We examined the effects of metallic silver colloids on the fluorescence spectral properties of in... more We examined the effects of metallic silver colloids on the fluorescence spectral properties of indocyanine green (ICG), which is a dye widely used for in vivo medical testing. Silver colloids from a suspension bind spontaneously to amine-coated surfaces. These colloid-coated surfaces were found to cause a 30-fold increase in the intensity of ICG, which was held close to the metal surface by adsorbed albumin. The increased intensities of ICG were also associated with decreased lifetimes and increased photostability, which are indicative of modifying the fluorophores radiative decay rate. These results suggest the use of metal colloid-enhanced ICG for applications to retinal angiography and vascular imaging and as a contrast agent for optical tomography.
, except for brief excerpts in connection with reviews or scholarly analysis. Use in connection w... more , except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights.
Polymerized stealth liposomes were developed for improving the anti-inflammatory efficacy of dexa... more Polymerized stealth liposomes were developed for improving the anti-inflammatory efficacy of dexamethasone in the treatment of rheumatoid arthritis.
The formation of multi-layer nylon-6 (PA-6) nanofibrous membranes by electrostatic spinning coupl... more The formation of multi-layer nylon-6 (PA-6) nanofibrous membranes by electrostatic spinning coupled with a hot pressing process, and they can be used for efficient and continuous indigo dye filtration.
Journal of Materials Science and Chemical Engineering, 2017
J-aggregates of dye molecules are a unique supramolecular structure, which shows great promise in... more J-aggregates of dye molecules are a unique supramolecular structure, which shows great promise in photoelectric devices due to its remarkable optical and transport properties. In this paper, we report the templated formation of J-aggregate nanotubes by the adsorption of 3,3'-diethylthiacarbocyanine iodide on the self-assembled nanotubes of lithocholic acid. The optical and electronic properties of the templated J-aggregate nanotubes are studied. A sensor platform is fabricated by depositing the J-aggregate nanotubes on interdigitated gold electrodes for the detection of dopamine (DA). We find that the current change of the J-aggregate nanotube-based sensor platform in response to DA is linear in the concentration range from 10 nM to 70 nM, giving the detection limit of 0.27 nM.
Journal of Materials Science and Chemical Engineering, 2015
A hydrogel is formed by the self-assembly of sodium deoxycholate (NaDC) in aqueous solution with ... more A hydrogel is formed by the self-assembly of sodium deoxycholate (NaDC) in aqueous solution with sodium chloride at pH-7.0. The NaDC hydrogel made of the three-dimensional network of nanofibers shows pH-dependent swelling behaviors. Polystyrene particles with a diameter of 100 nm and doxorubicin hydrochloride (DOX) can be easily loaded into the NaDC hydrogel through swelling. By using the loaded polystyrene particles as a light scattering probe, we study the microrheology of the NaDC hydrogel, showing complex viscoelastic properties. The viscous component dominates at both low and high frequencies, while the elastic component dominates in the intermediate range. The cavity size of the nanofiber network can also be estimated to be ~180 nm. We show that the loaded DOX can be slowly released from the hydrogels into aqueous solution. The release profile of DOX is found to depend on the pH value of the solution.
Chemical communications (Cambridge, England), Jan 20, 2015
β-CD-C14TAB complex-coated 5CB droplets are designed by the adsorption of β-CD-C14TAB complexes a... more β-CD-C14TAB complex-coated 5CB droplets are designed by the adsorption of β-CD-C14TAB complexes at the 5CB/aqueous interface. We show that the 5CB droplets can be used as an optical probe for the selective detection of cholic acid in aqueous solution containing uric acid and urea via competitive host-guest recognition.
