Article pubs.acs.org/Langmuir
ATP-Responsive Controlled Release System Using AptamerFunctionalized Mesoporous Silica Nanoparticles Xiaoxiao He,† Yingxiang Zhao,† Dinggeng He, Kemin Wang,* Fengzhou Xu, and Jinlu Tang State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Biology, College of Chemistry and Chemical Engineering, Hunan University, Key Laboratory for Bio-Nanotechnology and Molecular Engineering of Hunan Province, Changsha 410082, People’s Republic of China S Supporting Information *
ABSTRACT: Adenosine-5′-triphosphate (ATP) is a multifunctional nucleotide, which plays a vital role in many biological processes, including muscle contraction, cells functioning, synthesis and degradation of important cellular compounds, and membrane transport. Thus, the development of ATP-responsive controlled release system for bioorganism application is very significative. Here, an original and facile ATP-responsive controlled release system consisting of mesoporous silica nanoparticles (MSN) functionalized with an aptamer as cap has been designed. In this system, the ATP aptamer was first hybridized with arm single-stranded DNA1 (arm ssDNA1) and arm single-stranded DNA2 (arm ssDNA2) to form the sandwich-type DNA structure and then grafted onto the MSN surface through click chemistry approach, resulting in blockage of pores and inhibition of guest molecules release. In the presence of ATP, the ATP aptamer combined with ATP and got away from the pore, leaving the arm ssDNA1 and ssDNA2 on the surface of MSN. The guest molecules can be released because single-stranded DNA is flexible. The release of the guest molecules from this system then can be triggered by the addition of ATP. As a proof-of-principle, Ru(bipy)32+ was selected as the guest molecules, and the ATP-responsive loading and release of Ru(bipy)32+ have been investigated. The results demonstrate that the system had excellent loading efficiency (215.0 μmol g−1 SiO2) and the dye release percentage can reach 83.2% after treatment with 20 mM ATP for 7 h. Moreover, the ATP-responsive behavior shows high selectivity with ATP analogues. However, the leakage of Ru(bipy)32+ molecule is neglectable if ATP was not added, indicating an excellent capping efficiency. Interestingly, this system can respond not only to the commercial ATP but also to the ATP extracted from living cells. By the way, this system is also relatively stable in mouse serum solution at 37 °C. This proof of concept might promote the application of ATP-responsive devices and can also provide an idea to design various target-responsive systems using other aptamers as cap.
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INTRODUCTION Mesoporous silica nanoparticles (MSN) have been used as a promising carrier for the design of an “on-command” delivery system because of their distinctive characteristics, such as large load capacity, biocompatibility, high thermal stability, homogeneous porosity, inertness, tunable pore sizes (2−10 nm), and easy functionalization of the external and internal surfaces.1 To date, many MSN-based controlled-release systems have been constructed by using polymers,2 nanoparticles,3 small organic molecules,4 supramolecular assemblies,5 and biomolecules6 as capping agents. Triggered by the physical or chemical stimuli such as pH,7 redox,8 temperature,9 competitive binding,10 antigen,11 photoirradiation,12 and enzymes,13 the zero release of guest molecules from the MSN system can be achieved. Despite these burgeoning achievements, the development of MSN controlled-release systems responding to biogenic stimuli such as intracellular pH and ions, small biomolecules, and some metabolic products is very popular for practical application in biomedical fields. With this in mind, some pH-responsive MSN controlledrelease systems based on the lower pH of endosomes and lysosomes in cells have been reported. For example, Shi et al.14 © 2012 American Chemical Society
