Biological Window Research Articles

Nd3+-doped Bi2SiO5 nanospheres for stable ratiometric optical thermometry in the first biological window

The development of nanoscale thermal sensors with high sensitivity to ambient temperature change is crucial to monitor the biological processes from living forms. In this work, we report on the Nd3+-doped Bi2SiO5 nanospheres acting as nanothermometers in the first biological window. Uniform Bi2SiO5:Nd3+ nanospheres are synthesized by the diffusion and reaction between the bismuth-based precursor core and the silica shell. The as-synthesized Bi2SiO5:Nd3+ nanospheres can be effectively excited by 808 nm near infrared laser diode and emit in the near infrared range due to the characteristic transitions of Nd3+. The luminescence intensity ratio of two spectrally separated emission peaks located at 867 nm (P1) and 898 nm (P2) from the 4F3/2 → 4I9/2 transition of Nd3+ is found to be noticeably temperature-dependent, which can be used for luminescent ratiometric thermal sensing. The results reveal that the yielded Bi2SiO5:Nd3+ nanothermometers possess suitable values of relative sensitivity, temperature uncertainty and repeatability within the physiologically relevant temperature range. These Nd3+-doped Bi2SiO5 nanospheres emerge as very promising temperature probes for luminescence nanothermometry.

Multipath optical thermometry realized in CaSc2O4: Yb3+/Er3+ with high sensitivity and superior resolution

AbstractDesign and fabrication of contactless optical thermometer with rapid and accurate performance has become a research hotspot in recent years. Herein, CaSc2O4: Yb3+/Er3+ is employed as the intermediary for temperature sensing under the excitation of 980 nm, which is proven to afford an ultra‐sensitive and high‐resolution optical thermometry in multiple ways based on the fluorescence intensity ratio (FIR) technology. The optimal thermal sensing behaviors are realized by the FIR of Er3+:2H11/2 → 4I15/2 to 4S3/2 → 4I15/2 transition, which has a relative sensitivity of 1184/T2 and a minimal resolution of 0.03 K along with a maximal absolute error of 0.96 K. Besides that, the FIR between the thermally coupled Stark sublevels of Er3+:4F9/2 manifold (FIRR) as well as that of Er3+: 4I13/2 manifold (FIRN) can also provide excellent optical thermometry. The relative sensitivity of FIRR‐based and FIRN‐based optical thermometers are calculated to be 402/T2 and 366/T2, respectively, with a same minimal resolution of 0.09 K, which possess the potential to be used for biomedicine due to the inherent advantage of their operating wavelengths located in the biological window. The results demonstrate that CaSc2O4: Yb3+/Er3+ is a promising candidate for temperature sensing with multipath, high sensitivity, and superior resolution.

Multifunctional up/down-conversion luminescence of core/shell nanocomposite for self-monitored heating and fluorescence imaging

The simultaneous realization of real-time thermal sensing at physiological temperature range and fluorescence imaging during photothermal therapy (PTT) via single-component biocompatible nanocomposite could furthest avoid collateral damage and enhance phototherapeutic effect, which, up to now, is of great interest and still in a formidable challenge. Under near-infrared (NIR) light irradiation, Nd3+-doped nanoparticles (NPs) have emerged as candidates with outstanding properties such as down-conversion emissions in biological window (BW) and capable of light-to-heat conversion. However, these two properties associated with Nd3+ doping concentrations induce opposite changing trend and difficult to combine within one single nanocomposite. In this work, for breaking through the obstacles, core/shell NaLuF4:1%Nd@NaLuF4@NaLuF4:15%Yb,3%Er@NaLuF4:15%Yb@NaLuF4:85%Nd 808 nm light-triggered co-enhancement up/down-conversion luminescence (UCL/DCL) nanocomposite was purposely designed with efficient heating, thermal sensing and fluorescence imaging concurrently. The core emits high quantum yield (QY) DCL in BW while the outermost layer could convert the absorbed photon into thermal energy and also transfer a fraction of energy inwards to internal layer with exciting the UCL (Nd→Yb→Er) for thermal sensing via thermally coupled levels 2H11/2/4S3/2 of Er using the fluorescence intensity ratio (FIR) method. The simultaneously enhanced UCL/DCL and thermal effect in the engineered nanocomposite are satisfactorily realized due to suppressing the interionic quenching owing to the inert two layers NaLuF4 and NaLuF4:15%Yb. Such smart designed nanocomposite has potential application on PTT-based noninvasive cancer therapy.

