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Mechanical characteristics of free-standing DNA thin films tuned by gold nanoparticles, metal and lanthanide ions
Journal of Physics and Chemistry of Solids 135 (2019) 109104
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Mechanical characteristics of free-standing DNA thin films tuned by gold nanoparticles, metal and lanthanide ions
T
Sanghyun Yooa, Sreekantha Reddy Dugasania, Tai Hwan Hab,c,**, Sung Ha Parka,* a
Department of Physics and Sungkyunkwan Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon, 16419, South Korea Hazards Monitoring BNT Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), Daejeon, 34141, South Korea c Department of Nanobiotechnology, KRIBB School of Biotechnology, Korea University of Science and Technology (UST), Daejeon, 34113, South Korea b
A R T I C LE I N FO
A B S T R A C T
Keywords: DNA thin film Nanomaterial Mechanical property Stress-strain Modulus
DNA obtained from salmon fish exhibits outstanding characteristics such as low-cost, biodegradable, and nontoxic. Salmon DNA (SDNA) can be easily fabricated into free-standing thin films and functionalized by embedment of various nanomaterials such as gold nanoparticles (Au NP), metal ions (e.g., Cu2+) and lanthanide ions (e.g., Tb3+). Here, free-standing SDNA (FS-SDNA) and nanomaterial-embedded SDNA (FS-NM-SDNA) thin films by casting method were constructed and their tensile properties (e.g., stress-strain and Young's modulus) and dynamic mechanical properties (e.g., storage modulus (E′), loss modulus (E″) and tangent of phase angle (tan δ)) were studied. Young's moduli of FS-NM-SDNA thin films were significantly enhanced than those of FSSDNA possibly due to doping of NMs and variation in water contents. Dynamic mechanical analysis (i.e., E′, E″ and tan δ) of FS-SDNA and FS-NM-SDNA thin films as a function of temperature (T) was also performed to understand stiffness and structural stabilities of samples. Noticeable peaks in E″ were assigned to characteristic transition temperatures of FS-SDNA and FS-NM-SDNA such as β-transition, water evaporation, structural deformation and α-transition temperatures. Finally, differences in E′, E″ and tan δ at a given unit T (i.e., ΔE'/ΔT, ΔE''/ΔT and Δtan δ/ΔT) were analysed to better understand the transition mechanism.
1. Introduction
nanomaterial-embedded DNA thin films constructed on various substrates have been developed and discussed intensively, mechanical properties ‒ one of the most important intrinsic physical characteristics of materials ‒ of free-standing DNA thin films are rarely discussed [18–23]. The use of free-standing DNA thin film and fundamental study of its mechanical properties are gaining significant attraction such that it may replace use of chemically synthesized polymer which is nonenvironmental due to toxicity, non-degradability and large consumption of resources such as oil. Furthermore, while enhancing desirable properties (e.g., mechanical properties) of synthetic polymer requires complicated chemical reaction to polymerize, characteristics of freestanding DNA thin films can be easily improved and controlled by embedding proper nanomaterials. Thus understanding of mechanical properties (e.g., stress-strain and modulus) of DNA thin film that can be easily tuned by implementing certain nanomaterials might be essential in order to construct efficient mechanical devices and sensors. The objective of this study was to synthesize free-standing pristine SDNA and nanomaterial (i.e., gold nanoparticle (Au NP), Cu2+ and
Owing to its novel characteristics such as self-assembly, programmability and stability among biomolecules, deoxyribonucleic acid (DNA) has been widely explored in the last few decades, especially in physical, chemical and biological sciences. Recently, researchers have started to use DNA extracted from salmon (SDNA) due to its low-cost, high production yield, biodegradability and non-toxicity [1]. In addition, DNA can be used as a host material to decorate functionalized nanomaterials (e.g., metal and lanthanide ions, metal/magnetic/insulating nanoparticles, quantum dots, carbon-based materials, various drugs and proteins) by molecular recognition with various binding affinities to enhance their specific physical and chemical properties. Functionality-embedded DNA complexes are treated as fascinating new materials that can be used in variety of applications such as electronics, magnetics, photonics, plasmonics, chemical or biological sensors and medicine [2–17]. Although electrical, magnetic and optical properties of
*
Corresponding author. Corresponding author. Hazards Monitoring BNT Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), Daejeon, 34141, South Korea. E-mail addresses: [email protected] (T.H. Ha), [email protected] (S.H. Park). **
https://doi.org/10.1016/j.jpcs.2019.109104 Received 10 August 2018; Received in revised form 25 June 2019; Accepted 16 July 2019 Available online 16 July 2019 0022-3697/ © 2019 Elsevier Ltd. All rights reserved.
Journal of Physics and Chemistry of Solids 135 (2019) 109104
S. Yoo, et al.
Tb3+)-embedded SDNA thin films. Here, Au NP, Cu2+ and Tb3+ are chosen among variety of nanomaterials which can be easily embedded to DNA thin films with precise control of nanomaterial concentration. Au NP can be implemented to DNA thin films by non-specific binding with DNA molecules and both Cu2+ and Tb3+ bind with DNA molecules through chemical intercalation with nitrogenous base-pairs and electrostatic interaction to phosphate backbone. Furthermore, embedding these materials can lead possibilities for optoelectric and photonic applications due to intrinsic characteristics of each individual material. Such free-standing SDNA films (thickness controlled by DNA concentration) were constructed by simple but efficient casting method with high quality of films. Tensile properties (i.e., stress-strain and Young's modulus associated with strength, ductility and fracture toughness) and dynamic mechanical properties (i.e., temperature-dependent storage modulus (E′), loss modulus (E″) and tangent of phase angle (tan δ) associated with hardness, stiffness and friction) of synthesized films were then evaluated. Au NP (having interesting characteristics of strong absorption, interband transition and localized plasmon resonance), Cu2+ and Tb3+ (representative metallic and lanthanide ions having good conductivity, electromagnetism and photoluminescence) in SDNA thin films were carefully chosen to verify the feasibility of controlling their important mechanical quantities (i.e., Young's modulus, E′, E″ and tan δ) effectively and easily [15,24,25].
