Prostaglandin J2 br Fig a The standard curve
Fig. 5. (a) The standard curve for DOX detec-tion at the absorbance wavelength of 480 nm (inset is the Absorbance intensity for initial solution and supernate before and after drug loading process). (b) DOX release eﬃciency of FeSiAuO–DOX at pH 4.35 and 7.4 PBS buﬀers.
ratio and pore structure of the nano-carrier is indispensable. Fig. 4b and inset of Fig.4b show the N2 adsorption/desorption isotherms and the pore size distribution curve of FeSiAuO nanoparticles. It can be seen that the composite has a type IV isotherm and a typical type H1 hysteresis loop, which proves the existing of mesoporous structure. Besides, the specific surface area and average pore diameter of the material were calculated to be 365.24 m2/g and 10 nm respectively. The formation of the pore structure is derived from the etching eﬀect of alkaline solution to SiO2 and the simultaneous in-situ growth of the Au2O3 on its surface. Accordingly, FeSiAuO composites have a smaller particle size (about 20 nm) while maintaining a high specific surface area, which provides a foundation for its application in fields of drug release, magnetic separation and targeting localization.
3.2. Drug release assay
To further evaluate the ability to load and release DOX of FeSiAuO nanocarriers, the FeSiAuO-DOX system was obtained bymixing FeSiAuO and DOX in the dark for 24 h, whose supernatant were col-lected and absorbance was measured by UV–vis Prostaglandin J2 spectrum at wavelength of 480 nm. DOX loading eﬃciency (DLE) and DOX loading capacity (DLC) were calculated to be 62.3% and 5.2% (Fig.5a). Finally, as-obtained FeSiAuO-DOX was used to continue drug release studies. We chose PBS solution with pH = 4.35 and pH = 7.4 similar to the tumor site and the normal tissue physiological environment as the re-lease medium . Results was shown in Fig. 5b, revealing that only 15.7% of DOX was release after 25 h when the pH is 7.4. In contrast, from whole sustaining release at the condition of pH = 4.35, we can observe that 39.5% of DOX is rapidly released in the first 3 h. 54.6% of DOX has been released after 25 h, which is caused by the weakening of the interaction between −COOH in DOX and −OH in FeSiAuO in a slightly acidic environment. The DOX was released more eﬀectively from the drug-loaded system at the acid environment, indicating that release process has the characteristic of pH responsiveness. Moreover, release eﬃciency of DOX will increase when introduce light irradiation
into system during the release period. As shown in Fig. 5c, the release eﬃciency of DOX was significantly enhanced in a several periods of light irradiation. The final release eﬃciency reached 67% when pH value is 4.35. Meanwhile, the release eﬃciency of DOX is also increased to 21% at pH of 7.4 under the same light conditions. The TEM image of the FeSiAuO–DOX-PEG sample after 540 nm irradiation (560 nm, 0.2 W/cm2) was shown in Fig. 5d. It can be observed that the number of inlaid Au/Au2O3 nanoparticles were decreased compared with that in Fig. 1d, which further infer us that the transaction of the Au2O3 to Au and O2. When light is introduced, Au2O3 insides the SiO2 will decom-pose into Au and O2, and release O2. The O2 release process can also make the DOX molecule loaded in the SiO2 unstable and accelerate the drug releasing.
3.3. Biocompatibility, intracellular singlet oxygen and cell uptake
Biocompatibility of drug carriers is a key factor in biomedical ap-plications, only non-toxic nanocarriers can be used in drug delivery system. To evaluate the cell viability of FeSiAuO carrier, L929 fibro-blasts and diﬀerent concentrations of FeSiAuO nanocarrier solutions were co-cultured for 24 h and 48 h, and the cell viability was assayed by MTT analytical techniques. In Fig. 6a, compared with the blank control, The L929 cells has no obvious cytotoxic eﬀect when the concentration of FeSiAuO in the range of 7.813–500 μg/mL. The cell survival rate is up to 95% when the FeSiAuO of 500 μg/mL cultured with cells for 24 h, and survival rate of the cells is still above 90% when cultured for 48 h, which proves the good biocompatibility of FeSiAuO and preliminarily confirms its potential application in biomedical field. Afterward, the intracellular dissolved oxygen improving ability of the FeSiAuO was examined. Fig. 6b exhibits the change of dissolved oxygen concentra-tion of the FeSiAuO under light irradiation, during which the [Ru (dpp3)]Cl2 was used as the O2 probe because it can be oxidized by the dissolved O2 and fade under the excitation light. From the decreasing tendency of the fluorescence signal of the [Ru(dpp3)]Cl2, it can be concluded that the dissolved oxygen increases significantly during