Luminescent Lanthanides in Biorelated Applications: From Molecules to Nanoparticles and Diagnostic Probes to Therapeutics

Abstract

Lanthanides are particularly effective in their clinical applications in magnetic resonance imaging and diagnostic assays. They have open-shell 4f electrons that give rise to characteristic narrow, line-like emission which is unique from other fluorescent probes in biological systems. Lanthanide luminescence signal offers selection of detection pathways based on the choice of the ion from the visible to the near-infrared with long luminescence lifetimes that lend themselves to time-resolved measurements for optical multiplexing detection schemes and novel bioimaging applications. The delivery of lanthanide agents in cells allows localized bioresponsive activity for novel therapies. Detection in the near-infrared region of the spectrum coupled with technological advances in microscopies opens new avenues for deep-tissue imaging and surgical interventions. This review focuses on the different ways in which lanthanide luminescence can be exploited in nucleic acid and enzyme detection, anion recognition, cellular imaging, tissue imaging, and photoinduced therapeutic applications. We have focused on the hierarchy of designs that include luminescent lanthanides as probes in biology considering coordination complexes, multimetallic lanthanide systems to metal-organic frameworks and nanoparticles highlighting the different strategies in downshifting, and upconversion revealing some of the opportunities and challenges that offer potential for further development in the field.

Figure 1

A) Fingerprint emission spectrum of lanthanides in visible and NIR regions; B) Partial Dieke diagram highlighting the energy levels arising from the 4fⁿ configurations of Ln(III) and their primary electronic transitions. Reproduced with permission from ref (24). Copyright 2025 Elsevier.

Figure 2

Triplet mediated energy transfer in a lanthanide–antenna system. Abs. = absorbance, ISC = intersystem crossing, En.T = Energy Transfer, Lum. = Luminescence.

Figure 3

Possible perturbations to energy transfer and emission in lanthanide containing systems.

Figure 4

From molecular to nanoparticle designs of lanthanide sensitization schemes.

Figure 5

Schematic illustration of a typical FRET “sandwich” assay.

Figure 6

Schematic illustration of the heterogeneous DELFIA assay.

Figure 7

DNA base pairs.

Figure 8

Illustration of strategies in nucleic acid assays using Ln-complexes as probes.

Figure 9

Donor–acceptor distance mediated by DNA strands. Reproduced with permission from ref (154). Copyright 2017 John Wiley and Sons.

Figure 10

Self-assembly of Ln-Pt₂ metallohairpins. Adapted and reproduced with permission from ref (116) . Copyright 2003 American Chemical Society.

Figure 11

Illustration of strategies involving nanoparticle-based hybridization assays.

Figure 12

Approaches to using lanthanides for detection of enzymatic activity.

Figure 13

(A) Schematic representation of the biosensor. Upon phosphorylation, the phosphopeptide should bind to the recognition domain (PAABD), leading to a conformational change that should bring together the sensitizing antenna and the terbium complex, resulting in an increase in the luminescence emission. (B) The peptide sequence of the designed biosensors, where the phosphorylatable residue is bold and ϕ = Cys(DOTA-Tb(III)). Reproduced with permission from ref (246). Copyright 2017 Royal Society of Chemistry.

Figure 14

Essential design elements and structural features in emissive [Eu(TACN)] probe design from the Parker group. Reproduced with permission from ref (356). Copyright 2015 Royal Society of Chemistry.

Figure 15

Laser scanning confocal microscopy images of NIH-3T3 cells treated with Λ-[EuL^imag-22] (right) and Δ-[EuL^imag-22] (left) showing the predominant mitochondrial (P = 0.71) and lysosomal (P = 0.77) localization profiles, respectively (red for Eu(III) emission, green for Mitotracker Green and LysoTracker Green). Scale bar = 20 μm. Reproduced with permission from ref (358). Copyright 2018 Royal Society of Chemistry.

