DNA-Templated Rational Assembly of BaWO4 Nano Pair-Linear

Sep 13, 2010 - DNA-based nanowires. Towards bottom-up nanoscale electronics. Andrew Houlton , Scott M. D. Watson. Annual Reports Section "A" (Inorgani...
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DNA-Templated Rational Assembly of BaWO4 Nano Pair-Linear Arrays Na Li, Faming Gao,* Li Hou, and Dawei Gao Key Laboratory of Applied Chemistry, Yanshan UniVersity, Qinhuangdao 066004, China ReceiVed: February 10, 2010; ReVised Manuscript ReceiVed: August 27, 2010

Confining the growth of inorganic materials in patterns using DNA as a molecular guide represents a versatile system for nanoscale construction. Here, we report the first example of efficiently attaching BaWO4 nanocrystals to dsDNA skeleton forming in patterns of well-defined nano pair-linear arrays. We have studied the influences of solution temperatures and concentrations of reagents on the pair-linear morphology. Results indicate that the two factors play the important roles in synthesizing the stable and desired patterned pair-linear arrays. We have tested four kinds of oligonucleotides to investigate systematically how nucleotide functionalities influence nanoparticle growth. We find that the phosphate and possibly the amino moiety binding site on adenine are the favorable targets to feed nanoparticle growth. On the basis of our findings, possible mechanisms are discussed. 1. Introduction Research on nanoparticles has focused on the assembly strategies to control the arrangement of nanoparticles.1-5 Morphology-controlled synthesis of inorganic nanostructures has attracted significant interest due to the importance of the geometrical forms of materials in determining their widely varying properties.6-9 For this to be realized, a major advance would be to devise a method for constraining the growth of materials into desirable geometrical forms. At first glance, artificial templates could offer distinct advantages through template pattern control. However, the adjustment of the template pattern relies on, in many cases, the discrete choice of existing structures, which makes the tailorability a challenging task. Meanwhile, in some template self-assembly methods, such a strategy can be exploited only when the target materials are comprised of certain compositions or appropriate attachment chemistries.10 In this regard, a variety of less conventional techniques have been developed.11-15 Among these techniques, sacrificial molecular guides typically consist of soft materials that can physically guide nanoscale structures into complex patterns or geometries. Deoxyribonucleic acid (DNA) is arguably the most remarkable molecular guide and used as a structural material16-22 rather than as a carrier of biological information because of the many possibilities it offers for creating defined nanostructures. A great deal of progress has been made in the preparation of one-, two-, and three-dimensional (1D, 2D, and 3D) nanoparticle arrays using DNA as a molecular guide. Richter4 and Dong5 showed the DNA-templated 1D organization of metal or semiconductor material into well-defined nanochains and nanowires, respectively. Ingeniously, Rothemund23 presented a versatile and simple method for folding the long strand into the desired shapes by a number of smaller strands. Also, Sharma24 described an elegant strategy for using single-stranded DNA (ssDNA) as a molecular glue to direct gold nanoparticles (AuNPs) into periodic 3D architectures. These types of 1D, 2D, or 3D complexities reflect the power of DNA as building blocks for creating a number of more complex nanostructures. * Corresponding author. E-mail: [email protected].

DNA’s remarkable molecular recognition properties and structural features make it potentially ideal templates to dictate the precise positioning of materials and molecules into any deliberately designed structure. Nonetheless, the straight, wellordered assembly of BaWO4 nanoparticles with the guidance of DNA templates has remained unsuccessful so far. Barium tungstate (BaWO4) is an important potential material with its interesting optical properties and will have a high application potential for the development of medical laser treatment applications, up-conversion fiber lasers, and analogous spectroscopic, et al.25-27 A lot of efforts have been made to prepare BaWO4 nanostructures with different sizes and morphologies.28-32 However, the controlled morphology and rational assembly of BaWO4 nanoparticles still remain a significant challenge. Herein, we report a simple method for the preparation of BaWO4 nano pair-linear arrays using DNA as a template. The ability of DNA that leads DNA to separate the double strands close to denaturation provides a unique opportunity to create nano pair-linear arrays. However, this principle has not been hitherto noticed by materials scientists. While any double-strand DNA (ds-DNA) can be used as a template to form the nano pair-linear arrays, we chose E. coli B genomic DNA, which is inexpensive and readily available. To our best knowledge, such attempts have never been performed. 2. Experimental Section 2.1. Reagents. Barium nitrate [Ba(NO3)2] and sodium tungstate dehydrate (Na2WO4 · 2H2O) were purchased from Shanghai Chemistry Co. and used without further purification. For demonstrating the formation mechanism, the repeat 10-base oligonucleotides (oligo) were used in our experiments, and the corresponding base sequences were represented as follows: oligo(dA), 5′-AAAAAAAAAA-3′; oligo(dT), 5′-TTTTTTTTTT3′; oligo(dG), 5′-GGGGGGGGGG-3′; oligo(dC), 5′-CCCCCCCCCC3′. The oligonucleotides were purchased from Shanghai Sangon Biological Engineering Technology & Services Co., Ltd. Aqueous stock solutions of the oligonucleotides were freshly prepared with ultrapure water. Other chemicals including the tris-EDTA buffer (PH 7.4) and proteinaseK were purchased from Sigma Co., Ltd. and used as received. UltraPure DNase/RNase-