constructed a kind of nano-MDDS drugs@micelles@MSNs, which responded to pH quite well in both vitro condition and vivo condition. Lee et al.15 selected inorganic calcium phosphate (CaP) as pore blocker by enzyme-mediated mineralization on the Si-MP surfaces, which was capable of releasing guest drugs from the CaP-blocked pore under pH control. Besides the endosomes and lysosomes pH, the biogenic biomolecules in cells such as glucose,16 collagen,17 thiol-containing molecules,18 and so on can also be used as stimuli to design MSN controlled-release systems. As one of the important biogenic biomolecules, ATP is a multifunctional nucleotide that is the ubiquitous energy currency for all living organisms through breaking the phosphoanhydride bond. It is used for many biological processes and can be used as an indicator for living microbe existence in clinical microbiology, food quality control, and environmental analyses.19 Therefore, exploring gate molecules that can specifically recognize ATP Received: July 9, 2012 Revised: August 11, 2012 Published: August 14, 2012 12909
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transform infrared (FTIR) spectra were obtained from a TENSOR 27 spectrometer, Bruker Instruments Inc., Germany. UV−vis spectra were collected by DU-800. N2 adsorption−desorption isotherms were obtained at −196 °C on a Micromeritics ASAP 2010 sorptometer by static adsorption procedures. Samples were degassed at 100 °C and 10−3 Torr for a minimum of 12 h prior to analysis. Brunauer− Emmett−Teller (BET) surface areas were calculated from the linear part of the BET plot according to IUPAC recommendations. Pore size distribution was estimated from the adsorption branch of the isotherm by the Barrett−Joyner−Halenda (BJH) method. Small-angle powder X-ray diffraction patterns (XRD) of the MSN materials were obtained in a Scintag XDS-2000 powder diffractometer, using Cu Kα irradiation (λ = 0.154 nm). All fluorescence spectra were recorded on a Hitachi F7000 spectrophotometer in Tris-HCl buffer and physiological saline solution. Preparation of Mesoporous Silica Nanoparticle (MSN). 0.50 g of CTAB was dissolved in 240 mL of pure water. Next, sodium hydroxide (1.75 mL, 2 M) was added, followed by adjusting the solution temperature to 80 °C. TEOS (2.50 mL) was added dropwise into the mixture solution under vigorous stirring. The mixture was continually stirred for 2 h to give rise to white precipitates. The solid product was separated by centrifugation, and washed with deionized water and ethanol several times. Subsequently, the purified nanoparticles were dried in a high vacuum container at 60 °C overnight. Preparation of Chlorine-Modified MSN (MSN-Cl). 0.70 g of prepared MSN was refluxed for 20 h in 60 mL of anhydrous toluene with 0.70 mL of 3-chloropropyltrimethoxysilane (ClTMS) to yield the chlorine-modified MSN (MSN-Cl). To remove the surfactant template (CTAB), 0.50 g of MSN-Cl was stirred at 79 °C in a mixture containing 0.50 mL of HCl (37.2%) and 50 mL of ethanol. The resulting material was centrifuged and extensively washed with nanopure water and ethanol. The surfactant-free particles were then placed under high vacuum with heating at 60 °C to remove the remaining solvent from the mesopores. Preparation of MSN-N3. 100 mg of the obtained MSN-Cl sample was dispersed in 20 mL of anhydrous DMF, followed by transferring it into a 100 mL Schlenk flask equipped with a Soxhlet extractor under nitrogen atmosphere, which was filled with a dried molecular sieve with a 4 Å pore size. The drying process was carried out for 3 h at 90 °C, and the resulting suspension was saturated with 100 mg of NaN3. After being stirred for 5 h at 80 °C, the obtained particles were washed three times with 50 mL of water to yield sample MSN-N3. Ru(bipy)32+ Loading and Capping. 