Although TERS has been applied for

Although TERS has been applied for the sequence analysis of DNA [25], such a measurement is highly challenging from a practical point of view. Whether nanopores could be designed to yield plasmonic sensors appropriate for the direct detection of single tranylcypromine within the pore is a question that still remains. In other words, could the E-field be highly confined within the nanopore with a view to providing a sufficiently sensitive nanopore sensor for single molecule detection at translocation? Various groups have studied the plasmonic properties of 2-dimensional nanoporous gold films where a change in the pore size provides a shift in the wavelength of the band assign to plasmon resonance [26,27]. Unfortunately, so far, the level of plasmon enhancement is not reproducible which is possibly due to a variation in pore shape and size of the fabricated devices [28–32]. Various teams have studied plasmonic devices based upon the so-called ‘bowtie’ configuration [31–33]. These structures consist of sharp triangular metallic structures in the shape of a bowtie, where the distance between the two closest triangle tips (the bowtie antennas) can be used to tune the plasmon resonance. Where there is a nano-sized pore located between the bowtie antennas, the localized E-field is confined at the pore, in between these antennas [33], yielding a 2D-structured metallic device with an integrated pore. So far the only example of precise 3D-structured metallic substrates with pores have been reported by Lindquist et al., where the 3D nanopore device is a hybrid of metallic pyramid with C-shaped apertures to tailor the plasmonic properties for the application of TERS [29]. In this study we report the design, fabrication and first evaluation results of a 3D-structured nanoporous structure where the 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.
Materials and methods
Results and discussion
Conclusions After a variety of theoretical simulations, the optimal gold microcavity of 1.2μm with a 50nm square nanopore with rounded corners, was established. The fabrication of a gold 3D-structured nanoporous membrane provided a structure with relatively good agreement to the optimal theoretical design. This is the first report of this device that is developed for biosensing, notably with a view to yield a system for very sensitive detection of molecules traversing through the nanopore. Preliminary testing of this device provides evidence that there is an enhancement of the Raman signal for thiol molecules attached over the gold surface for the microcavities with nanopores. Our efforts are continuing in the optimization of the device and further testing to provide clearer experimental evidence for plasmon coupling by the nanopore with the micro-cavity. The following are the supplementary data related to this article.
Acknowledgements This work was supported by the BBSRC (Ref: BB/I023720/1, BB/I022791/1) and the Institute for Life Sciences “Focusing in on Nucleic Acids” programme and the CARIPLO Foundation for funding respectively GS and FC.
Introduction ZnO is multifunctional semiconductor. It has excellent electrical and optical properties which make it a more prominent material in the electronic and optoelectronic industries. It has a wide band gap (3.37eV), is environment friendly (nontoxic) and is an inexpensive material [1–2]. It provides a wide range of crystal growth technologies, is quite stable in air and its abundant occurrence makes it a more versatile material for commercial applications. Its existence in a one dimensional nanostructure enhances its usability in optoelectronic [3–4] devices and especially in energy harvesting devices. For energy harvesting applications, the semiconductor and piezoelectric properties of ZnO are of main importance. ZnO based piezoelectric nanogenerators have great compatibility with biologically flexible substrates and they can be integrated with different biological and organic materials. ZnO based nanogenerators can be used with flexible devices. They can be used in stretchable and portable devices [5–7].