was mixed with nanomaterials (i.e., Au NP, Cu2+ and Tb3+) and stirred with magnetic stirrer to obtain homogeneous solution. In order to control mechanical characteristics of SDNA thin films, Au NP (embedment into SDNA thin film), Cu2+ and Tb3+ (intercalation and electrostatic interaction with SDNA molecule) among various nanomaterials were tested. After mixing, sample solution was casted on a petri-dish followed by drying in oven at 45 °C for a few days. Once dried, a flexible and transparent free-standing film was formed. Fig. 1b–d depict synthesized FS-SDNA, FS-Cu2+-SDNA and FS-Au NP-SDNA thin films that showed high transparency (school logo placed underneath of the SDNA thin film was clearly visible) and excellent flexibility (rectangular shape SDNA thin film was bent without breakage). While FS-SDNA thin film was colorless, FS-Cu2+-SDNA and FS-Au NP-SDNA thin films showed light green and red colors, respectively. A thickness bar graph of FS-SDNA thin films as a function of SDNA casting volume (i.e. 20 and 30 mL) on a petri-dish at fixed SDNA concentrations ([SDNA]) (i.e. 0.5, 1.0 and 1.5 wt%) was obtained. Results are shown in Fig. 1e. Thicknesses of thin films were monotonically increased with increasing concentration of SDNA at a fixed pouring sample volume on a petri-dish ([SDNA]). They ranged from ~25 to ~100 μm. In order to study differences of mechanical characteristics with different functionalized NMs at a fixed thickness, we used pouring SDNA sample volume of 20 mL. Simplified thermo-mechanical characteristic representations of tensile (stress-strain and Young's modulus) and dynamic mechanical measurements (temperature-dependent E′, E″ and tan δ) are depicted in Fig. 1f–i. Dumbbell-shaped (having a weak spot at center) and rectangular-shaped (with dimensions of 25 × 6 mm2) FS-SDNA and FS-NMSDNA thin films were used for tensile and dynamic mechanical measurements, respectively. Insets in Fig. 1f–i shows samples cut into dumbbell-shaped and rectangular-shaped thin films with dimensions. Stress-strain obtained by tensile analysis could provide Young's modulus (slope of elastic region of stress-strain curve) indicating characteristics of strength and elasticity of a given sample (Fig. 1f). In addition, temperature-dependent E′, E″ and tan δ were measured by dynamic mechanical analysis (Fig. 1g–i). E′ was measured to depict stiffness of samples. It was strongly associated with Young's modulus. Relaxation and transition process of both FS-SDNA and FS-NM-SDNA thin films were estimated from peaks of E''. Finally, glass transition temperature was estimated from peak of tan δ defined by the ratio between E″ and E' (i.e., E''/E′). Fig. 2 showed tensile analysis at a fixed temperature (i.e., room temperature) and dynamic mechanical analysis with varying temperatures of FS-SDNA thin films at two different concentrations of SDNA (i.e., 1.0 and 1.5 wt%). Each FS-SDNA film was measured up to strain of 6% (Fig. 2a). By calculating slopes in strain range of 1–2%, Young's modulus of ~4.3 and ~6.3 MPa that were typical for rubbery polymer were obtained for 1.0 and 1.5 wt% of SDNA, respectively. This indicated an increase of hardness (stiffness) with increasing concentration of SDNA by factor of 1.5. Based on E′, two transitions of stiffness occurred around room temperature and 100 °C as varying temperature (Fig. 2b). Due to stiffer nature of FS-SNDA thin film with 1.5 wt% compared to that with 1.0 wt%, E′ values of 1.5 wt% samples were relatively higher through all measured temperature ranges of −100–200 °C. Contrary to E′, E″ values and number of peaks of 1.5 wt% of FS-SDNA thin film were lower and smaller than those of 1.0 wt% of FS-SDNA thin films within measured ranged of temperatures since E″ was heavily related to energy dissipation as a form of heat during deformation (Fig. 2c). Similar phenomena happened with tan δ where some peaks were diminished at higher concentration of SDNA (Fig. 2d). For nanomaterial embedment and evaluation of mechanical properties, we used FS-SDNA thin film with SDNA concentration of 1.0 wt% because transitions that were heavily related to peaks in E′ and E″ occurred at extrema, providing important clues and mechanism of physical characteristics of samples. Fig. 3 shows stress-strain curves and Young's modulus analysis of FS-
2. Materials and methods 2.1. Fabrication of free-standing pristine SDNA and nanomaterial (i.e., Au NP, Cu2+ and Tb3+)-embedded SDNA thin films First, 0.1, 0.2 and 0.3 g (or 0.15, 0.3 and 0.45 g) of DNA fibre extracted from salmon (SDNA) (GEM Corporation, Shiga, Japan) were dissolved in 20 mL (or 30 mL) of de-ionized (DI) water to obtain 0.5, 1 and 1.5 wt percent (wt%) of SDNA solution, respectively. Each solution was stirred for 10 h at 800 rpm to obtain homogeneous solution. Prepared solutions were then transferred to a 2-inch petri-dish and dried inside an oven at 45 °C for 3 days. After complete drying, SDNA thin film was peeled off gently from the petri-dish (Fig. 1 and Fig. 2). Similarly, free-standing nanomaterial (i.e., Au NP, Cu2+ and Tb3+)embedded SDNA thin films were constructed by pouring 20 mL of mixture of appropriate concentrations of SDNA and nanomaterial (i.e., Au NP (size of ~40 nm), Cu(NO3)2 and Tb(NO3)3·6H2O (Sigma Aldrich, USA)) solutions into a 2-inch petri-dish followed by incubation at 45 °C in an oven for 3 days. Final concentration of Au NP ([Au NP]) at 0.7 or 2.1 nM, [Cu2+] at 1 or 2 mM and [Tb3+] at 0.5 or 1 mM in 1.0 wt% of SDNA were achieved (Figs. 1 and 3 ~ Fig. 5). 2.2. Measurements of stress-strain and temperature-dependent dynamic mechanical analysis Free-standing SDNA and nanomaterial (i.e., Au NP, Cu2+ and Tb )-embedded SDNA thin films were cut into dumbbell-shape for stress-strain or rectangle-shape for temperature-dependent dynamic mechanical analysis. Detailed dimensions of samples are shown in Fig. 1f and g. Stress-strain curves were measured using Seiko DMS 6100 (Seiko Instruments Inc., Japan) with STRESS-STRAIN control mode under force rate of 400 mN/min at room temperature. Similarly, dynamic mechanical properties of free-standing thin films were obtained using the same instrument with tension mode under condition of a heating rate of 5 °C/min and frequency of 1 Hz with purge of nitrogen gas. 3+
3. Results and discussion Sample preparation procedure and appearances of free-standing pristine SDNA (FS-SDNA) and nanomaterial-embedded SDNA (FS-NMSDNA) thin films are shown in Fig. 1a–d. SDNA dissolved in DI water 2
Journal of Physics and Chemistry of Solids 135 (2019) 109104
S. Yoo, et al.
Fig. 1. Schematics showing sample preparation, representative photos and mechanical characteristics of freestanding pristine and nanomaterialembedded SDNA thin films. (a) A sample preparation procedure of a freestanding SDNA thin film through mixing by stirring and incubating in oven. (b, c) Photos of free-standing pristine SDNA and Cu2+-embedded SDNA thin films, respectively. (d) Photos of free-standing (top) Au nanoparticle-embedded and (bottom) Cu2+embedded SDNA thin films. Films with dimensions of 25 × 6 mm2 were bent to show flexibility. (e) A thickness bar graph of free-standing pristine SDNA thin films as a function of SDNA sample volume at fixed SDNA concentrations (i.e., 0.5, 1.0 and 1.5 wt%). (f) A representation curve of stress-strain behavior. A dumbbell-shaped SDNA thin film was used and its dimension was shown in the inset. (g–i) Typical behaviors of dynamic mechanical measurements, i.e., temperature-dependent storage modulus (E′), loss modulus (E″) and tangent of phase angle (tan δ), respectively. Insets showing rectangleshaped SDNA thin films with dimensions of 25 × 6 mm2.
