Two pseudo-para substituted bis-diimino[2.2]paracyclophane ligands (4,16-bis(picolinaldimine)-[2.... more Two pseudo-para substituted bis-diimino[2.2]paracyclophane ligands (4,16-bis(picolinaldimine)-[2.2]paracyclophane (BPPc) and 4,16-bis(methyl-picolinaldimine)-[2.2]paracyclophane (BmPPc)) were prepared by the condensation reaction of the appropriate picolinaldimine with 4,16-diamino-[2.2]paracyclophane (2). An improved synthesis of 2 from [2.2]paracyclophane also is reported. BPPc (3a): monoclinic, To investigate the binding properties of the bisdiimino[2.2]paracyclophane ligands, binuclear rhenium(I) tricarbonyl chloride complexes [Re(CO) 3 Cl] 2 (µ-BPPc) (5a) and [Re(CO) 3 Cl] 2 (µ-BmPPc) (5b) were prepared and fully characterized by infrared spectroscopy, 1 H NMR spectroscopy, elemental analysis, UV-visible absorption spectroscopy, and cyclic voltammetry. Two model complexes, Re(tolyl-pyCa)(CO) 3 Cl (4) (tolyl-pyCa ) N-(p-tolyl)-2-pyridinecarboxaldimine) and [Re(CO) 3 Cl] 2 (µ-PBP) (6) (PBP ) p-phenylenebis(picolinaldimine)), also are reported. The dimeric compounds 5 and 6 each undergo two one-electron, predominantly diimine-centered reduction processes. Spectroscopic data and comproportionation constants (5a, 23 ± 9; 5b, 23 ± 9; 6, 2750 ± 540) are consistent with relatively weak interactions between the diimine groups mediated by the paracyclophane bridging group, and these results are consistent with steric and electronic factors.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Journal of Photochemistry and Photobiology B: Biology, 2020
We studied the luminescence properties of indole in poly (vinyl alcohol) (PVA) film. The indole m... more We studied the luminescence properties of indole in poly (vinyl alcohol) (PVA) film. The indole molecules are effectively immobilized in this polymer film and display both fluorescence and phosphorescence emission at room temperature. We noticed that the phosphorescence of indole in PVA film can be effectively excited at a longer wavelength than its typical singlet to triplet population route involving intersystem crossing. The maximum of the phosphorescence excitation is about 410 nm which corresponds to the energy of indole's triplet state. Interestingly, the phosphorescence anisotropy excited with the longer wavelength (405 nm) is positive and reaches a value of about 0.25 in contrast to the phosphorescence anisotropy excited within the indole singlet absorption spectrum (290 nm), which is negative. Very different temperature dependences have been observed for fluorescence and phosphorescence of indole in PVA film. While fluorescence depends minimally, the phosphorescence decreases with temperature dramatically. The fluorescence lifetime was measured to be a single component 4.78 ns while the intensity weighted average phosphorescence lifetime with 290 nm and 405 nm excitations were 6.57 and 5.62 ms, respectively. We believe that the possibility of the excitation of indole phosphorescence in the blue region of visible light and its high anisotropy opens a new avenue for future protein studies.
Using the effect of the fluorescence enhancement in close proximity to metal nanostructures, we h... more Using the effect of the fluorescence enhancement in close proximity to metal nanostructures, we have been able to demonstrate ultrasensitive immunoassays suitable for the detection of biomarkers. Silver fractal-like structures have been grown by electrochemical reduction of silver on the surface of glass slides. A model immunoassay was performed on the slide surface with rabbit IgG (antigen) non-covalently immobilized on the slide, and Rhodamine Red-X labeled anti-rabbit IgG conjugate subsequently bound to the immobilized antigen. The fluorescence signal was measured from the glass-fractals surface using a confocal microscope, and the images were compared to the images from the same surface not coated with fractals. Our results showed significant enhancement (more than 100-fold) of the signal detected on fractals compared to bare glass. We thus demonstrate that such fractal-like structures can assist in improving the signals from assays used in medical diagnostics, especially those for analytes with molecular weight under 100 kD.
