Upconversion nanoparticles and their composite nanostructures for biomedical imaging and cancer therapy

Toward photophysical characteristics of triplet-triplet annihilation photon upconversion: a promising protocol from the perspective of optimally tuned range-separated hybrids

The photon upconversion (UC) process assisted by the triplet-triplet annihilation (TTA) mechanism has recently come into the spotlight. Given the rich collection of efforts in this area, theoretical explorations regarding TTA-UC are relatively limited and have proven to be challenging for its control in devices. In this contribution, the photophysical properties crucial for TTA-UC, such as triplet excited state energies and triplet-triplet energy transfer gaps of the essential ingredients involved in the process, namely sensitizers, annihilators and their pairs, have theoretically been investigated using optimally tuned range-separated hybrid functionals (OT-RSHs) and their screened exchange counterparts, OT-SRSHs. Taking a series of experimentally proven-to-work sensitizer/annihilator pairs as working models, we have constructed and validated several variants of OT-RSHs using both full time-dependent and Tamm-Dancoff formalisms for a reliable description of the TTA-UC photophysics. Given the bimolecular biphotonic nature of the TTA-UC process under study, particular attention is paid to the influence of the factors like the underlying density functional approximations and the tunable parameters such as short- and long-range exact-like exchanges as well as the range-separation parameter for both the sensitizers and annihilators separately. Dissecting all the aspects and relying on the appropriate choices from the tested models, we propose an OT-RSH with the correct asymptotic behavior as a cost-effective yet useful tool for this purpose. Not only against the standard RSHs but also in comparison to the conventional hybrids, the newly developed OT-RSH yields a more reliable description for the TTA-UC energetics in the gas phase and dielectric medium. Accountability of the proposed model has further been confirmed for several theoretically designed sensitizer/annihilator pairs prone to be used in the TTA-UC process. Summing up, in light of this study additional pieces of convincing evidence on the quality of OT-(S)RSHs for computational modeling and experimental verifications of the photophysics of the photon UC based on TTA and other possible technologies are showcased.

Wireless near-infrared electrical stimulation of neurite outgrowth

Herein, through using electropolymerized pyrrole (PPy) to coat near-infrared upconversion nanoparticles (UCNPs) on an indium tin oxide (ITO) electrode, the as-prepared PPy/UCNPs photoelectrode could generate an interfacial electric field, release rare earth ions and induce reactive oxygen species (ROS) in PC12 cells under NIR irradiation, which could realize wireless neurite development and outgrowth.

Seeing Better and Going Deeper in Cancer Nanotheranostics

Biomedical imaging modalities in clinical practice have revolutionized oncology for several decades. State-of-the-art biomedical techniques allow visualizing both normal physiological and pathological architectures of the human body. The use of nanoparticles (NP) as contrast agents enabled visualization of refined contrast images with superior resolution, which assists clinicians in more accurate diagnoses and in planning appropriate therapy. These desirable features are due to the ability of NPs to carry high payloads (contrast agents or drugs), increased in vivo half-life, and disease-specific accumulation. We review the various NP-based interventions for treatments of deep-seated tumors, involving "seeing better" to precisely visualize early diagnosis and "going deeper" to activate selective therapeutics in situ.

Siloxane-Encapsulated Upconversion Nanoparticle Hybrid Composite with Highly Stable Photoluminescence against Heat and Moisture

Herein, we report a siloxane-encapsulated upconversion nanoparticle hybrid composite (SE-UCNP), which exhibits excellent photoluminescence (PL) stability for over 40 days even at an elevated temperature, in high humidity, and in harsh chemicals. The SE-UCNP is synthesized through UV-induced free-radical polymerization of a sol-gel-derived UCNP-containing oligosiloxane resin (UCNP-oligosiloxane). The siloxane matrix with a random network structure by Si-O-Si bonds successfully encapsulates the UCNPs with chemical linkages between the siloxane matrix and organic ligands on UCNPs. This encapsulation results in surface passivation retaining the intrinsic fluorescent properties of UCNPs under severe conditions (e.g., 85 °C/85% relative humidity) and a wide range of pH (from 1 to 14). As an application example, we fabricate a two-color binary microbarcode based on SE-UCNP via a low-cost transfer printing process. Under near-infrared irradiation, the binary sequences in our barcode are readable enough to identify objects using a mobile phone camera. The hybridization of UCNPs with a siloxane matrix provides the capacity for highly stable UCNP-based applications in real environments.