ZnxMn1–XFe2O4@SiO2:zNd3+ Core–Shell Nanoparticles for Low-Field Magnetic Hyperthermia and Enhanced Photothermal Therapy with the Potential for Nanothermometry

Multifunctional magnetic nanoparticles (NPs) that can generate and monitor heat (in real-time) during thermal therapy are a major challenge in nanomedicine. Here, we report a trimodal system combining magnetic NP hyperthermia (MNH), photothermal therapy (PTT), and luminescent nanothermometry (LNT) properties with an all-in-one nanoplatform. Zinc–manganese ferrite NPs were optimized focusing on low field MNH, where Zn0.3Mn0.7Fe2O4 proved as a competitive nanoheater at clinically relevant conditions. Further, SiO2-coated Zn0.3Mn0.7Fe2O4/cit. with embedded Nd3+ (Zn0.3Mn0.7Fe2O4@SiO2:Nd) NPs were prepared for the potency of multifunctionality as LNT and enhanced PTT. Photothermal conversion efficiency (PCE), at low laser power conditions (1.5 W/cm2), varied from 17% for silica-coated magnetic NPs to 24% after embedding 1 mmol of Nd3+ in the SiO2 matrix. Increasing laser power to 11.8 W/cm2 decreased the PCE of Zn0.3Mn0.7Fe2O4@SiO2:Nd to 9%, but this deleterious effect was reduced significantly by the shell engineering strategy, that is, increasing the shell thickness Zn0.3Mn0.7Fe2O4@ SiO2@SiO2:Nd that maintained a PCE value of 18%. Additionally, as a potential nanothermometer, with excitation around 800 nm and emission at the second biological window, the thermal sensitivity of the system was found to be ∼1.1 % K–1 at 300 K (27 °C), ∼ 1.4% K–1 at 316 K (43 °C), and ∼1.5% K–1 at 319 K (46 °C). Additionally, simultaneous heating effects due to magnetic fields and photoexcitation (808 nm) on Zn0.3Mn0.7Fe2O4@SiO2@SiO2:Nd show synergy effects between MNH and PTT. Because of the high hemolytic activity toward the red blood cells due to the SiO2 layer, we also demonstrate that surface coating the nanocarrier with bovine serum albumin drastically reduced the hemolytic activity providing a capability for future in vivo applications with this multifunctional nanocarrier.

Frontispiece: Organic semiconducting nanomaterials‐assisted phototheranostics in near‐infrared‐II biological window (View 1/2021)

In article number 20200070, Quli Fan and his colleagues have displayed that several “spheres” with different characteristics float above the sea that dissolved lots of organic semiconducting molecules highlighted by the light beam from the lighthouse, symbolizing that nanomaterials constructed from organic semiconducting molecules have the versatility in biomedical diagnostics (fluorescence imaging and photoacoustic imaging) and therapy (photothermal therapy, chemotherapy, and surgery) assisted by light irradiation.

Engineering Red-Enhanced and Biocompatible Upconversion Nanoparticles

The exceptional optical properties of lanthanide-doped upconversion nanoparticles (UCNPs) make them among the best fluorescent markers for many promising bioapplications. To fully utilize the unique advantages of the UCNPs for bioapplications, recent significant efforts have been put into improving the brightness of small UCNPs crystals by optimizing dopant concentrations and utilizing the addition of inert shells to avoid surface quenching effects. In this work, we engineered bright and small size upconversion nanoparticles in a core–shell–shell (CSS) structure. The emission of the synthesized CSS UCNPs is enhanced in the biological transparency window under biocompatible excitation wavelength by optimizing dopant ion concentrations. We also investigated the biosafety of the synthesized CSS UCNP particles in living cell models to ensure bright and non-toxic fluorescent probes for promising bioapplications.