Metallic surfaces can have unusual effects on fluoro- phores such as increasing or decreasing the... more Metallic surfaces can have unusual effects on fluoro- phores such as increasing or decreasing the rates of radiative decay and the rates of resonance energy trans- fer (RET). In the present article we describe the effects of metallic silver island films on the emission spectra, lifetimes, and energy transfer for several fluorophores. The fluorophores are not covalently coupled to the
We examined the photostability of a double-stranded DNA oligomer, covalently labeled with Cy3 or ... more We examined the photostability of a double-stranded DNA oligomer, covalently labeled with Cy3 or Cy5 on one strand, in the presence of metallic silver island films. In our experimental configuration a minor fraction of the labeled DNA was close to the silver particles and the remainder was distant from the particles. Proximity of the fluorophores to silver island films resulted
Self-assembled lipid tubules with crystalline bilayer walls are promising candidates for controll... more Self-assembled lipid tubules with crystalline bilayer walls are promising candidates for controlled drug delivery vehicles on the basis of their ability to release preloaded biological molecules in a sustained manner. While a previous study has shown that the release rate of protein molecules from lipid tubules depends on the associated molecular mass, suggesting that the pertinent diffusion follows the well-known Stokes-Einstein relationship, only a few attempts have been made toward investigating the details of molecular diffusion in the tubule interior. Herein, we have characterized the diffusion rates of several molecules encapsulated in lipid tubules formed by 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DC 8,9 PC) using the techniques of fluorescence recovery after photobleaching (FRAP) and fluorescence correlation spectroscopy (FCS). Our results show that the mobility of these molecules depends not only on their positions in the DC 8,9 PC tubules but also on their respective concentrations. While the former indicates that the interior of the DC 8,9 PC tubules is heterogeneous in terms of diffusion, the latter further highlights the possibility of engineering specific conditions for achieving sustained release of a "drug molecule" over a targeted period of time. In addition, our FCS results indicate that the molecular diffusions inside the crystalline bilayer walls of the DC 8,9 PC tubules strongly deviate from the normal, stochastic processes, with features characterizing not only anomalous subdiffusions but also motions that are superdiffusive in nature.
We examined the effects of metallic silver colloids on the fluorescence spectral properties of in... more We examined the effects of metallic silver colloids on the fluorescence spectral properties of indocyanine green (ICG), which is a dye widely used for in vivo medical testing. Silver colloids from a suspension bind spontaneously to amine-coated surfaces. These colloid-coated surfaces were found to cause a 30-fold increase in the intensity of ICG, which was held close to the metal surface by adsorbed albumin. The increased intensities of ICG were also associated with decreased lifetimes and increased photostability, which are indicative of modifying the fluorophores radiative decay rate. These results suggest the use of metal colloid-enhanced ICG for applications to retinal angiography and vascular imaging and as a contrast agent for optical tomography.
The interaction between bile acids and surfactants at interfaces plays an important role in fat d... more The interaction between bile acids and surfactants at interfaces plays an important role in fat digestion. In this paper, we study the competitive adsorption of cholic acid (CA) at the sodium dodecyl sulfate (SDS)laden liquid crystal (LC)/aqueous interface formed with cyanobiphenyl (nCB, n ¼ 5-8) and the mixture of 5CB with 4-(4-pentylcyclohexyl)benzonitrile (5PCH). We find that the critical concentration of CA required to displace SDS from the interface linearly decreases from 160 mM to 16 mM by reducing the alkyl chain length of nCB from n ¼ 8 to n ¼ 5 and from 16 mM to 1.5 mM by increasing the 5PCH concentration from 0 wt% to 19 wt% in the 5PCH-5CB binary mixture. Our results clearly demonstrate that the sensitivity of 5PCH-5CB mixtures for monitoring the interaction between CA and SDS at the LC/ aqueous interface can be increased by one order of magnitude, compared to 5CB.
The mechanical behavior of self-assembled lipid tubules is an important property which determines... more The mechanical behavior of self-assembled lipid tubules is an important property which determines their suitability for technological applications. We study the instability of multibilayer lipid tubules ͑with wall thickness t and external radius R ext ͒ beyond elastic response under local radial atomic force microscopy indentations. A discontinuity in force-distance curves associated with the buckling instability of lipid tubules is observed. The critical force at which lipid tubules undergo a buckling transition linearly scales as t / R ext. In addition, a reduced critical buckling force is found to extend a distance of ϳ1 m from the end of lipid tubules.