We examined the photophysical properties of the new near infrared (NIR) fluorescent label SeTau-6... more We examined the photophysical properties of the new near infrared (NIR) fluorescent label SeTau-665 on a plasmonic platform of self-assembled colloidal structures (SACS) of silver prepared on a semitransparent silver film. A SeTau-665 immunoassay was performed on this platform and a control glass slide. The fluorescence properties of this label substantially change due to plasmonic interactions. While the average brightness increase of SeTau 665 in ensemble measurements was about 70-fold, fluorescence enhancements up to four-hundred times were observed on certain "hot spots" for single molecule measurements. The intensity increase is strongly correlated with a simultaneous decrease in fluorescence lifetime in these "hot spots". The large increase in brightness allows the reduction of the excitation power resulting in a reduced background and increased photostability. The remarkable fluorescence enhancements observed for SeTau 665 on our plasmonic platform should allow to substantially improve single molecule detection and to reduce the detection limits in sensing devices.
Selectivity and sensitivity are the two biggest challenges in modern chemical sensing. The combin... more Selectivity and sensitivity are the two biggest challenges in modern chemical sensing. The combination of two dif-ferent techniques, spectroscopy and electrochemistry, opens a new door in chemical sensing by improving the selectivity and sensitivity of measurements (15). As such, it is ...
In this report we discuss strong fluorescence enhancements on electro-chemically grown silver nan... more In this report we discuss strong fluorescence enhancements on electro-chemically grown silver nanostructures examined through fluorescence lifetime imaging microscopy (FLIM). Silver fractal-like nanostructures were deposited on three different substrates: glass, plastic, and silicon. For all of the surfaces the same dye was tested, DyLight 649, deposited in the form of a model immunoassay through excitation from a 635 nm pulsed solid-state laser. The brightness improvement in hot spots exceeded 300 fold, which is about two times higher than was observed previously on similar surfaces. The strongest enhancements correspond to the shortest lifetimes, indicating a strong interaction between excited molecules and silver nanostructures. Additionally, the photostability of the fluorescence dye was dramatically increased in the presence of electrochemically deposited silver nanostructures. The production of silver fractals is easy, very controllable, and can be applied to any surface. We therefore believe that silver fractal-like nanostructures can be used successfully in ultra-sensitive assays and fluorophore trace detection.
Gold nanoparticles covalently attached to the indium tin oxide coated glass slide drastically que... more Gold nanoparticles covalently attached to the indium tin oxide coated glass slide drastically quench fluorescence of a surface immu-noassay (approximately 5-fold). Silver electrochemically deposited over the gold particles leads to fluorescence amplification: signal increases approximately 7–8 times if compared to the signal on gold particles not covered with silver. This phenomenon allows enhancing of the surface immunoassays utilizing both types of nanoparticles.
Using the effect of the fluorescence enhancement in close proximity to metal nanostructures, we h... more Using the effect of the fluorescence enhancement in close proximity to metal nanostructures, we have been able to demonstrate ultrasensitive immunoassays suitable for the detection of biomarkers. Silver fractal-like structures have been grown by electrochemical reduction of silver on the surface of glass slides. A model immunoassay was performed on the slide surface with rabbit IgG (antigen) noncovalently immobilized on the slide, and rhodamine red-X-labeled antirabbit IgG conjugate was subsequently bound to the immobilized antigen. The fluorescence signal was measured from the glass-fractal's surface using a confocal microscope, and the images were compared to the images from the same surface not coated with fractals. Our results showed significant enhancement (more than 100-fold) of the signal detected on fractals compared to bare glass. We thus demonstrate that such fractal-like structures can assist in improving the signals from assays used in medical diagnostics, especially those for analytes with molecular weight under 100 kDa.
Electrochemically deposited silver structures with nanowires 50-100 nm in diameter show high fluo... more Electrochemically deposited silver structures with nanowires 50-100 nm in diameter show high fluorescence amplification and strongly reduced fluorescence lifetimes. Both quantities depend on the structure thickness. With increasing thickness the fluorescence amplification proportionally increases and the fluorescence lifetime decreases. This thickness dependence is caused by fluorophore interaction with a system of plasmon excitations in coupled nanowires extending over micrometer size regions. Thus the amplification is attributed to a combination of extended structure area and strong plasmonic coupling between nanowires which also help to radiatively scatter the fluorescence emission.