Reaction study of α-phase NaYF4:Yb,Er generation via a tubular microreactor: discovery of an efficient synthesis strategy

α-Phase NaREF4 is the necessary intermediate to obtain β-phase NaREF4, which is good at upconversion luminescence. We herein report microreaction research on the generation of α-NaYF4:Yb,Er nanoparticles. Owing to the fast heating and cooling ability of a quartz microreactor, α-NaYF4:Yb,Er was successfully generated within a reaction time of <10 min. The results showed that it was difficult to complete the α-NaYF4:Yb,Er generation reaction in such a short reaction time by using the traditional synthetic route with a precursor solution containing NaF. However, as we changed the precursor to a solution containing amorphous NaREF4, the yield of α-NaYF4:Yb,Er increased to 95%. By focusing on applying the new precursor solution, we investigated the influence of the reaction temperature on the morphology of α-NaYF4:Yb,Er and exhibited the effects of size and crystallinity of α-NaYF4:Yb,Er on the generation of β-NaYF4:Yb,Er. Finally, an improved microreaction system with an in-line mixing of NH4REF4 and NaOA solutions was developed, whose products were successfully converted to uniform β-NaYF4:Yb,Er nanocrystals through the Ostwald-ripening process. The new reaction path and the reaction device further opened a door for the highly efficient synthesis of upconversion luminescent nanoparticles.

Near-Infrared Upconversion Luminescence and Bioimaging In Vivo Based on Quantum Dots

Recently, upconversion luminescence (UCL) has been widely applied in bioimaging due to its low autofluorescence and high contrast. However, a relatively high power density is still needed in conventional UCL bioimaging. In the present study, an ultralow power density light, as low as 0.06 mW cm-2, is applied as an excitation source for UCL bioimaging with PbS/CdS/ZnS quantum dots (UCL-QDs) as probes. The speculated UCL mechanism is a phonon-assisted single-photon process, and the relative quantum yield is up to 4.6%. As determined by continuous irradiation with a 980 nm laser, the UCL-QDs show excellent photostability. Furthermore, UCL-QDs-based probe is applied in tumor, blood vessel, and lymph node bioimaging excited with an eye-safe low-power light-emitting diode light in a nude mouse with few heat effects.

Mapping Temperature Distribution Generated by Photothermal Conversion in Graphene Film Using Er,Yb:NaYF4 Nanoparticles Prepared by Microwave-Assisted Solvothermal Method

This study analyzes the mapping of temperature distribution generated by graphene in a glass slide cover after illumination at 808 nm with a good thermal resolution. For this purpose, Er,Yb:NaYF₄ nanoparticles prepared by a microwave-assisted solvothermal method were used as upconversion luminescent nanothermometers. By tuning the basic parameters of the synthesis procedure, such as the time and temperature of reaction and the concentration of ethanol and water, we were able to control the size and the crystalline phase of the nanoparticles, and to have the right conditions to obtain 100% of the β hexagonal phase, the most efficient spectroscopically. We observed that the thermal sensitivity that can be achieved with these particles is a function of the size of the nanoparticles and the crystalline phase in which they crystallize. We believe that, with suitable changes, these nanoparticles might be used in the future to map temperature gradients in living cells while maintaining a good thermal resolution.

SC, Chidangil S, George SD. Post annealing induced manipulation of phase and upconversion luminescence of Cr3+ doped NaYF4:Yb,Er crystals

The role of post synthesis annealing at different temperatures (200–600 °C) on the structural as well as luminescence properties of NaY_80%F₄:Yb_17%,Er_3% prepared via a coprecipitation method was found to change the structure from a cubic to hexagonal phase with a concomitant increase in upconversion luminescence by 12 times for the green region and 17 times for the red region. Addition of the Cr³⁺ ions (5–20 mol%) into the host followed by post annealing at 200–600 °C causes that the samples to exhibit phase dependent and upconversion luminescence behavior that depend upon the doping concentration as well as the annealing temperature. The inductively coupled optical emission spectroscopy reveals that only 1/600 times of the desired volume of the co-dopant goes to the lattice and it can manifest visible spectral changes in the diffuse reflectance spectra of the samples. The samples co-doped with Cr³⁺ ion concentrations of 10–15% and post-annealed at 600 °C were found to have maximum emission with an enhancement factor of 24 for the green region and 33 for the red region. In addition, the laser power dependent studies reveal that even for the power density levels 3.69 W cm⁻² to 32.14 W cm⁻², the samples are in the saturation regime and most of the samples investigated here follow a single photon process, and a few samples show a slope value less than 1 for laser power dependent intensity plots. The results show the remarkable promise of controlled tailoring of the properties of upconversion crystals via post annealing and co-doping.

