Label-Free Aptasensor Based on Ultrathin-Linker-Mediated Hot-Spot Assembly To Induce Strong Directional Fluorescence

Abstract

We have demonstrated the proof-of-concept of a label-free biosensor based on emission induced by an extreme hot-spot plasmonic assembly. In this work, an ultrathin linking layer composed of cationic polymers and aptamers was fabricated to mediate the assembly of a silver nanoparticles (AgNPs)-dyes-gold film with a strongly coupled architecture through sensing a target protein. Generation of directional surface plasmon coupled emission (SPCE) was thus stimulated as a means of reporting biorecognition. Both the biomolecules and the nanoparticles were totally free of labeling, thereby ensuring the activity of biomolecules and allowing the use of freshly prepared metallic nanoparticles with large dimensions. This sensor smartly prevents the plasmonic assembly in the absence of targets, thus maintaining no signal through quenching fluorophores loaded onto a gold film. In the presence of targets, the ultrathin layer is activated to link NPs-film junctions. The small gap of the junction (no greater than 2 nm) and the large diameter of the nanoparticles (~100 nm) ensure that ultrastrong coupling is achieved to generate intense SPCE. A >500-fold enhancement of the signal was observed in the biosensing. This strategy provides a simple, reliable, and effective way to apply plasmonic nanostructures in the development of biosensing.

Environmentally responsive plasmonic nanoassemblies for biosensing

“…Recently, Li et al reported a sensitive label-free aptamer sensor based on directional surface plasmon coupled emission in nanoscale assemblies. 48 As shown in Fig. 9b, a layer of dyecoated Au nanofilm was fabricated onto a quartz substrate, with efficiently quenched fluorescence because of NSET.…”

Integrated plasmon-enhanced Raman scattering (iPERS) spectroscopy

“…Next, the PSPs radiate in far field along a certain cone angle according to the vector-match law. Thus, an emission loop comes out and a cone pattern of the SERS emission can be obtained in far field 18 – 21 . In this design, the coupling of LSPs in near field and the SERS emission in far field are integrated by an elaborately designed ASIL.…”

“…2b shows the angle sweeps of SERS emission intensities of several Raman photons collected from far field. It can be found that the emission angles sharply focus into the narrow angle range and only part of the scattering signal appears in the air side, especially for the emitter with the wavelengths shorter than 830 nm 18 , 23 . The radiative patterns of the EM fields of 785, 830 and 950 nm radiators in the gap of the NOF are shown in Fig.…”

Surface plasmon–coupled emission imaging for biological applications

“…However, there is a great demand to achieve higher sensitivity and selectivity with the rapid development of life science. Recently, a surface-enhanced fluorescence technique, referred to as surface plasmon-coupled emission (SPCE), has been widely investigated [7][8][9][10][11]. The high collection efficiency, due to the directed radiation, greatly improves the sensitivity of SPCE.…”