SDNA, FS-Au NP-SDNA, FS-Cu2+-SNDA and FS-Tb3+-SDNA thin films. Each NM embedded in SDNA was prepared with two different concentrations in order to study the change in tensile properties with varying concentrations of NM. We carefully chose two different concentrations of NM (i.e., 0.7 and 2.1 nM of Au NP, 1 and 2 mM of Cu2+ and 0.5 and 1 mM of Tb3+) to guarantee that we could observe significance in mechanical properties in the presence of NMs without precipitation of SDNA molecules. With relatively higher concentrations of Cu2+ and Tb3+, precipitation of SDNA in solution during preparation of samples was visible. Stresses of all films were measured up to strain of 6%. Interestingly, stresses of all FS-NM-SDNA thin films were increased more rapidly than those of FS-SDNA with increasing strain. In addition, generally stresses with higher concentration of NM showed stiffer slopes (i.e., higher Young's modulus) than those with lower concentrations of NM. In order to analyse tensile and elastic properties of each sample, Young's modulus as a ratio of stress over strain was introduced
(Fig. 3d). Based on Young's modulus, we might be able to estimate viscoelastic characteristics of samples such as glassy state (≥~50 GPa), semicrystalline state and rubbery state (≤~100 MPa) [26]. We obtained Young's modulus from stress data in strain range of 1–2% measured at room temperature (Fig. 3a–c). Comparing Young's modulus of pristine FS-SDNA thin film (~4.3 MPa), Young's moduli obtained for FSNM-SDNA thin films were significantly enhanced. This might be due to doping of NMs and variation in water contents. As expected, higher concentration of NM showed higher Young's modulus. Interestingly, modulus of FS-SDNA with lanthanide Tb3+ (~26.3 MPa) was slightly higher than that of FS-SDNA having metallic Cu2+ (~18.0 MPa) obtained at constant ion concentration of 1 mM because of intrinsic physical characteristics of each ion. Fig. 4 shows dynamic mechanical analysis (i.e., E′, E″ and tan δ) results of FS-SDNA and FS-NM-SDNA thin films as a function of temperature ranging from −100 to 200 °C. E′ could provide information for material's stiffness and structural stability at a given temperature. E′
Fig. 2. Stress-strain and dynamic mechanical analysis of free-standing pristine SDNA thin films. (a) Stress-strain curve of free-standing pristine SDNA thin films with two different SDNA concentrations (i.e., 1.0 and 1.5 wt%). (b–d) Dynamic mechanical analysis, i.e., temperature-dependent storage modulus (E′), loss modulus (E″) and tangent of phase angle (tan δ) of free-standing pristine SDNA thin films, respectively. 3
Journal of Physics and Chemistry of Solids 135 (2019) 109104
S. Yoo, et al.
Fig. 3. Stress-strain curves and Young's modulus analysis of free-standing pristine SDNA and nanomaterial (i.e., Au NP, Cu2+ and Tb3+)-embedded SDNA thin films. (a) Stress-strain graphs of free-standing DNA thin films with 0, 0.7 and 2.1 nM of Au NPs labeled as SDNA, Au 0.7 and Au 2.1, respectively. (b) Stress-strain curves of free-standing SDNA thin films with 0, 1 and 2 mM of Cu2+ labeled as SDNA, Cu 1 and Cu 2, respectively. (c) Stress-strain curves of free-standing SDNA thin films with 0, 0.5 and 1 mM of Tb3+ labeled as SDNA, Tb 0.5 and Tb 1, respectively. (d) Young's modulus of each sample calculated from the slope of stress-strain curve.
values of FS-SDNA thin films were decreased until certain temperature (~30 °C). They were then increased up to structural deformation temperature (~100 °C) followed by a decrease with further increase of temperature. After embedment of either Au NPs, Cu2+, or Tb3+ into SDNA, slight increase of E′ and a shift of structural deformation peak to slightly higher temperature were observed. This indicated that FSSDNA thin films with NMs showed relatively higher thermal rigidity and stability than FS-SDNA due to enhancement of binding affinities between SDNA duplexes and NMs through electrostatic and non-specific bindings.
E″ is related to energy loss of samples during transition of formation. E″ values showed noticeable peaks that were assigned to characteristic transitions of FS-SDNA thin films. Each peak and hump shown in Fig. 4b corresponded to intrinsic behaviors of samples such as relaxation and transition process. The first hump appeared in FS-SDNA thin film was placed near −43 °C. This temperature was considered as a β-transition temperature provided by global molecular motion of hydrated SDNA molecule [27,28]. The second peak located at ~64 °C was connected to water evaporation temperature within the film. Structural deformation and α-transition (also known as glass transition) could be
Fig. 4. Dynamic mechanical analysis of free-standing pristine SDNA and nanomaterial-embedded SDNA thin films. (a) Temperature-dependent storage modulus (E′) of pristine SDNA and Au NP-, Cu2+- and Tb3+-embedded SDNA thin films. (b) Temperature-dependent loss modulus (E″) of pristine SDNA and Au NP-, Cu2+- and Tb3+-embedded SDNA thin films. (c) Temperature-dependent tangent of phase angle (tan δ) of pristine SDNA and Au NP-, Cu2+- and Tb3+-embedded SDNA thin films. Free-standing pristine SDNA and SDNA thin films with Au NP at 2.1 nM, Cu2+ at 2 mM and Tb3+ at 1 mM (labeled as SDNA, Au 2.1, Cu 2 and Tb 1) were used. 4
Journal of Physics and Chemistry of Solids 135 (2019) 109104
S. Yoo, et al.
Fig. 5. Temperature-dependent dynamic modulus and tangent of phase angle differences between free-standing pristine SDNA and nanomaterial-embedded SDNA thin films regarding temperature and loss modulus peak assignment. (a) Temperature-dependent dynamic storage modulus differences between free-standing pristine SDNA and Au NP-, Cu2+- and Tb3+-embedded SDNA thin films. (b) Temperature-dependent dynamic loss modulus differences between free-standing pristine SDNA and Au NP-, Cu2+- and Tb3+-embedded SDNA thin films. (c) Temperature-dependent tangent of phase angle differences between free-standing pristine SDNA and Au NP-, Cu2+- and Tb3+-embedded SDNA thin films. (d) Loss modulus peak assignments of β-transition, water evaporation, structural deformation and α-transition (known as glass transition) temperatures for each sample.