Co-dopant (Cr³⁺ ion) concentration as well as post annealing found to change the structural as well as luminescence properties of Cr³⁺ ion doped NaY_80%F₄:Yb_17%,Er_3% prepared via a co-precipitation method.

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.

Multimodal Cancer Theranosis Using Hyaluronate-Conjugated Molybdenum Disulfide

Among various 2D nanomaterials, molybdenum disulfide (MoS₂ ) exhibits unique visible photoluminescence with high absorption at the near-infrared (NIR) range. Despite these optical properties, the efforts to use MoS₂ nanomaterials for optical imaging and photothermal therapy are hampered by their instability and low intracellular delivery efficiency. Multifunctional MoS₂ conjugated with hyaluronate (HA) for cancer theranosis is reported herein. HA facilitates the delivery of MoS₂ to tumor cells by the HA-receptor mediated endocytosis. In BALB/c nude mice inoculated with a colorectal cancer cell line of HCT116, HA-MoS₂ conjugates appear to be accumulated in the primary tumor at a content more than that in the liver and kidney. The disulfide bonding between MoS₂ and thiolated HA seems to degrade in the cytoplasm, releasing MoS₂ sheets in stacks and enhancing luminescence efficiency. The HA-MoS₂ conjugates are readily detected via photoacoustic imaging as well as upconversion and downconversion fluorescence imaging. With NIR light illumination, HA-MoS₂ conjugates enable highly effective photothermal tumor ablation. All these results confirm the promising potential of HA-MoS₂ conjugates for cancer theranosis.

Advances in the application of upconversion nanoparticles for detecting and treating cancers

The detection and treatment of cancer cells at an early stage are crucial for prolonging the survival time and improving the quality of life of patients. Upconversion nanoparticles (UCNPs) have unique physical and chemical advantages and likely provide a platform for detecting and treating cancer cells at an early stage. In this paper, the principle of UCNPs as chemical sensors based on fluorescence resonance energy transfer (FRET) has been briefly introduced. Research progress in such chemical sensors for detecting and analyzing bioactive substances and heavy metal ions at the subcellular level has been summarized. The principle of UCNP-based nanoprobe-targeting of cancer cells has been described. The research progress in using nanocomposites for cancer cell detection, namely cancer cell targeted imaging and tissue staining, has been discussed. In the field of cancer treatment, the principles and research progress of UCNPs in photodynamic therapy and photothermal therapy of cancer cells are systematically discussed. Finally, the prospects for UCNPs and remaining challenges to UCNP application in the field of cancer diagnosis and treatment are briefly described. This review provides powerful theoretical guidance and useful practical information for the research and application of UCNPs in the field of cancer.

General synthesis of silica-based yolk/shell hybrid nanomaterials and in vivo tumor vasculature targeting

Multifunctional yolk/shell-structured hybrid nanomaterials have attracted increasing interest as theranostic nanoplatforms for cancer imaging and therapy. However, because of the lack of suitable surface engineering and tumor targeting strategies, previous research has focused mainly on nanostructure design and synthesis with few successful examples showing active tumor targeting after systemic administration. In this study, we report the general synthetic strategy of chelator-free zirconium-89 (⁸⁹Zr)-radiolabeled, TRC105 antibody-conjugated, silica-based yolk/shell hybrid nanoparticles for in vivo tumor vasculature targeting. Three types of inorganic nanoparticles with varying morphologies and sizes were selected as the internal cores, which were encapsulated into single hollow mesoporous silica nanoshells to form the yolk/shell-structured hybrid nanoparticles. As a proof-of-concept, we demonstrated successful surface functionalization of the nanoparticles with polyethylene glycol, TRC105 antibody (specific forCD105/endoglin), and ⁸⁹Zr (a positron-emitting radioisotope), and enhanced in vivo tumor vasculature-targeted positron emission tomography imaging in 4T1murine breast tumor-bearing mice. This strategy could be applied to the synthesis of other types of yolk/shell theranostic nanoparticles for tumor-targeted imaging and drug delivery.

