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Choi JH, Fremy G, Charnay T, Fayad N, Pécaut J, Erbek S, Hildebrandt N, Martel-Frachet V, Grichine A, Sénèque O. Luminescent Peptide/Lanthanide(III) Complex Conjugates with Push–Pull Antennas: Application to One- and Two-Photon Microscopy Imaging. Inorg Chem 2022; 61:20674-20689. [DOI: 10.1021/acs.inorgchem.2c03646] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Ji-Hyung Choi
- Université Grenoble Alpes, CNRS, CEA, IRIG, LCBM (UMR 5249), Grenoble F-38000, France
| | - Guillaume Fremy
- Université Grenoble Alpes, CNRS, CEA, IRIG, LCBM (UMR 5249), Grenoble F-38000, France
- Université Grenoble Alpes, CNRS, DCM (UMR 5250), Grenoble F-38000, France
| | - Thibault Charnay
- Université Grenoble Alpes, CNRS, CEA, IRIG, LCBM (UMR 5249), Grenoble F-38000, France
| | - Nour Fayad
- Laboratoire COBRA (Chimie Organique, Bioorganique, Réactivite et Analyse), UMR 6014, CNRS, Université de Rouen Normandie, INSA, Mont-Saint-Aignan Cedex 76821, France
| | - Jacques Pécaut
- Université Grenoble Alpes, CEA, CNRS, IRIG, SyMMES, Grenoble F-38000, France
| | - Sule Erbek
- Institute for Advanced Biosciences, Université Grenoble Alpes, INSERM U1209, CNRS UMR 5309, Grenoble F-38000, France
- EPHE, PSL Research University, 4-14 Rue Ferrus, Paris 75014, France
| | - Niko Hildebrandt
- Laboratoire COBRA (Chimie Organique, Bioorganique, Réactivite et Analyse), UMR 6014, CNRS, Université de Rouen Normandie, INSA, Mont-Saint-Aignan Cedex 76821, France
| | - Véronique Martel-Frachet
- Institute for Advanced Biosciences, Université Grenoble Alpes, INSERM U1209, CNRS UMR 5309, Grenoble F-38000, France
- EPHE, PSL Research University, 4-14 Rue Ferrus, Paris 75014, France
| | - Alexei Grichine
- Institute for Advanced Biosciences, Université Grenoble Alpes, INSERM U1209, CNRS UMR 5309, Grenoble F-38000, France
| | - Olivier Sénèque
- Université Grenoble Alpes, CNRS, CEA, IRIG, LCBM (UMR 5249), Grenoble F-38000, France
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Improved prediction and characterization of blood-brain barrier penetrating peptides using estimated propensity scores of dipeptides. J Comput Aided Mol Des 2022; 36:781-796. [DOI: 10.1007/s10822-022-00476-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2022] [Accepted: 09/15/2022] [Indexed: 11/27/2022]
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Pham H, Miller LW. Lanthanide-based resonance energy transfer biosensors for live-cell applications. Methods Enzymol 2021; 651:291-311. [PMID: 33888207 DOI: 10.1016/bs.mie.2021.01.010] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Lanthanide-based, Förster resonance energy transfer (LRET) biosensors enable sensitive, time-gated luminescence (TGL) imaging or multiwell plate analysis of protein-protein interactions (PPIs) in living mammalian cells. LRET biosensors are polypeptides that consist of an alpha-helical linker sequence sandwiched between a lanthanide complex-binding domain and a fluorescent protein (FP) with two interacting domains residing at each terminus. Interaction between the terminal affinity domains brings the lanthanide complex and FP in close proximity such that lanthanide-to-FP, LRET-sensitized emission is increased. A recent proof-of-concept study examined model biosensors that incorporated the affinity partners FKBP12 and the rapamycin-binding domain of m-Tor (FRB) as well as p53 (1-92) and HDM2 (1-128). The sensors contained an Escherichia coli dihydrofolate reductase (eDHFR) domain that binds with high selectivity and affinity to Tb(III) complexes coupled to the ligand trimethoprim (TMP). When cell lines that stably expressed the sensors were treated with TMP-Tb(III), TGL microscopy revealed dramatic differences (>500%) in donor- or acceptor-denominated, Tb(III)-to-GFP LRET ratios between open (unbound) and closed (bound) states of the biosensors. Much larger signal changes (>2500%) and Z'-factors of 0.5 or more were observed when cells were grown in 96-well or 384-well plates and analyzed using a TGL plate reader. In this chapter, we elaborate on the design and performance of LRET biosensors and provide detailed protocols to guide their use for live-cell microscopic imaging studies and high-throughput library screening.