external thermal energy, water molecules of hydrated DNA started to evaporate at water evaporation temperature over 60 °C. When the temperature is close to 100 °C, structural deformation of doublestranded DNA to single-stranded DNA started to occur by breaking hydrogen bonds of base-pairs. Finally, when temperature of the system reached to α-transition temperatures or glass-transition temperature around 173 °C, deformed single-stranded DNA molecules were mobile and started to flow within thin films indicating transition of state from hard glass-state to viscous rubbery state. β-transition temperatures (which were connected to collective motion of hydrated DNA) of FS-SDNA, FS-Au NP-SDNA (Au 2.1), FS-Cu2+SDNA (Cu 2) and FS-Tb3+-SDNA (Tb 1) were −43, −62, −82 and −57 °C, respectively. Global molecular motion of hydrated SDNA with NMs was initiated at relatively lower temperatures than that of pristine SDNA due to the presence of NMs that served as activator of molecular motion. Evaporation temperatures of FS-SDNA thin films were increased with the addition of NMs. Here, β-transition and evaporation temperatures of thin films might provide lower and upper bound regions of mechanically stable sample conditions. Difference in water evaporation and β-transition temperature of SDNA thin film was 107 °C (= 64 °C ‒ (−43 °C)) which provided stable temperature range for SDNA. By addition of Au NP, Cu2+ and Tb3+ into SDNA, such differences could be extended up to ~1.36, ~1.44 and ~1.28 times larger than SDNA, respectively. Structural deformation and alteration (from double-stranded to single-stranded DNA) of FS-SDNA, FS-Au NP-SDNA, FS-Cu2+-SDNA and FS-Tb3+-SDNA occurred at 93, 115, 102 and 100 °C, respectively. Finally, viscoelastic characteristics of FS-SDNA thin films were completely changed by passing α-transition (i.e., glass transition) temperature of 173 °C. Glass transition temperatures were not visible for FS-NM-SDNA thin films since measured temperature range was only up to 200 °C. Decrease of β-transition temperature and increase of water evaporation and structure deformation temperatures of FS-NM-SDNA were revealed due to intercalation and electrostatic interaction (non-specific interaction and entropic force) between Cu2+/ Tb3+ (Au NP) and SDNA. Consequently, this resulted in enhanced thermo-mechanical stabilities of FS-NM-SDNA thin films than those of FS-SDNA thin films.
acquired by analysis of third and fourth peaks placed at ~93 and ~173 °C, respectively. Interestingly, suppression and peak shifts of E″ were observed for FS-NM-SDNA thin films, indicating significant differences in transition behavior compared to FS-SDNA. Finally, graphs of tan δ (corresponded to E''/E′) for FS-SDNA and FS-NM-SDNA thin films were obtained. Results shown in Fig. 4c provided clues of the overall dynamic mechanical behavior of materials. Although glass transition temperature (i.e., transition temperature between glassy state and semicrystalline/rubbery state) might be obtained by a peak having maximum temperature of tan δ, glass transition temperatures of FS-NMSDNA thin films were hardly acquired within measured temperature range up to 200 °C. At temperatures of over 200 °C, samples started to show severe damage by burning. Fig. 5a–c illustrate differences of E′, E″ and tan δ per unit temperature which provided the number of transitions (obtained by finding temperatures having zero differences) and significant slope changes (by counting number of local extrema of differences) of dynamic modulus and tangent of phase angle. From temperature-dependent E′ difference of FS-SDNA thin films, two zero differences and two local extrema could be found at 40, 115 °C and −13, 90 °C which corresponded to local extrema and extreme slope changes of E′, respectively. Although E′ differences of FS-Cu2+-SDNA showed similar trend as FS-SDNA, FS-Au NP-SDNA showed roughly constant E′ differences. This meant that magnitudes of E′ change in measured range of temperature were minute and negligible. E″ and tan δ differences of FS-SDNA and FS-NM-SDNA thin films at a given unit temperature are shown in Fig. 5b and c. Differences of E″ for FS-Au NP-SDNA thin films were relatively small compared to those for FS-SDNA thin films. This meant that the amount of energy loss during deformation of thin films having Au NPs was independent of temperature. Interestingly, no significant differences of tan δ were observed. This indicated ratios of E″ and E′ along the whole range of measured temperatures were not much different. β-transition, water evaporation, structural deformation and αtransition temperatures for FS-SDNA and FS-NM-SDNA thin films obtained from E″ are shown in Fig. 5d. As the temperature of the system increased from low temperature, localized motion of chemical bonds within DNA molecules occurred such as bending and stretching (e.g., vibration mode of deoxyribose moiety, C–N and C]C stretching in cytosine). When temperature of the system reached to β-transition temperature, collective motion of DNA molecules was allowed due to expansion of free-space within films which then generated toughness to the system by absorbing thermal energy. As the system absorbed more
4. Conclusions We fabricated free-standing pristine SDNA (FS-SDNA) and nanomaterial-embedded SDNA (FS-NM-SDNA) thin films by casting method 5
Journal of Physics and Chemistry of Solids 135 (2019) 109104
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and studied their tensile properties (i.e., stress-strain and Young's modulus) and dynamic mechanical properties (i.e., temperature-dependent storage modulus (E′), loss modulus (E″) and tangent of phase angle (tan δ)). When stress-strain curves and Young's moduli of FSSDNA, FS-Au NP-SDNA, FS-Cu2+-SNDA and FS-Tb3+-SDNA thin films were examined, stresses of all FS-NM-SDNA thin films were increased rapidly than FS-SDNA thin films with increasing strain. Young's moduli of FS-NM-SDNA thin films were also significantly enhanced than those of FS-SDNA. This might be due to the doping of various NMs in water contents. Dynamic mechanical analysis (i.e., E′, E″ and tan δ) of FSSDNA and FS-NM-SDNA thin films as a function of temperature were also investigated in order to understand stiffness and structural stabilities of samples at a given temperature. When NMs were embedded into SDNA, slight increase in E′ and peak shifts were observed. This implied that FS-SDNA thin films with NMs showed relatively higher thermal rigidity and stability than FS-SDNA thin films due to their enhancement in binding affinities between SDNA duplexes and NMs. Noticeable peaks in E″ were assigned to characteristic transition temperatures of FS-SDNA and FS-NM-SDNA such as β-transition, water evaporation, structural deformation and α-transition. To obtain information of overall dynamic mechanical behaviors of FS-SDNA and FSNM-SDNA thin films, tan δ (corresponded to E''/E′) was also measured. Interestingly, β-transition temperatures of FS-NM-SDNA thin films were decreased whereas evaporation and structural deformation temperatures were increased compared to those of pristine SDNA thin films owing to the presence of binding affinities between NMs and SDNA in FS-NM-SDNA thin films. Accordingly, NM embedment into SDNA thin films significantly enhanced thermo-mechanical stabilities. Finally, differences in E′, E″ and tan δ per unit temperature were analysed by finding temperatures having zero differences and counting the number of local extrema of differences to better understand the transition mechanism. Our results might be very useful for constructing functional material-doped DNA thin films. They are also helpful for understanding thermo-mechanical properties that are very important for real devices and sensors used in piezoelectric materials and flexible substrates.