Upconversion Fluorescent Aptasensor for Polychlorinated Biphenyls Detection Based on Nicking Endonuclease and Hybridization Chain Reaction Dual-Amplification Strategy

A novel upconversion fluorescent aptasensor based on hybridization chain reaction and nicking endonuclease has been developed for detection of polychlorinated biphenyls (PCBs). It combined the dual advantages of UCNPs and HCR. Two harpins (H1 and H2) were first designed according to the partial complementary sequence (cDNA) of the PCB72/106. Since the aptamer specifically recognized the target, the cDNA was detached from the magnetic microspheres (MMPs). The cDNA could initiate hybridization chain reaction (HCR) and open the stems of H1 and H2. After the addition of nicking endonuclease, UCNPs were further away from the quenchers (BHQ-1). Hence, the fluorescence intensity of upconversion nanoparticals (UCNPs) could be restored via fluorescence resonance energy transfer (FRET). Therefore, the fluorescence of UCNPs was directly proportional to concentration of PCB72/106, which was the basis for the quantification of PCB72/106. PCB72/106 could be analyzed within the ranges of 0.004 to 800 ng/mL with a detection limit of 0.0035 ng/mL ( S/ N = 3). The aptasensor was also used for the detection of water and soil samples, and the average recoveries ranged from 93.4% to 109.7% and 83.2% to 118.5%, respectively. The relative standard deviations (RSDs) were all below 3.2%. The signal was first amplified through HCR and further amplified with the help of nicking endonuclease. This work also provided the opportunity to develop fluorescent aptasensors for other targets using this dual-amplification strategy.

Scalable Direct Writing of Lanthanide-Doped KMnF3 Perovskite Nanowires into Aligned Arrays with Polarized Up-Conversion Emission

The use of one-dimensional nano- and microstructured semiconductor and lanthanide materials is attractive for polarized-light-emission studies. Up-conversion emission from single-nanorod or anisotropic nanoparticles with a degree of polarization has also been discussed. However, microscale arrays of nanoparticles, especially well-aligned one-dimensional nanostructures as well as their up-conversion polarization characterization, have not been investigated yet. Herein, we present a novel and facile paradigm for preparing highly aligned arrays of lanthanide-doped KMnF₃ (KMnF₃:Ln) perovskite nanowires, which are good candidates for polarized up-conversion emission studies. These perovskite nanowires, with a width of 10 nm and length of a few micrometers, are formed through the oriented attachment of KMnF₃:Ln nanocubes along the [001] direction. By the employment of KMnF₃:Ln nanowire gel as nanoink, a direct-writing method is developed to obtain diverse types of aligned patterns from the nanoscale to the wafer scale. Up-conversion emissions from the highly aligned nanowire arrays are polarized along the array direction with a polarization degree up to 60%. Taking advantage of microscopic nanowire arrays, these polarized up-conversion emissions should offer potential applications in light or information transportation.

Highly-luminescent Eu,Sm,Mn-doped CaS up/down conversion nano-particles: application to ultra-sensitive latent fingerprint detection and in vivo bioimaging

Highly-luminescent upconversion: high efficiency (∼60%) UCL from CaS:Eu,Sm,Mn up/down conversion nanoparticles was achieved based on a totally different UCL mechanism.

Carbon Nanodots as Dual-Mode Nanosensors for Selective Detection of Hydrogen Peroxide

Hydrogen peroxide (H2O2) is an important product of oxidase-based enzymatic reactions, such as glucose/glucose oxidase (GOD) reaction. Therefore, the probing of generated H2O2 for achieving the detection of various carbohydrates and their oxidases is very significative. Herein, we report one kind of dual-emission carbon nanodots (CDs) that can serve as novel dual-mode nanosensors with both fluorometric and colorimetric output for the selective detection of H2O2. The dual-model nanosensors are established only by the undecorated dual-emission CDs, where significant fluorometric and colorimetric changes are observed with the addition of different concentrations of H2O2 in the CD solution, which benefit to the achievement of the naked-eye detection for H2O2. The mechanism of the nanosensors can be attributed to the fact that the external chemical stimuli like hydroxyl radicals from H2O2 bring about the change of surface properties and the aggregation of CDs, which dominate the emission and absorption of CDs. The constructed dual-mode nanosensors exhibit good biocompatibility and high selectivity toward H2O2 with a linear detection range spanning from 0.05 to 0.5 M and allow the detection of H2O2 as low as 14 mM.