10.1021/jp101292c  2010 American Chemical Society Published on Web 09/13/2010

Assembly of BaWO4 Nano Pair-Linear Arrays free distilled water (UPD water) (Invitrogen Corp.) was used in all synthesis experiments. 2.2. Synthetic Protocol. Before the experiment, a stock solution of E. coli B genomic DNA was prepared. E. coli B cells were cultured overnight in 50 mL of LB medium. Next, the cells were collected by centrifugation and resuspended in TE buffer [10 mM Tris (pH 8.0), 1 mM EDTA (pH 8.0)]. 10% SDS and 10 mg/mL proteinase K were added in the mixture, which was then incubated in a 50 °C water bath for 30 min. The mixture was extracted with equal volume phenol:chloroform:isoamyl alcohol (25:24:1) and centrifuged at 12 000 rpm for 10 min. The top layer was transferred to a new tube. The extraction process was repeated if necessary. Next, 2-fold volume absolute ethanol was added to the top layer. The solution was mixed by inverting to precipitate DNA. DNA was then spooled out and dissolved in deionized water. The electrophoresis and spectrophotometric analysis were used to check the purity of DNA. In our experiment, the BaWO4 nanoparticles were synthesized in aqueous solution without any surfactant. An aqueous solution of Ba(NO3)2 (200 µL, 5-20 mM) was added to a solution of E. coli B genomic DNA (200 µL, ca. 1.00 µg/µL). The mixtures were gently stirred for 24 h at 6 °C. An aqueous solution of Na2WO4 was dropped into an equimolar Ba(NO3)2 aqueous solution. The solution was mixed thoroughly and incubated for a further 24 h at 6 °C. The mixtures were heated at specific temperature (80-95 °C) for about 8 h. The reaction mixtures were allowed to store at 4 °C over more than 5 days for further analysis. These syntheses were reproducible and did not require post synthesis manipulation or processing. 2.3. Characterization. The size and morphology of the products were examined by transmission electron microscopy (TEM; JEM-2010). TEM samples were prepared by placing a droplet (20 µL) of our sample onto a 3 mm carbon-coated copper grid for 5 min. Afterward, the excess water evaporated at room temperature. The TEM investigations were operated at 200 kV for imaging. The presence of BaWO4-coated DNA provided very good contrast on the carbon-coated copper grid. The chemical composition of the products was characterized by energy-dispersive X-ray spectroscopy (EDXS). EDXS analysis was typically performed at an accelerating voltage of 200 kV, using an Oxford Link-ISIS X-ray EDXS microanalysis system attached to TEM. High-resolution TEM (HRTEM) and selected-area electron diffraction (SAED) were employed to examine the structure of the materials. HRTEM and SAED of the products were carried out on a JEM-2010 electron microscope instrument (JEOL Ltd.) and operated at an accelerating voltage of 200 kV. The crystalline phases were determined by X-ray powder diffraction (XRD). The XRD pattern of the BaWO4 nano pairlinear arrays was collected in the 2θ range 10°-100° with a D/max-2500/PC X-ray diffractometer using Cu KR (λ ) 0.15418 nm) radiation. The Raman measurements were performed in the backscattering geometry using a Renishaw Micro-Raman Spectroscopy System (inVia) at a laser excitation of 514.5 nm from an Ar+ laser. The typical spectral resolution for the Raman system was 1 cm-1. The Raman spectra were accumulated twice in the wavelength range of 100-3600 cm-1, and the accumulated time was 5 s. The system was calibrated by the spectra of a Si standard sample at room temperature, before and after recording the crystal spectra. Absorption spectra were recorded using a WFZ-26A UV-vis spectrophotometer. Our sample was characterized by adding

