Experimental and theoretical evaluation of surface plasmon-coupled emission for sensitive fluorescence detection (original) (raw)
Directional surface plasmon-coupled emission: a new method for high sensitivity detection
Biochemical and Biophysical Research Communications, 2003
High-sensitivity detection schemes are of great interest for a number of applications. Unfortunately, such schemes are usually high-cost. We demonstrate a low-cost approach to a high-sensitivity detection scheme based on surface plasmon-coupled emission (SPCE). The SPCE of a monomolecular layer of green fluorescent protein (GFP) is reported here. The protein was electrostatically attached to a thin, SiO 2protected silver film deposited on a quartz substrate. The visible, directional emission of GFP was observed at a sharp, well-defined angle of 47.5°from the normal to the coupling prism, and the spectrum corresponded to that of GFP. The SPCE resulting from the reverse Kretschmann configuration showed a 12-fold enhancement over the free space fluorescence. The directional emission was 97% p-polarized. The directionality and high polarization can be coupled with the intrinsic spectral resolution of SPCE to be used in the design miniaturized spectrofluorometers. The observation of SPCE in the visible region of the spectrum from a monolayer of protein opens up new possibilities in protein-based sensing.
Surface plasmon-coupled directional fluorescence emission
Plasmonics in Biology and Medicine, 2004
Directional fluorescence emission of a sulforhodamine 101 in polyvinyl alcohol film has been observed from samples deposited on semi-transparent silver mirror. The fully p-polarized fluorescence emerges through the glass prism in form of hollow cone. The angle of this cone of emission depends on the thickness of the sample, and does not depend on the mode of excitation. The angular dependence of surface plasmon-coupled emission (SPCE) on the sample thickness has been discussed as well as its relevance to the surface plasmon resonance (SPR) analysis.
Surface plasmon-coupled directional fluorescence emission
Plasmonics in Biology and Medicine, 2004
Directional fluorescence emission of a sulforhodamine 101 in polyvinyl alcohol film has been observed from samples deposited on semi-transparent silver mirror. The fully p-polarized fluorescence emerges through the glass prism in form of hollow cone. The angle of this cone of emission depends on the thickness of the sample, and does not depend on the mode of excitation. The angular dependence of surface plasmon-coupled emission (SPCE) on the sample thickness has been discussed as well as its relevance to the surface plasmon resonance (SPR) analysis.
Minimization of detection volume by surface-plasmon-coupled emission
Analytical Biochemistry, 2006
We report theoretical predictions and experimental observations of the reduced detection volume with the use of surface-plasmoncoupled emission (SPCE). The eVective Xuorescence volume (detection volume) in SPCE experiments depends on two near-Weld factors: the depth of evanescent wave excitation and a distance-dependent coupling of excited Xuorophores to the surface plasmons. With direct excitation of the sample (reverse Kretschmann excitation) the detection volume is restricted only by the distancedependent coupling of the excitation to the surface plasmons. However, with the excitation through the glass prism at surface plasmon resonance angle (Kretschmann conWguration), the detection volume is a product of evanescent wave penetration depth and distancedependent coupling. In addition, the detection volume is further reduced by a metal quenching of excited Xuorophores at a close proximity (below 10 nm). The height of the detected volume size is 40-70 nm, depending on the orientation of the excited dipoles. We show that, by using the Kretschmann conWguration in a microscope with a high-numerical-aperture objective (1.45) together with confocal detection, the detection volume can be reduced to 1-2 attoL. The strong dependence of the coupling to the surface plasmons on the orientation of excited dipoles can be used to study the small conformational changes of macromolecules.
Multicolor Directional Surface Plasmon-Coupled Chemiluminescence
The Journal of Physical Chemistry B, 2006
In reports over the past several years, we have demonstrated the efficient collection of optically excited fluorophore emission by its coupling to surface plasmons on thin metallic films, where the coupled luminescence was highly directional and polarized. This phenomenon is referred to as surface plasmon-coupled emission (SPCE). In this current study, we have extended this technique to include chemiluminescing species and subsequentially now report the observation of surface plasmon-coupled chemiluminescence (SPCC), where the luminescence from chemically induced electronic excited states couples to surface plasmons in thin continuous metal films. The SPCC is highly directional and predominantly p-polarized, strongly suggesting that the emission is from surface plasmons instead of the luminophores themselves. This indicates that surface plasmons can be directly excited from chemically induced electronic excited states and excludes the possibility that the plasmons are created by incident excitation light. This phenomenon has been observed for a variety of chemiluminescent species in the visible spectrum, ranging from blue to red, and also on a variety of metals, namely, aluminum, silver, and gold. Our findings suggest new chemiluminescence sensing strategies on the basis of localized, directional, and polarized chemiluminescence detection, especially given the wealth of assays that currently employ chemiluminescence-based detection.