Evidence of photodimerization-induced positional order in self-assembled monolayers (SAMs) is rep... more Evidence of photodimerization-induced positional order in self-assembled monolayers (SAMs) is reported. Scanning force microscopy studies of SAMs of an alkylsilane with an olefinic group on a silicon surface show that the terminal alkyl chains are initially disordered but become highly ordered upon irradiation with UV light. Development of the crystalline order in the SAMs is accompanied by changes in frictional properties.
We describe two reagentless methods of silver deposition for metal-enhanced fluorescence. Silver ... more We describe two reagentless methods of silver deposition for metal-enhanced fluorescence. Silver was deposited on glass positioned between two silver electrodes with a constant current in pure water. Illumination of the glass between the electrodes resulted in localized silver deposition. Alternatively, silver was deposited on an Indium Tin Oxide cathode, with a silver electrode as the anode. Both types of deposited silver produced a 5-18-fold increase in the fluorescence intensity of a nearby fluorophore, indocyanine green (ICG). Additionally, the photostability of ICG was dramatically increased by proximity to the deposited silver. These results suggest the use of silver deposited from pure water for surface-enhanced fluorescence, with potential applications in surface assays and lab-on-a-chip-based technologies, which ideally require highly fluorescent photostable systems.
The concentration level of cholic acid is a biomarker for the early diagnosis of liver and intest... more The concentration level of cholic acid is a biomarker for the early diagnosis of liver and intestinal diseases. We present a biosensor platform based on the anchoring transition of 4-cyano-4 0-pentylbiphenyl (5CB) liquid crystals at surfactant-laden 5CB/aqueous interfaces for the detection of cholic acid (CA) in aqueous solution. In the biosensor platform, the competitive adsorption of CA at the surfactant-laden 5CB/aqueous interfaces can trigger a homeotropic-to-planar anchoring transition of the 5CB at the interface, which can be easily observed using a polarizing optical microscope. We find that the detection limit of the 5CB based biosensors for CA depends on the pH and ionic strength of the aqueous phase and the headgroup of the surfactants.
, except for brief excerpts in connection with reviews or scholarly analysis. Use in connection w... more , except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights.
We examined the effects of metallic silver particles on resonance energy transfer (RET) between f... more We examined the effects of metallic silver particles on resonance energy transfer (RET) between fluorophores covalently bound to DNA. A coumarin donor and a Cy3 acceptor were positioned at opposite ends of a 23-bp double helical DNA oligomer. In the absence of silver particles the extent of RET is near 9%, consistent with a Forster distance R 0 near 50 Å and a donor to acceptor distance near 75 Å. The transfer efficiency increased when the solution of AMCA-DNA-Cy3 was placed between two quartz plates coated with silver island films to near 64%, as determined by both steadystate and time-resolved measurements. The apparent R 0 in the presence of silver island films increases to about 110 Å. These values of the transfer efficiency and R 0 represent weighted averages for donoracceptor pairs near and distant from the metallic surfaces, so that the values at an optimal distance are likely to be larger. The increased energy transfer is observed only between two sandwiched silvered slides. When we replaced one silvered slide with a quartz plate the effect vanished. Also, the increased energy transfer was not observed for silvered slides separated more than a few micrometers. These results suggest the use of metal-enhanced RET in PCR, hybridization, and other DNA assays, and the possibility of controlling energy transfer by the distance between silver surfaces. Fluorescence resonance energy transfer (RET) 3 is widely used in biochemistry [1-4] and in DNA biotechnology [5-7]. RET is a widely useful phenomenon because the Forster distance (R 0) can be readily calculated from the spectral properties of the donor (D) and acceptor (A), and the extent of RET is insensitive to the sample conditions if the sample remains transparent. A disadvantage of RET is the limited distances over which RET occurs. The largest known Forster distances are near 55 Å for organic fluorophores and near 90 Å for lanthanide donors [8-10]. In the case of DNA a Forster distance of 50 Å corresponds to approximately 16 bp, so that RET only occurs when the donor and acceptor are closely spaced within the DNA helix. DNA assays based on RET over larger distances have not been developed because longer range RET does not occur. In the present report we describe a new approach which promises to increase the Forster distances by several-fold. At present almost all fluorescent measurements are performed for fluorophores in the free-space conditions, meaning the surrounding medium is mostly homogeneous and transparent to the absorption and emission wavelengths. Under these conditions the observed far-field emission is well described by Maxwell's equations for an