Amplification of fluorescence is a nanoscale phenomenon which is particularly pronounced in close... more Amplification of fluorescence is a nanoscale phenomenon which is particularly pronounced in close proximity to metal nanostructures. Due to its sharp distance dependence, it is ideally suited to monitor biorecognition reactions. Using this effect we have been able to demonstrate ultrasensitive bioassays. Two types of metal nanostructures have been employed, nanometric silver islands deposited over an ultrathin metal mirror and silver fractal structures. For the first type, metal mirrors (aluminum, gold, or silver protected with a thin silica layer) were coated with SIFs and an immunoassay (model assay for rabbit IgG or myoglobin immunoassay) was performed on this surface using fluorescently labeled antibodies. Our results show that SIFs alone (on a glass surface not coated with metal) enhance the immunoassay signal approximately 3 to 10-fold. Using a metal mirror instead of glass as support for SIFs leads to up to 50-fold signal enhancement. The second type of metal nanostructures, silver fractals, were produced by electrochemical reduction of silver nitrate deposited on sapphire covered with a thin conductive film of indium tin oxide. These structures were used as a substrate for a model rabbit IgG bioassay. The fluorescence resulting from the binding of antibody labeled with Rhodamine was highly nonuniform with distinctive hot spots. These highly fluorescent regions were correlated with areas of higher Ag thickness and coverage. Such high values of fluorescence amplification in both types of nanostructures have been interpreted by using time-resolved fluorescence data and by considering the radiative properties of plasmons in the environments which promote plasmon coupling.
The optical and electrochemical properties of metallic films on ITO surfaces resulting from depos... more The optical and electrochemical properties of metallic films on ITO surfaces resulting from deposition of copper and cadmium were monitored by stripping voltammetry-attenuated internal reflectance spectroscopy. The voltammetric or optical responses of both metals were examined with respect to solution conditions such as pH and presence of dissolved oxygen. The morphologies of these films were also examined using environmental scanning electron microscopy, and the microscopic electrodeposition patterns were found to influence the optical response. The wavelength dependence of the optical response of deposited copper was determined and compared with calculations; optimal performance was at 400 nm for copper. A linear calibration curve was obtained over a range of 1 x 10(-7)-1 x 10(-4) M for copper and compared with that of cadmium. The simultaneous determination of cadmium and copper was demonstrated, and the mechanism of co-deposition is discussed.
In this report, we describe a plasmonic platform with silver fractals for metal enhanced fluoresc... more In this report, we describe a plasmonic platform with silver fractals for metal enhanced fluorescence (MEF) measurements. When a dye containing surface was brought into contact with silver fractals, a significantly enhanced fluorescence signal from the dye was observed. Fluorescence enhancement was studied with the N-methyl-azadioxatriangulenium chloride salt (Me-ADOTA·Cl) in PVA films made from 0.2% PVA (w/v) solution spin-coated on a clean glass coverslip. The Plasmonic Platforms (PP) were assembled by pressing together silver fractals on one glass slide and a separate glass coverslip spin-coated with a uniform Me-ADOTA·Cl in PVA film. In addition, we also tested ADOTA labeled human serum albumin (HSA) deposited on a glass slide for potential PP bioassay applications. Using the new PP, we could achieve more than a 20-fold fluorescence enhancement (bright spots) accompanied by a decrease in the fluorescence lifetime. The experimental results were used to calculate the extinction (excitation) enhancement factor (GA) and fluorescence radiative rate enhancements factor (GF). No change in emission spectrum was observed for a dye with or without contact with fractals. Our studies indicate that this type of PP can be a convenient approach for constructing assays utilizing metal enhanced fluorescence (MEF) without the need for depositing the material directly on metal structures platforms.
Nanoscale Imaging, Sensing, and Actuation for Biomedical Applications VII, 2010
Scattering from noble metallic nanoparticles with specific structures are strongly depolarized in... more Scattering from noble metallic nanoparticles with specific structures are strongly depolarized in contrast to dielectric particles. The effect depends on the shape and symmetry of the nanoparticles and can be explained by induced plasmonic multi-resonances along different axes of symmetry. In our experiments we found that the scattering from 'nanorod' structures of silver is more polarized than globular colloidal silver
Fluorescence intensity changes were investigated theoretically and experimentally using self-asse... more Fluorescence intensity changes were investigated theoretically and experimentally using self-assembled colloidal structures on silver semitransparent mirrors. Using a simplified quasi-static model and finite element method, we demonstrate that near-field interactions of metallic nanostructures with a continuous metallic surface create conditions that produce enormously enhanced surface plasmon resonances. The results were used to explain the observed enhancements and determine the optimal conditions for the experiment. The theoretical parts of the studies are supported with reports on detailed emission intensity changes which provided multiple fluorescence hot spots with 2-3 orders of enhancements. We study two kinds of the fluorophores: dye molecules and fluorescent nanospheres characterized with similar spectral emission regions. Using a lifetime-resolved fluorescence/reflection confocal microscopy technique, we find that the largest rate for enhancement (~1000-fold) comes from lo...