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Figure 1. TEM images of DNA-templated BaWO4 nano pair-linear arrays treated at 80 °C (a) and BaWO4 nanowire without heating process (c). The inset of (a) showing a higher magnified TEM image from a specific part of image a. Representative TEM images of bare DNA treated at 80 °C (b) and without heating process (d). Both (b) and (d) were negatively stained with 2% PTA. SAED pattern of our samples (e) indicates the crystalline nature of the particles. EDXS of DNAbased BaWO4 nano pair-linear arrays (f). The Cu and C peaks originate from the TEM grid.

deionized water until 3 mL aliquots, and deionized water was used as the reference. A standard quartz cell (Fisher) with a 10 mm path-length was used and rinsed with deionized water before each run. 3. Results and Discussion The controlled synthesis of nanoparticle pair-linear arrays is desirable for generating programmable structures with tunable properties. The ideal case would be to efficiently obtain regular pair-linear morphology by simply choosing pair-linear templates. DNA provides an excellent pair-linear template for spatially positioning inorganic materials with increased relative precision and programmability. A notable property of DNA is the melting of the double helix, which occurs over a narrow temperature range. Because of the notable nature typically associated with the discovery of new processes in this category, the reported systems thus far are very limited.33 In this contribution, we wish to report on a simple preparation route that relies on the use of DNA by facile adjustment of the temperature and the amount of reacting reagents. Figure 1a shows the striking features of DNA-based BaWO4 nano pair-linear arrays synthesized with 5 mM Ba(NO3)2 and

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Figure 2. HRTEM images of DNA-based BaWO4 nano pair-linear arrays from different parts. (a) HRTEM image taken at regularly aligned BaWO4 along the length of DNA chains (see black arrows). (b) HRTEM image taken at the “defective sites” where the BaWO4 particles are not fully developed on the DNA chain (see purple arrows).

Na2WO4 solutions at 80 °C. This sample is directly detected under the TEM without negative staining. It is well-known that the DNA itself is transparent to the electron beam; however, the pair-linear contours appear dark as shown in Figure 1a, and thus we can extrapolate that the BaWO4 nanoparticles are adhering on the separated double strands of DNA, and the image is mainly constructed from the BaWO4 bound to the DNA chain. Figure 1b shows a TEM image of pure DNA treated at 80 °C, and the sample was negatively stained with 2% PTA (phosphotungstic acid). The distance within two strands of pure DNA treated at 80 °C well matched that within BaWO4 nano pairlinear arrays (as compared to Figure 1a). To demonstrate that the growth of BaWO4 nano pair-linear arrays depends critically on the temperature, the controlled experiment was carried out under identical conditions at room temperature. As shown in Figure 1c, only BaWO4 nanowire can be obtained at ambient temperature. The DNA strands normally cannot break hydrogen bonds without heating process and are prone to form a single wire. This directly proves the importance of the temperature for the pair-linear configuration of the products. Figure 1d shows a TEM image of the bare linear DNA stained with 2% PTA without heating process. The width of pure DNA is much less than that of heated DNA in Figure 1b. This further confirms that the nano pair-linear arrays resulted from the heating process, and the binding of BaWO4 to DNA dramatically enhances its visibility by TEM. Figure 1e showing the selected area electron diffraction (SAED) pattern recorded from nano pair-linear arrays indicates the crystalline nature of the particles. From the diffraction pattern, we found that the values correspond to (112), (200), (204), (220), (312), and (316) planes of the expected scheelite structure, and the results are consistent with the XRD results (see below). Detailed chemical and structural analyses of the products were carried out using EDXS and HRTEM. Figure 1f shows the EDXS spectrum of the products. The chemical signatures obtained are identical within experimental accuracy, and essentially Ba, W, and O elements are observed. The C and Cu