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Affiliation(s)
- Ha Pham
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL, United States
| | - Lawrence W Miller
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL, United States.
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Chen T, Pham H, Mohamadi A, Miller LW. Single-Chain Lanthanide Luminescence Biosensors for Cell-Based Imaging and Screening of Protein-Protein Interactions. iScience 2020; 23:101533. [PMID: 33083762 PMCID: PMC7509216 DOI: 10.1016/j.isci.2020.101533] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2020] [Revised: 08/23/2020] [Accepted: 09/02/2020] [Indexed: 11/27/2022] Open
Abstract
Lanthanide-based, Förster resonance energy transfer (LRET) biosensors enabled sensitive, time-gated luminescence (TGL) imaging or multiwell plate analysis of protein-protein interactions (PPIs) in living cells. We prepared stable cell lines that expressed polypeptides composed of an alpha helical linker flanked by a Tb(III) complex-binding domain, GFP, and two interacting domains at each terminus. The PPIs examined included those between FKBP12 and the rapamycin-binding domain of m-Tor (FRB) and between p53 (1–92) and HDM2 (1–128). TGL microscopy revealed dramatic differences (>500%) in donor- or acceptor-denominated, Tb(III)-to-GFP LRET ratios between open (unbound) and closed (bound) states of the biosensors. We observed much larger signal changes (>2,500%) and Z′-factors of 0.5 or more when we grew cells in 96- or 384-well plates and analyzed PPI changes using a TGL plate reader. The modular design and exceptional dynamic range of lanthanide-based LRET biosensors will facilitate versatile imaging and cell-based screening of PPIs. Non-invasive, microscopic imaging or screening of protein-protein interactions Intracellular assembly of sensor polypeptides with luminescent Tb(III) complexes High dynamic range with time-gated detection of Tb(III)-to-GFP sensitized emission
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Affiliation(s)
- Ting Chen
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL, USA
| | - Ha Pham
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL, USA
| | - Ali Mohamadi
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL, USA
| | - Lawrence W. Miller
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL, USA
- Corresponding author
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5
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Starck M, Fradgley JD, Di Vita S, Mosely JA, Pal R, Parker D. Targeted Luminescent Europium Peptide Conjugates: Comparative Analysis Using Maleimide and para-Nitropyridyl Linkages for Organelle Staining. Bioconjug Chem 2019; 31:229-240. [DOI: 10.1021/acs.bioconjchem.9b00735] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Matthieu Starck
- Department of Chemistry, Durham University, South Road, Durham DH1 3LE, United Kingdom
| | - Jack D. Fradgley
- Department of Chemistry, Durham University, South Road, Durham DH1 3LE, United Kingdom
| | - Stefania Di Vita
- Department of Chemistry, Durham University, South Road, Durham DH1 3LE, United Kingdom
| | - Jackie A. Mosely
- Department of Chemistry, Durham University, South Road, Durham DH1 3LE, United Kingdom
| | - Robert Pal
- Department of Chemistry, Durham University, South Road, Durham DH1 3LE, United Kingdom
| | - David Parker
- Department of Chemistry, Durham University, South Road, Durham DH1 3LE, United Kingdom
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Kovacs D, Kiraev SR, Phipps D, Orthaber A, Borbas KE. Eu(III) and Tb(III) Complexes of Octa- and Nonadentate Macrocyclic Ligands Carrying Azide, Alkyne, and Ester Reactive Groups. Inorg Chem 2019; 59:106-117. [DOI: 10.1021/acs.inorgchem.9b01576] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Daniel Kovacs
- Department of Chemistry, Ångström Laboratory, Box 523, Uppsala University, 75120, Uppsala, Sweden
| | - Salauat R. Kiraev
- Department of Chemistry, Ångström Laboratory, Box 523, Uppsala University, 75120, Uppsala, Sweden
| | - Dulcie Phipps
- Department of Chemistry, Ångström Laboratory, Box 523, Uppsala University, 75120, Uppsala, Sweden
| | - Andreas Orthaber
- Department of Chemistry, Ångström Laboratory, Box 523, Uppsala University, 75120, Uppsala, Sweden
| | - K. Eszter Borbas
- Department of Chemistry, Ångström Laboratory, Box 523, Uppsala University, 75120, Uppsala, Sweden
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Hu J, Lou Y, Wu F. Improved Intracellular Delivery of Polyarginine Peptides with Cargoes. J Phys Chem B 2019; 123:2636-2644. [PMID: 30830784 DOI: 10.1021/acs.jpcb.8b10483] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Complementary to endocytosis, cell-penetrating peptides (CPPs) at high concentrations can penetrate the cell membrane in a direct way, which further makes CPPs popular candidates for delivering therapeutic or diagnostic agents. Although featured as rapid uptake, the translocation efficiency and potential toxicity of the direct penetration are usually affected by cargoes, which is still unclear. Here, using coarse-grained molecular dynamics simulations, we show that the polyarginine (R8) peptides penetrate the membrane through a water pore in the membrane, and the transmembrane efficiency is improved by conjugating to small nanoparticles (NPs) with proper linkers. It can be attributed to both the extension of the lifetime of the water pore by the NPs and outward diffusion of negative lipids in the asymmetry membrane, which induces the surrounding R8-NP conjugates to the water pore before it is closed. The translocation efficiency is closely related to the length of the linkers, and it gets the maximum value when the length of the linkers is around half of the membrane thickness. Overlong linkers not only decrease the transmembrane efficiency because of the blockage of NPs in the water pore but may also cause cytotoxicity because of the unclosed water pore. The results provide insights into the internalization of CPPs and facilitate the design of CPP and drug conjugates with high efficiency and low toxicity.