1.5 mL of 100 μM of arm ssDNA1, arm ssDNA2, and ATP-aptamer was added into the centrifuge tube, with heating at 95 °C for 5 min. The DNA mixture solution was then cooled slowly for hybridization to obtain the ATP aptamer-containing sandwich-type DNA structure. Separately, 10 mg of MSN-N3 was soaked in a solution of Ru(bipy)32+ (2 mM) in TrisHCl buffer for 24 h, followed by the addition of 150 nmol of prehybridized ATP aptamer-containing sandwich-type DNA. Thereafter, 1 μL of CuBr solution (0.1 M in DMSO/tBuOH 3:1) and 2 μL of the tris-(benzyltriazolylmethylamine) ligand solution (0.1 M in DMSO/tBuOH 3:1) were added into the mixture and stirred at 4 °C for 48 h to form the ATP aptamer-containing sandwich-type DNA capped MSN. The obtained nanoparticles were then centrifuged and washed thoroughly with Tris-HCl buffer to remove the adsorb guest molecules and then dried in a vacuum freeze drier to yield the ATP aptamer-containing sandwich-type DNA-capped MSN (aptamer− MSN) with encapsulation of Ru(bipy)32+. The control DNAcontaining sandwich-type DNA-capped MSN (denoted as con DNA−MSN) was obtained by the same procedures above using control DNA instead of ATP aptamer. All of the washing solutions were collected, and the loading amount of Ru(bipy)32+ was calculated from the different absorbances between the initial and left dyes. In addition, the stability of the aptamer−MSN system in mouse serum at 37 °C has been investigated by estimation of the precipitation of the aptamer−MSN and the dye leakage from the pores. Extraction of ATP from the Ramos Cells. Ramos cells were used to demonstrate the application of this ATP-responsive controlled release system upon the ATP obtained from the living cells. Ramos
and design the ATP-responsive MSN-based system is very encouraging. It is well-known that a variety of fluorescent,20 electrochemical,21 and colorimetric aptasensors22 have been developed for ATP detection based on the aptamer−ATP interaction.23 Meanwhile, taking advantages of the unique characteristic and chemical structure of ATP aptamer, the ATP-responsive MSNbased systems have also been reported and demonstrated improved performance in controlled release. For example, Yang et al.24 employed aptamer-modified Au nanoparticle to close the pores, which can be opened in the presence of ATP through the competitive binding. They have demonstrated for the first time that the aptamer−target interaction could be used as a stimuli-responsive mechanism in controlled-release systems. However, the Au nanoparticles must be involved in this system. Subsequently, Ö zalp et al.25 selected ATP aptamer, which extended 8 bases so that it can hybridize with the first 8 bases in its 5′-end to close the pore. As we known, the extending or decreasing of aptamer sequence might affect its affinity and selectivity. For overcoming the above limitations, we design a facile and effective ATP-responsive controlledrelease system using ATP aptamer-functionalized MSN. In the system, ATP aptamer was hybridized with arm ssDNA1 and arm ssDNA2 to form sandwich-type DNA structure and subsequently grafted on the pore outlets of MSN to block the nanochannels of MSN. In the absence of ATP, the pores of MSN were blocked, and the leakage of guest molecules was inhibited. In the presence of ATP, a competitive reaction took place due to higher affinity and tighter binding of ATP aptamer with ATP than that of ATP aptamer with arm ssDNA, resulting in the opening of pores and the release of guest molecules. To demonstrate the feasibility of this principle, Ru(bipy)32+ was selected as a model guest molecule to investigate the controlled release behavior of the aptamer-functionalized MSN system.