Figure 16

(top) Illustration of the consecutive binding of an IR-dye labeled agonist acceptor to the Eu-SNAP-tagged cholecystokinin-2 cell surface receptor followed by competitive displacement of the agonist by an added antagonist; (bottom) (a) Time-resolved luminescence microscopy image of SNAP cholecystokinin-2 receptor-transfected HEK293 cells labeled with [EuL^imag-41]. (b) Time-resolved FRET channel image after adding red- cholecystokinin-2 receptor (26–33) dye to transfected HEK293 cells labeled with [EuL^imag-41] to reveal emission from the dye and quenching of Eu(III) luminescence. Adapted with permission from ref (366). Copyright 2014 John Wiley and Sons.

Figure 17

Fluorescence imaging of human breast cancer cells (MCF-7) incubated with [EuL^imag-46] for 24 h. Scale bar: 10 μm. Reproduced with permission from ref (369). Copyright 2020 American Chemical Society.

Figure 18

Schematic illustration of the dominant intracellular localization profiles of the emissive Eu(III) and Tb(III) macrocyclic complexes reported by Parker et al. Reproduced with permission from ref (45). Copyright 2009 American Chemical Society.

Figure 19

Two-photon imaging of T24 cells costained for 4 h with [YbL^imag-53]⁺ (c = 10^–5 mol L^–1, two-photon excitation at λ_ex = 800 nm, detection in a descanned mode in the residual ILCT emission) (right) and transmitted light DIC image (left) using an LSM710 NLO (Carl Zeiss) microscope. Reproduced with permission from ref (372). Copyright 2017 Royal Society of Chemistry.

Figure 20

NIR time-resolved images of living HeLa cells incubated with 10 μM [YbL^imag-78] and [YbL^imag-79]. Scale bar: 10 μm. Reproduced with permission from ref (385). Copyright 2018 Royal Society of Chemistry.

Figure 21

Three-photon confocal fluorescent microscopy images of [TbL^imag-87] incubated in human lung carcinoma A549 (left) and human cervical carcinoma HeLa cells (right) (λ_ex = 800 nm). Reproduced with permission from ref (394). Copyright 2008 American Chemical Society.

Figure 22

X-ray fluorescence mapping of intracellular distribution of CeL-AuNP_imag1 in two neighboring cryofixed lyophilized MRC5VA cells. (A–D) Representative comparative elemental subcellular distributions of Zn, Au, Mn, and Fe. Scanning step-size: 200 nm; dwell time: 100 ms; the white size bar in the Au panel represents the distance of 5 μm. Reproduced with permission from ref (506). Copyright 2010 Taylor and Francis.

Figure 23

(left) (a) TEM image and (b–d) corresponding EDX mapping: (b) Si, (c) Tb, and (d) overlapping Tb and Si signals of TbL-SiO₂NP_imag6. (right) Confocal fluorescence microscopy images of C. albicans cells, stained with TbL-SiO₂NP_imag6 after 15 and 30 min of incubation with 10 μg mL^–1 of each sample, at 37 °C. Reproduced with permission from ref (524). Copyright 2013 Royal Society of Chemistry.

Figure 24

Live-cell images of HeLa cells incubated with Eu-PMMA. (A) Time-gated photoluminescent images with PMMA-COOH 10% (A1), PMMA-SO3H 3% (A2), and PMMA-SO3H 1% (A3) NPs at 40% [Eu(tta)₃phen] loading. For a better comparison between the different images, the intensity scale was fixed at 0 to 2 × 104 counts. (B) Differential interference contrast (DIC) images. (C) Overlay of images from A and B (ECP-NP PL is shown in red, PL intensities were normalized to the highest values in A1, A2, and A3). (D) Projections of a z-stack of images of a HeLa cell incubated with Eu-PMMA (PMMA-COOH 10% at 40% [Eu(tta)₃phen]). ECP-NPs are shown in magenta and the cell membranes in turquoise (costained with DiD). Large image: x/y-optical section at 6 μm from the surface; small images are optical sections of cell along the x- and y-axis of the z-stack with a x/z side view (bottom) and y/z side view (right). Lines in the images indicate positions of the sections; white and yellow arrows point to ECP-NPs in endosomes/lysosomes. Scale bars in all images: 10 μm. Reproduced with permission from ref (528). Copyright 2019 American Chemical Society.