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Affiliation(s)
- Juanmei Hu
- Key Laboratory of Optical Field Manipulation & Center for Optoelectronics Materials and Devices of Zhejiang Province, Department of Physics , Zhejiang Sci-Tech University , Hangzhou 310018 , China
| | - Yimin Lou
- Key Laboratory of Optical Field Manipulation & Center for Optoelectronics Materials and Devices of Zhejiang Province, Department of Physics , Zhejiang Sci-Tech University , Hangzhou 310018 , China
| | - Fengmin Wu
- Key Laboratory of Optical Field Manipulation & Center for Optoelectronics Materials and Devices of Zhejiang Province, Department of Physics , Zhejiang Sci-Tech University , Hangzhou 310018 , China
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Mathieu E, Sipos A, Demeyere E, Phipps D, Sakaveli D, Borbas KE. Lanthanide-based tools for the investigation of cellular environments. Chem Commun (Camb) 2018; 54:10021-10035. [PMID: 30101249 DOI: 10.1039/c8cc05271a] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Biological probes constructed from lanthanides can provide a variety of readout signals, such as the luminescence of Eu(iii), Tb(iii), Yb(iii), Sm(iii) and Dy(iii), and the proton relaxation enhancement of Gd(iii) and Eu(ii). For numerous applications the intracellular delivery of the lanthanide probe is essential. Here, we review the methods for the intracellular delivery of non-targeted complexes (i.e. where the overall complex structure enhances cellular uptake), as well as complexes attached to a targeting unit (i.e. to a peptide or a small molecule) that facilitates delivery. The cellular applications of lanthanide-based supramolecules (dendrimers, metal organic frameworks) are covered briefly. Throughout, we emphasize the techniques that can confirm the intracellular localization of the lanthanides and those that enable the determination of the fate of the probes once inside the cell. Finally, we highlight methods that have not yet been applied in the context of lanthanide-based probes, but have been successful in the intracellular delivery of other metal-based probes.
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Affiliation(s)
- Emilie Mathieu
- Department of Chemistry, Ångström Laboratory, Uppsala University, Box 523, 75120, Uppsala, Sweden.
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Azevedo C, Macedo MH, Sarmento B. Strategies for the enhanced intracellular delivery of nanomaterials. Drug Discov Today 2018; 23:944-959. [PMID: 28919437 PMCID: PMC7108348 DOI: 10.1016/j.drudis.2017.08.011] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Revised: 06/13/2017] [Accepted: 08/23/2017] [Indexed: 11/25/2022]
Abstract
The intracellular delivery of nanomaterials and drugs has been attracting increasing research interest, mainly because of their important effects and functions in several organelles. Targeting specific organelles can help treat or decrease the symptoms of diabetes, cancer, infectious, and autoimmune diseases. Tuning biological and chemical properties enables the creation of functionalized nanomaterials with enhanced intracellular uptake, ability to escape premature lysosome degradation, and to reach a specific target. Here, we provide an update of recent advances in the intracellular delivery mechanisms that could help drugs reach their target more efficiently.
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Affiliation(s)
- Cláudia Azevedo
- i3S - Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Rua Alfredo Allen, 208, 4200-135 Porto, Portugal; Instituto de Ciências Biomédicas Abel Salazar, University of Porto, Porto, Portugal
| | - Maria Helena Macedo
- i3S - Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Rua Alfredo Allen, 208, 4200-135 Porto, Portugal
| | - Bruno Sarmento
- i3S - Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Rua Alfredo Allen, 208, 4200-135 Porto, Portugal; CESPU, Instituto de Investigação e Formação Avançada em Ciências e Tecnologias da Saúde & Instituto Universitário de Ciências da Saúde, Gandra, Portugal.
