Label-Free Biosensing Based on Multilayer Fluorescent Nanocomposites and a Cationic Polymeric Transducer

Abstract

This study describes the preparation and characterization of a DNA sensing architecture combining the molecular recognition capabilities of a cationic conjugated polymer transducer with highly fluorescent core-shell nanoparticles (NPs). The very structure of the probe-labeled NPs and the polymer-induced formation of NP aggregates maximize the proximity between the polymer donor and acceptor NPs that is required for optimal resonant energy transfer. Each hybridization event is signaled by a potentially large number of excited reporters following the efficient plasmon-enhanced energy transfer between target-activated polymer transducer and fluorophores located in the self-assembled core-shell aggregates, resulting in direct molecular detection of target nucleic acids at femtomolar concentrations.

Regeneration of Limbal Stem Cells in the Presence of Silver and Gold Nanoparticles

“…Recent studies doubted the safety of nano-sized gold particles [19], due to their electrical, chemical, mechanical, thermal and optical properties [1,[19][20][21]. Indeed, gold nanoparticles unlike the bioinert bulk gold, are able to enter cells and exert adverse effects by interacting with membranes and smaller subcellular compartments, while unable to enter the nucleus [22][23][24][25][26].…”

Metal-Enhanced Fluorescence and FRET in Multilayer Core-Shell Nanoparticles

“…Since the polymer exists in its quenched planar conformation in the target-ready NPs, the latter are not fluorescent when observed by imaging flow cytometry (IFC) and excited near the nominal excitation wavelength of the polymer donor. However, they were easily detectable when excited directly at the nominal excitation wavelength of the eosin acceptor at 488 nm and, upon the addition of complementary oligonucleotides to the target-ready NPs, excitation of CCP resulted in the appearance of fluorescent objects that were on average significantly larger than on images recorded from probe-grafted NPs before addition of the CCP [19].…”

“…For example, core-shell multilayer dye-doped acceptor NPs grafted with short single-stranded DNA (ssDNA) probes and complexed with a cationic conjugated polymer (CCP) were demonstrated as a sensitive DNA sensor ( Figure 15) [19]. This approach exploits the chromism of the CCP, that is, intensity and spectral changes in absorption and luminescence caused by conformational changes in the CCP's conjugated backbone upon electrostatic binding to DNA strands.…”

“…This phenomenon, termed metal-enhanced fluorescence (MEF), is being investigated intensively and represents a powerful technology to increase the detection sensitivity of various biological assays [12][13][14][15][16][17][18][19]. Most of the studies performed to date involved twodimensional metallic surfaces, particularly those composed of silver islands, silver colloids (nanospheres, nanotriangles, nanorods), and even fractal-like silvered surfaces where glass or plastic slides were used as the primary substrates [20][21][22][23][24][25][26].…”

“…Controlled growth of a dielectric silica shell around the core ensures easy tunability of the dyemetal separation and of the resulting fluorescence enhancement [39]. Also, this shell protects the organic dyes against collisional quenching and can be functionalized to covalently bind target biomolecules or fluorophores or form electrostatic complexes with charged molecules [19,41]. Finally, plasmonic enhancement in core-shell nanostructures improves the efficiency, range, and transfer rate of Förster resonance energy transfer (FRET) by increasing the strength of donor-acceptor interactions, which can in turn lead to the excitation by a single donor of several acceptors molecules over distances exceeding the natural range of FRET [39,41].…”