The surface-confined assay format is one of the most convenient detection formats used in many im... more The surface-confined assay format is one of the most convenient detection formats used in many immunoassays. Fluorescence emission from monolayers of dyes requires a strong excitation and good detection system. Such samples are susceptible to artifacts due to background fluorescence from substrates. We demonstrate that using silver nanostructures deposited on the slide substrate can significantly enhance measured fluorescence, reduce unwanted background and increase photostability of the used probes. Using thin layers of polymer doped with fluorescein, we tested two nanostructures--silver island films (SIFs) deposited on glass slides and self-assembled colloidal structures (SACS) deposited on thin silver film. The SACS surfaces show extraordinary fluorescence enhancements: over 100-folds in hot spots. We applied these surfaces for enhanced Alexa488 model immunoassay.
In this report we describe a preparation of silver wires (SWs) on gold mirrors and its applicatio... more In this report we describe a preparation of silver wires (SWs) on gold mirrors and its application to surface enhanced fluorescence (SEF) using a new methodology. Silica protected gold mirrors were drop-coated with a solution of silver triangular nanoprisms. The triangular nanoprisms were slowly air-dried to get silver wires that self-assembled on the gold mirrors. Fluorescence enhancement was studied using methyl azadioxatriangulenium chloride (Me-ADOTA · Cl) dye in PVA spin-coated on a clean glass coverslip. New Plasmonic Platforms (PPs) were assembled by placing a mirror with SWs in contact with a glass coverslip spin-coated with a uniform Me-ADOTA · Cl film. It was shown that surface enhanced fluorescence is a real phenomenon, not just an enhancement of the fluorescence signal due to an accumulation of the fluorophore on rough nanostructure surfaces. The average fluorescence enhancement was found to be about 15-fold. The lifetime of Me-ADOTA · Cl dye was significantly reduced (∼...
Two pseudo-para substituted bis-diimino[2.2]paracyclophane ligands (4,16-bis(picolinaldimine)-[2.... more Two pseudo-para substituted bis-diimino[2.2]paracyclophane ligands (4,16-bis(picolinaldimine)-[2.2]paracyclophane (BPPc) and 4,16-bis(methyl-picolinaldimine)-[2.2]paracyclophane (BmPPc)) were prepared by the condensation reaction of the appropriate picolinaldimine with 4,16-diamino-[2.2]paracyclophane (2). An improved synthesis of 2 from [2.2]paracyclophane also is reported. BPPc (3a): monoclinic, To investigate the binding properties of the bisdiimino[2.2]paracyclophane ligands, binuclear rhenium(I) tricarbonyl chloride complexes [Re(CO) 3 Cl] 2 (µ-BPPc) (5a) and [Re(CO) 3 Cl] 2 (µ-BmPPc) (5b) were prepared and fully characterized by infrared spectroscopy, 1 H NMR spectroscopy, elemental analysis, UV-visible absorption spectroscopy, and cyclic voltammetry. Two model complexes, Re(tolyl-pyCa)(CO) 3 Cl (4) (tolyl-pyCa ) N-(p-tolyl)-2-pyridinecarboxaldimine) and [Re(CO) 3 Cl] 2 (µ-PBP) (6) (PBP ) p-phenylenebis(picolinaldimine)), also are reported. The dimeric compounds 5 and 6 each undergo two one-electron, predominantly diimine-centered reduction processes. Spectroscopic data and comproportionation constants (5a, 23 ± 9; 5b, 23 ± 9; 6, 2750 ± 540) are consistent with relatively weak interactions between the diimine groups mediated by the paracyclophane bridging group, and these results are consistent with steric and electronic factors.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Journal of Photochemistry and Photobiology B: Biology, 2020
We studied the luminescence properties of indole in poly (vinyl alcohol) (PVA) film. The indole m... more We studied the luminescence properties of indole in poly (vinyl alcohol) (PVA) film. The indole molecules are effectively immobilized in this polymer film and display both fluorescence and phosphorescence emission at room temperature. We noticed that the phosphorescence of indole in PVA film can be effectively excited at a longer wavelength than its typical singlet to triplet population route involving intersystem crossing. The maximum of the phosphorescence excitation is about 410 nm which corresponds to the energy of indole's triplet state. Interestingly, the phosphorescence anisotropy excited with the longer wavelength (405 nm) is positive and reaches a value of about 0.25 in contrast to the phosphorescence anisotropy excited within the indole singlet absorption spectrum (290 nm), which is negative. Very different temperature dependences have been observed for fluorescence and phosphorescence of indole in PVA film. While fluorescence depends minimally, the phosphorescence decreases with temperature dramatically. The fluorescence lifetime was measured to be a single component 4.78 ns while the intensity weighted average phosphorescence lifetime with 290 nm and 405 nm excitations were 6.57 and 5.62 ms, respectively. We believe that the possibility of the excitation of indole phosphorescence in the blue region of visible light and its high anisotropy opens a new avenue for future protein studies.