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10
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Romero O, de las Rivas B, Lopez-Tejedor D, Palomo JM. Effect of Site-Specific Peptide-Tag Labeling on the Biocatalytic Properties of Thermoalkalophilic Lipase from Geobacillus thermocatenulatus. Chembiochem 2018; 19:369-378. [DOI: 10.1002/cbic.201700466] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Indexed: 12/19/2022]
Affiliation(s)
- Oscar Romero
- Department of Biocatalysis; Institute of Catalysis (CSIC); Marie Curie 2 Cantoblanco CampusUAM 28049 Madrid Spain
| | - Blanca de las Rivas
- Laboratorio de Biotecnología Microbiana; Instituto de Ciencia y Tecnología de alimentos y Nutrición (ICTAN-CSIC); José Antonio Novais, 10 28040 Madrid Spain
| | - David Lopez-Tejedor
- Department of Biocatalysis; Institute of Catalysis (CSIC); Marie Curie 2 Cantoblanco CampusUAM 28049 Madrid Spain
| | - Jose M. Palomo
- Department of Biocatalysis; Institute of Catalysis (CSIC); Marie Curie 2 Cantoblanco CampusUAM 28049 Madrid Spain
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Mohamadi A, Miller LW. Efficient route to pre-organized and linear polyaminopolycarboxylates: Cy-TTHA, Cy-DTPA and mono/di- reactive, tert-butyl protected TTHA/Cy-TTHA. Tetrahedron Lett 2017; 58:1441-1444. [PMID: 29176914 PMCID: PMC5699510 DOI: 10.1016/j.tetlet.2017.02.056] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Pre-organized polyaminopolycarboxylate chelators Cy-TTHA and Cy-DTPA were synthesized via modular five-step syntheses from commercially available starting materials in ~ 62% and 47% overall yields, respectively. Furthermore, strategies are reported for the efficient preparation of mono- and di-reactive, tert-butyl-protected TTHA/Cy-TTHA to selectively functionalize central chelators' carboxylic acids.
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Affiliation(s)
- Ali Mohamadi
- University of Illinois at Chicago, Department of Chemistry, 845 W. Taylor Street, MC 111, Chicago, IL 60607
| | - Lawrence W Miller
- University of Illinois at Chicago, Department of Chemistry, 845 W. Taylor Street, MC 111, Chicago, IL 60607
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Yao Y, Kong C, Yin L, Jain AD, Ratia K, Thatcher GRJ, Moore TW, Driver TG, Miller LW. Time-Gated Detection of Cystathionine γ-Lyase Activity and Inhibition with a Selective, Luminogenic Hydrogen Sulfide Sensor. Chemistry 2016; 23:752-756. [PMID: 27734530 DOI: 10.1002/chem.201604786] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Indexed: 12/18/2022]
Abstract
Herein, we report the design, synthesis, and characterization of a lanthanideIII complex-based probe for the time-gated luminescence detection of hydrogen sulfide (H2 S) in aqueous media. The probe's unique sensing mechanism relies on the selective reduction of azide to amine by sulfide, followed by intramolecular cyclization to form a quinolinone. The quinolinone is a sensitizer that absorbs near-UV light and transfers excitation energy to coordinated TbIII or EuIII ions to trigger a strong "turn-on" luminescence response with ms-scale lifetimes characteristic of lanthanide complexes. Using this probe, we developed a robust, high throughput screening (HTS) assay for detecting H2 S generated by cystathionine γ-lyase (CSE), one of the main producers of H2 S in mammalian cells. In a 240-compound screen to identify potential CSE inhibitors, the EuIII analogue of the sensor showed a low false-positive rate and high Z'-factor (>0.7).
