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Heterogeneous Oxysulfide@Fluoride Core/ Shell Nanocrystals for Upconversion-Based Nanothermometry
(2022)
Lanthanide (Ln3+)-doped upconversion nanoparticles (UCNPs) often suffer from weak luminescence, especially when their sizes are ultrasmall (less than 10 nm). Enhancing the upconversion luminescence (UCL) efficiency of ultrasmall UCNPs has remained a challenge that must be undertaken if any practical applications are to be envisaged. Herein, we present a Ln3+-doped oxysulfide@fluoride core/shell heterostructure which shows efficient UCL properties under 980nm excitation and good stability in solution. Through epitaxial heterogeneous growth, a ∼4 nm optically inert β-NaYF4 shell was coated onto ∼5 nm ultrasmall Gd2O2S:20%Yb,1%Tm. These Gd2O2S:20%Yb,1%Tm@NaYF4 core/shell UCNPs exhibit a more than 800-fold increase in UCL intensity compared to the unprotected core, a 180-fold increase in luminescence decay time of the 3H4 → 3H6 Tm3+ transition from 5 to 900 μs, and an upconversion quantum yield (UCQY) of 0.76% at an excitation power density of 155 W/cm2. Likewise, Gd2O2S:20%Yb,2%Er@NaYF4 core/shell UCNPs show a nearly 5000-fold
increase of their UCL intensity compared to the Gd2O2S:20%Yb,2%Er core and a maximum UCQY of 0.61%. In the Yb/Er core−shell UCNP system, the observed variation of luminescence intensity ratio seems to originate from a change in lattice strain as the temperature is elevated. For nanothermometry applications, the thermal sensitivities based on thermally coupled levels are estimated for both Yb/Tm and Yb/Er doped Gd2O2S@NaYF4 core/shell UCNPs.
Light-induced NO release based on exogenous NO donors has attracted substantial attention in clinical applications; the induction light source usually converts near-infrared light to blue or ultraviolet light.
However, the low efficiency of near-infrared light-assisted chemical light energy conversion remains a challenge, especially for NaYF4:Yb3+/Tm3+ photoconverting near-infrared light to ultraviolet (UV) and blue light. In this paper, a luminescence-enhanced strategy is reported by doping Ca2+ into NaYF4:Yb3+/Tm3+ and coating it with NaGdF4 through a two-step solvothermal method. Then, UCNPs modified with methyl-b-cyclodextrin (M-b-CD) are loaded on a ruthenium nitrosyl complex [(3)Ru(NO)(Cl)] as nitric oxide release-molecules (NORMs). X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) data demonstrated that Ca2+ was successfully doped into NaYF4:Yb3+/Tm3+ nanoparticles as the core, and a pure hexagonal phase, NaYF4, was obtained from the doping of Ca2+. TEM revealed that the crystallinity was significantly improved after Ca2+ doping, and the core–shell structure was successfully synthesized, with NaGdF4 directionally grown on the NaYF4:Ca/Yb/Tm core. Fluorescence tests showed that, especially in the ultraviolet and blue light excitation wavelength regions, the UC emission intensity of the Ca-doped NaYF4:Yb3+/Tm3+@NaGdF4 core–shell UCNPs increased by 302.95 times vs. NaYF4:Yb3+/Tm3+ UCNPs. Finally, the release of NO was tested by the Griess method. Under 980 nm irradiation, the cell viability distinctly decreased with increasing UCNPs@M-b-CD-NORMs concentration. This study Shows that NORM release of NO is triggered by enhanced up-converted UV and blue light, which can be used for the development of UV photo-sensitive drugs.
We synthesized a generation of water-soluble, atomically precise gold nanoclusters (Au NCs) with anisotropic Surface containing a short dithiol pegylated chain (AuMHA/TDT). The AuMHA/TDT exhibit a high brightness (QY ∼ 6%) in the shortwave infrared (SWIR) spectrum with a detection above 1250 nm.