Using the effect of the fluorescence enhancement in close proximity to metal nanostructures, we h... more Using the effect of the fluorescence enhancement in close proximity to metal nanostructures, we have been able to demonstrate ultrasensitive immunoassays suitable for the detection of biomarkers. Silver fractal-like structures have been grown by electrochemical reduction of silver on the surface of glass slides. A model immunoassay was performed on the slide surface with rabbit IgG (antigen) non-covalently immobilized on the slide, and Rhodamine Red-X labeled anti-rabbit IgG conjugate subsequently bound to the immobilized antigen. The fluorescence signal was measured from the glass-fractals surface using a confocal microscope, and the images were compared to the images from the same surface not coated with fractals. Our results showed significant enhancement (more than 100-fold) of the signal detected on fractals compared to bare glass. We thus demonstrate that such fractal-like structures can assist in improving the signals from assays used in medical diagnostics, especially those for analytes with molecular weight under 100 kD.
We examined the photophysical properties of the new near infrared (NIR) fluorescent label SeTau-6... more We examined the photophysical properties of the new near infrared (NIR) fluorescent label SeTau-665 on a plasmonic platform of self-assembled colloidal structures (SACS) of silver prepared on a semitransparent silver film. A SeTau-665 immunoassay was performed on this platform and a control glass slide. The fluorescence properties of this label substantially change due to plasmonic interactions. While the average brightness increase of SeTau 665 in ensemble measurements was about 70-fold, fluorescence enhancements up to four-hundred times were observed on certain "hot spots" for single molecule measurements. The intensity increase is strongly correlated with a simultaneous decrease in fluorescence lifetime in these "hot spots". The large increase in brightness allows the reduction of the excitation power resulting in a reduced background and increased photostability. The remarkable fluorescence enhancements observed for SeTau 665 on our plasmonic platform should allow to substantially improve single molecule detection and to reduce the detection limits in sensing devices.
Selectivity and sensitivity are the two biggest challenges in modern chemical sensing. The combin... more Selectivity and sensitivity are the two biggest challenges in modern chemical sensing. The combination of two dif-ferent techniques, spectroscopy and electrochemistry, opens a new door in chemical sensing by improving the selectivity and sensitivity of measurements (15). As such, it is ...
In this report we discuss strong fluorescence enhancements on electro-chemically grown silver nan... more In this report we discuss strong fluorescence enhancements on electro-chemically grown silver nanostructures examined through fluorescence lifetime imaging microscopy (FLIM). Silver fractal-like nanostructures were deposited on three different substrates: glass, plastic, and silicon. For all of the surfaces the same dye was tested, DyLight 649, deposited in the form of a model immunoassay through excitation from a 635 nm pulsed solid-state laser. The brightness improvement in hot spots exceeded 300 fold, which is about two times higher than was observed previously on similar surfaces. The strongest enhancements correspond to the shortest lifetimes, indicating a strong interaction between excited molecules and silver nanostructures. Additionally, the photostability of the fluorescence dye was dramatically increased in the presence of electrochemically deposited silver nanostructures. The production of silver fractals is easy, very controllable, and can be applied to any surface. We therefore believe that silver fractal-like nanostructures can be used successfully in ultra-sensitive assays and fluorophore trace detection.
