Abstract
The adoption of plasmonic nanomaterials in optical sensors, coupled with the advances in detection techniques, has opened the way for biosensing with single plasmonic particles. Single nanoparticle sensors offer the potential to analyse biochemical interactions at a single-molecule level, thereby allowing us to capture even more information than ensemble measurements. We introduce the concepts behind single nanoparticle sensing and how the localised surface plasmon resonances of these nanoparticles are dependent upon their materials, shape and size. Then we outline the different synthetic approaches, like citrate reduction, seed-mediated and seedless growth, that enable the synthesis of gold and silver nanospheres, nanorods, nanostars, nanoprisms and other nanostructures with tunable sizes. Further, we go into the aspects related to purification and functionalisation of nanoparticles, prior to the fabrication of sensing surfaces. Finally, the recent developments in single nanoparticle detection, spectroscopy and sensing applications are discussed.
Highlights
The interaction of light with matter is one of the fundamental ways to characterise and understand the properties of matter
The review is divided into four sections; in the first section, we briefly review the synthesis of plasmonic nanoparticles, followed by the functionalisation and surface modification of these nanoparticles
The individual surface plasmon sensors that are discussed in this review are optical sensors that display a change in the surface plasmon resonance upon the binding of a molecule or plasmonic nanoparticles or enzyme-linked immunoprecipitation
Summary
The interaction of light with matter is one of the fundamental ways to characterise and understand the properties of matter. Two prominent approaches have been employed in the literature: (1) bottom-up chemical procedures that allow for the large-scale synthesis of plasmonic nanostructures with a wide range of shapes and sizes (see Figure 1) After synthesis, these nanostructures are modified with suitable functional molecules that allow for bio-recognition along with an anti-fouling surface. Post-synthesis separation techniques could be used in combination with a synthetic approach, to provide highly monodisperse, shape- and size-controlled nanocrystals for the preparation of single particle plasmonic sensors. To improve biocompatibility as well as from the perspective of green chemistry, synthetic approaches have been developed using less hazardous substances, involving the replacement of toxic stabilizing and reducing agents with non-toxic plant extracts [52,53] Such modifications can produce non-toxic nanoparticles (CTAB-free), with numerous simple purification techniques available, the use of green-chemistry may be more complicated and time-consuming. For the fabrication of single plasmonic nanoparticle sensor, the well-established seed-mediated or seedless surfactant-assisted approach is preferred
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