Abstract
Plasmonic immunosensors are usually made of a noble metal (in the form of a film or nanoparticles) on which bioreceptors are grafted to sense analytes based on the antibody/antigen or other affinity mechanism. Optical fiber configurations are a miniaturized counterpart to the bulky Kretschmann prism and allow easy light injection and remote operation. To excite a surface plasmon (SP), the core-guided light is locally outcoupled. Unclad optical fibers were the first configurations reported to this end. Among the different architectures able to bring light in contact with the surrounding medium, a great quantity of research is today being conducted on metal-coated fiber gratings photo-imprinted in the fiber core, as they provide modal features that enable SP generation at any wavelength, especially in the telecommunication window. They are perfectly suited for use with cost-effective high-resolution interrogators, allowing both a high sensitivity and a low limit of detection to be reached in immunosensing. This paper will review recent progress made in this field with different kinds of gratings: uniform, tilted and eccentric short-period gratings as well as long-period fiber gratings. Practical cases will be reported, showing that such sensors can be used in very small volumes of analytes and even possibly applied to in vivo diagnosis.
Highlights
Biosensors bring a solution to the demand for direct, accurate and in situ monitoring in numerous fields such as genomics, proteomics, medical diagnosis, environmental monitoring, food analysis and security
In the case of fiber gratings, the polarization-dependent loss (PDL) spectrum relates to the difference between orthogonally polarized spectra [114], which contains information about (L)surface plasmon resonance (SPR)
Since the first reports about the use of bare fiber gratings for biosensing [115,116], numerous experimental demonstrations, most often in complex media mimicking the final environment where the sensors should be used in practice, have confirmed that metal-coated fiber gratings can be successfully used for biochemical sensing
Summary
Biosensors bring a solution to the demand for direct, accurate and in situ monitoring in numerous fields such as genomics, proteomics, medical diagnosis, environmental monitoring, food analysis and security. Optical methods of transduction are usually minimally invasive, safe and provide multi-dimensional detection based on wavelength, intensity, phase or polarization metrology They rely on well-established technologies (light sources, detectors, etc.) available from both telecommunication and micro-nano technologies industries, at optical frequencies in the visible and near-infrared regions.
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