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EXPERIMENTAL SECTION
Chemicals and Materials. N-Cetyltrimethylammonium bromide (CTAB, ≥99%), CuBr (99.9%), tris(hydroxymethyl)aminomethane (Tris), and 3-chloropropyltrimethoxysilane (ClTMS, 97+%) were purchased from Alfa Aesar. Sodium azide (NaN3, 99%) and mouse serum were obtained from Dingguo reagent Co. (Beijing, China). [Ru(bipy)3]Cl2 (bipy = 2,2′-bipyridine) dye (Ru(bipy)32+) was purchased from Sigma-Aldrich. Sodium hydroxide (NaOH), ammonium hydroxide solution (25%), N,N-dimethylformamide (DMF), and tetraethylorthosilicate (TEOS, 28%) were purchased from Xilong reagent Co. (Guangdong, China). Adenosine 5′-triphosphate (ATP), guanosine 5′-triphosphate (GTP), cytosine 5′-triphosphate (CTP), and uridine 5′-triphosphate (UTP) were purchased from ShangHai BoYa Biotechnology Co. Ltd. All buffers were prepared with ultrapure Milli-Q water (resistance >18.2 MΩ cm−1). The oligonucleotides were synthesized by Sangon Biotechnology Inc. (Shanghai, China). The sequences are as follows: ATP-aptamer, 5′-CAC CTG GGG GAG TAT TGC GGA GGA AGG TT-3′; arm single-stranded DNA1 (arm ssDNA1), 5′-alkyne-TTC CTC CGC A-3′; arm single-stranded DNA2 (arm ssDNA2), 5′-alkyne-ATA CTC CC-3′; nonaptamer structure DNA (control DNA), 5′-TTT TTT TGG GAG TAT TGC GGA GGA ATT TT-3′. The Tris-HCl buffer contains 10 mM Tris and 100 mM NaCl, pH 7.4. Ramos cells (B cell line, human Burkitt’s lymphoma) were purchased from the Cancer Institute & Hospital (Chinese Academy of Medical Sciences). Characterization. High-resolution transmission electron microscopy (HRTEM) image was obtained from a JEOL 3010 microscope with an accelerating voltage of 100 kV. Scanning electron microscopy (SEM) image was obtained from a JSM-6700F microscope. The hydrodynamic diameter and size distribution of MSN were measured by dynamic light scattering (DLS), Malvern Inc., England. Fourier 12910
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cells were cultured in RPMI 1640 medium supplemented with 15% fetal bovine serum (FBS) and 100 IU/mL penicillin−streptomycin solution and incubated at 37 °C in a humidified incubator containing 5 wt %/vol CO 2 . The cell density was determined using a hemocytometer prior to any experiments. Well cultured Ramos cells were centrifuged at 3000 rpm for 5 min to remove the growth medium and washed with physiological saline solution three times, and then resuspended in 1 mL of physiological saline solution. The suspension was experimentally subjected to three freeze−thaw cycles (30 min each at −20 and +40 °C) to break the cell membrane so that the ATP can skip into the physiological saline solution. Ru(bipy)32+ Releasing. One milligram of aptamer−MSN was dispersed in 1 mL of Tris-HCl buffer containing 20 mM commercial ATP at 25 °C. Subsequently, 0.20 mL of supernatant was taken periodically from the suspension at 25 °C followed by centrifugation (15 000 rpm, 10 min). The release of Ru(bipy)32+ from the pore voids to the buffer solution was determined by fluorescence emission spectroscopy (ex at 454 nm, em at 598 nm). In addition, the response of the aptamer−MSN to the ATP obtained from living cells has also been investigated following the same procedures.
of as-synthesized MSN was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction patterns (XRD), and N2 adsorption−desorption isotherms. As shown in Figure 1, the SEM image (Figure 1a) illustrated that the as-
Figure 1. SEM (a) and TEM (b) images of as-synthesized MSN.