Furthermore, they show an extended half-life in blood (t1/2ß = 19.54 ± 0.05 h) and a very weak accumulation in organs. We also developed a non-invasive, whole-body vascular imaging system in the SWIR window with high-resolution, benefiting from a series of Monte Carlo image processing. The imaging process enabled to improve contrast by 1 order of magnitude and enhance the spatial Resolution by 59%. After systemic administration of these nanoprobes in mice, we can quantify vessel complexity in depth (>4 mm), allowing to detect very subtle vascular disorders non-invasively in bone morphogenetic protein 9 (Bmp9)-deficient mice. The combination of these anisotropic surface charged Au NCs plus an improved SWIR imaging device allows a precise mapping at high-resolution and an in depth understanding of the organization of the vascular network in live animals.
Objective: The utilization of fluorescein-guided biopsies and resection has been recently discussed as a suitable strategy to improve and expedite operative techniques for the resection of central nervous system (CNS) tumors. However, little is known about the optical properties of sodium fluorescein (NaFl) in human tumor tissue and their potential impact on ex vivo analyses involving fluorescence-based methods.
Methods: Tumor tissue was obtained from a study cohort of an observational study on the utilization of fluorescein-guided biopsy and resection (n=5). The optical properties of fluorescein-stained tissue were compared to the optical features of the dye in vitro and in control samples consisting of tumor tissue of high-grade glioma patients (n=3) without intravenous (i.v.) application of NaFl. The dye-exposed tumor tissues were used for optical measurements to confirm the detectability of NaFl emission ex vivo. The tissue samples were fixed in 4%PFA, immersed in 30% sucrose, embedded in Tissue-Tek OCT compound, and cut to 10 mm cryosections. Spatially resolved emission spectra from tumor samples were recorded on representative slides with a Confocal Laser Scanning Microscope FV1000 (Olympus GmbH, Hamburg, Germany) upon excitation with lexc = 488 nm.
Results: Optical measurements of fluorescein in 0.9% sodium chloride (NaCl) under in vitro conditions showed an absorption maximum of lmax abs = 479 nm as detected with spectrophotometer Specord 200 and an emission peak at lmax em = 538 nm recorded with the emCCD detection system of a custom-made microscope-based single particle setup using a 500 nm long-pass filter. Further measurements revealed pH- and concentration-dependent emission spectra of NaFl. Under ex vivo conditions, confocal laser scanning microscopy of fluorescein tumor samples revealed a slight bathochromic shift and a broadening of the emission band.
Conclusion: Tumor uptake of NaFl leads to changes in the optical properties – a bathochromic shift and broadening of the emission band – possibly caused by the dye’s high pH sensitivity and concentration-dependent reabsorption acting as an innerfilter of the dye’s emission, particularly in the short wavelength region of the Emission spectrum where absorption and fluorescence overlap. Understanding the ex vivo optical properties of fluorescein is crucial for testing and validating its further applicability as an optical probe for intravital microscopy, immunofluorescence localization studies, and flow cytometry analysis.
There is an increasing interest in chromophores absorbing and emitting in the near-infrared (NIR) spectral region, e.g., for applications as fluorescent reporters for optical imaging techniques and hence, in reliable methods for the characterization of their signal-relevant properties like the fluorescence quantum yield (Φf) and brightness. The lack of well established Φf standards for the NIR region in conjunction with the need for accurate Φf measurements in transparent and scattering media encouraged us to built up an integrating sphere setup for spectrally resolved measurements of absolute fluorescence traceable to radiometric scales. Here, we present the design of this setup and its characterization and validation including an uncertainty budget for the determination of absolute Φf in the visible and NIR. To provide the basis for better measurements of Φf in the spectral window from ca. 600 to 1000 nm used, e.g., for optical imaging, the absolute Φf of a set of NIR chromophores covering this spectral region are measured and compared to relative values obtained using rhodamine 101 as Φf standard. Additionally, the absolute Φf values of some red dyes that are among the most commonly used labels in the life sciences are presented as well as the absolute quantum yield of an optical probe for tumor imaging.
