Optical Detection of E. coli Bacteria by Mesoporous Silicon Biosensors

Naama Massad-Ivanir; Giorgi Shtenberg; Ester Segal

doi:10.3791/50805

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Method Article

Optical Detection of E. coli Bacteria by Mesoporous Silicon Biosensors

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DOI:

10.3791/50805

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November 20th, 2013

Naama Massad-Ivanir^*¹ , Giorgi Shtenberg^*² , Ester Segal¹^,³

¹Department of Biotechnology and Food Engineering, Technion - Israel Institute of Technology, ²The Inter-Departmental Program of Biotechnology, Technion - Israel Institute of Technology, ³The Russell Berrie Nanotechnology Institute, Technion - Israel Institute of Technology

^* These authors contributed equally

Summary

A label-free optical biosensor for rapid bacteria detection is introduced. The biosensor is based on a nanostructured porous Si, which is designed to directly capture the target bacteria cells onto its surface. We use monoclonal antibodies, immobilized onto the porous transducer, as the capture probes. Our studies demonstrate the applicability of these biosensors for the detection of low bacterial concentrations within minutes with no prior sample processing (such as cell lysis).

Abstract

A label-free optical biosensor based on a nanostructured porous Si is designed for rapid capture and detection of Escherichia coli K12 bacteria, as a model microorganism. The biosensor relies on direct binding of the target bacteria cells onto its surface, while no pretreatment (e.g. by cell lysis) of the studied sample is required. A mesoporous Si thin film is used as the optical transducer element of the biosensor. Under white light illumination, the porous layer displays well-resolved Fabry-Pérot fringe patterns in its reflectivity spectrum. Applying a fast Fourier transform (FFT) to reflectivity data results in a single peak. Changes in the intensity of the FFT peak are monitored. Thus, target bacteria capture onto the biosensor surface, through antibody-antigen interactions, induces measurable changes in the intensity of the FFT peaks, allowing for a 'real time' observation of bacteria attachment.

The mesoporous Si film, fabricated by an electrochemical anodization process, is conjugated with monoclonal antibodies, specific to the target bacteria. The immobilization, immunoactivity and specificity of the antibodies are confirmed by fluorescent labeling experiments. Once the biosensor is exposed to the target bacteria, the cells are directly captured onto the antibody-modified porous Si surface. These specific capturing events result in intensity changes in the thin-film optical interference spectrum of the biosensor. We demonstrate that these biosensors can detect relatively low bacteria concentrations (detection limit of 10⁴ cells/ml) in less than an hour.

Introduction

Early and accurate identification of pathogenic bacteria is extremely important for food and water safety, environmental monitoring, and point-of-care diagnostics¹. As traditional microbiology techniques are time consuming, laborious, and lack the ability to detect microorganisms in "real-time" or outside the laboratory environment, biosensors are evolving to meet these challenges^2-5.

In recent years, porous Si (PSi) has emerged as a promising platform for the design of sensors and biosensors^6-20. Over the past decade numerous studies regarding PSi-based optical sensors and biosensors were published<....