickness on waveguides with 16.5 and 10 nm ridge heights, respectively. Beam propagation method simulations are in good agreement with the experimental sensitivities as well as the observation of leaky mode interference both within and after the adlayer region.

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    • "The simulation results show a difference in light intensity modulation ratio of ∼5% for the 3 nm adlayer thickness change, which is consistent with the measured results. As in many scanning probe measurements, it is possible that the probe modifies the field, but the excellent agreement between NSOM data and BPM simulation results on similar samples, including mode beating [13], offers confidence that the NSOM measurement TABLE I ADLAYER THICKNESS AND INTENSITY MODULATION does not significantly perturb the evanescent field distribution. However, the absolute value of the measured light intensity modulation ratio is ∼2% lower than the simulated results. "
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