signals arise from the TEM grid. Na signal may arise from Na2WO4, and P signal may arise from DNA. High-resolution TEM (HRTEM) analyses (Figure 2) revealed the highly crystalline features of the different parts of the products. Figure 2a shows the HRTEM image taken at regularly aligned BaWO4 along the length of DNA chains (see black arrows). The lattice spacing of 0.34 nm corresponds to the (112) plane of tetragonal phase BaWO4. Figure 2b shows the HRTEM image taken at the “defective sites” where the BaWO4 particles are not fully developed on the DNA chain (see purple arrows). Careful observation shows that the width of the pair-linear array is ca. 6-13 nm. As a step toward understanding the details of the metallization process, we have studied the effects of reagent concentration and temperature. Because the temperature is the key parameter for the morphology of the products, the temperature was altered to further identify the optimum controlling factors. Here, we show how this factor influences the morphology using varying temperatures, 80, 85, 90, and 95 °C. This can have a dramatic effect on the final products, leading to the formation of pairlinear arrays or to a very coarse DNA metallization, or even random cluster agglomerates. In the case of temperature, 80 °C can induce the optimum formation of BaWO4 nano pair-linear arrays (Figures 3 and 4a). Figure 3 shows a lower magnified TEM image of our products treated at 80 °C. It is demonstrated that the observed features are indeed representative. A higher magnified image is shown in Figure 4a. We find that the small variations around the optimum set of parameters have little influence on the morphology of the products. The pair-linear arrays are also formed when the temperature is raised to 85 °C (Figure 4b), and this makes our method simpler and more robust. Figure 4c shows the TEM image of sample prepared at 90 °C. As compared to Figure 4a and b, the extent of random aggregation is increased because of the much higher temperature, which has dramatic effects on both DNA and the products. On one side, the further higher temperature will cause DNA to be compacted rather than stretch to the analogous straight line. Because the structure of the DNA

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Figure 3. A lower magnified TEM image of DNA-based BaWO4 nano pair-linear arrays.

determines its function, the DNA can no longer perform its function once it has been denatured, and it will result in a very coarse DNA metallization. On the other side, both the heterogeneous formation of BaWO4 on DNA and the homogeneous formation of BaWO4 particles in solution simultaneously happened, and such high temperature can enhance the rate of homogeneous growth, so the random agglomerates of particles are obtained. DNA was disrupted seriously especially at 95 °C. This generally resulted in a much coarser and irregular metallization, and even no products were obtained at all (not shown). To probe the extent to which the parallel morphology could be tuned through the control of reaction concentrations, a series of experiments were carried out using varying concentrations, 5, 10, 15, and 20 mM. The morphology of the BaWO4 nanoparticle aggregated on DNA with the varied concentrations at 80 °C was revealed by TEM. Figure 5a is a typical TEM image of the BaWO4 nano pair-linear arrays formed at the concentration of 5 mM. It can be seen clearly that in the conditions when the concentrations of Ba(NO3)2 and Na2WO4 are 5 mM, it will yield the best results in terms of improving the morphology and lowering the nonspecific homogeneous formation of BaWO4 self-aggregation. When the concentrations increase to 10 mM, the BaWO4 nanoparticles can also adhere on the strands of DNA; however, the BaWO4 particles are not fully developed on the DNA chain. The obtained nano pair-linear arrays are vacant at certain sites, as indicated with red arrows (see Figure 5b). The higher concentration promoted the homogeneous growth of particles rather than nuclei formation, which may induce fusion between primary nanoparticles during particle growth. Figure 5c shows the TEM image of the BaWO4 nano pair-linear arrays formed

Figure 5. Typical TEM images of our samples treated with four concentrations at 80 °C (a, 5 mM; b, 10 mM; c, 15 mM; d, 20 mM).

at the concentration of 15 mM. The sizes of the BaWO4 particles were much larger than those formed at 10 mM, and each particle seemed to be aggregated by the fusion of smaller primary nanoparticles. We further increased the Ba2+ and WO42concentrations to 20 mM and observed the conjugation of larger BaWO4 particles (see Figure 5d). DNA chains were cross-linked with each other, and BaWO4 particles on DNA aggregated. The excess amount of Ba2+ ion caused larger agglomeration by the conjugation of primary BaWO4 particles. The difference in degree of nanoparticle aggregation on DNA can be accounted for by the different concentrations. This means that the balance between homogeneous and heterogeneous nucleation is shifted toward the homogeneous nucleation channel at higher concentrations of reagents, and it inevitably results in the formation of random aggregates of homogeneously nucleated particles. This represents a distinct feature of our BaWO4 nanoparticle assembly method. However, for the synthesis of stable and desired patterned BaWO4 nano pair-linear arrays, the solution reagent concentration could not be increased beyond a certain threshold. An important observation is that, when the solution reagent concentration was increased at a certain threshold, the resulting solution was very unstable, and most nanoparticles formed in the solution precipitated immediately to the bottom of the reaction vessel. This is likely due to the destabilizing

Figure 4. TEM images of samples prepared at different temperatures (a, 80 °C; b, 85 °C; c, 90 °C). The concentrations of Ba(NO3)2 and Na2WO4 solutions were both 5 mM, and that of DNA was ca. 1 µg/µL in all samples.

