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  1. Article: Plasmon- and Waveguide-Coupled Fluorescence at the Ultraviolet Region.

    Badugu, Ramachandram / Lakowicz, Joseph R

    The journal of physical chemistry. C, Nanomaterials and interfaces

    2023  Volume 127, Issue 25, Page(s) 12084–12095

    Abstract: Surface plasmon-coupled emission (SPCE) has been well studied for its coupled, directional, and enhanced P-polarized radiation due to the interactions of fluorophores with surface plasmon polaritons (SPPs) on thin metal films. Such surface plasmon ... ...

    Abstract Surface plasmon-coupled emission (SPCE) has been well studied for its coupled, directional, and enhanced P-polarized radiation due to the interactions of fluorophores with surface plasmon polaritons (SPPs) on thin metal films. Such surface plasmon polariton-assisted directional fluorescence has various applications in biosensing. Herein, we demonstrate 2-aminopurine (2AP, a UV-absorbing and -emitting fluorophore) emission coupling to modes in aluminum-based plasmon-coupled waveguides (Al-PCWs). Directional emission from 2-aminopurine on plasmon-coupled waveguides was observed at specific angles as P-polarized SPCE and/or as P- or S-polarized waveguide-coupled emission (WGCE). All S-polarized waveguide modes showed clear angularly resolved emission as compared to that of P-polarized surface plasmon-coupled emission or P-polarized waveguide-coupled emission. The coupling angles, efficiencies, and polarizations of the modes were sensitive to the optical properties and overall dimensions of the top dielectric layer in PCWs. The effective plasmon-coupled waveguide can consist of either a thin probe-containing layer on top of the undoped silica film, or a single dielectric PVA layer with probes distributed throughout the film on the Al layer. The former structures with probes confined to the top of the undoped silica layer showed much higher angular resolutions and coupling efficiencies, as well as mode-dependent changes in lifetimes. These results demonstrate that the plasmon and waveguide modes can be used for selective detection of surface-bound and bulk fluorophores, simultaneously.
    Language English
    Publishing date 2023-06-20
    Publishing country United States
    Document type Journal Article
    ISSN 1932-7447
    ISSN 1932-7447
    DOI 10.1021/acs.jpcc.3c01231
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article: Fluorescence Resonance Energy Transfer in Calf Thymus DNA from a Long-Lifetime Metal-Ligand Complex to Nile Blue.

    Kang, Jung Sook / Lakowicz, Joseph R

    Journal of biochemistry and molecular biology

    2021  Volume 34, Issue 6, Page(s) 551–558

    Abstract: We extended the measurable time scale of DNA dynamics to submicrosecond using a long-lifetime metal-ligand complex, [Ru(phen) ...

    Abstract We extended the measurable time scale of DNA dynamics to submicrosecond using a long-lifetime metal-ligand complex, [Ru(phen)
    Language English
    Publishing date 2021-09-15
    Publishing country Korea (South)
    Document type Journal Article
    ZDB-ID 1238454-9
    ISSN 0219-1024 ; 1225-8687
    ISSN (online) 0219-1024
    ISSN 1225-8687
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    In stock of ZB MED Cologne/Königswinter

    Zs.A 4202: Show issues Location:
    Je nach Verfügbarkeit (siehe Angabe bei Bestand)
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    Jg. 1995 - 2021: Lesesall (2.OG)
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  3. Article: Frequency-domain lifetime measurements and sensing in highly scattering media.

    Szmackinski, Henryk / Lakowicz, Joseph R

    Sensors and actuators. B, Chemical

    2021  Volume 30, Issue 3, Page(s) 207–215

    Abstract: For clinical chemistry, or for non-invasive sensing through skin, it is often necessary to obtain quantitative information in highly scattering media. We describe two simple methods for fluorescence lifetime measurements in highly scattering media, and ... ...

    Abstract For clinical chemistry, or for non-invasive sensing through skin, it is often necessary to obtain quantitative information in highly scattering media. We describe two simple methods for fluorescence lifetime measurements in highly scattering media, and in particular in an intralipid suspension. Lifetimes can be measured using an intensity decay law that accounts for the time delays and pulse-broadening effects of multiple light-scattering events in the intralipid. Alternatively, the phase and modulation measurements can be performed relative.to a reference fluorophore with a known lifetime. These approaches provide reliable lifetime data for a pH-sensitive fluorophore contained within a microeuvette 4 mm under the surface of the intralipid suspension. Fluorescence lifetime-based sensing is now recognized as a valuable methodology in clinical and analytical chemistry, and the possibility of lifetime-based sensing in turbid media has been demonstrated.
    Language English
    Publishing date 2021-06-08
    Publishing country Switzerland
    Document type Journal Article
    ZDB-ID 1021505-0
    ISSN 0925-4005
    ISSN 0925-4005
    DOI 10.1016/0925-4005(96)80051-7
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  4. Article: Fluorophore Interactions with the Surface Modes and Internal Modes of a Photonic Crystal.