The deficiency of dopamine (DA) is clinically linked to several neurological diseases. The detect... more The deficiency of dopamine (DA) is clinically linked to several neurological diseases. The detection of urinary DA provides a noninvasive method for diagnosing these diseases and monitoring therapies. In this paper, we report the coassembly of lithocholic acid (LCA) and 3,3′-diethythiadicarbocyanine iodide (DiSC 2 (5)) at the equimolar ratio in ammonia solution into J-aggregate nanotubes. By integrating the J-aggregate nanotubes into transparent agarose hydrogel films formed on the wall of quartz cuvettes, we fabricate a portable and reproducible sensor platform for the optical detection of DA in synthetic urine. The J-band intensity of the integrated J-aggregate nanotubes is found to linearly decrease with the increase of DA concentrations from 10 to 80 nM, giving the limit of detection of ∼7 nM. The detection mechanism is based on the photoinduced electron transfer (PET) from the excited J-aggregate nanotubes to adsorbed DA-quinone. The PET process used in the sensor platform can reduce the interference of ascorbic acid and uric acid in the detection of DA in synthetic urine. The high sensitivity of the sensor platform is contributed by the delocalized exciton of J-aggregate nanotubes.
We examined the fluorescence spectral properties of DNA oligomers, labeled with Cy3 or Cy5, when ... more We examined the fluorescence spectral properties of DNA oligomers, labeled with Cy3 or Cy5, when bound to quartz surfaces coated with metallic silver particles. Prior to binding of labeled DNA the surfaces were treated with polylysine or 3-aminopropyl triethoxysilane or were coated with avidin for binding of biotinylated oligomers. The fluorescence intensities were increased an average of 8fold on these surfaces. Despite the increased emission intensity, the photostability of the labeled DNA was the same or higher on the silver-coated surfaces than on the uncoated slides. The timeintegrated intensities, that is the area under the intensity plots with continuous illumination, increased an average of 6-fold. In all cases the lifetimes were dramatically shortened on the silver particles, indicating an over 100-fold increase in the radiative decay rates. These results suggest the use of substrates containing silver particles for increased sensitivity of DNA detection on DNA arrays. The introduction of DNA or "gene chips" has allowed comprehensive studies of gene expression [1-3]. These arrays contain a large number of DNA sequences at known locations and frequently known sequence. These sequences are hybridized with cDNA from a cell or organism, allowing determination of the expressed mRNA sequences. The most common approach is to use cDNA which is labeled with fluorescent probes. The cyanine dyes Cy3 and Cy5 are commonly used for this purpose [4,5]. While fluorescence provides sensitive detection, the need for increased sensitivity exists. This need is particularly urgent for small-copy-number or single-copy detection of biohazards. In these cases the detection limits are determined by the spectral properties of the fluorophores and the amount of background signal from the sample and instrumentation. The signal from a fluorophore is typically limited by photobleaching or photodecomposition. For example, the most stable fluorophores can undergo about 10 6 excitation-relaxation cycles before loss of signal [6-8]. Because of the difficulties of collecting the isotropic emission, a single fluorophore may yield 10 3 or 10 4 observable photons. Another limitation to small-copynumber detection is the finite rate at which a fluorophore can emit photons. The maximal emission rate is near 1/τ, where τ is the decay time. A fluorophore with a 1 ns lifetime can emit at most 10 9 photons per second. Finally, background signal from the sample or optical components can result in an inability to detect weak signals. In recent publications we examined the effects of metallic silver particles on fluorophores [9, 10] and showed that proximity of fluorophores to a conducting metallic surface can result in
We examined the effects of metallic silver colloids on the fluorescence spectral properties of in... more We examined the effects of metallic silver colloids on the fluorescence spectral properties of indocyanine green (ICG), which is a dye widely used for in vivo medical testing. Silver colloids from a suspension bind spontaneously to amine-coated surfaces. These colloid-coated surfaces were found to cause a 30-fold increase in the intensity of ICG, which was held close to the metal surface by adsorbed albumin. The increased intensities of ICG were also associated with decreased lifetimes and increased photostability, which are indicative of modifying the fluorophores radiative decay rate. These results suggest the use of metal colloid-enhanced ICG for applications to retinal angiography and vascular imaging and as a contrast agent for optical tomography.