Plasmon-controlled fluorescence: a new detection technology
SPIE Proceedings, 2006
Fluorescence is widely used in biological research. Future advances in biology and medicine often depend on the advances in the capabilities of fluorescence measurements. In this overview paper we describe how a combination of fluorescence, and plasmonics, and nanofabrication can fundamentally change and increase the capabilities of fluorescence technology. This change will be based on the use of surface plasmons which are collective oscillations of free electrons in metallic surfaces and particles. Surface plasmon resonance is now used to measure bioaffinity reactions. However, the uses of surface plasmons in biology are not limited to their optical absorption or extinction. We have shown that fluorophores in the excited state can create plasmons which radiate into the far field; additionally fluorophores in the ground state can interact with and be excited by surface plasmons. These interactions suggest that the novel optical absorption and scattering properties of metallic nanostructures can be used to control the decay rates, location and direction of fluorophore emission. We refer to this technology as plasmon-controlled fluorescence. We predict that plasmon-controlled fluorescence (PCF) will result in a new generation of probes and devices. PCF is likely to allow design of structures which enhance emission at specific wavelengths and the creation of new devices which control and transport the energy from excited fluorophores in the form of plasmons, and then convert the plasmons back to light.
ANALYTICAL BIOCHEMISTRY Minimization of detection volume by surface-plasmon-coupled emission
We report theoretical predictions and experimental observations of the reduced detection volume with the use of surface-plasmon-coupled emission (SPCE). The eVective Xuorescence volume (detection volume) in SPCE experiments depends on two near-Weld factors: the depth of evanescent wave excitation and a distance-dependent coupling of excited Xuorophores to the surface plasmons. With direct excitation of the sample (reverse Kretschmann excitation) the detection volume is restricted only by the distance-dependent coupling of the excitation to the surface plasmons. However, with the excitation through the glass prism at surface plasmon resonance angle (Kretschmann conWguration), the detection volume is a product of evanescent wave penetration depth and distance-dependent coupling. In addition, the detection volume is further reduced by a metal quenching of excited Xuorophores at a close proximity (below 10 nm). The height of the detected volume size is 40–70 nm, depending on the orientation of the excited dipoles. We show that, by using the Kretschmann conWguration in a microscope with a high-numerical-aperture objective (1.45) together with confocal detection, the detection volume can be reduced to 1–2 attoL. The strong dependence of the coupling to the surface plasmons on the orientation of excited dipoles can be used to study the small conformational changes of macromolecules.
Analytical Chemistry, 2004
The highly sensitive nature of surface plasmon resonance (SPR) spectroscopy and surface plasmon field-enhanced fluorescence spectroscopy (SPFS) are governed by the strong surface plasmon resonance-generated evanescent field at the metal/dielectric interface. The greatest evanescent field amplitude at the interface and the maximum attenuation of the reflectance are observed when a nonabsorbing dielectric is employed. An absorbing dielectric decreases the evanescent field enhancement at the interface. The SPR curve of an absorbing dielectric is characterized by a greater reflectance minimum and a broader curve, as compared to those of the nonabsorbing dielectric with the same refractive index. For a weakly absorbing dielectric, such as nanometer-thick surface-confined fluorophores, the absorption is too small to induce a significant change in the SPR curve. However, the presence of a minute amount of the fluorophore can be detected by the highly sensitive SPFS. The angle with the maximum fluorescence intensity of an SPFS curve is always smaller than the resonance angle of the corresponding SPR curve. This discrepancy is due to the differences of evanescent field distributions and their decay characteristics within the metal film and the dielectric medium. The fluorescence intensity in an SPFS curve can be expressed in terms of the evanescent field amplitude. Excellent correlations between the experimentally measured fluorescence intensities and the evanescent field amplitudes are observed.
Characteristics of Fluorescence Emission Excited by Grating-Coupled Surface Plasmons
Plasmonics, 2018
Dye molecules placed on metallic gratings can experience an enhanced electromagnetic field if illuminated under surface plasmon excitation conditions, a situation that can be employed for sensor applications. The fluorescence emission in this situation exhibits a characteristic emission polarization and geometry given by the fluorophore/grating interaction. We present experiments visualizing the full shape of the emission profiles and demonstrate how they can be manipulated by means of the grating constant. The excitation and emission processes taking place on the grating surface are characterized by polarization sensitive measurements.
Analytical and Bioanalytical Chemistry, 2010
We have presented novel surface plasmon-coupled emission (SPCE) based on solid-state electrochemiluminescence (ECL) of Nafion films containing tris(2,2 0-bipyridyl)ruthenium(II). This approach combines the advantages of ECL, efficient emission in the absence of an external light source, with the highly directional emission of SPCE. We described theoretical calculations and optimal Nafion film thickness to get SPCE based on solid-state ECL. We confirmed the SPCE and dose-dependent SPCE response from the concentration range of 0.05-0.5% (w/v) [Ru(bpy) 3 ] 2+ in the Nafion film. SPCE based on solid-state ECL can be used as a useful platform for the analysis of chemical and biomolecular interactions.