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Figure 6. X-ray diffraction patterns of DNA-templated BaWO4 nano pair-linear arrays treated at 80 °C. The theoretical XRD pattern was shown as a line pattern (JCPDS file no. 8-457).

Figure 7. Raman spectra of DNA-templated BaWO4 nano pair-linear arrays.

effect incurred by a large concentration of reagent, a phenomenon typically observed in a solution. X-ray diffraction analysis was used to examine the crystal structure of the products. A typical XRD pattern of our samples treated at 80 °C is shown in Figure 6. Diffraction peaks in Figure 6 can be indexed to a scheelite-structured, tetragonal phase BaWO4 with calculated cell constants of a ) 5.589 Å and c ) 12.753 Å, which are numerically close to the reported values of the bulk materials (JCPDS file no. 8-457). No impurity peaks were detected in the experimental range. From the line broadening of the X-ray diffraction peaks, we have estimated the average particle size of 8.73 nm according to the Scherer equation. The calculated particle size is in agreement with the results of TEM observation. Thus the phase-pure tetragonal structure BaWO4 nano pair-linear arrays have been successfully synthesized under our simple preparation route. BaWO4 with a scheelite structure is an important luminescent material, which has received much attention because of its wide applications, such as solid-state Raman laser and laser host materials.34-37 Here, the Raman spectra were measured to investigate the optical properties. Figure 7 shows a typical Raman spectrum of our products, which exhibit typical Raman bands attributed to crystalline BaWO4. As it can be seen from Figure 7, all Raman modes

Li et al. observed for the BaWO4 nano pair-linear arrays obtained in this work are characteristic of a tetragonal structure in agreement with refs 38, 39. The intensity of the Raman mode at 924 cm-1 is the highest in all observed Raman modes, which indicate high SRS gain coefficient during the SRS process. The Raman line at 1122 cm-1 is attributed to DNA. Other Raman-active optical phonon modes are not recorded in our experiments. The results of Raman data further corroborate the other data collected, confirming the identity of our DNA-based nano pairlinear arrays as indeed BaWO4. The generation of these materials provides the basis for a more thorough future investigation of their novel optical, optoelectronic, and catalytic properties for possible incorporation into nanoscale devices. We believe that the lasing and photocatalytic properties of these materials will be particularly intriguing. An investigation of the formation mechanism is extremely important for future elaboration of our method. Although the formulation of a detailed mechanism is premature at this stage, it seems reasonable to assume that base and phosphate functionalities found in DNA act as key roles, thanks to their strong absorption in the UV, and further investigation will be necessary to prove it. Here, we investigate systematically how nucleotide functionalities influence nanoparticle growth. Individual functionalities on the bases were varied by choosing different nucleotides. We began by testing four kinds of oligonucleotides, and each kind of oligonucleotide (oligo) consists of the same 10 bases. They are referred as oligo(dA), oligo(dT), oligo(dG), and oligo(dC), respectively. We sought to determine whether these oligonucleotides, which display the base and phosphate functionalities found in oligonucleotides, could serve as useful ligands. It is well-known that the charged group plays an essential role in the synthesis, by seeding and controlling nanoparticle growth. Therefore, it appears that phosphates participate in nanocrystal growth by binding Ba2+ from the solution, thereby altering (following WO42- source injection) the degree of supersaturation and thus the conditions for nucleation and the rate at which nanoparticles grow. In addition, given their charge and steric bulk, the phosphates also likely play a key role in solubilizing the nanoparticles in water. Figure 8 depicts the UV-vis absorption spectra of varying the oligonucleotide on the results of BaWO4 nanocrystal synthesis. Note from Figure 8, in the presence of oligo(dT), oligo(dG), and oligo(dC), the absorption spectra remain the same before and after adding the Ba2+ and WO42- sources, and instead the oligo(dA) produced a slight blue shift. This result seems to be responsible for the interaction between BaWO4 and oligo(dA) and probably indicates that, under the synthetic conditions chosen here, only oligo(dA) served as a competent ligand for nucleation, growth, and capping of soluble BaWO4 nanocrystals. This observation can be explained in part by hydrogen-bonding interactions between the Ba · · · O · · · H structures on the particle surface (see Chart 1). We have explored the structures of A, T, G, and C. The difference between adenine and other bases is the unique amino group. Although G and C also have amino groups, the carbonyl group is prone to hinder WO42- binding because of electrostatic rejection, let alone T, which has two carbonyl groups. After the Ba2+ binds to the phosphates backbone, the oxygen of WO42- interacts preferentially with amino moieties of adenine due to the hydrogen-bonding interactions. Herein, WO42- ions react with Ba2+ to produce BaWO4 nuclei

