Metal-Enhanced Fluorescence Immunosensor Based on Plasmonic Arrays of Gold Nanoislands on an Etched Glass Substrate

Abstract

The recent advances in nanofabrication processes offer encouraging opportunities for designing highly sensitive detection tools. One example is metal-enhanced fluorescence (MEF)-based biosensors: by effectively coupling the metal nanostructures with the fluorescent dye used for the detection of the target molecule, MEF-based sensors exhibit higher sensitivity and lower limit of detection in comparison to traditional optical biosensors. Ordered arrays of nanostructures with coupled fluorophores can potentially achieve thousand-fold enhancement in fluorescence intensity. However, nanofabrication techniques required for ordered nanostructures tend to be time consuming and costly. On the other hand, with moderate enhancement, randomly assembled nanoplasmonic arrays on large-scale substrates can be realized by easy, cost-effective, and reliable methodologies in a relatively short time, thus being more suitable for mass production. In this work, we develop a MEF-based immunosensor involving randomly assembled plasmonic arrays of gold nanoparticles fabricated by a simple and versatile three-step process to modulate the size, the interparticle distance, and the optical properties of the gold nanostructures to achieve the optimal fluorescence enhancement. Specifically, we have tested three different fluorescent dyes (Alexa Fluor 488, Alexa Fluor 546, and PE-Cy7) coupled with optimized gold nanostructures and achieved up to ≈170-fold enhancement in the fluorescence emission, significantly better than those achieved by metal nanostructures in solutions and by randomly assembled nanoplasmonic arrays. Our MEF immunosensor is then employed for detecting immunoglobulins in a model antigen−antibody system, achieving a limit of detection of 4.3 ng/mL. This value is lower than that of similar immunoglobulin detection assays and offers promising opportunities for a wide range of biosensing applications.

Recent Advances in the Fabrication and Functionalization of Flexible Optical Biosensors: Toward Smart Life-Sciences Applications

“…In this context, LSPR biosensors show appealing properties such as miniaturization, minimal interferences, and scalable production. However, while both periodic [ 34 , 35 ] and non-periodic [ 31 ] arrays of noble-metal nanoparticles on hard substrates have been already proposed as sensing platforms, there is still a lot of active research to propose novel approaches toward the fabrication of flexible, polymer-based LSPR biosensors. The main issue associated with the fabrication of such optical platforms is the limited number of polymers that can be used as substrates.…”

“…All the advantages shown by optical devices based on plasmonic nanoparticles have stimulated the continuous improvement of their fabrication techniques. The nanotechnological fabrication processes are based on two main approaches: top-down and bottom-up, which are sometimes combined to obtain a “hybrid approach” [ 30 , 31 ]. While the top-down approach usually requires nanolithographic techniques, which permits the mechanical or chemical etching of the bulk material, the bottom-up approach is based on the chemical synthesis of nanoparticles [ 32 , 33 , 34 ], starting from “molecular bricks.” In the case of the bottom-up approach some other methods are required to graft the nanomaterials onto the substrates, usually made of rigid materials (glass, silicon, quartz, etc.)…”

Plasmonic gold nanostructures for biosensing and bioimaging

“…By controlling the ratio of Cy3 signal on the AuNSs via changing the nanoassembly synthesis conditions and a biotin displacement experiment, enhancement factors ranging from 1.2 to 3.5 were obtained. Using immunosensor based on metal-enhanced fluorescence, Miranda et al [ 62 ] realized the immunoglobulins analysis in a common antigen-antibody model. In this assay, the gold nanostructures arrays which were constructed by a simple and efficient three-step process were adjusted by modulating the size, interparticle distance, and optical properties of AuNPs.…”

Nanomaterial-Based Fluorescence Resonance Energy Transfer (FRET) and Metal-Enhanced Fluorescence (MEF) to Detect Nucleic Acid in Cancer Diagnosis

“…In addition, the MEF process simultaneously enhances the photostability and sensitivity as well as the intensities. Recently, MEF-based nanobiosensors have been developed to improve the detection sensitivity for target biomarkers, including nucleic acids and proteins, to the level of ultra-low concentrations [74,81,82]. The presence of fluorescent materials near the noble metal NPs increases the rate of excitation and emission by inducing the fluorophores to assume additional electron configurations.…”