, except for brief excerpts in connection with reviews or scholarly analysis. Use in connection w... more , except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights.
Polymerized stealth liposomes were developed for improving the anti-inflammatory efficacy of dexa... more Polymerized stealth liposomes were developed for improving the anti-inflammatory efficacy of dexamethasone in the treatment of rheumatoid arthritis.
The formation of multi-layer nylon-6 (PA-6) nanofibrous membranes by electrostatic spinning coupl... more The formation of multi-layer nylon-6 (PA-6) nanofibrous membranes by electrostatic spinning coupled with a hot pressing process, and they can be used for efficient and continuous indigo dye filtration.
Journal of Materials Science and Chemical Engineering, 2017
J-aggregates of dye molecules are a unique supramolecular structure, which shows great promise in... more J-aggregates of dye molecules are a unique supramolecular structure, which shows great promise in photoelectric devices due to its remarkable optical and transport properties. In this paper, we report the templated formation of J-aggregate nanotubes by the adsorption of 3,3'-diethylthiacarbocyanine iodide on the self-assembled nanotubes of lithocholic acid. The optical and electronic properties of the templated J-aggregate nanotubes are studied. A sensor platform is fabricated by depositing the J-aggregate nanotubes on interdigitated gold electrodes for the detection of dopamine (DA). We find that the current change of the J-aggregate nanotube-based sensor platform in response to DA is linear in the concentration range from 10 nM to 70 nM, giving the detection limit of 0.27 nM.
Journal of Materials Science and Chemical Engineering, 2015
A hydrogel is formed by the self-assembly of sodium deoxycholate (NaDC) in aqueous solution with ... more A hydrogel is formed by the self-assembly of sodium deoxycholate (NaDC) in aqueous solution with sodium chloride at pH-7.0. The NaDC hydrogel made of the three-dimensional network of nanofibers shows pH-dependent swelling behaviors. Polystyrene particles with a diameter of 100 nm and doxorubicin hydrochloride (DOX) can be easily loaded into the NaDC hydrogel through swelling. By using the loaded polystyrene particles as a light scattering probe, we study the microrheology of the NaDC hydrogel, showing complex viscoelastic properties. The viscous component dominates at both low and high frequencies, while the elastic component dominates in the intermediate range. The cavity size of the nanofiber network can also be estimated to be ~180 nm. We show that the loaded DOX can be slowly released from the hydrogels into aqueous solution. The release profile of DOX is found to depend on the pH value of the solution.
Chemical communications (Cambridge, England), Jan 20, 2015
β-CD-C14TAB complex-coated 5CB droplets are designed by the adsorption of β-CD-C14TAB complexes a... more β-CD-C14TAB complex-coated 5CB droplets are designed by the adsorption of β-CD-C14TAB complexes at the 5CB/aqueous interface. We show that the 5CB droplets can be used as an optical probe for the selective detection of cholic acid in aqueous solution containing uric acid and urea via competitive host-guest recognition.