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Figure 8. The UV-vis absorption spectra of varying the nucleotide on the results of BaWO4 nanocrystal synthesis.

on adenine. The BaWO4 particles grow in adjacent areas and finally form a notable registry of the particles along the length of DNA chains. The discussed effects cannot be proved by TEM investigations due to the limited resolution.

On the basis of these results, we propose a general mechanistic framework describing how nucleotides promote and control nanocrystal growth (see Scheme 1). The phosphate and possibly the amino moiety binding site on adenine are the favorable targets to feed nanoparticle

SCHEME 1: Schematic Illustration of the Formation of DNA-Based BaWO4 Nano Pair-Linear Arrays (Drawing Not to Scale)

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CHART 1: Cartoon Representation of the Possible Modes of Interaction of Anionic Surface Oxygen Sites of BaWO4 with Amino Moieties of the Purine Bases of Oligo(dA)

Li et al. BaWO4 clusters would grow in adjacent areas during the incubation. DNA thermal denaturation is induced to separate its two strands and result in notable regular nano pair-linear arrays. The mechanism hypothesis herein might be viewed as the extremely important guide for future elaboration of the methodology for the preparation of better-controlled structures. To investigate the accurate mechanism, further efforts are currently being undertaken in our lab. Acknowledgment. We acknowledge financial support from the National Natural Science Foundation of China (Grant No. 50672080) and the Natural Science Foundation of Hebei (No. E20100001169). References and Notes

growth. Therefore, it appears that oligo(dA), through a combination of amine and phosphate functionalities, is effective at controlling nanoparticle growth and capping the structures with a stable ligand system. Accordingly, we assume that a part of the Ba2+ is directly bonded to the functionalities present on adenine when Ba2+ source is added to the solution. During the process of direct bonding, such sites might act as crystallization cores so that the nanocrystals are still located at such sites. Although a part of the Ba2+ can be fixed on the functionalities present on adenine electrostatically, this is certainly not true for whole nanocrystals. We suppose not all of the sites on DNA are bonded with Ba2+ (see black arrows in Scheme 1). It means that only a part of the Ba2+ is attached to the DNA, and the rest is then used for crystal growth when the WO42- ions are added. After subsequently adding the Na2WO4 solution, WO42- ions react with Ba2+ to produce BaWO4 nuclei. The growth of the particles takes place in multistep on the DNA chains present in solution. The smaller sized BaWO4 nuclei crystallize in the preferential direction, aggregate and stabilize on the DNA chain, and may form protuberant morphology at certain sites (see purple arrows in Scheme 1). During the incubation, BaWO4 clusters would grow in adjacent areas at certain regime and result in a notable registry of the particles along the length of DNA chains. DNA thermal denaturation is induced by reducing the interactions within the double strands structure to separate into two single strands. Herein, the well-defined nano pair-linear arrays with regularly aligned BaWO4 clusters can be observed without any chemical or genetic modification of DNA. 4. Conclusion We have coupled the natural properties of DNA with its ability to template BaWO4 nanocrystal synthesis and have investigated the influences of temperatures and concentrations of reagents on the morphology. We finally found the optimum conditions that could effectively drive the formation of precise defined nano pair-linear structures. The formation and a probable mechanism of BaWO4-DNA pair-linear hybrid structures have also been described. We suppose the phosphate and possibly the amino moiety binding site on adenine are the favorable targets to feed nanoparticle growth, and

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