The commercial availability of stand-alone setups for the determination of absolute photoluminescence quantum yields (φf) in conjunction with the increasing use of integrating sphere accessories for spectrofluorometers is expected to have a considerable influence not only on the characterization of chromophore systems for use in optical and opto-electronic devices, but also on the determination of this key parameter for (bio)analytically relevant dyes and functional luminophores. Despite the huge potential of systems measuring absolute φf values and the renewed interest in dependable data, evaluated protocols for even the most elementary case, the determination of the fluorescence quantum yield of transparent dilute solutions of small organic dyes with integrating sphere methods, are still missing. This encouraged us to evaluate the performance and sources of uncertainty of a simple commercial integrating sphere setup with dilute solutions of two of the best characterized fluorescence quantum yield standards, quinine sulfate dihydrate and rhodamine 101, strongly differing in spectral overlap between absorption and emission. Special attention is dedicated to illustrate common pitfalls of this approach, thereby deriving simple procedures to minimize measurement uncertainties and improve the comparability of data for the broad community of users of fluorescence techniques.
High sensitizer and activator concentrations have been increasingly examined to improve the performance of multi-color emissive upconversion (UC) nanocrystals (UCNC) like NaYF4:Yb,Er and first strategies were reported to reduce concentration quenching in highly doped UCNC. UC luminescence (UCL) is, however, controlled not only by dopant concentration, yet by an interplay of different parameters including size, crystal and shell quality, and excitation power density (P). Thus, identifying optimum dopant concentrations requires systematic studies of UCNC designed to minimize additional quenching pathways and quantitative spectroscopy. Here, we quantify the dopant concentration dependence of the UCL quantum yield (ΦUC) of solid
NaYF4:Yb,Er/NaYF4:Lu upconversion core/shell nanocrystals of varying Yb3+ and Er3+ concentrations (Yb3+ series: 20%‒98% Yb3+; 2% Er3+; Er3+ series: 60% Yb3+; 2%‒40% Er3+). To circumvent other luminescence quenching processes, an elaborate synthesis yielding OH-free UCNC with record ΦUC of ~9% and ~25 nm core particles with a thick surface shell were used. High Yb3+ concentrations barely reduce ΦUC from ~9% (20% Yb3+) to ~7% (98% Yb3+) for an Er3+ concentration of 2%, thereby allowing to strongly increase the particle absorption cross section and UCNC brightness. Although an increased Er3+ concentration reduces ΦUC from ~7% (2% Er3+) to 1% (40%) for 60% Yb3+. Nevertheless, at very high P (> 1 MW/cm2) used for microscopic studies, highly Er3+-doped UCNC display a high brightness because of reduced saturation. These findings underline the importance of synthesis control and will pave the road to many fundamental studies of UC materials.
The photoluminescence quantum yield (Φf) that presents a direct measure for the efficiency of the conversion of absorbed photons into emitted photons is one of the spectroscopic key parameters of functional fluorophores. It determines the suitability of such materials for applications in, for example, (bio)analysis, biosensing, and fluorescence imaging as well as as active components in optical devices. The reborn interest in accurate Φf measurements in conjunction with the controversial reliability of reported Φf values of many common organic dyes encouraged us to compare two relative and one absolute fluorometric method for the determination of the fluorescence quantum yields of quinine sulfate dihydrate, coumarin 153, fluorescein, rhodamine 6G, and rhodamine 101. The relative methods include the use of a chain of Φf transfer standards consisting of several 'standard dye' versus 'reference dye' pairs linked to a golden Φf standard that covers the ultraviolet and visible spectral region, and the use of different excitation wavelengths for standard and sample, respectively. Based upon these measurements and the calibration of the instruments employed, complete uncertainty budgets for the resulting Φf values are derived for each method, thereby providing evaluated standard operation procedures for Φf measurements and, simultaneously, a set of assessed Φf standards.
To establish the methodical basis for the development and certification of fluorescence quantum yield standards, we determined the fluorescence quantum yield Φf of rhodamine 6G (R6G) with two absolute methods with complementary measurement principles, here optical spectroscopy using an integrating sphere setup and pulsed laser photoacoustic spectroscopy (PAS). For the assessment of aggregation- and reabsorption-induced distortions of measured fluorescence quantum yields and procedures for the reliable consideration of such effects, this systematic comparison was performed in ethanol and in water employing different concentrations of R6G. In addition, the relative and absolute fluorescence quantum yields of these solutions were obtained with a calibrated spectrofluorometer and a commercialized integrating sphere setup. Based upon this systematic comparison, experimental advantages and systematic sources of variation were identified for both methods.