Nanohole Biosensor-Origin and Application as Multiplex Biosensing Platform


Austin J Biosens & Bioelectron. 2015;1(3): 1012.

Nanohole Biosensor-Origin and Application as Multiplex Biosensing Platform

Shibsekhar Roy¹* and Joseph O’Mahony²

¹Pharmaceutical and Molecular Biotechnology Research Centre, Waterford Institute of Technology, Ireland

²School of Engineering, Waterford Institute of Technology, Ireland

*Corresponding author: Shibsekhar Roy, Pharmaceutical and Molecular Biotechnology Research Centre, Waterford Institute of Technology, Cork Road Campus, Waterford, Ireland

Received: June 22, 2015; Accepted: June 23, 2015; Published: June 25, 2015


One of the primary challenges faced by the present day diagnostic industry is to develop novel strategies for analysing multiple samples in parallel without compromising the target specificity and Limit of Detection (LOD). This requirement has led to the emergence of assay platforms that can efficiently analyse multiple samples or to put it into context, a sample containing multiple bio-markers with a single test. These new generations of assay methods are commonly known as multiplex bioassays. Clinical diagnostic industries embracing this multiplex platform are capable of offering simultaneous analysis of up to 100 biomarkers within a single sample. The target analytes are more often customizable and include (but not limited to) metabolic, immune/auto-immune, isotyping, cell/tissue-typing, cytokines, and genotyping.

The modes of detection for multiplexed bioassays mainly are absorbance, fluorescence, Raman scattering, and Surface Plasmon Resonance (SPR). However, one bottleneck for various multiplex techniques occurs when multiple targets are present in an analyte with a highly disproportionate ratio. The presence of trace amounts of key analytes may remain undetected or more commonly get masked by some abundant co-analytes. Hence, very often vital information may be potentially lost as a key component remains undiagnosed. This limits the very basic requirement of multiplex bio-assays, which is to detect all the target analytes efficiently from a mixture.

To address this limitation, scientists have come up with an approach, which can significantly improve the detection efficiency for trace analytes by enhancing the optical signals (transmission) by introducing an assay platform involving a specifically patterned noble metal nano surface. This platform, which is an extension of traditional SPR methodologies, is known as Enhanced Optical Transmission (EOT) and the patterns formed on the noble metal surfaces are arrays of nanoholes with defined diameter and periodicity. This generation of assay platform or sensors is known as ‘Nanohole Biosensors’ [1].

EOT-Breaking the Dogma

In aperture theory an old school of thought was that the amount of transmitted light through an aperture in a metal sheet (necessarily opaque) should be inversely proportional to the hole-area. This notion was built upon some interesting optical experiments performed by Bethe et al during 1930s [2]. In this work, he showed that, if the hole diameter is smaller than wavelength of transmitted light, then transmittance, T α (d/λ)4 (d=hole diameter and λ= wavelength). This classical aperture theory was based on a single hole in an infinitely thin slab and was further extended to real metals and hole arrays.

However, it took the physicists nearly six decades to discover something very different. In 1998, Ebbesen’s research group performed a pioneering experiment on the transmission of light through nanohole arrays fabricated on Gold and Silver thin films [3]. They observed a significant deviation from the classical aperture theory as the amount of transmitted light was observed to be significantly larger than that predicted for particular wavelengths. They also observed that the noble metal thin film had become more transparent than predicted. This is indicative of more light transmission than the amount impacted on the hole. This highly unpredicted observation was termed as Extraordinary Optical Transmission (EOT). However, the effect gradually wore off when noble metals were replaced by other metals. The maximum transmission peaks were found to be a function of the nanohole periodicity. From the outset, EOT looked like a potential game-changer in optical instrumentation, especially for high precision sensing devices (Figure 1).

Citation: Roy S and O’Mahony J. Nanohole Biosensor-Origin and Application as Multiplex Biosensing Platform. Austin J Biosens & Bioelectron. 2015;1(3): 1012. ISSN :2473-0629