Publications by authors named "J R Lakowicz"

631 Publications

Fluorescence Coupling to Internal Modes of 1D Photonic Crystals Characterized by Back Focal Plane Imaging.

J Opt 2021 Mar 18;23(3). Epub 2021 Feb 18.

University of Maryland School of Medicine, Department of Biochemistry and Molecular Biology, Center for Fluorescence Spectroscopy, Baltimore, Maryland 21201.

The coupling of fluorescence with surface electromagnetic modes, such as surface plasmons on thin metal films or Bloch surface waves (BSW) on truncated one-dimensional photonic crystals (1DPC), are presently utilized for many fluorescence-based applications. In addition to the surface wave, 1DPCs also support other electromagnetic modes that are confined within the 1DPC structure. These internal modes (IMs) have not received much attention for fluorescence coupling due to lack of spatial overlap of their electric fields with the surface bound fluorophores. However, our recent studies have indicated that the fluorescence coupling with IMs occurs quite efficiently. This observed internal mode-coupled emission (IMCE) is (similar to BSW-coupled emission) indeed wavelength dependent, directional and S-polarized. In this paper, we have carried out back-focal plane (BFP) imaging to reveal that the IMs of 1DPCs can couple with surface bound excited dye molecules, with or without a BSW mode presence. Depending on the emission wavelength, the coupling is observed with BSW and IMs or only IMs of the 1DPC structure. The experimental results are well matching with numerical simulations. The occurrence of IMCE regardless of the availability of BSWs removes the dependence on just the surface mode for obtaining coupled emission from 1DPCs. The observation of IMCE is expected to widen the scope of 1DPCs for surface-based fluorescence sensing and assays.
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http://dx.doi.org/10.1088/2040-8986/abd986DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8082491PMC
March 2021

Vortex Beam Generation by Spin-Orbit Interaction with Bloch Surface Waves.

ACS Photonics 2020 Mar 10;7(3):774-783. Epub 2020 Feb 10.

Department of Applied Science and Technology (DISAT), Politecnico di Torino, Corso Duca degli Abruzzi 24, Torino, IT-10129, Italy.

Axis-symmetric grooves milled in metallic slabs have been demonstrated to promote the transfer of Orbital Angular Momentum (OAM) from far- to near-field and vice versa, thanks to spin-orbit coupling effects involving Surface Plasmons (SP). However, the high absorption losses and the polarization constraints, which are intrinsic in plasmonic structures, limit their effectiveness for applications in the visible spectrum, particularly if emitters located in close proximity to the metallic surface are concerned. Here, an alternative mechanism for vortex beam generation is presented, wherein a free-space radiation possessing OAM is obtained by diffraction of Bloch Surface Waves (BSWs) on a dielectric multilayer. A circularly polarized laser beam is tightly focused on the multilayer surface by means of an immersion optics, such that TE-polarized BSWs are launched radially from the focused spot. While propagating on the multilayer surface, BSWs exhibit a spiral-like wavefront due to the Spin-Orbit Interaction (SOI). A spiral grating surrounding the illumination area provides for the BSW diffraction out-of-plane and imparts an additional azimuthal geometric phase distribution defined by the topological charge of the spiral structure. At infinity, the constructive interference results into free-space beams with defined combinations of polarization and OAM satisfying the conservation of the Total Angular Momentum, based on the incident polarization handedness and the spiral grating topological charge. As an extension of this concept, chiral diffractive structures for BSWs can be used in combination with surface cavities hosting light sources therein.
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http://dx.doi.org/10.1021/acsphotonics.9b01625DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7901667PMC
March 2020

Sodium-Sensitive Contact Lens for Diagnostics of Ocular Pathologies.

Sens Actuators B Chem 2021 Mar 9;331. Epub 2021 Jan 9.

Center for Fluorescence Spectroscopy, Department of Biochemistry and Molecular Biology University of Maryland School of Medicine, 725 West Lombard St., Baltimore, MD 21201, USA.

The ability to measure all the electrolyte concentrations in tears would be valuable in ophthalmology for research and diagnosis of dry eye disease (DED) and other ocular pathologies. However, tear samples are difficult to collect and analyze because the total volume is small and the chemical composition changes rapidly. Measurements of electrolytes in tears is challenging because typical clinical assays for proteins and other biomarkers cannot be used to detect ion concentrations tears. Here, we report the contact lens which is sensitive to sodium ion (Na), one of the dominant electrolytes in tears. The Na ions in tears is diagnostic for DED. Three sodium-sensitive fluorophores (SG-C16, SG-LPE and SG-PL) were synthesized by derivatizing the sodium green with 1-hexadecyl amine, 1-oleoyl-2-hydroxy-sn-glycero-3-phosphoethanolamine or poly-L-lysine, respectively. These probes were bound to modern silicone hydrogel (SiHG) contact lens, Biofinity from Cooper Vision. Doped lenses were tested for sodium ion dependent spectral properties of probes within the contact lens. The probes displayed changes in intensity and lifetime in response to Na concentration, were completely reversible, no significant probe wash-out from the lenses, were not affected by proteins in tears and were not removed after repeated washing. These results are the first step to our long-term goal, which is a lens sensitive to all the electrolytes in tears. We presented design, synthesis and implementation of three new sodium sensitive probes within a silicon hydrogel lens. Contact lenses to measure the other electrolytes in tears can be developed using the same approach by synthesis and testing of new ion-sensitive fluorophores.
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http://dx.doi.org/10.1016/j.snb.2021.129434DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7861470PMC
March 2021

Fluorescent contact lens for continuous non-invasive measurements of sodium and chloride ion concentrations in tears.

Anal Biochem 2020 11 12;608:113902. Epub 2020 Aug 12.

Center for Fluorescence Spectroscopy, Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 725 West Lombard St., Baltimore, MD, 21201, USA. Electronic address:

Rapid and non-invasive measurement of hydration status is medically important because even mild levels of dehydration can have a significant impact on physical and cognitive performance. Despite the potential value of determining whole-body hydration based on the electrolytes found in tears, very few tests are available. An area of intense interest is the development of a contact lens which could measure ion concentrations in tears, specifically that of sodium (Na) and chloride (Cl) ions, the dominant electrolytes in blood plasma and tears. Here, we describe a method to make fluorescent contact lenses which allow determination of Na and Cl ion concentrations in tears. Fluorophores known to be sensitive to Na and Cl were derivatized to bind non-covalently to two commercially-available silicone hydrogel (SiHG) contact lenses-the Biofinity (Comfilcon A) or MyDay (Stenfilcon A) lenses. The sodium- and chloride-sensitive fluorophores displayed spectral changes in the physiological range for Na and Cl ions in tears. The lenses for both Na and Cl ions were completely reversible. The sodium responses were not sensitive to protein interference including human lysozyme, human serum albumin and mucin type 2. The chloride sensitivity was similar with both lenses, but the sodium-sensitive range was different in the Biofinity and MyDay lenses. We also fabricated a lens with both the Na and Cl probes in a single MyDay lens resulting in a contact lens that independently measured Na and Cl concentrations without physical separation of the fluorophores. Our findings indicated that a sodium and chloride-sensitive contact lens (NaCl-lens) could be used for rapid non-invasive detection of whole-body hydration, as well as associated diseases or other infections.
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http://dx.doi.org/10.1016/j.ab.2020.113902DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7530058PMC
November 2020