Engineering Persistent Luminescence Nanoparticles for Biological Applications: From Biosensing/Bioimaging to Theranostics

X-ray/red-light excited ZGGO:Cr,Nd nanoprobes for NIR-I/II afterglow imaging

NIR-I/II afterglow nanoprobes for deep-tissue autofluorescence-free bioimaging were developed based on the persistent energy transfer.

Near-infrared-persistent luminescence/bioluminescence imaging tracking of transplanted mesenchymal stem cells in pulmonary fibrosis

A dual-labeling strategy integrating near-infrared-persistent luminescence and RfLuc-based bioluminescence imaging techniques has been developed to track the transplanted stem cells, deepening the understanding of the role played by stem cells in PF treatment.

Raspberry-Like Mesoporous Zn1.07Ga2.34Si0.98O6.56:Cr0.01 Nanocarriers for Enhanced Near-Infrared Afterglow Imaging and Combined Cancer Chemotherapy

Near-infrared (NIR) persistent luminescence (PersL) nanoparticles based on trivalent chromium-doped gallates (ZGO) as nanocarriers show great potential for theranostics, owing to their autofluorescence-free background and deep tissue penetration. However, high drug loading capacity of ZGO nanocarriers remains a big challenge. Herein, raspberry-like mesoporous Zn_1.07Ga_2.34Si_0.98O_6.56:Cr_0.01 (designated as Si-ZGO) is first developed via a unique silica-assisted targeted etching strategy. The composition, morphology, NIR PersL capacities, and drug loading/releasing abilities of Si-ZGO have been explored. These results exhibit that Si-ZGO possess multiple inspiring characteristics including (i) spherical raspberry-like mesoporous morphology with a large cavity (total pore size ∼5.0 nm) and high specific surface area (∼80.653 m²·g^-1), promising excellent drug loading capacity (∼62 wt %); (ii) tunable sizes from 80 to 180 nm and improved aqueous-dispersibility, facilitating cellular uptake and permeation and retention (EPR) effect; (iii) new deep traps related to oxygen vacancies, achieving the brighter NIR PersL. These outstanding merits enable the further nanosystem (DOX-BSA@Si-ZGO) for proof-of-concept theranostics excellent chemotherapy effect, tumor-specific trackable ability, and pronounced NIR afterglow imaging in vivo. This work demonstrates the great potentials of Si-ZGO nanorasperries as a multifunctional theranostics platform, even more it hopefully could inspire other constructions of advanced functional materials.

Affinity binding-mediated fluorometric protein assay based on the use of target-triggered DNA assembling probes and aptamers labelled with upconversion nanoparticles: application to the determination of platelet derived growth factor-BB

The target-triggered DNA assembling probe is presented for highly selective protein detection. Target-triggered DNA assembling is used in an amplification strategy based on affinity binding for identification and determination of proteins in general. Specifically, it was applied to the platelet derived growth factor-BB (PDGF-BB). A hairpin DNA (H-DNA) probe was designed containing (a) an aptamer domain for protein recognition and (b) a blocked DNAzyme domain for DNAzyme cleavage. An assistant DNA (A-DNA) probe containing aptamer and complementary domains was also employed to recognize protein and to induce DNA assembly. Once H-DNA and A-DNA recognize the same protein, H-DNA and A-DNA are in close proximity to each other. This induces DNA assembling for protein-triggered complex (Protein-Complex) with free DNAzyme domains. The free DNAzymes trigger the circular cleavage of molecular beacons for amplified signals. The assay is performed by fluorometry at an excitation wavelength of 980 nm and by collecting fluorescence at 545 nm. The platelet derived growth factor-BB (PDGF-BB) was accurately identified and selectively determined by this assay with a 22 pM detection limit (using the 3σ criterion). The responses for PDGF-BB is nearly 6-fold higher than for PDGF-AB, and 16-fold higher than PDGF-AA. This upconversion assay avoids any interference by the autofluorescence of biological fluids. Graphical abstractSchematic representation of the principle of the target-triggered DNA assembling probes mediated amplification strategy based on affinity binding for PDGF-BB. The UCNP probe is used for the quantitation of PDGF-BB with high selectivity.