Stable ICG-loaded upconversion nanoparticles: silica core/shell theranostic nanoplatform for dual-modal upconversion and photoacoustic imaging together with photothermal therapy

We report here the design and multiple functions of a new hierarchical nanotheronostic platform consisting of an upconversion nanoparticle (UCNP) core: shell with an additional mesoporous silica (mSiO2) matrix load shell containing sealed, high concentration of ICG molecules. We demonstrate that this UCNP@mSiO2-ICG nanoplatform can perform the following multiple functions under NIR excitation at 800 nm: 1) Light harvesting by the UCNP shell containing Nd and subsequent energy transfer to Er in the Core to produce efficient green and red upconversion luminescence for optical imaging; 2) Efficient nonradiative relaxation and local heating produced by concentration quenching in aggregated ICG imbedded in the mesopourous silica shell to enable both photoacoustic imaging and photothermal therapy. Compared to pure ICG, sealing of mesoporous silica platforms prevents the leak-out and improves the stability of ICG by protecting from rapid hydrolysis. Under 800 nm laser excitation, we performed both optical and photoacoustic (PA) imaging in vitro and in vivo. Our results demonstrated that UCNP@mSiO2-ICG with sealed structures could be systemically delivered to brain vessels, with a long circulation time. In addition, these nanoplatforms were capable of producing strong hyperthermia efforts to kill cancer cells and hela cells under 800 nm laser irradiation.

Green synthesis of highly dispersed ytterbium and thulium co-doped sodium yttrium fluoride microphosphors for in situ light upconversion from near-infrared to blue in animals

We report a simple, low cost and environmentally friendly method to prepare NaYF₄:Yb³⁺, Tm³⁺ upconversion microphosphors (UCMPs) by thermal decomposition of rare earth-trifluoroacetate precursors using paraffin as the high boiling non-coordinating solvent. The UCMPs exhibited cubic phase with defined shape and bright upconversion luminescence. After coating with amphiphilic polymers of phospholipid-polyethylene glycol, the NaYF₄:Yb³⁺, Tm³⁺ UCMPs were highly dispersed in aqueous solutions and exhibited low cytotoxicity. Furthermore, we explored the use of the micro-injected micro-sized NaYF₄:Yb³⁺, Tm³⁺ particles for converting of near infrared into blue light in mice brain. The in vivo macroscopic upconversion luminescence imaging results showed that UCMPs located at 1mm depth in the brain could be clearly distinguished. Microscopic upconversion luminescence imaging of the brain sections in vitro revealed that the UCMPs embedded at the particular location in brain tissues of mice were stable without significant diffusion in two weeks.

Upconversion processes: versatile biological applications and biosafety

Lanthanide-doped photon upconverting nanomaterials are evolving as a new class of imaging contrast agents, offering highly promising prospects in the area of biomedical applications. Owing to their ability to convert long-wavelength near-infrared excitation radiation into shorter-wavelength emissions, these nanomaterials are well suited to yield properties of low imaging background, large anti-Stokes shift, along with high optical penetration depth of NIR light for deep tissue optical imaging or light-activated drug release and therapy. Such materials have potential for significant advantages in analytical applications compared to molecular fluorophores and quantum dots. The use of IR radiation as an excitation source diminishes autofluorescence and scattering of excitation radiation, which leads to a reduction of background in optical experiments. The upconverting nanocrystals show exceptional photostability and are constituted of materials that are not significantly toxic to biological organisms. Excitation at long wavelengths also minimizes damage to biological materials. In this detailed review, various mechanisms operating for the upconversion process, and methods that are utilized to synthesize and decorate upconverting nanoparticles are investigated to elucidate by what means absorption and emission can be tuned. Up-to-date reports concerning cellular internalization, biodistribution, excretion, cytotoxicity and in vivo toxic effects of UCNPs are discussed. Specifically, studies which assessed the relationship between the chemical and physical properties of UCNPs and their biodistribution, excretion, and toxic effects are reviewed in detail. Finally, we also deliberate the challenges of guaranteeing the biosafety of UCNPs in vivo.

Fabricating upconversion fluorescent nanoparticles modified substrate for dynamical control of cancer cells and pathogenic bacteria

Lanthanide-doped upconversion nanoparticles (UCNPs) have attracted widespread interests in the field of biomedicine because of their unique upconverting capability by converting near infrared (NIR) excitation to visible or ultraviolet (UV) emission. Here, we developed a novel UCNP-based substrate for dynamic capture and release of cancer cells and pathogenic bacteria under NIR-control. The UCNPs harvest NIR light and convert it to ultraviolet light, which subsequently result in the cleavage of photoresponsive linker (PR linker) from the substrate, and on demand allows the release of a captured cell. The results show that after seeding cells for 5 h, the cells were efficiently captured on the surface of the substrate and ˜89.4% of the originally captured S. aureus was released from the surface after exposure to 2 W/cm² NIR light for 30 min, and ˜92.1% of HepG2 cells. These findings provide a unique platform for exploring an entirely new application field for this promising luminescent nanomaterial.