Metallic surfaces can have unusual effects on fluoro- phores such as increasing or decreasing the... more Metallic surfaces can have unusual effects on fluoro- phores such as increasing or decreasing the rates of radiative decay and the rates of resonance energy trans- fer (RET). In the present article we describe the effects of metallic silver island films on the emission spectra, lifetimes, and energy transfer for several fluorophores. The fluorophores are not covalently coupled to the
We examined the photostability of a double-stranded DNA oligomer, covalently labeled with Cy3 or ... more We examined the photostability of a double-stranded DNA oligomer, covalently labeled with Cy3 or Cy5 on one strand, in the presence of metallic silver island films. In our experimental configuration a minor fraction of the labeled DNA was close to the silver particles and the remainder was distant from the particles. Proximity of the fluorophores to silver island films resulted
Self-assembled lipid tubules with crystalline bilayer walls are promising candidates for controll... more Self-assembled lipid tubules with crystalline bilayer walls are promising candidates for controlled drug delivery vehicles on the basis of their ability to release preloaded biological molecules in a sustained manner. While a previous study has shown that the release rate of protein molecules from lipid tubules depends on the associated molecular mass, suggesting that the pertinent diffusion follows the well-known Stokes-Einstein relationship, only a few attempts have been made toward investigating the details of molecular diffusion in the tubule interior. Herein, we have characterized the diffusion rates of several molecules encapsulated in lipid tubules formed by 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DC 8,9 PC) using the techniques of fluorescence recovery after photobleaching (FRAP) and fluorescence correlation spectroscopy (FCS). Our results show that the mobility of these molecules depends not only on their positions in the DC 8,9 PC tubules but also on their respective concentrations. While the former indicates that the interior of the DC 8,9 PC tubules is heterogeneous in terms of diffusion, the latter further highlights the possibility of engineering specific conditions for achieving sustained release of a "drug molecule" over a targeted period of time. In addition, our FCS results indicate that the molecular diffusions inside the crystalline bilayer walls of the DC 8,9 PC tubules strongly deviate from the normal, stochastic processes, with features characterizing not only anomalous subdiffusions but also motions that are superdiffusive in nature.
We examined the effects of metallic silver colloids on the fluorescence spectral properties of in... more We examined the effects of metallic silver colloids on the fluorescence spectral properties of indocyanine green (ICG), which is a dye widely used for in vivo medical testing. Silver colloids from a suspension bind spontaneously to amine-coated surfaces. These colloid-coated surfaces were found to cause a 30-fold increase in the intensity of ICG, which was held close to the metal surface by adsorbed albumin. The increased intensities of ICG were also associated with decreased lifetimes and increased photostability, which are indicative of modifying the fluorophores radiative decay rate. These results suggest the use of metal colloid-enhanced ICG for applications to retinal angiography and vascular imaging and as a contrast agent for optical tomography.
The interaction between bile acids and surfactants at interfaces plays an important role in fat d... more The interaction between bile acids and surfactants at interfaces plays an important role in fat digestion. In this paper, we study the competitive adsorption of cholic acid (CA) at the sodium dodecyl sulfate (SDS)laden liquid crystal (LC)/aqueous interface formed with cyanobiphenyl (nCB, n ¼ 5-8) and the mixture of 5CB with 4-(4-pentylcyclohexyl)benzonitrile (5PCH). We find that the critical concentration of CA required to displace SDS from the interface linearly decreases from 160 mM to 16 mM by reducing the alkyl chain length of nCB from n ¼ 8 to n ¼ 5 and from 16 mM to 1.5 mM by increasing the 5PCH concentration from 0 wt% to 19 wt% in the 5PCH-5CB binary mixture. Our results clearly demonstrate that the sensitivity of 5PCH-5CB mixtures for monitoring the interaction between CA and SDS at the LC/ aqueous interface can be increased by one order of magnitude, compared to 5CB.
The mechanical behavior of self-assembled lipid tubules is an important property which determines... more The mechanical behavior of self-assembled lipid tubules is an important property which determines their suitability for technological applications. We study the instability of multibilayer lipid tubules ͑with wall thickness t and external radius R ext ͒ beyond elastic response under local radial atomic force microscopy indentations. A discontinuity in force-distance curves associated with the buckling instability of lipid tubules is observed. The critical force at which lipid tubules undergo a buckling transition linearly scales as t / R ext. In addition, a reduced critical buckling force is found to extend a distance of ϳ1 m from the end of lipid tubules.