Figure 25

Confocal imaging studies of zebrafish embryos injected with [EuL^imag-46] (10^–4 M) and their control images with no optical probes under single (top) and two photon excitation (bottom), Scale bar: 500 μm. Reproduced with permission from ref (369). Copyright 2020 American Chemical Society.

Figure 26

(a) In vivo optical imaging upon administration of [¹⁸F]-fluorodeoxyglucose. [¹⁸F]-FDG and [EuL^tiss-5]⁺. (b) Excised tumors imaged at 1 and 3 h postinjection (p.i.) demonstrate the persistent, detectable emission signal of [EuL^tiss-5]⁺. Adapted with permission from ref (541). Copyright 2021 American Chemical Society.

Figure 27

(a) Schematic illustration of the metabolic process of [YbL^tiss-10] from the stomach to the intestine. (b) NIR fluorescence intensity imaging (exposure time, 25 ms) of the Yb(III) complex. (c) FLIM images (exposure time, 250 ms). λ_ex, 532 nm; λ_em, 1000 nm long-pass. Reproduced with permission from ref (544). Copyright 2019 Royal Society of Chemistry.

Figure 28

Fast in vivo brain imaging with NaYbF₄:2%Er,2%Ce@NaYF₄ coated with PMAh, PEG in the NIR-IIb region. (a) Color photograph of a C57Bl/6 mouse (with hair shaved off) preceding NIR-IIb fluorescence imaging. (b–d) Time-course NIR-IIb brain fluorescence images (exposure time: 20 ms) showing the perfusion of RENPs into various cerebral vessels. The blood-flow velocities of cerebral vessels are given in (c) (scale bar corresponds to (b–d): 2 mm). (e, f) Cerebral vascular image (exposure time: 20 ms) in NIR-IIb region with corresponding PCA overlaid image (f) showing arterial (red) and venous (blue) vessels. (g) SBR analysis of NIR-IIb cerebrovascular image (d) by plotting the cross-sectional intensity profiles. Reproduced with permission from ref (567). Copyright 2017 Springer Nature.

Figure 29

Comparison of fluorescence intensity image with fluorescence lifetime image of whole-body vascular in mice detected by Er-fluorescence signal. Reproduced with permission from ref (569). Copyright 2023 John Wiley and Sons.

Figure 30

Illustration and images of Lewis Lung Carcinoma (LLC) bearing mice. (a) Schematic illustration of NIR-IIb optical imaging-guided LLC tumor vessel detection. (b) Bright field image (up) and digital photograph (down) of the LLC tumor. (c) The time coursed NIR-IIb imaging of a mouse tumor under the excitation of 980 nm lase with an excitation power density of 100 mW/cm². (d) Magnified tumor vascular image. (e) Cross-sectional fluorescence intensity profiles along blue lines 1 and 2 of the tumor site. The scale bar is 2 mm in (d), and the white circles in (b) and (d) indicate the necrosis region in the epidermis of the primary tumor. Reproduced with permission from ref (572). Copyright 2019 American Chemical Society.

Figure 31

Temporal multiplexed in vivo upconversion imaging. (a) Schematic illustration of nanoparticles administration followed by imaging in a home-built time-resolved upconversion luminescence imaging system. (b) Measured upconversion luminescence decay profiles of PAA-coated core/multishell nanoparticles with lifetimes of τ₂, τ₅, and τ₉ (aqueous dispersion). (c) Upconversion luminescence intensity (top left) and lifetime (top right) imaging with lifetimes of τ₂ and τ₉ in a Kunming mouse and in a second Kunming mouse (bottom) (subcutaneous injection of these nanoparticles into abdomen). Intravenous administration of nanoparticles with a lifetime of τ₅ was implemented for the second mouse, enabling to light up the internal organs for both luminescence intensity (bottom left) and lifetime (bottom right) upconversion imaging. τ values correspond to those of nanoparticles. Reproduced with permission from ref (579). Copyright 2020 American Chemical Society.

