Engineering Nanostructured Porous SiO₂ Surfaces for Bacteria Detection via “Direct Cell Capture”

Abstract

An optical label-free biosensing platform for bacteria detection ( Escherichia coli K12 as a model system) based on nanostructured oxidized porous silicon (PSiO(2)) is introduced. The biosensor is designed to directly capture the target bacteria cells on its surface with no prior sample processing (such as cell lysis). The optical reflectivity spectrum of the PSiO(2) nanostructure displays Fabry-Pérot fringes characteristic of thin-film interference, enabling direct, real-time observation of bacteria attachment within minutes. The PSiO(2) optical nanostructure is synthesized and used as the optical transducer element. The porous surface is conjugated with specific monoclonal antibodies (immunoglobulin G's) to provide the active component of the biosensor. The immobilization of the antibodies onto the biosensor system is confirmed by attenuated total reflectance Fourier transform infrared spectroscopy, fluorescent labeling experiments, and refractive interferometric Fourier transform spectroscopy. We show that the immobilized antibodies maintain their immunoactivity and specificity when attached to the sensor surface. Exposure of these nanostructures to the target bacteria results in "direct cell capture" onto the biosensor surface. These specific binding events induce predictable changes in the thin-film optical interference spectrum of the biosensor. Our preliminary studies demonstrate the applicability of these biosensors for the detection of low bacterial concentrations. The current detection limit of E. coli K12 bacteria is 10(4) cells/mL within several minutes.

Bioengineered Surfaces for Real-Time Label-Free Detection of Cancer Cells

“…The reaction between the oxidized surface and the organosilane is based on the condensation between the Si-O-Si of the silane and the OH present on the device; generally, besides the hydroxyl groups already present on the native silicon oxide layer, a thermal oxidation is a common procedure to form a new efficient oxide film [40][41][42] in order to assure a plenty of silanol groups for an efficient coverage of the organic layer.…”

Porous Silicon Biosensors Employing Emerging Capture Probes

“…For label-free PSi biosensors based on reflectance, two different signals can be monitored: the shift in the wavelength due to RI variation [16] and a change in the intensity of the reflected light due to scattering effects [9]. Different PSi architectures e.g., single and double layers [88,100], microcavities [78,101], and photonic crystals [90,102], have been used for the construction of reflectivity-based optical biosensors.…”

Recent developments in rapid multiplexed bioanalytical methods for foodborne pathogenic bacteria detection

“…A representative example shows target bacteria captured onto the surface of the optical label-free porous Si-based biosensors, inducing changes in the thin-film optical interference spectrum. Low bacterial concentrations for E. coli, in the range of 10 3 -10 5 cells mL −1 , could de detected in few minutes without the need of any pretreatment cell lysis [68,69].…”