Evidence of photodimerization-induced positional order in self-assembled monolayers (SAMs) is rep... more Evidence of photodimerization-induced positional order in self-assembled monolayers (SAMs) is reported. Scanning force microscopy studies of SAMs of an alkylsilane with an olefinic group on a silicon surface show that the terminal alkyl chains are initially disordered but become highly ordered upon irradiation with UV light. Development of the crystalline order in the SAMs is accompanied by changes in frictional properties.
We describe two reagentless methods of silver deposition for metal-enhanced fluorescence. Silver ... more We describe two reagentless methods of silver deposition for metal-enhanced fluorescence. Silver was deposited on glass positioned between two silver electrodes with a constant current in pure water. Illumination of the glass between the electrodes resulted in localized silver deposition. Alternatively, silver was deposited on an Indium Tin Oxide cathode, with a silver electrode as the anode. Both types of deposited silver produced a 5-18-fold increase in the fluorescence intensity of a nearby fluorophore, indocyanine green (ICG). Additionally, the photostability of ICG was dramatically increased by proximity to the deposited silver. These results suggest the use of silver deposited from pure water for surface-enhanced fluorescence, with potential applications in surface assays and lab-on-a-chip-based technologies, which ideally require highly fluorescent photostable systems.
The concentration level of cholic acid is a biomarker for the early diagnosis of liver and intest... more The concentration level of cholic acid is a biomarker for the early diagnosis of liver and intestinal diseases. We present a biosensor platform based on the anchoring transition of 4-cyano-4 0-pentylbiphenyl (5CB) liquid crystals at surfactant-laden 5CB/aqueous interfaces for the detection of cholic acid (CA) in aqueous solution. In the biosensor platform, the competitive adsorption of CA at the surfactant-laden 5CB/aqueous interfaces can trigger a homeotropic-to-planar anchoring transition of the 5CB at the interface, which can be easily observed using a polarizing optical microscope. We find that the detection limit of the 5CB based biosensors for CA depends on the pH and ionic strength of the aqueous phase and the headgroup of the surfactants.
, except for brief excerpts in connection with reviews or scholarly analysis. Use in connection w... more , except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights.
We examined the effects of metallic silver particles on resonance energy transfer (RET) between f... more We examined the effects of metallic silver particles on resonance energy transfer (RET) between fluorophores covalently bound to DNA. A coumarin donor and a Cy3 acceptor were positioned at opposite ends of a 23-bp double helical DNA oligomer. In the absence of silver particles the extent of RET is near 9%, consistent with a Forster distance R 0 near 50 Å and a donor to acceptor distance near 75 Å. The transfer efficiency increased when the solution of AMCA-DNA-Cy3 was placed between two quartz plates coated with silver island films to near 64%, as determined by both steadystate and time-resolved measurements. The apparent R 0 in the presence of silver island films increases to about 110 Å. These values of the transfer efficiency and R 0 represent weighted averages for donoracceptor pairs near and distant from the metallic surfaces, so that the values at an optimal distance are likely to be larger. The increased energy transfer is observed only between two sandwiched silvered slides. When we replaced one silvered slide with a quartz plate the effect vanished. Also, the increased energy transfer was not observed for silvered slides separated more than a few micrometers. These results suggest the use of metal-enhanced RET in PCR, hybridization, and other DNA assays, and the possibility of controlling energy transfer by the distance between silver surfaces. Fluorescence resonance energy transfer (RET) 3 is widely used in biochemistry [1-4] and in DNA biotechnology [5-7]. RET is a widely useful phenomenon because the Forster distance (R 0) can be readily calculated from the spectral properties of the donor (D) and acceptor (A), and the extent of RET is insensitive to the sample conditions if the sample remains transparent. A disadvantage of RET is the limited distances over which RET occurs. The largest known Forster distances are near 55 Å for organic fluorophores and near 90 Å for lanthanide donors [8-10]. In the case of DNA a Forster distance of 50 Å corresponds to approximately 16 bp, so that RET only occurs when the donor and acceptor are closely spaced within the DNA helix. DNA assays based on RET over larger distances have not been developed because longer range RET does not occur. In the present report we describe a new approach which promises to increase the Forster distances by several-fold. At present almost all fluorescent measurements are performed for fluorophores in the free-space conditions, meaning the surrounding medium is mostly homogeneous and transparent to the absorption and emission wavelengths. Under these conditions the observed far-field emission is well described by Maxwell's equations for an