Multicomponent nanocrystals with anti-Stokes luminescence as contrast agents for modern imaging techniques

Lanthanide-doped upconversion nanoparticles (UCNPs) have recently attracted great attention in theranostics due to their exceptional optical and physicochemical properties, which enable the design of a novel UCNP-based nanoplatform for luminescent imaging, temperature mapping, sensing, and therapy. In addition, UCNPs are considered to be ideal building blocks for development of multimodal probes for cells and whole body imaging, exploiting simple variation of host matrix, dopant ions, and surface chemistry. Modalities responsible for magnetic resonance imaging (MRI), computed tomography (CT), and positron emission tomography (PET)/single-photon emission computed tomography (SPECT) are embedded in a single UC nanocrystal, providing integrating effect over any modality alone in terms of the efficiency and sensitivity for clinical innovative diagnosis through multimodal bioimaging. In particular, we demonstrate applications of UCNPs as a new nanoplatform for optical and multimodal cancer imaging in vitro and in vivo and extend discussions to delivery of UCNP-based therapeutic agents for photodynamic and photothermal cancer treatments.

Silver triangular nanoplates as an high efficiently FRET donor-acceptor of upconversion nanoparticles for ultrasensitive "Turn on-off" protamine and trypsin sensor

Silver triangular nanoplates (STNPs) as a high efficient fluorescence quenching reagent of upconversion nanoparticles (UCNPs) was used to constract a novel label-free fluorescence nanosensor for ultrasensitive detection of protamine and trypsin based on fluorescence resonance energy transfer (FRET) between STNPs and UCNPs. In this assay, the negatively charged STNPs can bind with positively charged UCNPs through electrostatic interaction, and then quenched the fluorescence of UCNPs. When protamine was added to the mixture of UCNPs-STNPs, the STNPs interacted with protamine and then detached from the surface of UCNPs and aggregated, which result in the recovery of the fluorescence of UCNPs. Trypsin could catalyze the hydrolysis of protamine and effectively quench the fluorescence recovered by protamine. By measuring the changes of the fluorescence of UCNPs, the concentrations of protamine and trypsin were determined. Under the optimized conditions, the linear response range was obtained from 10 to 500ng/mL, 5-80ng/mL and with the low detection limit of 3.1ng/mL and 1.8ng/mL for protamine and trypsin, respectively. Meanwhile, the nanosensor shows good selectivity, sensitivity and can be successfully applied to detection of protamine and trypsin in serum samples.

Efficient up-conversion in Yb:Er:NaT(XO4)2 thermal nanoprobes. Imaging of their distribution in a perfused mouse

Yb and Er codoped NaT(XO4)2 (T = Y, La, Gd, Lu and X = Mo, W) disordered oxides show a green (Er3+ related) up-conversion (UC) efficiency comparable to that of Yb:Er:β-NaYF4 compound and unless 3 times larger UC ratiometric thermal sensitivity. The similar UC efficiency of Yb:Er doped NaT(XO4)2 and β-NaYF4 compounds allowed testing equal subcutaneous depths of ex-vivo chicken tissue in both cases. This extraordinary behavior for NaT(XO4)2 oxides with large cutoff phonon energy (ħω≈ 920 cm-1) is ascribed to 4F9/2 electron population recycling to higher energy 4G11/2 level by a phonon assisted transition. Crystalline nanoparticles of Yb:Er:NaLu(MoO4)2 have been synthesized by sol-gel with sizes most commonly in the 50-80 nm range, showing a relatively small reduction of the UC efficiency with regards to bulk materials. Fluorescence lifetime and multiphoton imaging microscopies show that these nanoparticles can be efficiently distributed to all body organs of a perfused mouse.

Neuroendocrine Tumor-Targeted Upconversion Nanoparticle-Based Micelles for Simultaneous NIR-Controlled Combination Chemotherapy and Photodynamic Therapy, and Fluorescence Imaging

Although neuroendocrine tumors (NETs) are slow growing, they are frequently metastatic at the time of discovery and no longer amenable to curative surgery, emphasizing the need for the development of other treatments. In this study, multifunctional upconversion nanoparticle (UCNP)-based theranostic micelles are developed for NET-targeted and near-infrared (NIR)-controlled combination chemotherapy and photodynamic therapy (PDT), and bioimaging. The theranostic micelle is formed by individual UCNP functionalized with light-sensitive amphiphilic block copolymers poly(4,5-dimethoxy-2-nitrobenzyl methacrylate)-polyethylene glycol (PNBMA-PEG) and Rose Bengal (RB) photosensitizers. A hydrophobic anticancer drug, AB3, is loaded into the micelles. The NIR-activated UCNPs emit multiple luminescence bands, including UV, 540 nm, and 650 nm. The UV peaks overlap with the absorption peak of photocleavable hydrophobic PNBMA segments, triggering a rapid drug release due to the NIR-induced hydrophobic-to-hydrophilic transition of the micelle core and thus enabling NIR-controlled chemotherapy. RB molecules are activated via luminescence resonance energy transfer to generate 1O2 for NIR-induced PDT. Meanwhile, the 650 nm emission allows for efficient fluorescence imaging. KE108, a true pansomatostatin nonapeptide, as an NET-targeting ligand, drastically increases the tumoral uptake of the micelles. Intravenously injected AB3-loaded UCNP-based micelles conjugated with RB and KE108-enabling NET-targeted combination chemotherapy and PDT-induce the best antitumor efficacy.