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RESULTS AND DISCUSSION For the design of the stated controlled release system, two components were chosen, a solid supporter and the ATPresponsive molecule-gated switch. In this work, MCM-41-type MSN was selected as a suitable inorganic material because of its unique features. For the gating mechanism, our attention was focused on the ATP aptamer. The working principle was illustrated in Scheme 1. ATP aptamer, arm ssDNA1, and arm
synthesized MSN had narrow size distribution. The TEM image (Figure 1b) showed a typical hexagonally arranged porosity and well disparity of MSN containing parallel pores with two openings. From the TEM image, it was demonstrated that the diameter of MSN was about 80 nm. Here, we also measured the particle size in aqueous suspension by DLS. It was shown that the diameter of MSN was 208 nm with a polydispersity index (PDI) of 0.105 (Figure S1). The reason for this was that the DLS values of nanoparticles in aqueous solution are always larger than solid-state diameters in a monolayer in air by TEM due to the swell in aqueous solution. The low-angle reflection typical of a hexagonal array, which could be indexed as (100) Bragg peaks, further confirmed the structure of MSN (Figure 2a). Moreover, the N2 adsorption− desorption isotherms (Figure 2b) of the material presented an
Scheme 1. Schematic Illustration of Aptamer-Based ATPResponsive MSN System
ssDNA2 were first hybridized to each other to form ATP aptamer-containing sandwich-type DNA structure. The immobilization of the sandwich-type DNA structure on the surface of MSN would then result in the blockage of pores and the package of guest molecules. However, the addition of ATP as the target molecule induced a competitive displacement reaction to the sandwich-type DNA structure. ATP aptamer combined with ATP molecule and departed from the sandwichtype DNA structure. The guest molecules could be released because the left flexible arm ssDNA on the surface of MSN could not block the pores. To clearly show the loading and release processes, Ru(bipy)32+ dye was chosen as a model guest molecule. Following this procedure, we first synthesized MSN according to the previously reported procedure.18 The structure
Figure 2. (a) XRD and (b) BET nitrogen sorption isotherms of MSN. Inset: BJH pore volume and pore size distribution plots of MSN. 12911
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adsorption step at an intermediate P/P0 value (0.2−0.4) typical of MCM-41-type structure. The application of BET model resulted in a value that the total surface area is 963.5 m2 g−1. The BJH curve showed a narrow pore size distribution of MSN with an average pore diameter of 2.8 nm and pore volume of 1.0 cm3 g−1 (Figure 2b, inset). The characteristics of the assynthesized MSN were all summarized in Table S1. The as-synthesized MSN was then modified with a chlorine group and further treated with sodium azide in DMF to obtained MSN-N3. Ru(bipy)32+ was then chosen as guest molecule to load into the pores of MSN-N3 by soaking the particles into 2 mM of Ru(bipy)32+ solution. Subsequently, the preobtained ATP aptamer-containing sandwich-type DNA structure was immobilized on the MSN-N3 surface to block the pores and reserve the Ru(bipy)32+, giving rise to the aptamer−MSN samples. The loading amount of Ru(bipy)32+ was determined to be 215.0 μmol g−1 SiO2 calculated using the standard curve of Ru(bipy)32+ (Figure S2 in the Supporting Information). The successful conversion of the MSN surface was confirmed by FTIR. As shown in Figure 3, the absorption
Figure 4. Time course of Ru(bipy)32+ release profiles: (a) aptamer− MSN without ATP, (b) con DNA−MSN without ATP, (c) aptamer− MSN with 20 mM ATP, and (d) con DNA−MSN with 20 mM ATP.
pores would be opened. As for the con DNA−MSN, in the presence of ATP, the release of Ru(bipy)32+ from the pores was much lower than that from the aptamer−MSN system (Figure 4d). Of course, 21.2% release was still observed when the con DNA−MSN was treated with 20 mM ATP for 7 h. The most probable reason was that the control DNA sequence has the same 18 bases as that of the ATP−aptamer. Therefore, the ATP might also nonspecifically bind with the control DNA and result in some release. In addition, the amount of released Ru(bipy)32+ from the aptamer−MSN was dependent on the added amount of ATP molecules (Figure 5). In a lower ATP
Figure 3. FTIR spectra of materials before and after modification: (a) MSN, (b) MSN-N3, and (c) aptamer−MSN.