The deficiency of dopamine (DA) is clinically linked to several neurological diseases. The detect... more The deficiency of dopamine (DA) is clinically linked to several neurological diseases. The detection of urinary DA provides a noninvasive method for diagnosing these diseases and monitoring therapies. In this paper, we report the coassembly of lithocholic acid (LCA) and 3,3′-diethythiadicarbocyanine iodide (DiSC 2 (5)) at the equimolar ratio in ammonia solution into J-aggregate nanotubes. By integrating the J-aggregate nanotubes into transparent agarose hydrogel films formed on the wall of quartz cuvettes, we fabricate a portable and reproducible sensor platform for the optical detection of DA in synthetic urine. The J-band intensity of the integrated J-aggregate nanotubes is found to linearly decrease with the increase of DA concentrations from 10 to 80 nM, giving the limit of detection of ∼7 nM. The detection mechanism is based on the photoinduced electron transfer (PET) from the excited J-aggregate nanotubes to adsorbed DA-quinone. The PET process used in the sensor platform can reduce the interference of ascorbic acid and uric acid in the detection of DA in synthetic urine. The high sensitivity of the sensor platform is contributed by the delocalized exciton of J-aggregate nanotubes.
We examined the fluorescence spectral properties of DNA oligomers, labeled with Cy3 or Cy5, when ... more We examined the fluorescence spectral properties of DNA oligomers, labeled with Cy3 or Cy5, when bound to quartz surfaces coated with metallic silver particles. Prior to binding of labeled DNA the surfaces were treated with polylysine or 3-aminopropyl triethoxysilane or were coated with avidin for binding of biotinylated oligomers. The fluorescence intensities were increased an average of 8fold on these surfaces. Despite the increased emission intensity, the photostability of the labeled DNA was the same or higher on the silver-coated surfaces than on the uncoated slides. The timeintegrated intensities, that is the area under the intensity plots with continuous illumination, increased an average of 6-fold. In all cases the lifetimes were dramatically shortened on the silver particles, indicating an over 100-fold increase in the radiative decay rates. These results suggest the use of substrates containing silver particles for increased sensitivity of DNA detection on DNA arrays. The introduction of DNA or "gene chips" has allowed comprehensive studies of gene expression [1-3]. These arrays contain a large number of DNA sequences at known locations and frequently known sequence. These sequences are hybridized with cDNA from a cell or organism, allowing determination of the expressed mRNA sequences. The most common approach is to use cDNA which is labeled with fluorescent probes. The cyanine dyes Cy3 and Cy5 are commonly used for this purpose [4,5]. While fluorescence provides sensitive detection, the need for increased sensitivity exists. This need is particularly urgent for small-copy-number or single-copy detection of biohazards. In these cases the detection limits are determined by the spectral properties of the fluorophores and the amount of background signal from the sample and instrumentation. The signal from a fluorophore is typically limited by photobleaching or photodecomposition. For example, the most stable fluorophores can undergo about 10 6 excitation-relaxation cycles before loss of signal [6-8]. Because of the difficulties of collecting the isotropic emission, a single fluorophore may yield 10 3 or 10 4 observable photons. Another limitation to small-copynumber detection is the finite rate at which a fluorophore can emit photons. The maximal emission rate is near 1/τ, where τ is the decay time. A fluorophore with a 1 ns lifetime can emit at most 10 9 photons per second. Finally, background signal from the sample or optical components can result in an inability to detect weak signals. In recent publications we examined the effects of metallic silver particles on fluorophores [9, 10] and showed that proximity of fluorophores to a conducting metallic surface can result in
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