[5] X. Shen, C. Song, J. Wang, D. Shi, Z. Wang, N. Liu, B. Ding, Rolling up gold nanoparticle-dressed DNA origami into three-dimensional plasmonic chiral nanostructures, J. Am. Chem. Soc. 134 (2011) 146–149. [6] A. Kuzyk, R. Schreiber, Z. Fan, G. Pardatscher, E.-M. Roller, A. Högele, F.C. Simmel, A.O. Govorov, T. Liedl, DNA-based self-assembly of chiral plasmonic nanostructures with tailored optical response, Nature 483 (2012) 311–314. [7] V.V. Thacker, L.O. Herrmann, D.O. Sigle, T. Zhang, T. Liedl, J.J. Baumberg, U.F. Keyser, DNA origami based assembly of gold nanoparticle dimers for surfaceenhanced Raman scattering, Nat. Commun. 5 (2014) 3448. [8] Z. Ge, M. Lin, P. Wang, H. Pei, J. Yan, J. Shi, Q. Huang, D. He, C. Fan, X. Zuo, Hybridization chain reaction amplification of microRNA detection with a tetrahedral DNA nanostructure-based electrochemical biosensor, Anal. Chem. 86 (2014) 2124–2130. [9] M. Lin, J. Wang, G. Zhou, J. Wang, N. Wu, J. Lu, J. Gao, X. Chen, J. Shi, X. Zuo, Programmable engineering of a biosensing interface with tetrahedral DNA nanostructures for ultrasensitive DNA detection, Angew. Chem. Int. Ed. 54 (2015) 2151–2155. [10] H. Pei, N. Lu, Y. Wen, S. Song, Y. Liu, H. Yan, C. Fan, A DNA nanostructure‐based biomolecular probe carrier platform for electrochemical biosensing, Adv. Mater. 22 (2010) 4754–4758. [11] X. Chen, C.-Y. Hong, Y.-H. Lin, J.-H. Chen, G.-N. Chen, H.-H. Yang, Enzyme-free and label-free ultrasensitive electrochemical detection of human immunodeficiency virus DNA in biological samples based on long-range self-assembled DNA nanostructures, Anal. Chem. 84 (2012) 8277–8283. [12] J. Li, H. Pei, B. Zhu, L. Liang, M. Wei, Y. He, N. Chen, D. Li, Q. Huang, C. Fan, Selfassembled multivalent DNA nanostructures for noninvasive intracellular delivery of immunostimulatory CpG oligonucleotides, ACS Nano 5 (2011) 8783–8789. [13] R. Hu, X. Zhang, Z. Zhao, G. Zhu, T. Chen, T. Fu, W. Tan, DNA nanoflowers for multiplexed cellular imaging and traceable targeted drug delivery, Angew. Chem. Int. Ed. 126 (2014) 5931–5936. [14] Y. Lee, S.R. Dugansani, S.H. Jeon, S.H. Hwang, J.-H. Kim, S.H. Park, J.-H. Jeong, Drug-Delivery system based on salmon DNA nano-and micro-scale structures, Sci. Rep. 7 (2017) 9724. [15] P. Chopade, S.R. Dugasani, M.R. Kesama, S. Yoo, B. Gnapareddy, Y.W. Lee, S. Jeon, J.-H. Jeong, S.H. Park, Phase, current, absorbance, and photoluminescence of double and triple metal ion-doped synthetic and salmon DNA thin films, Nanotechnology 28 (2017) 405702. [16] M.R. Kesama, S.R. Dugasani, S. Yoo, P. Chopade, B. Gnapareddy, S.H. Park, Morphological and optoelectronic characteristics of double and triple lanthanide ion-doped DNA thin films, ACS Appl. Mater. Interfaces 8 (2016) 14109–14117. [17] S.B. Mitta, S.R. Dugasani, S.-G. Jung, S. Vellampatti, T. Park, S.H. Park, Electromagnetic and optical characteristics of Nb5+-doped double-crossover and salmon DNA thin films, Nanotechnology 28 (2017) 405703. [18] Y. Kawabe, L. Wang, S. Horinouchi, N. Ogata, Amplified spontaneous emission from fluorescent‐dye‐doped DNA–surfactant complex films, Adv. Mater. 12 (2000) 1281–1283. [19] Z. Yu, W. Li, J.A. Hagen, Y. Zhou, D. Klotzkin, J.G. Grote, A.J. Steckl, Photoluminescence and lasing from deoxyribonucleic acid (DNA) thin films doped with sulforhodamine, Appl. Opt. 46 (2007) 1507–1513. [20] O. Krupka, A. El-ghayoury, I. Rau, B. Sahraoui, J.G. Grote, F. Kajzar, NLO properties of functionalized DNA thin films, Thin Solid Films 516 (2008) 8932–8936. [21] Y. Okahata, T. Kobayashi, K. Tanaka, Orientation of DNA double strands in a Langmuir−Blodgett film, Langmuir 12 (1996) 1326–1330. [22] T. Nagamura, M. Yamamoto, M. Terasawa, K. Shiratori, High performance sensing of nitrogen oxides by surface plasmon resonance excited fluorescence of dye-doped deoxyribonucleic acid thin films, Appl. Phys. Lett. 83 (2003) 803–805. [23] K. Aoi, A. Takasu, M. Okada, DNA-based polymer hybrids Part 1. Compatibility and physical properties of poly (vinyl alcohol)/DNA sodium salt blend, Polymer 41 (2000) 2847–2853. [24] S.D. Perrault, W.C. Chan, Synthesis and surface modification of highly monodispersed, spherical gold nanoparticles of 50−200 nm, J. Am. Chem. Soc. 131 (2009) 17042–17043. [25] S.R. Dugasani, M. Kim, I. Lee, J.A. Kim, B. Gnapareddy, K.W. Lee, T. Kim, N. Huh, G.-H. Kim, S.C. Park, Construction and characterization of Cu2+, Ni2+, Zn2+, and Co2+ modified-DNA crystals, Nanotechnology 26 (2015) 275604. [26] J. Zhan, H. Matsuno, H. Masunaga, H. Ogawa, K. Tanaka, Green solid films with tunable mechanical properties made from deoxyribonucleic acid, NPG Asia Mater. 6 (2014) e92. [27] H. Matsuno, J. Nakahara, K. Tanaka, Dynamic mechanical properties of solid films of deoxyribonucleic acid, Biomacromolecules 12 (2010) 173–178. [28] A.P. Sokolov, H. Grimm, A. Kisliuk, A.J. Dianoux, Slow relaxation process in DNA, J. Biol. Phys. 27 (2001) 313–327.
Acknowledgements This work was financially supported by Korea Research Institute of Bioscience and Biotechnology Research Initiative Program and the National Research Foundation (NRF) of Korea (2016R1D1A1B03933768, and 2018R1A2B6008094). References [1] L. Wang, J. Yoshida, N. Ogata, S. Sasaki, T. Kajiyama, Self-assembled supramolecular films derived from marine deoxyribonucleic acid (DNA)− cationic surfactant complexes: large-scale preparation and optical and thermal properties, Chem. Mater. 13 (2001) 1273–1281. [2] A.M. Hung, C.M. Micheel, L.D. Bozano, L.W. Osterbur, G.M. Wallraff, J.N. Cha, Large-area spatially ordered arrays of gold nanoparticles directed by lithographically confined DNA origami, Nat. Nanotechnol. 5 (2010) 121–126. [3] G.P. Acuna, M. Bucher, I.H. Stein, C. Steinhauer, A. Kuzyk, P. Holzmeister, R. Schreiber, A. Moroz, F.D. Stefani, T. Liedl, Distance dependence of singlefluorophore quenching by gold nanoparticles studied on DNA origami, ACS Nano 6 (2012) 3189–3195. [4] B. Ding, Z. Deng, H. Yan, S. Cabrini, R.N. Zuckermann, J. Bokor, Gold nanoparticle self-similar chain structure organized by DNA origami, J. Am. Chem. Soc. 132 (2010) 3248–3249.