Gold nanoparticles covalently attached to the indium tin oxide coated glass slide drastically que... more Gold nanoparticles covalently attached to the indium tin oxide coated glass slide drastically quench fluorescence of a surface immu-noassay (approximately 5-fold). Silver electrochemically deposited over the gold particles leads to fluorescence amplification: signal increases approximately 7–8 times if compared to the signal on gold particles not covered with silver. This phenomenon allows enhancing of the surface immunoassays utilizing both types of nanoparticles.
Using the effect of the fluorescence enhancement in close proximity to metal nanostructures, we h... more Using the effect of the fluorescence enhancement in close proximity to metal nanostructures, we have been able to demonstrate ultrasensitive immunoassays suitable for the detection of biomarkers. Silver fractal-like structures have been grown by electrochemical reduction of silver on the surface of glass slides. A model immunoassay was performed on the slide surface with rabbit IgG (antigen) noncovalently immobilized on the slide, and rhodamine red-X-labeled antirabbit IgG conjugate was subsequently bound to the immobilized antigen. The fluorescence signal was measured from the glass-fractal's surface using a confocal microscope, and the images were compared to the images from the same surface not coated with fractals. Our results showed significant enhancement (more than 100-fold) of the signal detected on fractals compared to bare glass. We thus demonstrate that such fractal-like structures can assist in improving the signals from assays used in medical diagnostics, especially those for analytes with molecular weight under 100 kDa.
Electrochemically deposited silver structures with nanowires 50-100 nm in diameter show high fluo... more Electrochemically deposited silver structures with nanowires 50-100 nm in diameter show high fluorescence amplification and strongly reduced fluorescence lifetimes. Both quantities depend on the structure thickness. With increasing thickness the fluorescence amplification proportionally increases and the fluorescence lifetime decreases. This thickness dependence is caused by fluorophore interaction with a system of plasmon excitations in coupled nanowires extending over micrometer size regions. Thus the amplification is attributed to a combination of extended structure area and strong plasmonic coupling between nanowires which also help to radiatively scatter the fluorescence emission.
Amplification of fluorescence is a nanoscale phenomenon which is particularly pronounced in close... more Amplification of fluorescence is a nanoscale phenomenon which is particularly pronounced in close proximity to metal nanostructures. Due to its sharp distance dependence, it is ideally suited to monitor biorecognition reactions. Using this effect we have been able to demonstrate ultrasensitive bioassays. Two types of metal nanostructures have been employed, nanometric silver islands deposited over an ultrathin metal mirror and silver fractal structures. For the first type, metal mirrors (aluminum, gold, or silver protected with a thin silica layer) were coated with SIFs and an immunoassay (model assay for rabbit IgG or myoglobin immunoassay) was performed on this surface using fluorescently labeled antibodies. Our results show that SIFs alone (on a glass surface not coated with metal) enhance the immunoassay signal approximately 3 to 10-fold. Using a metal mirror instead of glass as support for SIFs leads to up to 50-fold signal enhancement. The second type of metal nanostructures, silver fractals, were produced by electrochemical reduction of silver nitrate deposited on sapphire covered with a thin conductive film of indium tin oxide. These structures were used as a substrate for a model rabbit IgG bioassay. The fluorescence resulting from the binding of antibody labeled with Rhodamine was highly nonuniform with distinctive hot spots. These highly fluorescent regions were correlated with areas of higher Ag thickness and coverage. Such high values of fluorescence amplification in both types of nanostructures have been interpreted by using time-resolved fluorescence data and by considering the radiative properties of plasmons in the environments which promote plasmon coupling.
The optical and electrochemical properties of metallic films on ITO surfaces resulting from depos... more The optical and electrochemical properties of metallic films on ITO surfaces resulting from deposition of copper and cadmium were monitored by stripping voltammetry-attenuated internal reflectance spectroscopy. The voltammetric or optical responses of both metals were examined with respect to solution conditions such as pH and presence of dissolved oxygen. The morphologies of these films were also examined using environmental scanning electron microscopy, and the microscopic electrodeposition patterns were found to influence the optical response. The wavelength dependence of the optical response of deposited copper was determined and compared with calculations; optimal performance was at 400 nm for copper. A linear calibration curve was obtained over a range of 1 x 10(-7)-1 x 10(-4) M for copper and compared with that of cadmium. The simultaneous determination of cadmium and copper was demonstrated, and the mechanism of co-deposition is discussed.