Optically Active Nanomaterials for Bioimaging and Targeted Therapy

Non-invasive tracking for monitoring the selective delivery and transplantation of biotargeted agents in vivo has been employed as one of the most effective tools in the field of nanomedicine. Different nanoprobes have been developed and applied to bioimaging tissues and the treatment of diseases ranging from inflammatory and cardiovascular diseases to cancer. Herein, we will review the recent advances in the development of optics-responsive nanomaterials, including organic and inorganic nanoparticles, for multimodal bioimaging and targeted therapy. The main focus is placed on nanoprobe fabrication, mechanistic illustrations, and diagnostic, or therapeutical applications. These nanomedicine strategies have promoted a better understanding of the biological events underlying diverse disease etiologies, thereby facilitating diagnosis, illness evaluation, therapeutic effect, and drug discovery.

Smart H2S-Triggered/Therapeutic System (SHTS)-Based Nanomedicine

Hydrogen sulfide (H2S) is of vital importance in several biological and physical processes. The significance of H2S-specific detection and monitoring is emphasized by its elevated levels in various diseases such as cancer. Nanotechnology enhances the performance of chemical sensing nanoprobes due to the enhanced efficiency and sensitivity. Recently, extensive research efforts have been dedicated to developing novel smart H2S-triggered/therapeutic system (SHTS) nanoplatforms for H2S-activated sensing, imaging, and therapy. Herein, the latest SHTS-based nanomaterials are summarized and discussed in detail. In addition, therapeutic strategies mediated by endogenous H2S as a trigger or exogenous H2S delivery are also included. A comprehensive understanding of the current status of SHTS-based strategies will greatly facilitate innovation in this field. Lastly, the challenges and key issues related to the design and development of SHTS-based nanomaterials (e.g., morphology, surface modification, therapeutic strategies, appropriate application, and selection of nanomaterials) are outlined.

Autoluminescence-Free Prostate-Specific Antigen Detection by Persistent Luminous Nanorods and Au@Ag@SiO2 Nanoparticles

The sensitive detection of biomarker with high selectivity and accuracy is of remarkable significance for the early screening and clinical diagnosis of malignant cancer. Persistent phosphors play a role in illumination-free biosensing owing to their unparalleled optical properties, which produces long-lasting luminescence without the illumination to eliminate the interference of autofluorescence and scattering light from biological matrix. In this study, ZnGeO:Mo persistent luminescence nanorods (PLNRs) were prepared and showed tunable luminescence intensity and decay patterns. An excitation-free luminescent aptasensor was proposed for the detection of prostate specific antigen (PSA) by using ZnGeO:Mo PLNRs as probes and Au@Ag@SiO₂ nanoparticles as quenchers. Under optimal conditions, the limit of detection for PSA was 9.2 pg mL^-1. This work creates a possibility for the preparation of multiplex colored persistent luminescence nanomaterials with desired decay patterns for multiple bioassay and time-resolved fluoroimmunoassay.

Bacterial Biofilm Bioinspired Persistent Luminescence Nanoparticles with Gut-Oriented Drug Delivery for Colorectal Cancer Imaging and Chemotherapy

Colorectal cancer (CRC) is now one of the leading causes of cancer incidence and mortality. Although nanomaterial-based drug delivery has been used for the treatment of colorectal cancer, inferior targeting ability of existing nanocarriers leads to inefficient treatment and side effects. Moreover, the majority of intravenously administered nanomaterials aggregate into the reticuloendothelial system, leaving a certain hidden risk to human health. All those problems gave great demands for further construction of well-performed and biocompatible nanomaterials for in vivo theranostics. In the present work, from a biomimetic point of view, Lactobacillus reuteri biofilm (LRM) was coated on the surface of trackable zinc gallogermanate (ZGGO) near-infrared persistent luminescence mesoporous silica to create the bacteria bioinspired nanoparticles (ZGGO@SiO₂@LRM), which hold the inherent capability of withstanding the digestion of gastric acid and targeted release 5-FU to colorectum. Through the background-free persistent luminescence bioimaging of ZGGO, the coating of LRM facilitated the localization of ZGGO@SiO₂@LRM to the tumor area of colorectum for more than 24 h after intragastric administration. Furthermore, ZGGO@SiO₂@LRM hardly entered the blood, which avoided possible damage to immune organs such as the liver and spleen. In vivo chemotherapy experiment demonstrated the number of tumors per mouse in ZGGO@SiO₂@LRM group decreased by one-half compared with the 5-FU group (P < 0.001). To sum up, this LRM bioinspired nanoparticles could tolerate the digestion of gastric acid, avoid aggregation by the immune system, favor gut-oriented drug delivery, and targeted release oral 5-FU into colorectum for more than 24 h, which may give new application prospects for targeted delivery of oral drugs into the colorectum.