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Journal of Physics and Chemistry of Solids journal homepage: www.elsevier.com/locate/jpcs
Mechanical characteristics of free-standing DNA thin films tuned by gold nanoparticles, metal and lanthanide ions
T
Sanghyun Yooa, Sreekantha Reddy Dugasania, Tai Hwan Hab,c,**, Sung Ha Parka,* a
Department of Physics and Sungkyunkwan Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon, 16419, South Korea Hazards Monitoring BNT Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), Daejeon, 34141, South Korea c Department of Nanobiotechnology, KRIBB School of Biotechnology, Korea University of Science and Technology (UST), Daejeon, 34113, South Korea b
A R T I C LE I N FO
A B S T R A C T
Keywords: DNA thin film Nanomaterial Mechanical property Stress-strain Modulus
DNA obtained from salmon fish exhibits outstanding characteristics such as low-cost, biodegradable, and nontoxic. Salmon DNA (SDNA) can be easily fabricated into free-standing thin films and functionalized by embedment of various nanomaterials such as gold nanoparticles (Au NP), metal ions (e.g., Cu2+) and lanthanide ions (e.g., Tb3+). Here, free-standing SDNA (FS-SDNA) and nanomaterial-embedded SDNA (FS-NM-SDNA) thin films by casting method were constructed and their tensile properties (e.g., stress-strain and Young's modulus) and dynamic mechanical properties (e.g., storage modulus (E′), loss modulus (E″) and tangent of phase angle (tan δ)) were studied. Young's moduli of FS-NM-SDNA thin films were significantly enhanced than those of FSSDNA possibly due to doping of NMs and variation in water contents. Dynamic mechanical analysis (i.e., E′, E″ and tan δ) of FS-SDNA and FS-NM-SDNA thin films as a function of temperature (T) was also performed to understand stiffness and structural stabilities of samples. Noticeable peaks in E″ were assigned to characteristic transition temperatures of FS-SDNA and FS-NM-SDNA such as β-transition, water evaporation, structural deformation and α-transition temperatures. Finally, differences in E′, E″ and tan δ at a given unit T (i.e., ΔE'/ΔT, ΔE''/ΔT and Δtan δ/ΔT) were analysed to better understand the transition mechanism.
1. Introduction
nanomaterial-embedded DNA thin films constructed on various substrates have been developed and discussed intensively, mechanical properties ‒ one of the most important intrinsic physical characteristics of materials ‒ of free-standing DNA thin films are rarely discussed [18–23]. The use of free-standing DNA thin film and fundamental study of its mechanical properties are gaining significant attraction such that it may replace use of chemically synthesized polymer which is nonenvironmental due to toxicity, non-degradability and large consumption of resources such as oil. Furthermore, while enhancing desirable properties (e.g., mechanical properties) of synthetic polymer requires complicated chemical reaction to polymerize, characteristics of freestanding DNA thin films can be easily improved and controlled by embedding proper nanomaterials. Thus understanding of mechanical properties (e.g., stress-strain and modulus) of DNA thin film that can be easily tuned by implementing certain nanomaterials might be essential in order to construct efficient mechanical devices and sensors. The objective of this study was to synthesize free-standing pristine SDNA and nanomaterial (i.e., gold nanoparticle (Au NP), Cu2+ and
Owing to its novel characteristics such as self-assembly, programmability and stability among biomolecules, deoxyribonucleic acid (DNA) has been widely explored in the last few decades, especially in physical, chemical and biological sciences. Recently, researchers have started to use DNA extracted from salmon (SDNA) due to its low-cost, high production yield, biodegradability and non-toxicity [1]. In addition, DNA can be used as a host material to decorate functionalized nanomaterials (e.g., metal and lanthanide ions, metal/magnetic/insulating nanoparticles, quantum dots, carbon-based materials, various drugs and proteins) by molecular recognition with various binding affinities to enhance their specific physical and chemical properties. Functionality-embedded DNA complexes are treated as fascinating new materials that can be used in variety of applications such as electronics, magnetics, photonics, plasmonics, chemical or biological sensors and medicine [2–17]. Although electrical, magnetic and optical properties of
*
Corresponding author. Corresponding author. Hazards Monitoring BNT Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), Daejeon, 34141, South Korea. E-mail addresses: [email protected] (T.H. Ha), [email protected] (S.H. Park). **
https://doi.org/10.1016/j.jpcs.2019.109104 Received 10 August 2018; Received in revised form 25 June 2019; Accepted 16 July 2019 Available online 16 July 2019 0022-3697/ © 2019 Elsevier Ltd. All rights reserved.
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Tb3+)-embedded SDNA thin films. Here, Au NP, Cu2+ and Tb3+ are chosen among variety of nanomaterials which can be easily embedded to DNA thin films with precise control of nanomaterial concentration. Au NP can be implemented to DNA thin films by non-specific binding with DNA molecules and both Cu2+ and Tb3+ bind with DNA molecules through chemical intercalation with nitrogenous base-pairs and electrostatic interaction to phosphate backbone. Furthermore, embedding these materials can lead possibilities for optoelectric and photonic applications due to intrinsic characteristics of each individual material. Such free-standing SDNA films (thickness controlled by DNA concentration) were constructed by simple but efficient casting method with high quality of films. Tensile properties (i.e., stress-strain and Young's modulus associated with strength, ductility and fracture toughness) and dynamic mechanical properties (i.e., temperature-dependent storage modulus (E′), loss modulus (E″) and tangent of phase angle (tan δ) associated with hardness, stiffness and friction) of synthesized films were then evaluated. Au NP (having interesting characteristics of strong absorption, interband transition and localized plasmon resonance), Cu2+ and Tb3+ (representative metallic and lanthanide ions having good conductivity, electromagnetism and photoluminescence) in SDNA thin films were carefully chosen to verify the feasibility of controlling their important mechanical quantities (i.e., Young's modulus, E′, E″ and tan δ) effectively and easily [15,24,25].
