Porous silicon Bloch surface and sub-surface wave structure for simultaneous detection of small and large molecules.

John D Lonai,Raymond L Mernaugh,Sharon M Weiss,Gilberto A Rodriguez

doi:10.1186/1556-276x-9-383

John D Lonai, Raymond L Mernaugh + Show 2 more

Open Access

https://doi.org/10.1186/1556-276x-9-383

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Abstract

A porous silicon (PSi) Bloch surface wave (BSW) and Bloch sub-surface wave (BSSW) composite biosensor is designed and used for the size-selective detection of both small and large molecules. The BSW/BSSW structure consists of a periodic stack of high and low refractive index PSi layers and a reduced optical thickness surface layer that gives rise to a BSW with an evanescent tail that extends above the surface to enable the detection of large surface-bound molecules. Small molecules were detected in the sensor by the BSSW, which is a large electric field intensity spatially localized to a desired region of the Bragg mirror and is generated by the implementation of a step or gradient refractive index profile within the Bragg mirror. The step and gradient BSW/BSSW sensors are designed to maximize both resonance reflectance intensity and sensitivity to large molecules. Size-selective detection of large molecules including latex nanospheres and the M13KO7 bacteriophage as well as small chemical linker molecules is reported.

Highlights

Porous silicon (PSi) has excelled as a biosensing platform due to its cost-effective and versatile fabrication, enhanced surface area, and chemical and biological compatibility
A resonance condition is distinctly excited when the effective index of a Bloch surface wave (BSW) or Bloch sub-surface wave (BSSW) mode is matched by the coupling conditions of either a prism or diffraction grating
The implementation of a single step to break the periodicity of the Bragg mirror refractive index profile shifts the band edge of the Bragg mirror and gives rise to a single BSSW mode confined within the corresponding layer with reduced optical thickness

Summary

Introduction

Porous silicon (PSi) has excelled as a biosensing platform due to its cost-effective and versatile fabrication, enhanced surface area, and chemical and biological compatibility. The PSi BSW/ BSSW biosensor offers the possibility to detect both small molecules that infiltrate the pores and large molecules attached to the sensor's surface [8]. The novel BSSW mode is confined by a step or gradient refractive index within the multilayer and can selectively detect small molecules attached within the pores with an enhanced sensitivity (>2,000 nm/refractive index unit (RIU)) in comparison to band edge modes of the multilayer, microcavities, or traditional WG modes [8,12,16]. The first fabricated step index and an optimized gradient index PSi BSW/BSSW biosensor are presented. Large M13KO7 bacterial viruses and 60 nm diameter latex nanospheres as well as small 3aminopropyltriethoxysilane (APTES) and gluteraldehyde (GA) molecules are used as model systems to demonstrate the size-selective detection scheme

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