Optically Stimulated Nanodosimeters with High Storage Capacity

In this work we report on the thermoluminescence (TL) and optically stimulated luminescence (OSL) properties of β-Na(Gd,Lu)F4:Tb3+ nanophosphors prepared via a standard high-temperature coprecipitation route. Irradiating this phosphor with X-rays not only produces radioluminescence but also leads to a bright green afterglow that is detectable up to hours after excitation has stopped. The storage capacity of the phosphor was found to be (2.83 ± 0.05) × 1016 photons/gram, which is extraordinarily high for nano-sized particles and comparable to the benchmark bulk phosphor SrAl2O4:Eu2+,Dy3+. By combining TL with OSL, we show that the relatively shallow traps, which dominate the TL glow curves and are responsible for the bright afterglow, can also be emptied optically using 808 or 980 nm infrared light while the deeper traps can only be emptied thermally. This OSL at therapeutically relevant radiation doses is of high interest to the medical dosimetry community, and is demonstrated here in uniform, solution-processable nanocrystals.

Star-Shaped ESIPT-Active Mechanoresponsive Luminescent AIEgen and Its On-Off-On Emissive Response to Cu2+/S2

Design and development of multifunctional materials have drawn incredible attraction in recent years. Herein, we report the design and construction of versatile star-shaped intramolecular charge transfer (ICT)-coupled excited-state intramolecular proton transfer (ESIPT)-active mechanoresponsive and aggregation-induced emissive (AIE) luminogen triaminoguanidine-diethylaminophenol (LH3 ) conjugate from simple precursors triaminoguanidine hydrochloride and 4-(N,N-diethylamino)salicylaldehyde. Solvent-dependent dual emission in nonpolar to polar protic solvents implies the presence of ICT-coupled ESIPT features in the excited state. Aggregation-enhanced emissive feature of LH3 was established in the CH3CN/water mixture. Furthermore, this compound exhibits mechanochromic fluorescence behavior upon external grinding. Fluorescence microscopy images of pristine, crystal, and crushed crystals confirm the naked-eye mechanoresponsive characteristics of LH3 . In addition, LH3 selectively sensed a Cu2+ ion through a colorimetric and fluorescence "turn-off" route, and subsequently, the LH3 -Cu2+ ensemble could act as a selective and sensitive sensor for S2- in a "turn-on" fluorescence manner via a metal displacement approach. Reversible "turn-off-turn-on" features of LH3 with Cu2+/S2- ions were efficiently demonstrated to construct the IMPLICATION logic gate function. The Cu2+/S2--responsive sensing behavior of LH3 was established in the paper strip experiment also, which can easily be characterized by the naked eye under daylight as well as a UV lamp (λ = 365 nm).

A persistent luminescence-based label-free probe for the ultrasensitive detection of hemoglobin in human serum

Hemoglobin (Hb) plays an important role in oxygen carriage for mammals, which is also a typical biomarker for certain diseases. Although numerous methods had been developed for the detection of Hb in red blood cells, analytical technology for the monitoring of low-abundance Hb in serum or plasma is still a challenge. Herein, persistent luminescence nanoparticles (PLNPs) with strong near-infrared (NIR) emission character behaving as a label-free probe for the highly sensitive and selective detection of Hb were developed. Further studies revealed that the sensing mechanism should be attributed to the Hb-induced dynamic quenching process. Moreover, the nanoprobe showed high selectivity to Hb against the common existing substances in human serum and a linear response to Hb ranging from 1 to 50 nM with an extremely high limit of detection (LOD) of 0.13 nM. Finally, applicability of the proposed probe for the detection of Hb in human serum samples was validated.