    Badugu, Ramachandram / Blair, Steve / Descrovi, Emiliano / Lakowicz, Joseph R

    Optical Materials

    2023  Volume 147

    Abstract: The metal-ligand complex tris(2,2'-bipyridine)ruthenium(II) chloride (Ru probe) displays a broad emission spectrum ranging from 540 to 730 nm. The emission spectra of Ru probe were measured when placed on top of a one-dimensional photonic crystal (1DPC), ...

    Abstract The metal-ligand complex tris(2,2'-bipyridine)ruthenium(II) chloride (Ru probe) displays a broad emission spectrum ranging from 540 to 730 nm. The emission spectra of Ru probe were measured when placed on top of a one-dimensional photonic crystal (1DPC), which supports both Bloch surface wave (BSW) and internal modes for wavelengths below 640 nm and only internal modes above 640 nm. The S-polarized emission spectra, with the electric vector parallel to the 1DPC surface, were found to be strongly dependent on the observation angle through the coupling prism. Also, the usual single broad-emission spectrum of Ru probe on glass was converted into two or more narrow-band-spectrum on the 1DPC, with emission band maxima dependent on the observation angle. The two S-polarized emission band peaks for Ru probe were found to be consistent with coupling to the BSW and first internal mode (IM1) of the 1DPC. The same spectral shifts and changes in emission maxima were observed by using Kretschmann and reverse Kretschmann illuminations. As the coupling requires the emitter to be in proximity with the photonic structure, we calculated near- and far-field distributions of a dipole directly located on the 1DPC surface. Finite-Difference Time-Domain (FDTD) simulations were performed to confirm fluorophore coupling to the BSW and internal modes (IMs). Both the measured and simulated results showed that IM coupled emission is significant. Coupling to the IM mode occurred at longer wavelengths where the 1DPC did not support a BSW. These results demonstrate that a simple Bragg grating, without a BSW mode, can be used for detection of surface-bound fluorophores.
    Language English
    Publishing date 2023-12-15
    Publishing country Netherlands
    Document type Journal Article
    ZDB-ID 2015659-5
    ISSN 1873-1252 ; 0925-3467
    ISSN (online) 1873-1252
    ISSN 0925-3467
    DOI 10.1016/j.optmat.2023.114718
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  5. Article: Remote Measurements of Tear Electrolyte Concentrations on Both Sides of an Inserted Contact Lens.

    Lakowicz, Joseph R / Badugu, Ramachandram / Sivashanmugan, Kundan / Reece, Albert

    Chemosensors (Basel, Switzerland)

    2023  Volume 11, Issue 8

    Abstract: In this paper, a method is described to perform ion concentration measurements on both sides of an inserted contact lens, without physical contact with the eye or the contact lens. The outer surface of an eye is covered with a tear film that has multiple ...

    Abstract In this paper, a method is described to perform ion concentration measurements on both sides of an inserted contact lens, without physical contact with the eye or the contact lens. The outer surface of an eye is covered with a tear film that has multiple layers. The central aqueous layer contains electrolytes and proteins. When a contact lens is inserted, it becomes localized in the central layer, which creates two layers known as the pre-lens tear film (PLTF) and the post-lens tear film (PoLTF). The PoLTF is in direct contact with the sensitive corneal epithelial cells which control electrolyte concentrations in tears. It is difficult to measure the overall electrolyte concentration in tears because of the small 7 μL volume of bulk tears. No methods are known, and no method has been proposed, to selectively measure the concentrations of electrolytes in the smaller volumes of the PLTF and the PoLTF. In this paper, we demonstrate the ability to localize fluorophores on each side of a contact lens without probe mixing or diffusion across the lens. We measured the concentration of sodium in the region of the PoLTF using a sodium-sensitive fluorophore positioned on the inner surface of a contact lens. The fluorescence measurements do not require physical contact and are mostly independent of eye motion and fluorophore concentration. The method is generic and can be combined with ion-sensitive fluorophores for the other electrolytes in tears. Instrumentation for non-contact measurements is likely to be inexpensive with modern opto-electronic devices. We expect these lenses to be used for measurements of other ions in the PLTF and the PoLTF, and thus become useful for both research and in the diagnosis of infections, keratitis and biomarkers for diseases.
    Language English
    Publishing date 2023-08-17
    Publishing country Switzerland
    Document type Journal Article
    ZDB-ID 2704218-2
    ISSN 2227-9040
    ISSN 2227-9040
    DOI 10.3390/chemosensors11080463
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  6. Article ; Online: OPHTHALMIC GLUCOSE MONITORING USING DISPOSABLE CONTACT LENSES.

    Badugu, Ramachandram / Lakowicz, Joseph R / Geddes, Chris D

    Reviews in fluorescence

    2021  Volume 2005, Page(s) 363–397

    Language English
    Publishing date 2021-04-30
    Publishing country United States
    Document type Journal Article
    ISSN 2511-8579
    ISSN (online) 2511-8579
    DOI 10.1007/0-387-23690-2_15
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  7. Article ; Online: Measurement of the Intensity of Long-Lifetime Luminophores in the Presence of Background Signals Using Phase-Modulation Fluorometry.

