Abstract
Design and fabrication of three-dimensionally structured, gold membranes containing hexagonally close-packed microcavities with nanopores in the base, are described. Our aim is to create a nanoporous structure with localized enhancement of the fluorescence or Raman scattering at, and in the nanopore when excited with light of approximately 600nm, with a view to provide sensitive detection of biomolecules. A range of geometries of the nanopore integrated into hexagonally close-packed assemblies of gold micro-cavities was first evaluated theoretically. The optimal size and shape of the nanopore in a single microcavity were then considered to provide the highest localized plasmon enhancement (of fluorescence or Raman scattering) at the very center of the nanopore for a bioanalyte traversing through. The optimized design was established to be a 1200nm diameter cavity of 600nm depth with a 50nm square nanopore with rounded corners in the base. A gold 3D-structured membrane containing these sized microcavities with the integrated nanopore was successfully fabricated and ‘proof of concept’ Raman scattering experiments are described.
Highlights
Biosensors for the direct detection of biomolecules at the single molecule level would be highly desirable for a range of diagnostic applications, especially if these bioanalytes could be delivered sequentially through a nanopore
In this study we report the design, fabrication and first evaluation results of a 3D-structured nanoporous structure where the electric field (E-field) intensity is highly localized ‘at’ and ‘inside’ the pore for sensitive biosensing applications where the analyte is to be passed through the pore
Micro-cavities of the configuration shown in Fig. 1(a) with diameters of 1200 nm, 1000 nm, 800 nm and 600 nm and with depths of half the diameter were evaluated theoretically to obtain dispersion maps
Summary
Biosensors for the direct detection of biomolecules at the single molecule level would be highly desirable for a range of diagnostic applications, especially if these bioanalytes could be delivered sequentially through a nanopore. Metallic nanostructures have been shown to provide an enhancement factor of 1014 with a large cross-sectional area of 10−16 cm2/molecule using surface enhanced Raman scattering approaches [1]. The potential of nanostructured metallic structures for optical applications has been demonstrated for (i) biosensing applications [3], (ii) surface enhanced Raman spectroscopy (SERS) [4], (iii) guiding and manipulating the light [5], (iv) sub-diffraction limited imaging [6] and (v) trapping of micro/nano-sized particles [7]. Various metallic nanostructures have been proposed for sensing using a range of different shapes and geometries [9], materials [10,11] and fabrication methods [12], notably for the optimization of SERS measurements [13] tip-enhanced Raman scattering, (TERS) [14] and fluorescent enhancement [15]. More recently planar plasmonic substrates have been developed for ‘nanofocusing of plasmons’ [17,18,19,20,21,22] and SERS [23,24]
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