Figure 32

Schematic illustration of enzyme-triggered covalent cross-linking of peptide-premodified UCNP in tumor areas. The enhanced upconversion amplifies the singlet oxygen generation from the Ce6 onto the UCNP for enhanced photodynamic therapy treatment in vitro and in vivo. Reproduced with permission from ref (615). Copyright 2016 Springer Nature.

Figure 33

UCNP-mediated NIR upconversion optogenetics. (a, b) Deep brain stimulation. Reproduced with permission from ref (648). Copyright 2018 American Association for the Advancement of Science. (a) Schematic principle of UCNP-mediated NIR upconversion optogenetics and design of a blue-emitting NaYF₄:Yb/Tm@SiO₂ particle. (b) Scheme of in vivo fiber photometry for measuring UCNP-mediated NIR upconversion in deep brain tissue; upconversion emission at the VTA upon 980 nm NIR irradiation from varying distances; measured (n = 4 mice) and simulated intensity of upconversion emission at the VTA as a function of the distance from the NIR irradiation source. (c) Activation of photoreceptors. Reproduced with permission from ref (649). Copyright 2017 American Chemical Society. UCNP deliver plasmid DNA into the cell and then work as a nanotransducer to convert external deep-tissue-penetrating NIR light to local blue light to noninvasively activate photoreceptors leading to apoptotic signaling pathways of cancer cells in vivo. (d) Programmable photoactivation in cardiac pacing. Reproduced with permission from ref (650). Copyright 2022 Springer Nature. Schematic illustration of programmable activation of ion channel proteins Jaws and VChR1 through controlling the power and duration times of 980 and 808 nm lasers. The green emission produced upon 808 nm excitation of the UCNP activates VChR1 resulting in calcium cation influx, while the red emission produced by 980 nm excitation activates Jaws for chloride anion influx.

Figure 34

Schematic diagram of the visible and NIR imaging and the NF-κB inhibition capability of [Yb/EuL^bio-26] on LMP1-positive cells (orange line, with the addition of probe; violet line, without Ln-probe). Reproduced with permission from ref (653). Copyright 2021 American Chemical Society.

Figure 35

Time-gated luminescence images of [Eu/TbL^bio-42]^–-loaded HepG2 cells. (A) Bright-field image; (B) Tb(III) luminescence image; (C) Eu(III) luminescence image; and (D) ratiometric image (ratio = I_green/I_red). Scale bar: 10 μm Reproduced with permission from ref (693). Copyright 2014 American Chemical Society.

Figure 36

(a) Schematic showing the UV light-activatable ATP sensing mechanism of the aptamer-based probe. (b) Design of DNA nanodevices based on the integration of the aptamer probe with upconversion nanotransducer for NIR-activated intracellular ATP sensing. Reproduced with permission from ref (708). Copyright 2017 American Chemical Society.

Figure 37

Top: Structure of [Eu/TbL^bio-53] and the proposed reaction mechanism of the probe with O₂^•–. Bottom: Ratiometric time-gated luminescence imaging of endogenously produced O₂^•– in HK-2 cells via cisplatin stimulation using [Eu/TbL^bio-53] as a probe ratiometric: I_green/I_red. Adapted with permission from ref (711). Copyright 2019 American Chemical Society.

Figure 38

Schematic illustration of the engineering of lanthanide bioprobes for urinary TRPL diagnosis of mice organ injuries. The synthesized Eu–DTPA complex and Eu–DTPA-integrated silica nanoprobes were designed for the diagnosis of AKI and DILI, respectively. TRPL = time-resolved photoluminescence. Reproduced with permission from ref (739). Copyright 2023 American Chemical Society.