Future of Plasmonic Biosensors

Introduction

Biosensors represent the technological side of the living senses that have found a routine application in amperometry enzyme electrodes for the decentralization of blood glucose measurement, for the interaction analysis by surface plasmon resonance in drug development, and to some extent, DNA chips for enzyme polymorphisms and expression analysis. These technologies have already reached a highly advanced level and need only minor improvement now.

Fundamentals

In the field of optics, the phenomenon of surface plasmon resonance (SPR), is widely used as optical biosensors. This was established from studies that involved the excitation of the surface plasmons on the metallic surfaces, especially noble metals. In this process, the metallic surfaces are exposed to light, a photon is trapped near them and that prompts electrons to move as a single entity. The oscillation of electrons on the metal film results in the formation of an electromagnetic field that decays out on the surface and is also known as the evanescent field.

Potential Applications

Point of Care

  • One of the primary applications of the biosensors is the development of the point- of-care testing system for prompt and precise therapy. This can be achieved by the integration of technologies such as disposable chips, portable platforms, miniaturization of the analytical machines and so on.
  • A smartphone-integrated analytical system can be used, which enables rapid diagnoses by allowing the data collected on the smartphone to be connected to medical doctors and institutions via Wi-Fi. In addition to this, disposable chips have also been developed as convenient devices with a simple operation such as color-change detection. Thus, the SPR sensors (e.g. immunosensor, etc.) have a great potential to utilize measurement of bio-markers due to their label-free, cost-effective analysis, and with the rapid response time. Because of these advantages, SPR-based sensors can facilitate high throughput and multiplex measurement of biomarkers when integrated with the microfluidic system.

SPR and Sensitivity

One of the challenges of the existing surface plasmon resonance (SPR) based sensors is that the sensitivity (if you would like to learn more about the biosensor sensitivity, click here) is not high enough for the measurement of biomarkers in small volumes of body fluids. Also, it is not a natural color change-based method, except for that of Au nano-particles.

Several efforts have been made to improve the sensitivity of the biosensors. These include metal surfaces, magnetic activity, grating or photonic crystals, etc. Meanwhile, the plasmonic effect which stimulates the SPR phenomena, can also stimulate another phenomenon that can also be applied to the development of immuno-sensors, including surface-enhanced Raman scattering (SERS), fluorescence resonance energy transfer (FERT), and metal-enhanced fluorescence) (MEF). If the SERS, FRET, MEF based analytical methods could be assimilated with an SPR-based sensor that employs plasmonic effects, targets can be measured in a better way and the drawbacks of each analytical method can be supplemented.

MOSPR and Sensitivity

  • Several plasmonic-based analytical methods have advantages with nano-structures and noble metals, and there is a possibility to develop a magneto-optic SPR sensor with high performance using an integrated platform.
  • Significant potential exists to develop MOSPR-based sensors with noble metals and nanostructures, for improvement in functionality as effective biosensors. The best advantage of this analytical method is in-situ, label-free detection. This could result in the development of several new types of sensors that can measure targets in a simple, rapid and cost-effective manner.


Figure: A microfluidic channel incorporated biosensor, and optical excitation scheme.

Currently, there are signific shortcomings in SPR-based immuno-sensor systems which is a challenge for effective detection. However, now the integration of magneto-plasmonic-based sensing systems can offer a breakthrough for the development of effective MOSPR sensors, for early diagnosis and point of care testing of various diseases, which in turn can significantly improve pharmaceutical, biomedical and clinical applications.

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