Turning solid into gel for high-efficient persistent luminescence-sensitized photodynamic therapy

Bioavailable persistent luminescence material is an ideal internal light source for long-term photodynamic therapy, but inevitably suffers from low utilization efficiency and weak persistent luminescence due to corrosion and screening processes. Herein, we show a facile and smart "turning solid into gel" strategy to fabricate persistent luminescence hydrogel for high-efficient persistent luminescence-sensitized photodynamic therapy. The homogeneous persistent luminescence hydrogel was synthesized via dispersing high-temperature calcined persistent luminescence material without corrosion and screening into a biocompatible alginate-Ca²⁺ hydrogel. The simple synthesis strategy allows 100% of utilization efficiency and intact persistent luminescence of persistent luminescence material. The persistent luminescence hydrogel possesses favorable biocompatibility, bright persistent luminescence, red light renewability, good syringeability, and strong fixing ability in tumors. The persistent luminescence hydrogel can be easily injected in vivo as a powerful localized light source for superior persistent luminescence-sensitized photodynamic therapy of tumors. The "turning solid into gel" strategy enables taking full advantages of persistent luminescence for biological applications, and shows great potential in utilizing diverse theranostic agents regardless of hydrophilicity and hydrophobicity.

Cell-Penetrating Peptide-Functionalized Persistent Luminescence Nanoparticles for Tracking J774A.1 Macrophages Homing to Inflamed Tissues

Recruitment of leukocytes exhibiting arguable and ambiguous processes is involved in the inflammatory response, a specific reaction of organisms to tissue damage. Tracking leukocytes is of great importance for understanding the recruitment of leukocytes. Here, we report the fabrication of carboxyl silane and TAT cell-penetrating peptide-functionalized near-infrared-emitting persistent luminescence nanoparticles (PLNP-TAT) with deep tissue penetration in bioimaging for autofluorescence-free tracking of J774A.1 macrophages homing to inflamed tissues. The PLNP-TAT enables effective labeling of the J774A.1 macrophages and the tracking of the migration of cells to the simulated endothelial inflammatory microenvironment in vitro. Moreover, the PLNP-TAT also allows the tracking of J774A.1 macrophages homing to inflamed tissues in vivo under discontinuous illumination with a red light-emitting diode light. The PLNP-TAT allows in vivo tracking of leukocytes without the need for conventional continuous excitation and offers great potential in cell-tracking and diagnostic applications without the autofluorescence background and thermal damages brought about by continuous excitation.

Crucial Breakthrough of Functional Persistent Luminescence Materials for Biomedical and Information Technological Applications

Persistent luminescence is a phenomenon in which luminescence is maintained for minutes to hours without an excitation source. Owing to their unique optical properties, various kinds of persistent luminescence materials (PLMs) have been developed and widely employed in numerous areas, such as bioimaging, phototherapy, data-storage, and security technologies. Due to the complete separation of two processes, -excitation and emission-, minimal tissue absorption, and negligible autofluorescence can be obtained during biomedical fluorescence imaging using PLMs. Rechargeable PLMs with super long afterglow life provide novel approaches for long-term phototherapy. Moreover, owing to the exclusion of external excitation and the optical rechargeable features, multicolor PLMs, which have higher decoding signal-to-noise ratios and high storage capability, exhibited an enormous application potential in information technology. Therefore, PLMs have significantly promoted the application of optics in the fields of multimodal bioimaging, theranostics, and information technology. In this review, we focus on the recently developed PLMs, including inorganic, organic and inorganic-organic hybrid PLMs to demonstrate their superior applications potential in biomedicine and information technology.

A generic approach towards afterglow luminescent nanoparticles for ultrasensitive in vivo imaging

Afterglow imaging with long-lasting luminescence after cessation of light excitation provides opportunities for ultrasensitive molecular imaging; however, the lack of biologically compatible afterglow agents has impeded exploitation in clinical settings. This study presents a generic approach to transforming ordinary optical agents (including fluorescent polymers, dyes, and inorganic semiconductors) into afterglow luminescent nanoparticles (ALNPs). This approach integrates a cascade photoreaction into a single-particle entity, enabling ALNPs to chemically store photoenergy and spontaneously decay it in an energy-relay process. Not only can the afterglow profiles of ALNPs be finetuned to afford emission from visible to near-infrared (NIR) region, but also their intensities can be predicted by a mathematical model. The representative NIR ALNPs permit rapid detection of tumors in living mice with a signal-to-background ratio that is more than three orders of magnitude higher than that of NIR fluorescence. The biodegradability of the ALNPs further heightens their potential for ultrasensitive in vivo imaging.

