One of the most significant challenges facing physical and biological scientists is the accurate detection and identification of single molecules in free-solution environments. The ability to perform such sensitive and selective measurements opens new avenues for a large number of applications in biological, medical and chemical analysis, where small sample volumes and low analyte concentrations are the norm. Access to information at the single or few molecules scale is rendered possible by a fine combination of recent advances in technologies. We propose a novel detection method that combines highly sensitive label-free resonant sensing obtained with high-Q microcavities and position control in nanoscale pores (nanopores). In addition to be label-free and highly sensitive, our technique is immobilization free and does not rely on surface biochemistry to bind probes on a chip. This is a significant advantage, both in term of biology uncertainties and fewer biological preparation steps. Through combination of high-Q photonic structures with translocation through nanopore at the end of a pipette, or through a solid-state membrane, we believe significant advances can be achieved in the field of biosensing. Silicon microrings are highly advantageous in term of sensitivity, multiplexing, and microfabrication and are chosen for this study. In term of nanopores, we both consider nanopore at the end of a nanopipette, with the pore being approach from the pipette with nanoprecise mechanical control. Alternatively, solid state nanopores can be fabricated through a membrane, supporting the ring. Both configuration are discussed in this paper, in term of implementation and sensitivity.
Determination of both thickness and refractive index of a thin biomolecular or polymer layer in wet conditions is a task not easily performed. Available tools such as XPS, AFM, ellipsometry and integrated photonic sensors often have difficulties with the native wet condition of said agents-under-test, perform poorly in the sub-5 nm regime or do not determine both characteristics in an absolute simultaneous way. The thickness of a multilayer system is often determined by averaging over a large amount of layers, obscuring details of the individual layers. Even more, the interesting behavior of the first bound layers can be covered in noise or assumptions might be made on either thickness or refractive index in order to determine the other. To demonstrate a solution to these problems, a silicon-on-insulator (SOI) microring is used to study the adsorption of a bilayer polymer system on the silicon surface of the ring. To achieve this, the microring is simultaneously excited with TE and TM polarized light and by tracking the shifts of both resonant wavelengths, the refractive index and the thickness of the adsorbed layer can be determined with a resolution on thickness smaller than 0.1 nm and a resolution on refractive index smaller than 0.01 RIU. An adhesive polyethyleneimine (PEI) layer is adsorbed to the surface, followed by the adsorption of poly(sodium-4-styrene sulfonate) (PSS) and poly(allylamine) hydrochloride (PAH). This high-resolution performance in wet conditions with the added benefits of the SOI microring platform such as low cost and multiplexibility make for a powerful tool to analyze thin layer systems, which is promising to research binding conformation of proteins as well.
We present two different platforms integrating silicon photonic biosensors. One is based on integration with reaction tubes to be compatible with traditional lab approaches. The other uses through-chip fluidics in order to achieve better mixing of the analyte.
In this paper, two recent advances in silicon ring resonator biosensors are presented. First, we address the problem that
due to the high index contrast, small deviations from perfect symmetry lift the degeneracy of the normal resonator mode.
This severely deteriorates the quality of the output signal. To address this, we discuss an integrated interferometric
approach to give access to the unsplit, high-quality normal modes of the microring resonator. Second, we demonstrate
how digital microfluidics can be used for effective fluid delivery to nanophotonic microring resonator sensors fully
constructed in SOI.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.