    Szmacinski, Henryk / Lakowicz, Joseph R

    Applied spectroscopy

    2020  Volume 53, Issue 12, Page(s) 1490–1495

    Abstract: We describe a method to correct for background fluorescence and to measure the intensity of long-lifetime probes using phase-modulation fluorometry. The theoretically predicted and simulated data were supported by two experiments. The fractional ... ...

    Abstract We describe a method to correct for background fluorescence and to measure the intensity of long-lifetime probes using phase-modulation fluorometry. The theoretically predicted and simulated data were supported by two experiments. The fractional contribution of background fluorescence in the sample was determined by measurement of phase angle and/or modulation at single modulation frequency. In certain experimental situations, where the mean decay times of the background and the long lifetime probe are widely separated, determination of background signals in the sample does not require a blank sample or information about the nature of intensity decay of the background. Hence, phase-modulation fluorometry can be used to directly determine the intensity of the long-lifetime probe in the presence of an unknown short-lifetime background. We also discuss the effects of ambient light (indefinitely long lifetime) and scattered excitation light (zero lifetime) on phase-modulation measurements.
    Language English
    Publishing date 2020-04-13
    Publishing country United States
    Document type Journal Article
    ISSN 1943-3530
    ISSN (online) 1943-3530
    DOI 10.1366/0003702991946109
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  8. Article ; Online: Fiber Optic pH Sensor Based on Phase Fluorescence Lifetimes.

    Thompson, Richard B / Lakowicz, Joseph R

    Analytical chemistry

    2019  Volume 65, Issue 7, Page(s) 853–856

    Abstract: A fiber optic pH sensor based on single fiber phase fluorescence lifetime measurements of commercially available fluorescence indicators is described. The apparatus is a straightforward modification of an existing phase fluorometer and exhibits accuracy ... ...

    Abstract A fiber optic pH sensor based on single fiber phase fluorescence lifetime measurements of commercially available fluorescence indicators is described. The apparatus is a straightforward modification of an existing phase fluorometer and exhibits accuracy and precision of approximately 0.02 pH unit. The approach is applicable to other analytes and indicators, as well as evanescent wave sensing schemes.
    Language English
    Publishing date 2019-12-12
    Publishing country United States
    Document type Journal Article
    ZDB-ID 1508-8
    ISSN 1520-6882 ; 0003-2700
    ISSN (online) 1520-6882
    ISSN 0003-2700
    DOI 10.1021/ac00055a005
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    In stock of ZB MED Cologne/Königswinter

    Zs.A 4033: Show issues Location:
    Je nach Verfügbarkeit (siehe Angabe bei Bestand)
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    Jg. 1995 - 2021: Lesesall (2.OG)
    ab Jg. 2022: Lesesaal (EG)

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  9. Article ; Online: Phase-modulation fluorometry using a frequency-doubled pulsed laser diode light source.

    Berndt, Klaus W / Gryczynski, Ignacy / Lakowicz, Joseph R

    Proceedings of SPIE--the International Society for Optical Engineering

    2021  Volume 1204

    Abstract: We used the Hamamatsu model PLP-01 picosecond light pulser as a 413-nm excitation light source for frequency-domain fluorescence measurements. In comparison with sync-pumped/cavity dumped/frequency-doubled dye lasers, the 413-nm PLP-01 shows a longer ... ...

    Abstract We used the Hamamatsu model PLP-01 picosecond light pulser as a 413-nm excitation light source for frequency-domain fluorescence measurements. In comparison with sync-pumped/cavity dumped/frequency-doubled dye lasers, the 413-nm PLP-01 shows a longer FWHM (40 ps), a similar pulse repetition rate (up to 10 MHz), much less output power at a fixed wavelength (0.44 mW peak, 220 nW maximum average power), but is less expensive, small-sized, and easy to handle. Using the PLP-01, we have been able to perform fluorescence measurements up to an upper modulation frequency of about 2000 MHz, and to resolve mixtures of fluorophores exhibiting different lifetimes. During our tests, we observed remarkable and lasting (2 h) time drifts between the optical output and the electrical trigger input or output. At present, work is in progress at Hamamatsu to eliminate these drifts.
    Language English
    Publishing date 2021-05-25
    Publishing country United States
    Document type Journal Article
    ISSN 1996-756X
    ISSN (online) 1996-756X
    DOI 10.1117/12.17758
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  10. Article ; Online: Luminescent Blinking from Noble-Metal Nanostructures: New Probes for Localization and Imaging.

    Geddes, Chris D / Parfenov, Alexandr / Lakowicz, Joseph R

    Journal of fluorescence

    2020  Volume 13, Issue 4, Page(s) 297–299

    Language English
    Publishing date 2020-01-02
    Publishing country Netherlands
    Document type Journal Article
    ZDB-ID 2016892-5
    ISSN 1573-4994 ; 1053-0509
    ISSN (online) 1573-4994
    ISSN 1053-0509
    DOI 10.1023/A:1025369509842
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