Tailoring bifunctional hybrid organic-inorganic nanoadsorbents by the choice of functional layer composition probed by adsorption of Cu2+ ions

Spherical silica particles with bifunctional (≡Si(CH₂)₃NH₂/≡SiCH₃, ≡Si(CH₂)₃NH₂/≡Si(CH₂)₂(CF₂)₅CF₃) surface layers were produced by a one-step approach using a modified Stöber method in three-component alkoxysilane systems, resulting in greatly increased contents of functional components. The content of functional groups and thermal stability of the surface layers were analyzed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, and ¹³C and ²⁹Si solid-state NMR spectroscopy revealing their composition and organization. The fine chemical structure of the surface in the produced hybrid adsorbent particles and the ligand distribution were further investigated by electron paramagnetic resonance (EPR) and electron spectroscopy of diffuse reflectance (ESDR) spectroscopy using Cu²⁺ ion coordination as a probe. The composition and structure of the emerging surface complexes were determined and used to provide an insight into the molecular structure of the surfaces. It was demonstrated that the introduction of short hydrophobic (methyl) groups improves the kinetic characteristics of the samples during the sorption of copper(II) ions and promotes fixation of aminopropyl groups on the surface of silica microspheres. The introduction of long hydrophobic (perfluoroctyl) groups changes the nature of the surface, where they are arranged in alternately hydrophobic/hydrophilic patches. This makes the aminopropyl groups huddled and less active in the sorption of metal cations. The size and aggregation/morphology of obtained particles was optimized controlling the synthesis conditions, such as concentrations of reactants, basicity of the medium, and the process temperature.

The influence of energy migration on luminescence kinetics parameters in upconversion nanoparticles

The mechanism of upconversion at the nanoscale is still under discussion. In this paper, we report on the experimental results of anti-Stokes luminescence kinetics in the upconversion nanoparticles of β-NaYF₄: 20%Yb³⁺; 0.6%Tm³⁺. The parameters of the luminescence kinetics were found to be unambiguously dependent on the number of excitation quanta n, which are necessary for certain transitions between the energy states of thulium ions. The observed correlation has been explained by means of the long-lasting energy migration between the ytterbium ions. The spread in time between the luminescent maxima of the corresponding thulium transitions not only shows the nonlinear character of upconversion, but also reveals the time scale of energy migration as well. From these, we derive that the conventional Förster formalism applied to the estimation of energy transfer efficiency in UCNP-fluorophore pairs can provide misleading results.

Resonance Energy Transfer in Upconversion Nanoplatforms for Selective Biodetection

Resonance energy transfer (RET) describes the process that energy is transferred from an excited donor to an acceptor molecule, leading to a reduction in the fluorescence emission intensity of the donor and an increase in that of the acceptor. By this technique, measurements with the good sensitivity can be made about distance within 1 to 10 nm under physiological conditions. For this reason, the RET technique has been widely used in polymer science, biochemistry, and structural biology. Recently, a number of RET systems incorporated with nanoparticles, such as quantum dots, gold nanoparticles, and upconversion nanoparticles, have been developed. These nanocrystals retain their optical superiority and can act as either a donor or a quencher, thereby enhancing the performance of RET systems and providing more opportunities in excitation wavelength selection. Notably, lanthanide-doped upconversion nanophosphors (UCNPs) have attracted considerable attention due to their inherent advantages of large anti-Stoke shifts, long luminescence lifetimes, and absence of autofluorescence under low energy near-infrared (NIR) light excitation. These nanoparticles are promising for the biodetection of various types of analytes. Undoubtedly, the developments of those applications usually rely on resonance energy transfer, which could be regarded as a flexible technology to mediate energy transfer from upconversion phosphor to acceptor for the design of luminescent functional nanoplatforms. Currently, researchers have developed many RET-based upconversion nanosystems (RET-UCNP) that respond to specific changes in the biological environments. Specifically, small organic molecules, biological molecules, metal-organic complexes, or inorganic nanoparticles were carefully selected and bound to the surface of upconversion nanoparticles for the preparation of RET-UCNP nanosystems. Benefiting from the advantage and versatility offered by this technology, the research of RET-based upconversion nanomaterials should have significant implications for advanced biomedical applications. It should be noted that energy transfer in a UCNP based nanosystem is most often related to resonance energy transfer but that reabsorption (and maybe other energy transfer processes) may also play an important role and that more studies regarding the fundamental aspects for energy transfer with UCNPs is necessary. In this Account, we present an overview of recent advances in RET-based upconversion nanocomposites for biodetection with a particular focus on our own work. We have designed a series of upconversion nanoplatforms with remarkably high versatility for different applications. The experience gained from our strategic design and experimental investigations will allow for the construction of next-generation luminescent nanoplatform with marked improvements in their performance. The key aspects of this Account include fundamental principles, design and preparation strategies, biodetection in vitro and in vivo, future opportunities, and challenges of RET-UCNP nanosystems.

