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Molecules 2019, 24, 2692 3 of 17 groups on the surface of UCNPs [20]. In the NaYF4:Yb,Er/Ce6 composites, after hydrolysis, the silane forms a very thin hydrophilic coating, which means the hydrophobic UCNPs were converted to hydrophilic ones without increasing size and influencing the luminescent centers on the surface of UCNPs, since the hydrophobic side chain of the silane does not touch the surface of UCNPs. In addition, this design successfully avoids the leakage problem in conventional photosensitizer carriers by physical adsorption, such as photosensitizer loading in mesopores UCNP@mSiO2 NPs [19], which may lead to serious leakage problems, causing systemic toxic side effects as well. As the PDT function of Ce6 molecule should be triggered by excitation of red light, Mn doping is involved in this work, which greatly improves the probability of the red emission transition [18,21]. As a result, the enhanced upconversion red emission greatly improved the PDT effect on periodontal disease. The Ce6 loaded UCNPs composites with efficient red upconversion luminescence could be potentially employed for aPDT applications. 2. Experiments 2.1. Preparation of NaYF4:Yb3+,Er3+-Mn UCNPs All experiments NaYF4:Yb3+,Er3+ UCNPs were synthesized by a high temperature thermal decomposition method. The specific experimental steps are as follows: 2.5 mmol NaOH and 4 mmol NH4F were dissolved in the 5 mL of methanol.0.78 mmol YCl3•6H2O, 0.20 mmol YbCl3•6H2O and 0.02 mmol ErCl3•6H2O were added in a three-necked flask and dissolved in 15 mL octadecene and 6 mL oleic acid and stirred. After the contents in the three-necked flask were dissolved at 80 ◦C, the whole three-necked flask was cooled to 30 ◦C, and the methanol solution was added dropwise, and the mixed solution was magnetically stirred for 30 min. Then the solution was heated to 125 ◦C and the methanol solution was evaporated. After the complete evaporation of methanol, it was heated to 320 ◦C under nitrogen for one hour. When the temperature of the solution was cooled to room temperature, the product was washed with a 1/1 ratio of ethanol and deionized water, and the final sample was obtained. Note that during the reaction those products are rapidly oxidized by oxygen in the air, and the desired sample cannot be prepared. Therefore, nitrogen is used as an inert gas, which is very necessary for protection. For the NaYF4:Yb3+,Er3+,Mn2+ UCNPs, the corresponding MnCl2 were added together with lanthanide elements, and the doping ratio of Mn is 0%, 10%, 20%, 30%, respectively [21]. 2.2. Preparation of NaYF4:Yb3+,Er3+@Ce6@Silane Composites with and without Mn Doping The amphiphilic silane has a hydrophobic alkane chain with a chain length of 18 carbon atoms. The silane was first dissolved in tetrahydrofuran solvent according to a mass ratio of silane/NaYF4=1/2. After that, Ce6 molecules were added to the mixed solution of NaYF4:Yb3+,Er3+ and silane in a certain ratio, and mixed under ultrasonic conditions for half an hour. Then the mixed solution was quickly injected into ammonia water with a pH of 9. After 3 hours of the hydrolysis reaction, it was transferred into a dialysis bag (molecular weight cutoff of 8000–14,000) for dialysis. The resulting upconversion composite not only has the function of up-converting fluorescent labeling, but also has PDT function. Mn doped UCNPs followed the same modification process with Ce6 and silane. 2.3. Characterization of NaYF4:Yb3+,Er3+@Ce6@Silane Composites with and without Mn Doping The XRD measurement of the prepared samples was carried out using a Rigaku D/max 2550 X-ray diffractometer with a test angle of 15 to 80 degrees; the morphology of the synthesized samples was measured by a transmission electron microscope (TEM) of Hitachi H-800 (Hitachi, Ltd., Tokyo, Japan) with an operating voltage of 200 kV; The Fourier infrared (FTIR) spectra Shimadzu DT-40 model 883 IR spectrophotometer (Shimadzu Co., Kyoto, Japan) was used to measure the organic groups on the surface of UCNPs. For the specific operation process, 3 mL of the samples (UCNPs and UCNPs@silane at an approximate concentration of 4 μg/mL) was taken to be tested with the addition of potassium bromide powder, placed in an oven at 60 degrees Celsius, and the samples were dried for two daysPDF Image | Anti-Biofilm Property of Bioactive Upconversion Nanocomposites
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