Recent Progress of Near-Infrared Fluorescence in vivo Bioimaging in the Second and Third Biological Window.

Near-infrared (NIR) fluorescence bioimaging using above to 1000 nm wavelength region is a promising analytical method on visualizing deep tissues. As compared to the short-wavelength ultraviolet (UV: < 400 nm) or visible (VIS: 400 - 700 nm) region, which results in an extremely low absorption or scattering of biomolecules and water in the body, NIR light passes through the tissues. Various fluorescent probes that emit NIR emission in the second (1100 - 1400 nm) or third (1550 - 1800 nm) biological windows have been developed and used for NIR in vivo imaging. Single-walled carbon nanotubes (SWCNTs), quantum dots (QDs), rare-earth doped ceramic nanoparticles (RED-CNPs), and organic dye-based probes have been proposed by many researchers, and are used to successfully visualize the bloodstream, organs, and disease-affected regions, such as cancer. NIR imaging in the second and third biological windows is an effective analytical method on visualizing deep tissues.

Lanthanide doped luminescence nanothermometers in the biological windows: strategies and applications.

The development of lanthanide-doped non-contact luminescent nanothermometers with accuracy, efficiency and fast diagnostic tools attributed to their versatility, stability and narrow emission band profiles has spurred the replacement of conventional contact thermal probes. The application of lanthanide-doped materials as temperature nanosensors, excited by ultraviolet, visible or near infrared light, and the generation of emissions lying in the biological window regions, I-BW (650 nm-950 nm), II-BW (1000 nm-1350 nm), III-BW (1400 nm-2000 nm) and IV-BW (centered at 2200 nm), are notably growing due to the advantages they present, including reduced phototoxicity and photobleaching, better image contrast and deeper penetration depths into biological tissues. Here, the different mechanisms used in lanthanide ion-doped nanomaterials to sense temperature in these biological windows for biomedical and other applications are summarized, focusing on factors that affect their thermal sensitivity, and consequently their temperature resolution. Comparing the thermometric performance of these nanomaterials in each biological window, we identified the strategies that allow boosting of their sensing properties.

Focus on photonics, spectroscopy, and spectrometry

Focus on photonics, spectroscopy, and spectrometry

Synthesis and characterisation of N-gene targeted NIR-II fluorescent probe for selective localisation of SARS-CoV-2.

Tracking the viral progression of SARS-CoV-2 in COVID-19 infected body tissues is an emerging need of the current pandemic. Imaging at near infrared second biological window (NIR-II) offers striking benefits over the other technologies to explore deep-tissue information. Here we design, synthesise and characterise a molecular probe that selectively targets the N-gene of SARS-CoV-2. Highly specific antisense oligonucleotides (ASOs) were conjugated to lead sulfide quantum dots using a UV-triggered thiol-ene click chemistry for the recognition of viral RNA. Our ex vivo imaging studies demonstrated that the probe exhibits aggregation induced NIR-II emission only in presence of SARS-CoV-2 RNA which can be attributed to the efficient hybridisation of the ASOs with their target RNA strands.

Controlling the pyridinium-zwitterionic ligand ratio on atomically precise gold nanoclusters allowing for eradicating Gram-positive drug-resistant bacteria and retaining biocompatibility.