Nanomaterials for In Vivo Imaging

In vivo imaging, which enables us to peer deeply within living subjects, is producing tremendous opportunities both for clinical diagnostics and as a research tool. Contrast material is often required to clearly visualize the functional architecture of physiological structures. Recent advances in nanomaterials are becoming pivotal to generate the high-resolution, high-contrast images needed for accurate, precision diagnostics. Nanomaterials are playing major roles in imaging by delivering large imaging payloads, yielding improved sensitivity, multiplexing capacity, and modularity of design. Indeed, for several imaging modalities, nanomaterials are now not simply ancillary contrast entities, but are instead the original and sole source of image signal that make possible the modality's existence. We address the physicochemical makeup/design of nanomaterials through the lens of the physical properties that produce contrast signal for the cognate imaging modality-we stratify nanomaterials on the basis of their (i) magnetic, (ii) optical, (iii) acoustic, and/or (iv) nuclear properties. We evaluate them for their ability to provide relevant information under preclinical and clinical circumstances, their in vivo safety profiles (which are being incorporated into their chemical design), their modularity in being fused to create multimodal nanomaterials (spanning multiple different physical imaging modalities and therapeutic/theranostic capabilities), their key properties, and critically their likelihood to be clinically translated.

Crystal structure, NIR luminescence and X-ray computed tomography of Nd3+:Ba0.3Lu0.7F2.7 nanospheres

Uniform, hydrophilic Nd³⁺-doped Ba_0.3Lu_0.7F_2.7 50 nm spheres are obtained in the absence of additives. Their NIR excitation and emission as well as their X-ray absorption make them ideal candidates as bioimaging probes.

Enhancement of upconversion, temperature sensing and cathodoluminescence in the K+/Na+ compensated CaMoO4:Er3+/Yb3+ nanophosphor

Enhancing upconversion, temperature sensing and cathodoluminescence in the CaMoO₄:Er³⁺/Yb³⁺ nanophosphor via K⁺/Na⁺ simultaneous codoping.

Thermo-activatable PNIPAM-functionalized lanthanide-doped upconversion luminescence nanocomposites used for in vitro imaging

Stimuli-responsive nanocomposite has a great potential application for cell imaging, drug delivery, and improving therapeutic effect.

Choline sensing based on in situ polymerization of aniline on the surface of upconverting nanoparticles

We found that the upconversion luminescence of UCNPs could be efficiently quenched by PANI, and a novel choline detection strategy has been developed based on in situ polymerization of aniline on the surface of UCNPs.

A label-free detection of diethylstilbestrol based on molecularly imprinted polymer-coated upconversion nanoparticles obtained by surface grafting

The novel MIPs-coated UCNPs fluorescent sensor could be used for on-field detection of diethylstilbestrol in real samples.

NIR-Mediated Nanohybrids of Upconversion Nanophosphors and Fluorescent Conjugated Polymers for High-Efficiency Antibacterial Performance Based on Fluorescence Resonance Energy Transfer

A novel nanohybrid comprised of upconversion nanophosphors (UCNPs) and fluorescent conjugated polymers (PFVCN) is rationally fabricated. The new UCNP/PFVCN nanohybrids combine the excellent antibacterial ability of PFVCN and the near IR (NIR) absorbing property of UCNPs, which allows for NIR-mediated antibacterial through the effective fluorescence resonance energy transfer from UCNPs to PFVCN accompanied with generation of reactive oxygen species to kill bacteria.