was mixed with nanomaterials (i.e., Au NP, Cu2+ and Tb3+) and stirred with magnetic stirrer to obtain homogeneous solution. In order to control mechanical characteristics of SDNA thin films, Au NP (embedment into SDNA thin film), Cu2+ and Tb3+ (intercalation and electrostatic interaction with SDNA molecule) among various nanomaterials were tested. After mixing, sample solution was casted on a petri-dish followed by drying in oven at 45 °C for a few days. Once dried, a flexible and transparent free-standing film was formed. Fig. 1b–d depict synthesized FS-SDNA, FS-Cu2+-SDNA and FS-Au NP-SDNA thin films that showed high transparency (school logo placed underneath of the SDNA thin film was clearly visible) and excellent flexibility (rectangular shape SDNA thin film was bent without breakage). While FS-SDNA thin film was colorless, FS-Cu2+-SDNA and FS-Au NP-SDNA thin films showed light green and red colors, respectively. A thickness bar graph of FS-SDNA thin films as a function of SDNA casting volume (i.e. 20 and 30 mL) on a petri-dish at fixed SDNA concentrations ([SDNA]) (i.e. 0.5, 1.0 and 1.5 wt%) was obtained. Results are shown in Fig. 1e. Thicknesses of thin films were monotonically increased with increasing concentration of SDNA at a fixed pouring sample volume on a petri-dish ([SDNA]). They ranged from ~25 to ~100 μm. In order to study differences of mechanical characteristics with different functionalized NMs at a fixed thickness, we used pouring SDNA sample volume of 20 mL. Simplified thermo-mechanical characteristic representations of tensile (stress-strain and Young's modulus) and dynamic mechanical measurements (temperature-dependent E′, E″ and tan δ) are depicted in Fig. 1f–i. Dumbbell-shaped (having a weak spot at center) and rectangular-shaped (with dimensions of 25 × 6 mm2) FS-SDNA and FS-NMSDNA thin films were used for tensile and dynamic mechanical measurements, respectively. Insets in Fig. 1f–i shows samples cut into dumbbell-shaped and rectangular-shaped thin films with dimensions. Stress-strain obtained by tensile analysis could provide Young's modulus (slope of elastic region of stress-strain curve) indicating characteristics of strength and elasticity of a given sample (Fig. 1f). In addition, temperature-dependent E′, E″ and tan δ were measured by dynamic mechanical analysis (Fig. 1g–i). E′ was measured to depict stiffness of samples. It was strongly associated with Young's modulus. Relaxation and transition process of both FS-SDNA and FS-NM-SDNA thin films were estimated from peaks of E''. Finally, glass transition temperature was estimated from peak of tan δ defined by the ratio between E″ and E' (i.e., E''/E′). Fig. 2 showed tensile analysis at a fixed temperature (i.e., room temperature) and dynamic mechanical analysis with varying temperatures of FS-SDNA thin films at two different concentrations of SDNA (i.e., 1.0 and 1.5 wt%). Each FS-SDNA film was measured up to strain of 6% (Fig. 2a). By calculating slopes in strain range of 1–2%, Young's modulus of ~4.3 and ~6.3 MPa that were typical for rubbery polymer were obtained for 1.0 and 1.5 wt% of SDNA, respectively. This indicated an increase of hardness (stiffness) with increasing concentration of SDNA by factor of 1.5. Based on E′, two transitions of stiffness occurred around room temperature and 100 °C as varying temperature (Fig. 2b). Due to stiffer nature of FS-SNDA thin film with 1.5 wt% compared to that with 1.0 wt%, E′ values of 1.5 wt% samples were relatively higher through all measured temperature ranges of −100–200 °C. Contrary to E′, E″ values and number of peaks of 1.5 wt% of FS-SDNA thin film were lower and smaller than those of 1.0 wt% of FS-SDNA thin films within measured ranged of temperatures since E″ was heavily related to energy dissipation as a form of heat during deformation (Fig. 2c). Similar phenomena happened with tan δ where some peaks were diminished at higher concentration of SDNA (Fig. 2d). For nanomaterial embedment and evaluation of mechanical properties, we used FS-SDNA thin film with SDNA concentration of 1.0 wt% because transitions that were heavily related to peaks in E′ and E″ occurred at extrema, providing important clues and mechanism of physical characteristics of samples. Fig. 3 shows stress-strain curves and Young's modulus analysis of FS-
2. Materials and methods 2.1. Fabrication of free-standing pristine SDNA and nanomaterial (i.e., Au NP, Cu2+ and Tb3+)-embedded SDNA thin films First, 0.1, 0.2 and 0.3 g (or 0.15, 0.3 and 0.45 g) of DNA fibre extracted from salmon (SDNA) (GEM Corporation, Shiga, Japan) were dissolved in 20 mL (or 30 mL) of de-ionized (DI) water to obtain 0.5, 1 and 1.5 wt percent (wt%) of SDNA solution, respectively. Each solution was stirred for 10 h at 800 rpm to obtain homogeneous solution. Prepared solutions were then transferred to a 2-inch petri-dish and dried inside an oven at 45 °C for 3 days. After complete drying, SDNA thin film was peeled off gently from the petri-dish (Fig. 1 and Fig. 2). Similarly, free-standing nanomaterial (i.e., Au NP, Cu2+ and Tb3+)embedded SDNA thin films were constructed by pouring 20 mL of mixture of appropriate concentrations of SDNA and nanomaterial (i.e., Au NP (size of ~40 nm), Cu(NO3)2 and Tb(NO3)3·6H2O (Sigma Aldrich, USA)) solutions into a 2-inch petri-dish followed by incubation at 45 °C in an oven for 3 days. Final concentration of Au NP ([Au NP]) at 0.7 or 2.1 nM, [Cu2+] at 1 or 2 mM and [Tb3+] at 0.5 or 1 mM in 1.0 wt% of SDNA were achieved (Figs. 1 and 3 ~ Fig. 5). 2.2. Measurements of stress-strain and temperature-dependent dynamic mechanical analysis Free-standing SDNA and nanomaterial (i.e., Au NP, Cu2+ and Tb )-embedded SDNA thin films were cut into dumbbell-shape for stress-strain or rectangle-shape for temperature-dependent dynamic mechanical analysis. Detailed dimensions of samples are shown in Fig. 1f and g. Stress-strain curves were measured using Seiko DMS 6100 (Seiko Instruments Inc., Japan) with STRESS-STRAIN control mode under force rate of 400 mN/min at room temperature. Similarly, dynamic mechanical properties of free-standing thin films were obtained using the same instrument with tension mode under condition of a heating rate of 5 °C/min and frequency of 1 Hz with purge of nitrogen gas. 3+
3. Results and discussion Sample preparation procedure and appearances of free-standing pristine SDNA (FS-SDNA) and nanomaterial-embedded SDNA (FS-NMSDNA) thin films are shown in Fig. 1a–d. SDNA dissolved in DI water 2
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Fig. 1. Schematics showing sample preparation, representative photos and mechanical characteristics of freestanding pristine and nanomaterialembedded SDNA thin films. (a) A sample preparation procedure of a freestanding SDNA thin film through mixing by stirring and incubating in oven. (b, c) Photos of free-standing pristine SDNA and Cu2+-embedded SDNA thin films, respectively. (d) Photos of free-standing (top) Au nanoparticle-embedded and (bottom) Cu2+embedded SDNA thin films. Films with dimensions of 25 × 6 mm2 were bent to show flexibility. (e) A thickness bar graph of free-standing pristine SDNA thin films as a function of SDNA sample volume at fixed SDNA concentrations (i.e., 0.5, 1.0 and 1.5 wt%). (f) A representation curve of stress-strain behavior. A dumbbell-shaped SDNA thin film was used and its dimension was shown in the inset. (g–i) Typical behaviors of dynamic mechanical measurements, i.e., temperature-dependent storage modulus (E′), loss modulus (E″) and tangent of phase angle (tan δ), respectively. Insets showing rectangleshaped SDNA thin films with dimensions of 25 × 6 mm2.