Infections caused by multidrug-resistant (MDR) bacteria are an increasing global healthcare concern. In this study, we developed a dual-ligand-functionalised Au25(SR1)x(SR2)18−x-type gold nanocluster and determined its antibacterial activity against MDR bacterial strains. The pyridinium ligand (SR1) provided bactericidal potency and the zwitterionic ligand (SR2) enhanced the stability and biocompatibility. By optimising the ligand ratio, our gold nanocluster could effectively kill MDR Gram-positive bacteria via multiple antibacterial actions, including inducing bacterial aggregation, disrupting bacterial membrane integrity and potential, and generating reactive oxygen species. Moreover, combining the optimised gold nanocluster with common antibiotics could significantly enhance the antibacterial activity against MDR bacteria both in in vitro and animal models of skin infections. Furthermore, the fluorescence of the gold nanocluster at the second near-infrared (NIR-II) biological window allowed for the monitoring of its biodistribution and body clearance, which confirmed that the gold nanoclusters had good renal clearance and biocompatibility. This study provides a new strategy to combat the MDR challenge using multifunctional gold nanomaterials.

Full-spectrum responsive WO3−x@HA nanotheranostics for NIR-II photoacoustic imaging-guided PTT/PDT/CDT synergistic therapy

A WO3−x-based nanotheranostic has been successfully fabricated for photoacoustic imaging-guided synergistic tumor targeting therapy in the second near-infrared (NIR-II) biological window.

Molecular crystalline capsules that release their contents by light.

Here, we present single crystalline capsules of a photoresponsive molecule produced by simple recrystallization from organic solutions without direct human processing. During the crystal growth process, a movie was taken of the capsule taking in the organic solution. The capsules responded rapidly (<1 s) to the UV light stimuli and released the captured solution or solute. In principle, they can take in any substance dissolved in organic solvents, and their size can be controlled. Moreover, the capsule can be broken by multi-photon excitation using a near-infrared laser within the biological window. Furthermore, because the molecular packing in the crystal is unidirectional, the response can be controlled by the polarization of the light. This study shows the new potential of photoresponsive molecules.

Gold nanoclusters performing as contrast agents for non-invasive imaging of tissue-like phantoms via two-photon excited fluorescence lifetime imaging.

Recently, gold nanoclusters (AuNCs) have received considerable scientific interest due to their ability to generate intrinsic photoluminescence (PL), making them suitable for a wide range of applications, such as sensing, biolabeling and bioimaging. Fluorescence lifetime imaging microscopy (FLIM) is an extremely promising technique when it comes to tissue imaging, especially once combined with near-infrared two-photon excitation (TPE) due to deep tissue penetration and improved spatial resolution. In this paper, we carried out an innovative study on the ability of bovine serum albumin stabilized gold nanoclusters (BSA-AuNCs) to perform as reliable label-free contrast agents for the visualization of tissue-like agarose phantoms via TPE-FLIM. We prove that BSA-AuNCs exhibit uniform and reproducible TPE PL in the first biological window, when embedded in phantoms, under 820 nm excitation provided by a Ti:Sapphire pulsed laser. The two-photon origin of the emission signal inside the phantom is demonstrated by the quadratic dependence of the PL intensity on the excitation power. Moreover, we focused on the evaluation of BSA-AuNCs' potential as contrast agents at different concentrations inside phantoms, simulating an ex vivo environment, at three NIR excitation wavelengths, in view of defining the optimal experimental conditions for future real-tissue imaging assays. The present study aims at translating our previous results on the successful performance of BSA-AuNCs as contrast agents for in vitro FLIM imaging, using visible light, towards non-invasive ex vivo NIR imaging applications. Besides the advantageous use of the combined techniques TPE-FLIM, the novelty of our work consists of demonstrating for the first time the capacity of BSA-AuNCs to perform as bright contrast agents inside cancer-tissue mimicking phantoms. We prove that BSA-AuNCs show great promise as fluorescent contrast agents for TPE-FLIM towards image-assisted tumor surgery.

DNA nanolantern as biocompatible drug carrier for simple preparation of a porphyrin/G-quadruplex nanocomposite photosensitizer with high photodynamic efficacy

DNA nanolanterns, a pure DNA assembly, are used as biocompatible drug carriers to prepare a nanocomposite photosensitizer for highly efficient photodynamic therapy in the biological transparent window.

Bi19S27I3 nanorods: a new candidate for photothermal therapy in the first and second biological near-infrared windows.