Afterglow luminescence is used to reduce background noise and increase sensitivity; however, biocompatible afterglow materials are limited. Here, the authors report on an approach to turn standard optical agents into afterglow nanoparticles and demonstrate the application in tumour imagining in vivo.

The Bioavailability, Biodistribution, and Toxic Effects of Silica-Coated Upconversion Nanoparticles in vivo

Lanthanide-doped upconversion nanoparticles can convert long wavelength excitation radiation to short wavelength emission. They have great potential in biomedical applications, such as bioimaging, biodetection, drug delivery, and theranostics. However, there is little information available on their bioavailability and biological effects after oral administration. In this study, we systematically investigated the bioavailability, biodistribution, and toxicity of silica-coated upconversion nanoparticles administrated by gavage. Our results demonstrate that these nanoparticles can permeate intestinal barrier and enter blood circulation by microstructure observation of Peyer's patch in the intestine. Comparing the bioavailability and the biodistribution of silica-coated upconversion nanoparticles with oral and intravenous administration routes, we found that the bioavailability and biodistribution are particularly dependent on the administration routes. After consecutive gavage for 14 days, the body weight, pathology, Zn and Cu level, serum biochemical analysis, oxidative stress, and inflammatory cytokines were studied to further evaluate the potential toxicity of the silica-coated upconversion nanoparticles. The results suggest that these nanoparticles do not show overt toxicity in mice even at a high dose of 100 mg/kg body weight.

Photothermal therapy and photoacoustic imaging via nanotheranostics in fighting cancer

The nonradiative conversion of light energy into heat (photothermal therapy, PTT) or sound energy (photoacoustic imaging, PAI) has been intensively investigated for the treatment and diagnosis of cancer, respectively. By taking advantage of nanocarriers, both imaging and therapeutic functions together with enhanced tumour accumulation have been thoroughly studied to improve the pre-clinical efficiency of PAI and PTT. In this review, we first summarize the development of inorganic and organic nano photothermal transduction agents (PTAs) and strategies for improving the PTT outcomes, including applying appropriate laser dosage, guiding the treatment via imaging techniques, developing PTAs with absorption in the second NIR window, increasing photothermal conversion efficiency (PCE), and also increasing the accumulation of PTAs in tumours. Second, we introduce the advantages of combining PTT with other therapies in cancer treatment. Third, the emerging applications of PAI in cancer-related research are exemplified. Finally, the perspectives and challenges of PTT and PAI for combating cancer, especially regarding their clinical translation, are discussed. We believe that PTT and PAI having noteworthy features would become promising next-generation non-invasive cancer theranostic techniques and improve our ability to combat cancers.

A ratiometric fluorescent nanoprobe based on naphthalimide derivative-functionalized carbon dots for imaging lysosomal formaldehyde in HeLa cells

Endogenous formaldehyde (FA) exists in many living cells and in inhomogeneous distribution in organelles. In particular, lysosomes play significant roles in FA generation and the biofunction of living cells. Herein, we developed a new ratiometric fluorescent nanoprobe, based on naphthalimide derivative (ND)-functionalized carbon dots (CDs), for monitoring endogenous FA in lysosomes. The fluorescence intensity (F535) of green-emitting ND at 535 nm serves as the response signal and the fluorescence intensity (F414) of blue-emitting CDs at 414 nm acts as the reference signal. The fluorescence intensity ratio (F535/F414) of the CD-ND probe is linearly correlated with FA concentration within the range of 1-40 μM in aqueous solution, and the detection limit (3σ/slope) is estimated to be 0.34 μM. As for practical application, this nanoprobe is utilized for the ratiometric fluorescence imaging of FA in live cells. Remarkably, this nanoprobe can specifically target and stain the lysosomes and detect exogenous and endogenous FA in HeLa cells. The new FA probe shows a superior lysosomal targeting ability with a Pearson's coefficient of 0.93, which is attributed to the macromolecular size and basic amine group functionalized surface of CD-ND.

