Single Molecule Immunoassay on Plasmonic Platforms (original) (raw)
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Coupled plasmon effects for the enhancement of fluorescent immunoassays
Physica B: Condensed Matter, 2007
We present a study of fluoroimmunoassays using Rhodamine-RedX labelled antibodies enhanced by nanoparticle silver island films (SIFs) in the presence of thin metallic layers. Our results show enhancement of the immunoassay signal by up to 10-fold for SIFs on glass and up to 50-fold enhancement for SIFs supported by a metal surface. An explanation for these effects is proposed by considering plasmonic coupling within the system and modification of the fluorophore spontaneous emission rate. r
Nature Nanotechnology, 2013
Single-molecule fluorescence techniques 1-3 are key for a number of applications, including DNA sequencing 4,5 , molecular and cell biology 6,7 and early diagnosis 8 . Unfortunately, observation of single molecules by diffraction-limited optics is restricted to detection volumes in the femtolitre range and requires pico-or nanomolar concentrations, far below the micromolar range where most biological reactions occur 2 . This limitation can be overcome using plasmonic nanostructures, which enable the confinement of light down to nanoscale volumes 9-13 . Although these nanoantennas enhance fluorescence brightness 14-20 , large background signals and/or unspecific binding to the metallic surface 23-25 have hampered the detection of individual fluorescent molecules in solution at high concentrations. Here we introduce a novel 'antenna-in-box' platform that is based on a gap-antenna inside a nanoaperture. This design combines fluorescent signal enhancement and background screening, offering high singlemolecule sensitivity (fluorescence enhancement up to 1,100fold and microsecond transit times) at micromolar sample concentrations and zeptolitre-range detection volumes. The antenna-in-box device can be optimized for single-molecule fluorescence studies at physiologically relevant concentrations, as we demonstrate using various biomolecules.
Nanoscale Research Letters, 2013
In this work, we focused on the label-free detection of simple protein binding using near-infrared light-responsive plasmonic nanoshell arrays with a controlled interparticle distance. The nanoshell arrays were fabricated by a combination of colloidal self-assembly and subsequent isotropic helium plasma etching under atmospheric pressure. The diameter, interparticle distance, and shape of nanoshells can be tuned with nanometric accuracy by changing the experimental conditions. The Au, Ag, and Cu nanoshell arrays, having a 240-nm diameter (inner, 200-nm polystyrene (PS) core; outer, 20-nm metal shell) and an 80-nm gap distance, exhibited a well-defined localized surface plasmon resonance (LSPR) peak at the near-infrared region. PS@Au nanoshell arrays showed a 55-nm red shift of the maximum LSPR wavelength of 885 nm after being exposed to a solution of bovine serum albumin (BSA) proteins for 18 h. On the other hand, in the case of Cu nanoshell arrays before/after incubation to the BSA solution, we found a 30-nm peak shifting. We could evaluate the difference in LSPR sensing performance by changing the metal materials.
The Journal of Physical Chemistry C, 2008
We examined the emission intensity and wavelength of 40 nm diameter silver particles covalently coated with organic fluorophores with different absorption and emission wavelengths. The objective of this study is to use the interactions of fluorophores with the plasmon in the metal particles to create the brightest possible probes. We refer to the complexes as plasmon-coupled fluorescence probes (PCPs). The fluorophores were separated from the metal cores by 10 nm long polymer backbones. The fluorescence was observed to be enhanced for seven fluorophores with emission wavelength from 450 to 700 nm. The enhancement efficiency was shown to approximately increase with long wavelengths for the silver particle-bound fluorophores. When comparing a single fluorophore free in solution and bound to the silver particle, the emission intensity increases 3-to 17-fold. The relationship between the enhancement efficiency and loading number of fluorophore on each silver particle was studied to optimize the conditions for PCP brightness. Compared with the free single fluorophores in the absence of metal, the optimized single labeled silver particles were even more than 1000-fold brighter, showing their potentials in the applications of sensitive clinical and biological assays.
Label-Free Plasmonic Detection of Biomolecular Binding by a Single Gold Nanorod
Analytical Chemistry, 2008
We report the use of individual gold nanorods as plasmonic transducers to detect the binding of streptavidin to individual biotin-conjugated nanorods in real time on a surface. Label-free detection at the single-nanorod level was performed by tracking the wavelength shift of the nanorod-localized surface plasmon resonant scattering spectrum using a dark-field microspectroscopy system. The lowest streptavidin concentration that was experimentally measured was 1 nM, which is a factor of 1000-fold lower than the previously reported detection limit for streptavidin binding by biotinylated single plasmonic nanostructures. We believe that the current optical setup is able to reliably measure wavelength shifts as small as 0.3 nm. Binding of streptavidin at 1 nM concentration induces a mean resonant wavelength shift of 0.59 nm suggesting that we are currently operating at close to the limit of detection of the system.
Nanoplasmonics, 2020
Recent developments in nanoplasmonic sensors promise highly sensitive detection of chemical and biomolecular analytes with quick response times, affordable costs, and miniaturized device footprints. These include plasmonic sensors that transduce analyte-dependent changes to localized refractive index, vibrational Raman signatures, or fluorescence intensities at the sensor interface. One of the key challenges, however, remains in producing such sensors reliably, at low cost, using manufacturing compatible techniques. In this chapter, we demonstrate an approach based on molecular self-assembly to deliver wafer-level fabrication of nanoplasmonic interfaces, with spatial resolutions down to a few nanometers, assuring high quality and low costs. The approach permits systematic variation to different geometric variables independent of each other, allowing the significant opportunity for the rational design of nanoplasmonic sensors. The ability to detect small molecules by SERS-based plasmonic sensing is compared across different types of metal nanostructures including arrays of nanoparticle clusters, nanopillars, and nanorod and nanodiscs of gold.
ACS Nano, 2012
In this work, we report a simple strategy to obtain ultrasensitive SERS nanostructures by selfassembly and bioconjugation of Au nanospheres (NSs). Homodimer aggregates with an interparticle gap of around 8 nm are generated in aqueous dispersions by the highly specific molecular recognition of biotinylated Au NSs to streptavidin (STV), while random Au NS aggregates with a gap of 5 nm are formed in the absence of STV due to hydrogen bonding among biotinylated NSs. Both types of aggregates depict SERS analytical enhancement factors (AEF) of around 10 7 and the capability to detect biotin concentrations lower than 1 Â 10 À12 M. Quite interesting, the AEF for an external analyte, Rhodamine 6G (RH6G), using the dimer aggregates is 1 order of magnitude greater (10 5 ) than using random aggregates (around 10 4 ).