Nanoscale porous silicon waveguide for label-free DNA sensing

Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, TN 37212, USA.
Biosensors & Bioelectronics (Impact Factor: 6.41). 06/2008; 23(10):1572-6. DOI: 10.1016/j.bios.2008.01.017
Source: PubMed


Porous silicon (PSi) is an excellent material for biosensing due to its large surface area and its capability for molecular size selectivity. In this work, we report the experimental demonstration of a label-free nanoscale PSi resonant waveguide biosensor. The PSi waveguide consists of pores with an average diameter of 20nm. DNA is attached inside the pores using standard amino-silane and glutaraldehyde chemistry. Molecular binding in the PSi is detected optically based on a shift of the waveguide resonance angle. The magnitude of the resonance shift is directly related to the quantity of biomolecules attached to the pore walls. The PSi waveguide sensor can selectively discriminate between complementary and non-complementary DNA. The advantages of the PSi waveguide biosensor include strong field confinement and a sharp resonance feature, which allow for high sensitivity measurements with a low detection limit. Simulations indicate that the sensor has a detection limit of 50nM DNA concentration or equivalently, 5pg/mm2.

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    • "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. Well-established Si surface functionalization chemistry has led to specific binding of several relevant molecules including DNA [1], proteins [2], explosives [3], and illicit drugs [4] to PSi platforms. However, PSi refractometric sensing applications have generally been size limited to molecules that diffuse into the porous matrix to cause a measurable change in effective optical thickness. "
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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.
    Full-text · Article · Aug 2014 · Nanoscale Research Letters
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    • "Although in certain cases, the reduction or even, if achievable , the prevention of protein and cellular adhesion is desirable, e.g., for antifouling surfaces and medical devices implanted into the bloodstream [13,20–24], in most cases, such as medical implants designed to become assimilated with their host tissue, the enhancement of surface adhesion is advantageous [2] [13] [25]. A commonly used strategy to improve adhesion is to increase the specific area of the surface [26] [27] [28]. In surface-sensitive biosensing, increasing the specific area of the sensing surface improves the sensitivity, because more target analyte can be captured. "
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    ABSTRACT: A new type of titanate nanotube (TNT) coating is investigated for exploitation in biosensor applications. The TNT layers were prepared from stable but additive-free sols without applying any binding compounds. The simple, fast spin-coating process was carried out at room temperature, and resulted in well-formed films around 10nm thick. The films are highly transparent as expected from their nanostructure and may, therefore, be useful as coatings for surface-sensitive optical biosensors to enhance the specific surface area. In addition, these novel coatings could be applied to medical implant surfaces to control cellular adhesion. Their morphology and structure was characterized by spectroscopic ellipsometry (SE) and atomic force microscopy (AFM), and their chemical state by X-ray photoelectron spectroscopy (XPS). For quantitative surface adhesion studies, the films were prepared on optical waveguides. The coated waveguides were shown to still guide light; thus, their sensing capability remains. Protein adsorption and cell adhesion studies on the titanate nanotube films and on smooth control surfaces revealed that the nanostructured titanate enhanced the adsorption of albumin; furthermore, the coatings considerably enhanced the adhesion of living mammalian cells (human embryonic kidney and preosteoblast).
    Full-text · Article · Jul 2014 · Colloids and surfaces B: Biointerfaces
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    • "Nanostructured porous Si (PSi) has emerged as a promising material for optical biosensing applications due to its large internal surface area and tunable optical properties [1-3]. Numerous biosensing applications, including the detection of DNA hybridization [4], proteins [5,6], and enzymatic activity [7,8], have been presented, demonstrating the advantages of these nanosystems in terms of improved detection sensitivity, label-free and real-time rapid analysis. However, the major challenge in designing these biosensors arises from the intrinsic instability of the recognition element during the immobilization procedures onto the transducer’s surface [9-11]. "
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    ABSTRACT: Multifunctional porous Si nanostructure is designed to optically monitor enzymatic activity of horseradish peroxidase. First, an oxidized PSi optical nanostructure, a Fabry-Pérot thin film, is synthesized and is used as the optical transducer element. Immobilization of the enzyme onto the nanostructure is performed through DNA-directed immobilization. Preliminary studies demonstrate high enzymatic activity levels of the immobilized horseradish peroxidase, while maintaining its specificity. The catalytic activity of the enzymes immobilized within the porous nanostructure is monitored in real time by reflective interferometric Fourier transform spectroscopy. We show that we can easily regenerate the surface for consecutive biosensing analysis by mild dehybridization conditions.
    Full-text · Article · Aug 2012 · Nanoscale Research Letters
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