In this report, we describe a plasmonic platform with silver fractals for metal enhanced fluoresc... more In this report, we describe a plasmonic platform with silver fractals for metal enhanced fluorescence (MEF) measurements. When a dye containing surface was brought into contact with silver fractals, a significantly enhanced fluorescence signal from the dye was observed. Fluorescence enhancement was studied with the N-methyl-azadioxatriangulenium chloride salt (Me-ADOTA·Cl) in PVA films made from 0.2% PVA (w/v) solution spin-coated on a clean glass coverslip. The Plasmonic Platforms (PP) were assembled by pressing together silver fractals on one glass slide and a separate glass coverslip spin-coated with a uniform Me-ADOTA·Cl in PVA film. In addition, we also tested ADOTA labeled human serum albumin (HSA) deposited on a glass slide for potential PP bioassay applications. Using the new PP, we could achieve more than a 20-fold fluorescence enhancement (bright spots) accompanied by a decrease in the fluorescence lifetime. The experimental results were used to calculate the extinction (excitation) enhancement factor (GA) and fluorescence radiative rate enhancements factor (GF). No change in emission spectrum was observed for a dye with or without contact with fractals. Our studies indicate that this type of PP can be a convenient approach for constructing assays utilizing metal enhanced fluorescence (MEF) without the need for depositing the material directly on metal structures platforms.
Nanoscale Imaging, Sensing, and Actuation for Biomedical Applications VII, 2010
Scattering from noble metallic nanoparticles with specific structures are strongly depolarized in... more Scattering from noble metallic nanoparticles with specific structures are strongly depolarized in contrast to dielectric particles. The effect depends on the shape and symmetry of the nanoparticles and can be explained by induced plasmonic multi-resonances along different axes of symmetry. In our experiments we found that the scattering from 'nanorod' structures of silver is more polarized than globular colloidal silver
Fluorescence intensity changes were investigated theoretically and experimentally using self-asse... more Fluorescence intensity changes were investigated theoretically and experimentally using self-assembled colloidal structures on silver semitransparent mirrors. Using a simplified quasi-static model and finite element method, we demonstrate that near-field interactions of metallic nanostructures with a continuous metallic surface create conditions that produce enormously enhanced surface plasmon resonances. The results were used to explain the observed enhancements and determine the optimal conditions for the experiment. The theoretical parts of the studies are supported with reports on detailed emission intensity changes which provided multiple fluorescence hot spots with 2-3 orders of enhancements. We study two kinds of the fluorophores: dye molecules and fluorescent nanospheres characterized with similar spectral emission regions. Using a lifetime-resolved fluorescence/reflection confocal microscopy technique, we find that the largest rate for enhancement (~1000-fold) comes from lo...
The surface-confined assay format is one of the most convenient detection formats used in many im... more The surface-confined assay format is one of the most convenient detection formats used in many immunoassays. Fluorescence emission from monolayers of dyes requires a strong excitation and good detection system. Such samples are susceptible to artifacts due to background fluorescence from substrates. We demonstrate that using silver nanostructures deposited on the slide substrate can significantly enhance measured fluorescence, reduce unwanted background and increase photostability of the used probes. Using thin layers of polymer doped with fluorescein, we tested two nanostructures--silver island films (SIFs) deposited on glass slides and self-assembled colloidal structures (SACS) deposited on thin silver film. The SACS surfaces show extraordinary fluorescence enhancements: over 100-folds in hot spots. We applied these surfaces for enhanced Alexa488 model immunoassay.
In this report we describe a preparation of silver wires (SWs) on gold mirrors and its applicatio... more In this report we describe a preparation of silver wires (SWs) on gold mirrors and its application to surface enhanced fluorescence (SEF) using a new methodology. Silica protected gold mirrors were drop-coated with a solution of silver triangular nanoprisms. The triangular nanoprisms were slowly air-dried to get silver wires that self-assembled on the gold mirrors. Fluorescence enhancement was studied using methyl azadioxatriangulenium chloride (Me-ADOTA · Cl) dye in PVA spin-coated on a clean glass coverslip. New Plasmonic Platforms (PPs) were assembled by placing a mirror with SWs in contact with a glass coverslip spin-coated with a uniform Me-ADOTA · Cl film. It was shown that surface enhanced fluorescence is a real phenomenon, not just an enhancement of the fluorescence signal due to an accumulation of the fluorophore on rough nanostructure surfaces. The average fluorescence enhancement was found to be about 15-fold. The lifetime of Me-ADOTA · Cl dye was significantly reduced (∼...
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