Chromium-Doped Zinc Gallogermanate@Zeolitic Imidazolate Framework-8: A Multifunctional Nanoplatform for Rechargeable In Vivo Persistent Luminescence Imaging and pH-Responsive Drug Release

Multifunctional theranostic nanoplatforms greatly improve the accuracy and effectiveness in tumor treatments. Much effort has been made in developing advanced optical imaging-based tumor theranostic nanoplatforms. However, autofluorescence and irradiation damage of the conventional fluorescence imaging technologies as well as unsatisfied curative effects of the nanoplatforms remain great challenges against their wide applications. Herein, we constructed a novel core-shell multifunctional nanoplatform, that is, chromium-doped zinc gallogermanate (ZGGO) near-infrared (NIR) persistent luminescent nanoparticles (PLNPs) as a core and zeolitic imidazolate framework-8 (ZIF-8) as a shell (namely ZGGO@ZIF-8). The ZGGO@ZIF-8 nanoplatform possessed dual functionalities of the autofluorescence-free NIR PersL imaging as well as the pH-responsive drug delivery, thus it has high potential in tumor theranostics. Notably, the loading content of doxorubicin (DOX) in ZGGO@ZIF-8 (LC = 93.2%) was quite high, and the drug release of DOX-loaded ZGGO@ZIF-8 was accelerated in an acidic microenvironment such as tumor cells. The ZGGO@ZIF-8 opens up a new material system in the combination of PLNPs with metal-organic frameworks and may offer new opportunities for the development of advanced multifunctional nanoplatforms for tumor theranostics, chemical sensing, and optical information storage.

Near-Infrared Afterglow Luminescent Aggregation-Induced Emission Dots with Ultrahigh Tumor-to-Liver Signal Ratio for Promoted Image-Guided Cancer Surgery

Afterglow imaging through the collection of persistent luminescence after the stopping of light excitation holds enormous promise for advanced biomedical uses. However, efficient near-infrared (NIR)-emitting afterglow luminescent materials and probes (particularly the organic and polymeric ones) are still very limited, and their in-depth biomedical applications such as precise image-guided cancer surgery are rarely reported. Here, we design and synthesize a NIR afterglow luminescent nanoparticle with aggregation-induced emission (AIE) characteristics (named AGL AIE dots). It is demonstrated that the AGL AIE dots emit rather-high NIR afterglow luminescence persisting over 10 days after the stopping of a single excitation through a series of processes occurring in the AIE dots, including singlet oxygen production by AIE luminogens (AIEgens), Schaap's dioxetane formation, chemiexcitation by dioxetane decomposition, and energy transfer to NIR-emitting AIEgens. The animal studies reveal that the AGL AIE dots have the innate property of fast afterglow signal quenching in normal tissues, including the liver, spleen, and kidney. After the intravenous injection of AGL AIE dots into peritoneal carcinomatosis bearing mice, the tumor-to-liver ratio of afterglow imaging is nearly 100-fold larger than that for fluorescence imaging. The ultrahigh tumor-to-liver signal ratio, together with low afterglow background noise, enables AGL AIE dots to give excellent performance in precise image-guided cancer surgery.

Persistent luminescent multifunctional drug delivery nano-platform based on nanomaterial ZnGa2O4:Cr3+,Sn4+ for imaging-guided cancer chemotherapy

A novel tumor-targeting and release-controllable drug delivery nano-platform with persistent luminescence was constructed for imaging-guided cancer chemotherapy based on the ZnGa₂O₄:Cr³⁺,Sn⁴⁺ (ZGCS) nanoparticles.

A review on graphene-based nanocomposites for electrochemical and fluorescent biosensors

Biosensors with high sensitivity, selectivity and a low limit of detection, reaching nano/picomolar concentrations of biomolecules, are important to the medical sciences and healthcare industry for evaluating physiological and metabolic parameters.

Construction of molecularly imprinted nanoplatforms with persistent luminescence for the in vitro specific adsorption and in vivo targeted regulation of food-borne biotoxins

Molecularly imprinted nanoplatforms with super-long afterglow persistent luminescence showed in vitro specific adsorption and in vivo targeted regulation ability of food-borne biotoxins by autofluorescence-free nanoimaging.

A multifunctional persistent luminescent nanoprobe for imaging guided dual-stimulus responsive and triple-synergistic therapy of drug resistant tumor cells

A novel multifunctional persistent luminescent nanoprobe was fabricated for imaging guided dual-stimulus responsive and triple-synergistic therapy for multiple drug resistant tumor cells.