Near-infrared (NIR) light-induced photothermal cancer therapy using nanomaterials as photothermal agents has attracted considerable research interest over the past few years. As the key factor in photothermal therapy systems, a variety of photothermal agents have been developed. However, the exploration of novel photothermal therapy nanoplatforms with high NIR absorption remains a significant challenge, especially those working in both NIR-I and NIR-II windows. In this work, Bi19S27I3 nanorods with remarkably high absorption covering the whole visible light to the entire NIR-I and NIR-II regions have been successfully prepared through a facile solvothermal approach. The as-synthesized Bi19S27I3 nanorods have a high photothermal conversion efficiency of 42.7% at 808 nm (NIR-I) and 41.5% at 1064 nm (NIR-II), making them a promising candidate for photothermal therapy. In vitro cell viability assay reveals that the Bi19S27I3 sample has good biocompatibility and exhibits significant cell-killing effect under NIR irradiation. In vivo anti-tumor experiments demonstrate that the tumor growth can be effectively inhibited by fatal hyperthermia ablation mediated by Bi19S27I3 nanorods under the irradiation of an 808 nm or 1064 nm laser. Therefore, this study should be primarily beneficial for the development of new materials for NIR photothermal therapy applications.

Antibody-functionalized theranostic protein nanoparticles for the synergistic deep red fluorescence imaging and multimodal therapy of ovarian cancer.

Among women, ovarian cancer is the fifth most frequent type of cancer, and despite benefiting from current standard treatment plans, 90% of patients relapse in the subsequent 18 months and, eventually, perish. As a result, via embracing nanotechnological advancements in the field of medical science, researchers working in the areas of cancer therapy and imaging are looking for the next breakthrough treatment strategy to ensure lower cancer recurrence rates and improved outcomes for patients. Herein, we design a novel phototheranostic agent with optical features in the biological window of the electromagnetic spectrum via encapsulating a newly synthesized phthalocyanine dye within biocompatible protein nanoparticles, allowing the targeted fluorescence imaging and synergistic dual therapy of ovarian cancer. The nanosized agent displays great biocompatibility and enhanced aqueous biostability and photothermal activity, as well as high reactive-oxygen-species generation efficiency. To achieve the active targeting of the desired malignant tissue and suppress the rapid clearance of the photosensitive agent from the peritoneal cavity, the nanoparticles are biofunctionalized with an anti-folate receptor antibody. A2780 ovarian cancer cells are employed to confirm the improved targeting capabilities and the in vitro cytotoxic efficiency of the theranostic nanoparticles after exposure to a 660 nm LED lamp; upon measurement via MTT and flow cytometry assays, a significant 95% decrease in the total number of viable cells is seen. Additionally, the therapeutic performance of our newly designed nanoparticles was evaluated in vivo, via real-time thermal monitoring and histopathological assays, upon the irradiation of tumour-bearing mice with a 660 nm LED lamp (0.05 W cm-2). Foremost, separately from steady-state fluorescence imaging, we found that, via utilizing FLIM investigations, the differences in fluorescence lifetimes of antibody biofunctionalized and non-functionalized nanoparticles can be correlated to different intracellular localization and internalization pathways of the fluorescent agent, which is relevant for the development of a cutting-edge method for the detection of cancer cells that overexpress folate receptors at their surfaces.

Super Bright Red Upconversion in NaErF4:0.5%Tm@NaYF4:20%Yb Nanoparticles for Anti-counterfeit and Bioimaging Applications.

