Nanohole arrays of mixed designs and microwriting for simultaneous and multiple protein binding studies

On-chip nanohole array based sensing: a review

The integration of nanohole array based plasmonic sensors into microfluidic systems has enabled the emergence of platforms with unique capabilities and a diversified palette of applications. Recent advances in fabrication techniques together with novel implementation schemes have influenced the progress of these optofluidic platforms. Here, we review the advances that nanohole array based sensors have experienced since they were first merged with microfluidics. We examine established and new fabrication methodologies that have enabled both the fabrication of nanohole arrays with improved optical attributes and a reduction in manufacturing costs. The achievements of several platforms developed to date and the significant benefits obtained from operating the nanoholes as nanochannels are also reviewed herein. Finally, we discuss future opportunities for on-chip nanohole array sensors by outlining potential applications and the use of the abilities of the nanostructures beyond the optical context.

Plasmonic nanohole array sensors fabricated by template transfer with improved optical performance

Surface plasmon resonance sensors of the nanohole array type provide a promising platform for label-free biosensing on surfaces. For their extensive use, an efficient fabrication procedure to make nanoscale features on metallic films is required. We develop a simple and robust template-transfer approach to structure periodic nanohole arrays in optically thick Au films on poly(dimethylsiloxane) substrates. This technique significantly simplifies the process of sensor fabrication and reduces the cost of the device. A spectral analysis approach is also developed for improving the sensor performance. The sensitivity of the resulting sensor to refractive index change is 522 nm/RIU (refractive index unit) and the resolution is improved to 2 × 10(-5) RIU, which are among the best reported values for localized surface plasmon resonance sensors. We also demonstrate the limit of detection of this sensor for cardiac troponin-I.

Label-free detection techniques for protein microarrays: prospects, merits and challenges

Protein microarrays, on which thousands of discrete proteins are printed, provide a valuable platform for functional analysis of the proteome. They have been widely used for biomarker discovery and to study protein–protein interactions. The accomplishments of DNA microarray technology, which had enabled massive parallel studies of gene expression, sparked great interest for the development of protein microarrays to achieve similar success at the protein level. Protein microarray detection techniques are often classified as being label‐based and label‐free. Most of the microarray applications have employed labelled detection such as fluorescent, chemiluminescent and radioactive labelling. These labelling strategies have synthetic challenges, multiple label issues and may exhibit interference with the binding site. Therefore, development of sensitive, reliable, high‐throughput, label‐free detection techniques are now attracting significant attention. Label‐free detection techniques monitor biomolecular interactions and simplify the bioassays by eliminating the need for secondary reactants. Moreover, they provide quantitative information for the binding kinetics. In this article, we will review several label‐free techniques, which offer promising applications for the protein microarrays, and discuss their prospects, merits and challenges.

Vertical plasmonic Mach-Zehnder interferometer for sensitive optical sensing

Vertical plasmonic Mach-Zehnder Interferometers are investigated theoretically and experimentally, and their potential for ultra-sensitive optical sensing is discussed. Plasmonic interferences arise from coherently coupled pairs of subwavelength slits, illuminated by a broadband optical source, and this interference modulates the intensity of the far-field scattering spectrum. Experimental results, obtained using a simple experimental setup, are presented to validate theoretically predicted interferences introduced by the surface plasmon modes on top and bottom surfaces of a metal film. By observing the wavelength shift of the peaks or valleys of the interference pattern, this highly compact device has the potential to achieve a very high sensitivity relative to other nanoplasmonic architectures reported.