Imaging and therapeutic applications of persistent luminescence nanomaterials

The development of probes for biomolecular imaging and diagnostics is a very active research area. Among the different imaging modalities, optics emerged since it is a noninvasive and cheap imaging technique allowing real time imaging. In vitro, this technique is very useful however in vivo, fluorescence suffers from low signal-to-noise ratio due to tissue autofluorescence under constant excitation. To address this limitation, novel types of optical nanoprobes are actually being developed and among them, persistent luminescence nanoparticles (PLNPs), with long lasting near-infrared (NIR) luminescence capability, allows doing optical imaging without constant excitation and so without autofluorescence. This review will begin by introducing the physical phenomenon associated to the long luminescence decay of such nanoprobes, from minutes to hours after ceasing the excitation. Then we will show how this property can be used to develop in vivo imaging probes and also more recently nanotheranostic agents. Finally, preliminary data on their biocompatibility will be mentioned and we will conclude by envisioning on the future applications and improvements of such nanomaterials.

Hemocompatibility investigation and improvement of near-infrared persistent luminescent nanoparticle ZnGa2O4:Cr3+ by surface PEGylation

ZnGa₂O₄:Cr³⁺ hemocompatibility was systematically investigated from the aspects of hemolysis, erythrocyte morphology, coagulation and complement system activation, and greatly improved by surface PEGylation.

Dual-functional persistent luminescent nanoparticles with enhanced persistent luminescence and photocatalytic activity

NIR persistent luminescence and photocatalytic activity of the PLNPs were significantly and simultaneously improved via additional doping of Bi³⁺.

EDTA etching: a simple way for regulating the traps, size and aqueous-dispersibility of Cr3+-doped zinc gallate

EDTA etching, the first strategy that simply generates deep traps while reducing the size and improving the aqueous-dispersibility, is presented.

Traps, size and aqueous-dispersibility are the most important parameters that affect the features and applications of persistent luminescent nanoparticles (PLNPs). However, simultaneous controlling of these parameters is rather difficult and has not been reported yet. We present the first exploration on adjusting the traps, size and aqueous-dispersibility of PLNPs via simple ethylenediaminetetraacetate (EDTA) etching. Cr_0.004³⁺:ZnGa₂O₄ (ZGO) was used as the PLNP model. EDTA etching of the sintered ZGO results in effective reduction of the size and great improvement in the aqueous-dispersibility. In addition, EDTA etching alters the density of mediate traps and generates new deep traps, thus achieving the massive production of (ultra)small ZGO–EDTA with fine aqueous-dispersibility, suitable mediate/deep traps and superlong bright afterglows (51 days). As EDTA can interact with most metals, this simple EDTA etching strategy is prospectively amenable to other PLNPs, and the resulting PLNPs–EDTA have wide applications in both biological field and information storage.

Afterglow Resonance Energy Transfer Inhibition for Fibroblast Activation Protein-α Assay

Traditional photoluminescence resonance energy transfer (PRET)-based sensors are widely applied, but still suffer from the severe background interference from in situ excitation. The afterglow nature of the persistent luminescence nanoparticles (PLNPs) allows optosensing after the stoppage of in situ illumination, and thus subtly overcomes that interference. We proposed a simple strategy for functionalizing PLNPs for bioanalytical applications and the new afterglow resonance energy transfer (ARET)-based assay for quantitative determination and imaging of fibroblast activation protein-alpha (FAPα) in live cells using Au-decorated Cr³⁺_0.004:ZnGa₂O₄ as donor and Cy5.5-KGPNQC-SH as acceptor. The ARET between the donor and acceptor quenches the afterglow of the donor, and the cleavage of peptide KGPNQC by FAPα inhibits the ARET and restores the afterglow of the donor. The ARET-based assay of FAPα, with the linear range of 0.1-2.0 mg·L^-1 (1.2-22.9 nM), LOD of 11 μg·L^-1 (115 pM), and RSD of 3.9% (for 0.5 mg·L^-1 FAPα, n = 5), displays higher sensitivity, lower limit of detection (LOD), and better anti-interference capability than the corresponding PRET-based assay. Besides, the ARET-based sensors are lighted up by the FAPα-positive U87MG and MDA-MB-435 cells, but kept in the dark when incubated in the FAPα-negative AD293 cells. The proposed ARET-based sensor can detect FAPα of U87MG and MDA-MB-435 living cells in human serum with the spiked recoveries of 95.6-103%. Our data demonstrated a simple and effective strategy for bridging PLNPs to bioanalytical applications, and an attractive ARET assay of FAPα.