band around 2110 cm−1 was assigned to the azide stretch. MSN (Figure 3a) had no adsorption around 2110 cm−1, while MSNN3 (Figure 3b) showed obvious absorption band at that wavenumber, indicating that the −N3 group was successfully grafted onto the surface of MSN. As compared to MSN-N3, the adsorption band of aptamer−MSN (Figure 3c) around 2110 cm−1 was distinctively declining, confirming the reaction between alkynes and −N3 group. It suggested that the ATP aptamer-containing sandwich-type DNA structure was successfully tethered to MSN-N3. The quantity of sandwich-type DNA anchored on the surface of MSN was determined by UV−vis spectroscopy to be approximately 1.6 μmol g−1 SiO2 (Figure S3 in the Supporting Information). Continuous guest molecules release experiments had been done to test the gate property of the designed system. The ATP-triggered release of Ru(bipy)32+ was monitored by fluorescence emission spectroscopy at 598 nm. To both Ru(bipy)32+ loaded aptamer−MSN and con DNA−MSN (Figure 4a and b), a negligible Ru(bipy)32+ release from the pores was observed when ATP was not added, indicating a good retention efficiency of Ru(bipy)32+ in the pores of the MSN by virtue of capping with sandwich-type DNA structure. In contrast, the Ru(bipy)32+ release from the aptamer−MSN system reached 83.2% of the total load after the introduction of 20 mM ATP for 7 h (Figure 4c). The result demonstrated that the aptamer-containing sandwich-type DNA structure could be dissociated through a competitive binding with ATP, and the
Figure 5. Controlled release of Ru(bipy)32+ from aptamer−MSN system triggered by ATP as a function of concentration, measured after 48 h.
concentration region, the fluorescence intensity of the released Ru(bipy)32+ increased dramatically with the increase of added ATP amount. While the rising rate of fluorescence intensity slowed when the ATP concentration was higher than 5 mM, it was mainly a constant when the ATP concentration was higher than 20 mM. The maximum release was observed at 20 mM of ATP, suggesting that the ATP aptamer combined with ATP thoroughly at this ATP concentration. In the design of controlled release systems, the selectivity is very important. Further control experiments were implemented to investigate the selectivity of the aptamer−MSN system. Figure 6 illustrated that ATP analogues, such as GTP, CTP, and UTP, induced a small quantity of guest molecules to release, while ATP induced a dramatic release of loaded guest molecules. This result obviously indicated that the aptamer− MSN system had sufficient selectivity to ATP and was able to discriminate ATP from its analogues. In addition, the stability of the particle is very important in cargo release application. To explore the application potential of the aptamer−MSN system, we investigated its stability in mouse serum at 37 °C by estimation of the precipitation of the 12912
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It is well-known ATP is a multifunctional nucleoside triphosphate and widely used in cells as energy metabolism. To demonstrate whether the developed aptamer−MSN controlled release system could be responsive to the ATP obtained from living cells, we investigated the release effect of the aptamer−MSN upon the ATP in the Ramos cells extracts. As shown in Figure 8, the fluorescence intensities in the
Figure 6. Selectivity of the aptamer−MSN system. The concentration of ATP, CTP, UTP, and GTP is 20 mM, respectively. The results were measured after incubation for 7 h.
particles and the dye release. As can be seen in Figure 7, the Ru(bipy)32+ released percentage was only about 4.1% when the
Figure 8. Dye release effect of the aptamer-based drug delivery system using ATP extracted from living cells as stimuli: (a) aptamer−MSN in physiological saline solution, (b) aptamer−MSN in broken cell suspension (7.1 × 107 cells mL−1), (c) con DNA−MSN in physiological saline solution, and (d) con DNA−MSN in broken cell suspension (7.1 × 107 cells mL−1). All were treated for 7 h.
supernatant of aptamer−MSN and con DNA−MSN were both relatively low when they were treated with the pure physiological saline solution at 25 °C for 7 h, indicating few leakages of guest. Differently, the fluorescence intensity in the supernatant of aptamer−MSN was greatly increased after it was incubated in the physiological saline solution containing extracted ATP from Ramos cells for 7 h, suggesting that the aptamer−MSN system could also respond to ATP, which was extracted from the living cells. What is more, the fluorescence intensity in the supernatant of con DNA−MSN was much lower than that of aptamer−MSN, indicating that the aptamer− MSN system also kept its good selectivity in cell lysates.