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Affiliation(s)
- Yao Yao
- Department of Chemistry, University of Illinois at Chicago, 845 W. Taylor Street, MC 111, Chicago, Illinois, 60607, USA
| | - Chen Kong
- Department of Chemistry, University of Illinois at Chicago, 845 W. Taylor Street, MC 111, Chicago, Illinois, 60607, USA
| | - Liang Yin
- Department of Medicinal Chemistry and Pharmacognosy, UICentre for Drug Discovery, University of Illinois Cancer Center, University of Illinois at Chicago, Chicago, Illinois, 60612, USA
| | - Atul D Jain
- Department of Medicinal Chemistry and Pharmacognosy, UICentre for Drug Discovery, University of Illinois Cancer Center, University of Illinois at Chicago, Chicago, Illinois, 60612, USA
| | - Kiira Ratia
- Department of Medicinal Chemistry and Pharmacognosy, UICentre for Drug Discovery, University of Illinois Cancer Center, University of Illinois at Chicago, Chicago, Illinois, 60612, USA
| | - Gregory R J Thatcher
- Department of Medicinal Chemistry and Pharmacognosy, UICentre for Drug Discovery, University of Illinois Cancer Center, University of Illinois at Chicago, Chicago, Illinois, 60612, USA
| | - Terry W Moore
- Department of Medicinal Chemistry and Pharmacognosy, UICentre for Drug Discovery, University of Illinois Cancer Center, University of Illinois at Chicago, Chicago, Illinois, 60612, USA
| | - Tom G Driver
- Institute of Next Generation Matter Transformation, College of Chemical Engineering, Huaqiao University, 668 Jimei Blvd. Xiamen, Fujian, 361021, P. R. China
| | - Lawrence W Miller
- Department of Chemistry, University of Illinois at Chicago, 845 W. Taylor Street, MC 111, Chicago, Illinois, 60607, USA
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Mohamadi A, Miller LW. Brightly Luminescent and Kinetically Inert Lanthanide Bioprobes Based on Linear and Preorganized Chelators. Bioconjug Chem 2016; 27:2540-2548. [PMID: 27684450 DOI: 10.1021/acs.bioconjchem.6b00473] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The synthesis, photophysical properties, and kinetic stability of a series of water-soluble, highly emissive Tb(III) and Eu(III) complexes featuring triethylenetetraamine hexaacetic acid (TTHA) and cyclohexyl triethylenetetraamine hexaacetic acid (cyTTHA) chelator scaffolds and carbostyril sensitizers are reported. The unique and modular design of the chelators gives rise to striking quantum yields of emission in aqueous solutions (up to 54%) as well as the characteristic lanthanides' photophysical properties (long excited-state lifetimes, large effective Stokes shifts, and narrow emission peaks). Furthermore, the preorganized chelators (L3, L4, and L6) bind metal within minutes at ambient temperature yet exhibit substantial resistance to transchelation in the presence of a challenge solution (EDTA, 1 mM). Moreover, the Eu(III) complex of L4 remains stably luminescent in HeLa cells over hours, demonstrating the suitability of these compounds for live-cell imaging applications. Representative chelators suitable for derivatization and protein bioconjugation were also prepared that were functionalized with clickable azide and alkyne moieties, biotin, and trimethoprim (TMP). With exceptional long-wavelength brightness, enhanced kinetic inertness, and an adaptable synthetic route, the reported lanthanide complexes are promising probes and labels for time-gated bioanalysis, biosensing, and optical microscopy.
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Affiliation(s)
- Ali Mohamadi
- Department of Chemistry, University of Illinois at Chicago , 845 West Taylor Street, MC 111, Chicago, Illinois 60607, United States
| | - Lawrence W Miller
- Department of Chemistry, University of Illinois at Chicago , 845 West Taylor Street, MC 111, Chicago, Illinois 60607, United States
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Abstract
Probes and biosensors that incorporate luminescent Tb(III) or Eu(III) complexes are promising for cellular imaging because time-gated microscopes can detect their long-lifetime (approximately milliseconds) emission without interference from short-lifetime (approximately nanoseconds) fluorescence background. Moreover, the discrete, narrow emission bands of Tb(III) complexes make them uniquely suited for multiplexed imaging applications because they can serve as Förster resonance energy transfer (FRET) donors to two or more differently colored acceptors. However, lanthanide complexes have low photon emission rates that can limit the image signal/noise ratio, which has a square-root dependence on photon counts. This work describes the performance of a wide-field, time-gated microscope with respect to its ability to image Tb(III) luminescence and Tb(III)-mediated FRET in cultured mammalian cells. The system employed a UV-emitting LED for low-power, pulsed excitation and an intensified CCD camera for gated detection. Exposure times of ∼1 s were needed to collect 5-25 photons per pixel from cells that contained micromolar concentrations of a Tb(III) complex. The observed photon counts matched those predicted by a theoretical model that incorporated the photophysical properties of the Tb(III) probe and the instrument's light-collection characteristics. Despite low photon counts, images of Tb(III)/green fluorescent protein FRET with a signal/noise ratio ≥ 7 were acquired, and a 90% change in the ratiometric FRET signal was measured. This study shows that the sensitivity and precision of lanthanide-based cellular microscopy can approach that of conventional FRET microscopy with fluorescent proteins. The results should encourage further development of lanthanide biosensors that can measure analyte concentration, enzyme activation, and protein-protein interactions in live cells.
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