Nanoluminofors based on siliсates and hermanates of REE for visualization of biotissues published by Ural Federal University eISSN2411-1414; chimicatechnoacta.ru LETTER 2022, vol. 9(2), No. 202292S12 DOI: 10.15826/chimtech.2022.9.2.S12 1 of 4 Nanoluminofors based on siliсates and germanates of rare earth elements for visualization of biotissues Mikhail G. Zuev a*, Vladislav G. Il’ves b, Sergey Yu. Sokovnin bc a: Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, Ekaterinburg 620990, Russia b: Institute of Electrophysics, Ural Branch of the Russian Academy of Sciences, Ekaterinburg 620016, Russia c: Institute of Physics and Technology, Ural Federal University, Ekaterinburg 620002, Russia * Corresponding author: zuev@ihim.uran.ru This paper belongs to the MOSM2021 Special Issue. © 2022, the Authors. This article is published in open access under the terms and conditions of the Creative Com- mons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Abstract Nanoparticles of silicates and germanates with a general formula Sr2R8–x–yErxYbyM6O26 (R = Y, La; M = Si, Ge) were produced in vacuum by the method of pulse electron beam evaporation. An upconversion photoluminescence of the nanoparticles was detected during the exci- tation by a laser with a wavelength of 980 nm with a predominance of lines in the red and near infrared regions of the spectrum. Due to their optical properties, the nanoparticles can be excited directly through the biotissues to visualize various pathologies. The obtained nanosamples have K-jumps of X-ray radiation absorption in the 10−100 keV energy region. This opens up prospects for the use of the nanoparticles as X-ray contrast agents. Thus, the nanoparticles have both optical and X-ray contrast characteristics, and therefore have the potential necessary for imaging and diagnosing pathologies in biolog- ical tissues. Keywords Er3+ Yb3+ upconversion nanoluminofor biotissues bimodal substances Received: 19.01.22 Revised: 14.07.22 Accepted: 14.07.22 Available online: 19.07.22 Key findings ● Silicates and germanates of rare earth elements are promising for visualization of biological tissues. ● Upconversion silicate and germanate nanoluminophores containing Er and Yb ions can be used for optical and X-ray bioimaging. 1. Introduction Single-mode nanoparticles (NP) with optical or magnetic characteristics are widely used in biosensing and biovisu- alization [1]. However, they do not provide all the neces- sary information about biological objects. The require- ments of modern biomedical technology suggest the devel- opment of new, multimodal bioprobes. Multimodal bi- oprobes combining two or more functions are emerging advances in biology and medicine. A number of nano- materials with such interesting properties have found var- ious biomedical applications, including imaging, separa- tion, and drug delivery [2]. Inorganic nanoparticles doped with Ln3+ ions are considered good candidates for multi- modal bioapplications, since they have unusual optical and magnetic properties [3]. Narrow width of f-f emission lines, long lifetime of photoluminescence (PL), IR excita- tion in the field of transparency of biological tissues (700– 1000 nm), large antistox shifts for separation of upconver- sion photoluminescence (UCPL) from excitation, weak background of intrinsic luminescence of biotissues, low cytotoxicity, high chemical resistance and resistance to photobleaching make them extremely suitable for use in various bio-applications [4–7]. The increased intensity of red radiation could be useful for various UCPL applica- tions, especially for deep tissue imaging [4]. Currently, magnetic resonance imaging (MRI), computed tomogra- phy (CT) positron emission tomography (PET), optical im- aging, and other methods provide vivid tissue imaging; however, they cannot provide comprehensive infor- mation in clinical practice. Therefore, various multi- modal imaging technologies have attracted considerable attention [8–11]. In this work, UCPL was studied and the dependencies of mass coefficients of weakening of X-ray radiation on the ra- diation energy for the nanopowders (NPs) produced by http://chimicatechnoacta.ru/ https://doi.org/10.15826/chimtech.2022.9.2.S12 mailto:zuev@ihim.uran.ru http://creativecommons.org/licenses/by/4.0/ https://orcid.org/0000-0002-8491-8980 