Figure 7. Time course of Ru(bipy)32+ release profile in mouse serum at 37 °C. Inset: (a) mouse serum; (b) aptamer−MSN in mouse serum, 0 h; (c) aptamer−MSN in mouse serum, 3 h; (d) aptamer−MSN in mouse serum, 7 h; and (e) the centrifugation of aptamer−MSN after incubating in mouse serum for 7 h.
aptamer−MSN particles were treated with mouse serum at 37 °C for 3 h. When the incubation time was further increased to 7 h, the Ru(bipy)32+ release percentage was increase to 9.2%. By comparison with the aptamer−MSN that was incubated with 20 mM ATP for 7 h, the dye release of aptamer−MSN in the mouse serum at 37 °C for 7 h was much lower. These results indicated that the ATP aptamer containing sandwich-type DNA can also effectively block the pores of MSN in the mouse serum. The photo pictures inset in Figure 7 displayed the precipitation procedure of aptamer−MSN in mouse serum at 37 °C. The color of mouse serum (Figure 7, inset a) was pale yellow and transparent, while the color of aptamer−MSN dispersed mixture (Figure 7, inset b) was deeper and nontransparent, implying that the particles dispersed in mouse serum well. As displayed in Figure 7, inset c, there was a small quantity of orange-yellow particles precipitate in the bottom of the centrifuge tube after it was dispersed in mouse serum for 3 h due to the action of gravity, but the supernatant was still relatively opaque. It suggested that the majority of the particles were still well-dispersed in the serum. Differently, a large proportion of the orange-yellow particles precipitated 7 h later, and the supernatant became semitransparent (Figure 7, inset d). When the mixture was centrifuged, as Figure 7, inset e displayed, the supernatant of the sample was transparent again, and the color was almost the same as that of the mouse serum, confirming there was no obvious leakage of Ru(bipy)32+ and good blockage behavior of the sandwich-type DNA. The data above indicated that the aptamer−MSN was stable in physiological-like conditions.
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CONCLUSION We have designed an easy-to-achieve and prevalent aptamerbased ATP-responsive MSN system. In this system, ATP aptamer was hybridized with two arm ssDNA to form the sandwich-type DNA structure and then tethered to the surface of MSN to inhibit the guest molecules from skipping out of the pores. The Ru(bipy)32+ molecules as model guests had been encapsulated into pores of MSN. The release profile was dependent on the leaving of aptamer due to the competitive binding between ATP and ATP aptamer. The results demonstrated that the system had a high loading amount of guests (215.0 μmol g−1 SiO2) and good release behavior in the presence of ATP. Furthermore, the system responded not only to the commercial ATP but also to the ATP, which was extracted from the living cells. This proof of concept might promote the application of aptamer in constructing other target-responsive MSN-based drug delivery systems by using aptamers of other targets such as ions, small biological molecules, biological macromolecules, bacteria, and cells instead of ATP−aptamer. Also, it can promote the application of ATP-responsive systems. 12913
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ASSOCIATED CONTENT
S Supporting Information *
Size distribution of as-synthesized MSN in aqueous suspension measured by dynamic light scattering (DLS), standard curve of Ru(bipy)32+ measured by UV−vis spectrometer and UV−vis spectra of initial and left Ru(bipy)32+, and a table corresponding to their characterization. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Author Contributions †
These authors contributed equally.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported in part by the Project of Natural Science Foundation of China (21175039, 20905023, and 21190044), Key Technologies Research and Development Program of China (2011AA02a114), Research Fund for the Doctoral Program of Higher Education of China (20110161110016), and the project supported by Hunan Provincial Natural Science Foundation and Hunan Provincial Science and Technology Plan of China (10JJ7002, 2011FJ2001).
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