Surface enhanced fluorescence immuno-biosensor based on gold nanorods

Gold nanoparticles (AuNPs) are attractive structures for biosensing, most due to different properties at nanoscale and biocompatibility. Localized surface plasmon resonance (LSPR) is one of these properties; LSPR enable the electromagnetic field enhancement closer to metallic surface, which allows surface-enhanced spectroscopies, like surface enhanced fluorescence (SEF). In this study, an immuno-biosensor based on gold nanorods (AuNRs) and SEF was constructed for simple and fast analysis to detect albumin antibody (anti-BSA) using antigen-antibody (anti-BSA/BSA) interaction as the biorecognition model. AuNRs were presented in two distinct configurations, in suspension (S-AuNRs) and adsorbed on glass slides (AuNRs-chip), and the detection was performed through an extrinsic method, wherein the SEF signal of a reporter molecule (IR-820 cyanine-type dye) was monitored. The analyte detection was evidenced by SEF mapping, where the average signal in the presence of anti-BSA was three times more intense than for the assay in the absence of analyte. A digital protocol was proposed to simplify the spectroscopic data analysis and reduce the intensity variability; in this protocol the number of positive events in the presence of anti-BSA is much larger (around two times) compared to the absence of analyte. The AuNRs based SEF immuno-biosensor allowed an efficient and simple analysis with specific biorecognition and may contribute as an efficient spectroscopy platform for immuno-biosensing.

Gold Nanorods for LSPR Biosensing: Synthesis, Coating by Silica, and Bioanalytical Applications

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.

Gold nanorods: from anisotropy to opportunity. An evolution update

Gold nanoparticles have drawn attention to nanomedicine for many years due to their physicochemical properties, which include: good stability; biocompatibility; easy surface chemistry and superior magnetic; and last, electronic properties. All of these properties distinguish gold nanoparticles as advantageous carriers to be exploited. The challenge to develop new gold nanostructures has led to anisotropy, a new property to exploit for various medical applications: diagnostic and imaging strategies as well as therapeutic options. Gold nanorods are the most studied anisotropic gold nanoparticles because of the presence of two absorption peaks according to their longitudinal and transversal plasmon resonances. The longitudinal surface plasmonic resonance can provide the absorption in the near-infrared region and this is an important aspect of using gold nanorods for medical purposes.

Au nanoshell-coated superparamagnetic Fe3O4–silica composite nanoparticles with surface-modification of an activatable cell-penetrating peptide for tumor-targeted multimode bioimaging and photothermal therapy

The superparamagnetic Fe₃O₄–silica composite nanoparticles coated with Au nanoshells were prepared and subsequently surface-modified with PEG conjugated ACPP for realizing the tumor site-specific multimode bioimaging and photothermal therapy.

Laser beam controlled drug release from Ce6-gold nanorod composites in living cells: a FLIM study

A new method to image drug release from drug-nanoparticle composites in living cells was established. The composites of silica coated gold nanorods (AuNR@SiO2) and chlorine e6 (Ce6) photosensitizers (AuNR@SiO2-Ce6) were formed by electrostatic force with a Ce6 loading efficiency of 80%. The strong resonance absorptions of AuNR@SiO2-Ce6 in the near-infrared (NIR) region enabled the effective release of Ce6 from AuNR@SiO2-Ce6 by 780 nm CW laser irradiation. The 780 nm laser beam was applied to not only control the releasing amount of Ce6 from cellular AuNR@SiO2-Ce6 by adjusting the irradiation dose (time), but also to spatially confine the Ce6 release in cells by focusing the laser beam on the target sites. Furthermore, the fluorescence lifetime of Ce6 was found to change drastically from 0.9 ns in the AuNR@SiO2-Ce6 complex to 6 ns after release, and therefore fluorescence lifetime imaging microscopy (FLIM) was introduced to image the photo-induced Ce6 release in living cells. Finally, the controllable killing effect of photodynamic cancer therapy (PDT) using AuNR@SiO2-Ce6 was demonstrated by changing the released amount of Ce6, which indicates that AuNR@SiO2-Ce6 is promising for targeted tumour PDT.