https://crossmark.crossref.org/dialog/?doi=https://doi.org/10.15826/chimtech.2022.9.2.S12&domain=pdf&date_stamp=2022-7-19 Chimica Techno Acta2022, vol. 9(2), No. 202292S12 LETTER 2 of 4 electronic evaporation of solid solutions with a general for- mula Sr2R8–x–yErxYbyM6O26 (R = Y, La; M = Si, Ge) were con- sidered. NPs can be promising as bioprobes for various bi- omedical applications, including photoluminescent and X-ray contrast images of body tissues [12]. Currently, io- dinated X-ray contrast agents are widely used to contrast organs and systems of the body. However, these means have a number of drawbacks. They have toxic effects on the blood system, liver, kidneys, pancreas, central nervous and endocrine systems. They also have a local irritating effect on the mucous membranes, including the epithelium of the hepatic and pancreatic ducts, the endothelium of the arte- rial, venous, lymphatic vessels and the heart, and the cere- bral membranes. They cause various types of allergic reac- tions. Therefore, there is a search for new effective X-ray contrast agents that do not have the noted drawbacks. The compounds discussed here can be characterized as two- modal substances promising for simultaneous use in optical and X-ray biovisualization. 2. Experimental Samples of the above compositions were selected to pro- duce NPs. The choice of the compositions is due to two fac- tors. Firstly, they should have a UCPL and, secondly, they should have a sufficiently high X-ray attenuation covering the entire range of X-ray energies (10-100 keV) used in medical X-ray diagnostics. The samples were synthesized by conventional ceramic technology. The high-purity reac- tants SrCO3, Y2O3, La2O3, Er2O3, Yb2O3, SiO2, GeO2 were used (the content of the main substance not less than 99.99%). The initial components taken in stoichiometric ratio were thoroughly ground. The obtained mixes were pressed in tablets and burned in air at a temperature of 1350–1400 °C for ~50 h. The X-ray difraction analysis was carried out by means of the Shimadzu XRD-7000 diffractometer (Cu Kα-radiation, counter monochromator CM-3121, detec- tor – Scintillation Counter) with use of an ICDD card file. The diffractograms of the samples were processed using the Ritveld full-profile analysis method with the use of an ICDD card-file. The NPs were produced by evaporating the tablets in vacuum by a pulsed electron beam (PEBE) in the NANOBIM-2 unit [13]. The electron energy was 40 keV, electron beam pulse energy 1.8 J, pulse duration 100 μs, repetition rate 100–200 pps. The time of evaporation of the targets was 40–60 minutes. The speed of rotation of the targets was ~8.3 revolutions/min. The specific surface area of the powders was determined by the known BET method in Micromeritics TriStar 3000. The microscopic analysis of the HP was performed on a JEOL JEM 2100 transmission electron microscope. The microscopic analysis of the NP was performed on a JEOL JEM 2100 transmission electron microscope. The PL spectra were recorded on a MDR-204 spectrometer (laser KLM-H980-200-5, λ = 980 nm, rated power 221 mW; photoelectronic multiplier R928 from Hama- matsu). 3. Results and Discussion Figure 1 shows the results of NPs microscopy based on solid solutions of Sr2La7.85Er0.075Yb0.075Ge6O26 (I) and Sr2Y6.8YbEr0.2Si6O26 (II). According to TEM HR microscopy and electronography, it can be seen that the nanoparticles are prone to agglomeration, have irregular shapes and amorphous character (insert) (Figures 1, 2). According to BET, the nanoparticles sized ~23 nm (sam- ple based on I) and ~4 nm (based on II) were found. It is known that nanopowders together with an organic additive obtained by evaporation of solid solutions of the composition Sr2Y8–x–yErxYbySi6O26 were proposed for diag- nostics of pathologies in biological tissues [14]. 