Nanocrystals having single-band red emission under near-infrared (NIR) excitation through the upconversion process offer great advantages in terms of enhanced cellular imaging in in vitro and in vivo experiments in the biological window (600-900 nm), as a security ink, in photothermal therapy (PTT), in photodynamic therapy (PDT), and so forth but are challenging for materials scientists. In this work, we report for the first time the preparation of a super bright red emitter at 655 nm from monodispersed NaErF4:0.5%Tm@NaYF4:20%Yb nanocrystals (core@active shell). This phosphor exhibits 35 times stronger photoluminescence as compared to NaErF4:0.5%Tm@NaYF4 (core@inactive shell). Here, an Er3+-enriched host matrix works simultaneously as an activator and a sensitizer under NIR excitation. Upconversion red emission at 655 nm arises due to the electronic transition of Er3+ via the involvement of a three-photon absorption (expected to be a two-photon absorption), which has been confirmed via a power-dependent luminescence study. Tm3+ ions incorporated into the core with the active shell act as trapping centers, which promote the red band emission via the back-energy transfer process. Moreover, the active shell containing Yb3+ ions efficiently transfers the energy to the Er3+-enriched core, which suppresses the nonradiative channel rate, and Tm3+ ions act as trapping centers, which reduce the luminescence quenching via reduction of energy migration to the surface of the host lattice. Also, we have shown the potential applications of these nanocrystals: cellular imaging through downconversion and upconversion processes and security ink.

Three-Photon Spectroscopy of Porphyrins.

Recent advances in laser technology have made three-photon (3P) microscopy a real possibility, raising interest in the phenomenon of 3P absorption (3PA). Understanding 3PA of organic chromophores is especially important in view of those imaging applications that rely on exogenous probes, whose optical properties can be manipulated and optimized. Here, we present measurements and theoretical analysis of the degenerate 3PA spectra of several phosphorescent metalloporphyrins, which are used in the construction of biological oxygen probes. The effective 3PA cross sections (σ(3)) of these porphyrins near 1700 nm, a new promising biological optical window, were found to be on the order of 1000 GM3 (1 GM3 = 10-83 cm6 s2), therefore being among the highest values reported to date for organic chromophores. To interpret our data, we developed a qualitative four-state model specific for porphyrins and used it in conjunction with quantitative analysis based on the time-dependent density functional theory (TDDFT)/a posteriori Tamm-Dancoff approximation (ATDA)/sum-over-states (SOS) formalism. The analysis revealed that B (Soret) state plays a key role in the enhancement of 3PA of porphyrins in the Q band region, while the low-lying two-photon (2P)-allowed gerade states interfere negatively and diminish the 3PA strength. This study features the first systematic examination of 3PA properties of porphyrins, suggesting ways to improve their performance and optimize them for imaging and other biomedical applications.

Functionalization with PEG/Angiopep-2 peptide to improve the delivery of gold nanoprisms to central nervous system: in vitro and in vivo studies

One of main drawbacks for the treatment of neurodegenerative pathologies is ensuring the delivery of therapeutic agents into the central nervous system (CNS). Nowadays, gold nanoprisms (GNPr) have become an emerging nanomaterial with a localized surface plasmon resonance in the biological window, showing applications in both detection and treatment of diseases. In this work, GNPr were functionalized with polyethylene glycol (PEG) and Angiopep-2 (Ang2) peptide to obtain a new highly stable nanomaterial and evaluate its toxicity and ability to cross the blood-brain barrier (BBB) in a zebrafish larvae model. The success in the functionalization was confirmed by a full characterization that showed the physicochemical changes at each step. In turn, the colloidal stability of GNPr-PEG-Ang2 in biologically relevant media also was demonstrated. The toxicity assays of GNPr-PEG-Ang2 performed on SH-SY5Y neuroblastoma cell line and on zebrafish larvae showed no effects both in vitro and in vivo. GNPr delivery to the CNS was studied in zebrafish larvae by immersion. We confirmed that functionalization with PEG-Ang2 improved the crossing through the BBB in this model compared with GNPr functionalized only with PEG. Notably, our nanomaterial was not detected in the CNS of zebrafish larvae 24 h after exposure that correlates with an adequate clearance of GNPr-PEG-Ang2 from the brain. This report is the first study of GNPr in the in vivo model of zebrafish larvae demonstrating that its functionalization with Ang2 allows the crossing of the BBB. Moreover, considering the stability achieved of the GNPr-PEG-Ang2 and the results of in vitro and in vivo studies, this work becomes a high contribution to the design of new nanomaterials with potential biomedical applications for CNS-related diseases.