Abstract
Nanoparticles made of coinage metals are well known to display unique optical properties stemming from the localized surface plasmon resonance (LSPR) phenomenon, allowing their use as transducers in various biosensing configurations. While most of the reports initially dealt with spherical gold nanoparticles owing to their ease of synthesis, the interest in gold nanorods (AuNR) as plasmonic biosensors is rising steadily. These anisotropic nanoparticles exhibit, on top of the LSPR band in the blue range common with spherical nanoparticles, a longitudinal LSPR band, in all respects superior, and in particular in terms of sensitivity to the surrounding media and LSPR-biosensing. However, AuNRs synthesis and their further functionalization are less straightforward and require thorough processing. In this paper, we intend to give an up-to-date overview of gold nanorods in LSPR biosensing, starting from a critical review of the recent findings on AuNR synthesis and the main challenges related to it. We further highlight the various strategies set up to coat AuNR with a silica shell of controlled thickness and porosity compatible with LSPR-biosensing. Then, we provide a survey of the methods employed to attach various bioreceptors to AuNR. Finally, the most representative examples of AuNR-based LSPR biosensors are reviewed with a focus put on their analytical performances.
Highlights
The part taken by plasmonic nanoparticles in biotechnologies has been expanding steadily over the last few decades
We have reviewed the recent findings related to AuNRs for localized surface plasmon resonance (LSPR) biosensing from their synthesis and coating by silica, to their characterization and further surface functionalization, and up to their bioanalytical applications
AuNR synthesis has been extensively investigated over the last decades; in the first part of the manuscript, we relied on the existing reviews and updated with the most recent literature on the topic
Summary
The part taken by plasmonic nanoparticles in biotechnologies has been expanding steadily over the last few decades. Along with the other biomedical applications, the use of AuNRs is expanding significantly and AuNRs are proving to be versatile and multipurpose actors allowing for the read-out of the transduction through multiple scenarios They can be used to enhance the response of existing transducing techniques such as propagative SPR [19,20,21] or to quench and/or enhance the fluorescence signal [22,23]. The second part of the synthesis section is devoted to silica coating very little examples of LSPR biosensing using AuNR@SiO2 can be found in the literature This poor use of such promising objects is mainly driven by the difficulty to achieve thin layers of silica on top of the nanorods. 1.5 nm), CTAB-stabilized, Au seeds and a growth solution containing a binary mixture of surfactants (benzyldodecylammonium chloride (BDAC) + CTAB), silver nitrate, and AA This second synthesis protocol produces thinner AuNR We will concentrate on the practical aspects of the synthesis and highlight the main difficulties (mostly leaving aside the literature related to the mechanisms of formation of AuNRs discussed extensively in the above-mentioned reviews)
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