3.1. Upconversion photoluminescence Figure 2 shows the spectra of UCPL nanopowders produced based on Sr2La8–x–yErxYbyGe6O26 (x = y = 0.075) and Sr2Y8–x–yErxYbySi6O26 (x = 0.2, y = 1). The excitement of UCPL of Er3+ions occurs in the pres- ence of Yb3+ because of the absorption of the 980 nanome- ter laser radiation upon 2F7/2→2F5/2 transition of Yb3+ ions with the subsequent transmission of energy in Er3+ in a state 4I11/2. In addition, there is a 4I11/2→4F7/2 transition at the excitement by the second photon from a state 2F5/2 of Yb3+ ion. Besides, the excitation of the state of the 4F9/2 ion Er3+ occurs directly by two laser photons with the partici- pation of the photons of the matrix. Figure 1 TEMHR snapshots and electronograms (inserts) NP based on Sr2Y6.8YbEr0.2Si6O26 (a) and Sr2La7.85Er0.075Yb0.075Ge6O26 (b). Chimica Techno Acta2022, vol. 9(2), No. 202292S12 LETTER 3 of 4 500 600 700 800 900 0 10000 20000 4 I 9/2 → 4 I 15/2 4 F 9/2 → 4 I 15/2 4 S 3/2 → 4 I 15/2 2 H 1 1 /2 → 4 I 1 5 /2 I, a . u . , nm a 500 600 700 800 900 0 200000 400000 600000 800000 4 S3/2→ 4 I15/2 4F 9/2 → 4I 15/2 , nm b Figure 2 PL spectra of NP based on samples I (a) and II (b). As is known, the primary importance of UCPL in the NIR-to-Red or NIR-to-NIR [15, 16] radiation transfor- mations regions of the spectrum are at the excitation radi- ation with a wavelength of typically about 980 nm. This is particularly important for biomedical purposes. Excitation in the NIR region of the spectrum in combination with UCNP in the NIR or RED is possible due to the high trans- parency of biological fluids and low tissue damage. Two intense peaks in NIR at 836 and RED at 670 nm (Figure 2a), and a very intense RED peak at ~665 nm (Figure 2b) were detected. This luminescence can be used in photodynamic therapy (PDT) to excite a photosensitizer (PS) localized in the diseased region. Photodynamic therapy (PDT) uses special drugs called photosensitizing agents that respond to a certain wavelength of light to kill cancer cells [17]. Currently, a new generation of photosensitizers is actively developing, which have a stronger absorption in the near infrared region of the spec- trum (NIR), corresponding to the optimal "transparency re- gion" of the biotissue (700–1000 nm) [18]. High red line in- tensities at λαmax = 670 nm and near IR line at λαmax = 836 nm (Figure 2a) as well as λαmax = 664 nm (Figure 2b) indicate the nanoparticles’ promise for deep tissue imaging [19]. 3.2. X-ray attenuation mass coefficients Let us consider the dependencies of mass attenuation coef- ficients (μ) on X-ray energy for the samples Sr2Y6.8YbEr0.2Si6O26 and Sr2La7.75Er0.075Yb0.075Ge6O26 (Fig- ures 3, 4). Figure 3 Dependence of mass coefficient of Sr2Y6.8YbEr0.2Si6O26 at- tenuation on X-ray energy. Figure 4 Dependence of mass coefficient of Sr2La7.85Er0.075Yb0.075Ge6O26 attenuation on X-ray energy. The schedules are constructed according to the previous work [20] (ρ – X-ray density). K absorption jumps of the ele- ments Sr, Y, Yb, La are indicated. The absorption of radiation by the nanoparticles in almost the entire range of quantum en- ergies used in X-ray diagnostics is ensured by the fact that the NP includes Sr, Y, Yb and La elements, the K absorption jumps of which lie in different parts of this range. Strontium has a K- jump at 16.10 keV, Yttrium – at 17.038 keV, Ytterbium – at 61.30 keV and Lanthanum at 39 keV. It should be noted that due to the low content of Er and Yb in the solid solutions, the K-jumps of these atoms practically do not affect the mass at- tenuation coefficients of the samples. 4. Conclusions Bimodal nanoparticles were produced by PEBE in vacuum. UCPL of NPs was detected during excitation by a laser with a wavelength of 980 nm with a predominance of RED and NIR lines. Due to their optical properties, nanoparticles can be excited directly through the biotissue to visualize vari- ous pathologies. In addition, K-jumps of X-ray absorption in the energy region of 10–90 eV make it promising to use NPs as X-ray contrast agents. Supplementary materials No supplementary materials are available. Funding This work was carried out in accordance with the state as- signment of the Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences. Chimica Techno Acta2022, vol. 9(2), No. 202292S12 LETTER 4 of 4 Acknowledgments None. Author contributions Conceptualization: M.G.Z. Data curation: S.Y.S. Investigation: M.G.Z., V.G.I. Conflict of interest The authors declare no conflict of interest. Additional information Author IDs: Mikhail G. Zuev, Scopus ID 7003705663; Vladislav G. Il’ves, Scopus ID 57219269059; Sergey Yu. Sokovnin, Scopus ID 6601905930. Websites: Institute of Solid State Chemistry, https://www.ihim.uran.ru; Institute of Electrophysics, http://iep.uran.ru; Ural Federal University, https://urfu.ru/ru. References 1. Erathodiyil N, Ying JY. 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