SDNA, FS-Au NP-SDNA, FS-Cu2+-SNDA and FS-Tb3+-SDNA thin films. Each NM embedded in SDNA was prepared with two different concentrations in order to study the change in tensile properties with varying concentrations of NM. We carefully chose two different concentrations of NM (i.e., 0.7 and 2.1 nM of Au NP, 1 and 2 mM of Cu2+ and 0.5 and 1 mM of Tb3+) to guarantee that we could observe significance in mechanical properties in the presence of NMs without precipitation of SDNA molecules. With relatively higher concentrations of Cu2+ and Tb3+, precipitation of SDNA in solution during preparation of samples was visible. Stresses of all films were measured up to strain of 6%. Interestingly, stresses of all FS-NM-SDNA thin films were increased more rapidly than those of FS-SDNA with increasing strain. In addition, generally stresses with higher concentration of NM showed stiffer slopes (i.e., higher Young's modulus) than those with lower concentrations of NM. In order to analyse tensile and elastic properties of each sample, Young's modulus as a ratio of stress over strain was introduced
(Fig. 3d). Based on Young's modulus, we might be able to estimate viscoelastic characteristics of samples such as glassy state (≥~50 GPa), semicrystalline state and rubbery state (≤~100 MPa) [26]. We obtained Young's modulus from stress data in strain range of 1–2% measured at room temperature (Fig. 3a–c). Comparing Young's modulus of pristine FS-SDNA thin film (~4.3 MPa), Young's moduli obtained for FSNM-SDNA thin films were significantly enhanced. This might be due to doping of NMs and variation in water contents. As expected, higher concentration of NM showed higher Young's modulus. Interestingly, modulus of FS-SDNA with lanthanide Tb3+ (~26.3 MPa) was slightly higher than that of FS-SDNA having metallic Cu2+ (~18.0 MPa) obtained at constant ion concentration of 1 mM because of intrinsic physical characteristics of each ion. Fig. 4 shows dynamic mechanical analysis (i.e., E′, E″ and tan δ) results of FS-SDNA and FS-NM-SDNA thin films as a function of temperature ranging from −100 to 200 °C. E′ could provide information for material's stiffness and structural stability at a given temperature. E′
Fig. 2. Stress-strain and dynamic mechanical analysis of free-standing pristine SDNA thin films. (a) Stress-strain curve of free-standing pristine SDNA thin films with two different SDNA concentrations (i.e., 1.0 and 1.5 wt%). (b–d) Dynamic mechanical analysis, i.e., temperature-dependent storage modulus (E′), loss modulus (E″) and tangent of phase angle (tan δ) of free-standing pristine SDNA thin films, respectively. 3
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Fig. 3. Stress-strain curves and Young's modulus analysis of free-standing pristine SDNA and nanomaterial (i.e., Au NP, Cu2+ and Tb3+)-embedded SDNA thin films. (a) Stress-strain graphs of free-standing DNA thin films with 0, 0.7 and 2.1 nM of Au NPs labeled as SDNA, Au 0.7 and Au 2.1, respectively. (b) Stress-strain curves of free-standing SDNA thin films with 0, 1 and 2 mM of Cu2+ labeled as SDNA, Cu 1 and Cu 2, respectively. (c) Stress-strain curves of free-standing SDNA thin films with 0, 0.5 and 1 mM of Tb3+ labeled as SDNA, Tb 0.5 and Tb 1, respectively. (d) Young's modulus of each sample calculated from the slope of stress-strain curve.
values of FS-SDNA thin films were decreased until certain temperature (~30 °C). They were then increased up to structural deformation temperature (~100 °C) followed by a decrease with further increase of temperature. After embedment of either Au NPs, Cu2+, or Tb3+ into SDNA, slight increase of E′ and a shift of structural deformation peak to slightly higher temperature were observed. This indicated that FSSDNA thin films with NMs showed relatively higher thermal rigidity and stability than FS-SDNA due to enhancement of binding affinities between SDNA duplexes and NMs through electrostatic and non-specific bindings.
E″ is related to energy loss of samples during transition of formation. E″ values showed noticeable peaks that were assigned to characteristic transitions of FS-SDNA thin films. Each peak and hump shown in Fig. 4b corresponded to intrinsic behaviors of samples such as relaxation and transition process. The first hump appeared in FS-SDNA thin film was placed near −43 °C. This temperature was considered as a β-transition temperature provided by global molecular motion of hydrated SDNA molecule [27,28]. The second peak located at ~64 °C was connected to water evaporation temperature within the film. Structural deformation and α-transition (also known as glass transition) could be
Fig. 4. Dynamic mechanical analysis of free-standing pristine SDNA and nanomaterial-embedded SDNA thin films. (a) Temperature-dependent storage modulus (E′) of pristine SDNA and Au NP-, Cu2+- and Tb3+-embedded SDNA thin films. (b) Temperature-dependent loss modulus (E″) of pristine SDNA and Au NP-, Cu2+- and Tb3+-embedded SDNA thin films. (c) Temperature-dependent tangent of phase angle (tan δ) of pristine SDNA and Au NP-, Cu2+- and Tb3+-embedded SDNA thin films. Free-standing pristine SDNA and SDNA thin films with Au NP at 2.1 nM, Cu2+ at 2 mM and Tb3+ at 1 mM (labeled as SDNA, Au 2.1, Cu 2 and Tb 1) were used. 4
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Fig. 5. Temperature-dependent dynamic modulus and tangent of phase angle differences between free-standing pristine SDNA and nanomaterial-embedded SDNA thin films regarding temperature and loss modulus peak assignment. (a) Temperature-dependent dynamic storage modulus differences between free-standing pristine SDNA and Au NP-, Cu2+- and Tb3+-embedded SDNA thin films. (b) Temperature-dependent dynamic loss modulus differences between free-standing pristine SDNA and Au NP-, Cu2+- and Tb3+-embedded SDNA thin films. (c) Temperature-dependent tangent of phase angle differences between free-standing pristine SDNA and Au NP-, Cu2+- and Tb3+-embedded SDNA thin films. (d) Loss modulus peak assignments of β-transition, water evaporation, structural deformation and α-transition (known as glass transition) temperatures for each sample.
external thermal energy, water molecules of hydrated DNA started to evaporate at water evaporation temperature over 60 °C. When the temperature is close to 100 °C, structural deformation of doublestranded DNA to single-stranded DNA started to occur by breaking hydrogen bonds of base-pairs. Finally, when temperature of the system reached to α-transition temperatures or glass-transition temperature around 173 °C, deformed single-stranded DNA molecules were mobile and started to flow within thin films indicating transition of state from hard glass-state to viscous rubbery state. β-transition temperatures (which were connected to collective motion of hydrated DNA) of FS-SDNA, FS-Au NP-SDNA (Au 2.1), FS-Cu2+SDNA (Cu 2) and FS-Tb3+-SDNA (Tb 1) were −43, −62, −82 and −57 °C, respectively. Global molecular motion of hydrated SDNA with NMs was initiated at relatively lower temperatures than that of pristine SDNA due to the presence of NMs that served as activator of molecular motion. Evaporation temperatures of FS-SDNA thin films were increased with the addition of NMs. Here, β-transition and evaporation temperatures of thin films might provide lower and upper bound regions of mechanically stable sample conditions. Difference in water evaporation and β-transition temperature of SDNA thin film was 107 °C (= 64 °C ‒ (−43 °C)) which provided stable temperature range for SDNA. By addition of Au NP, Cu2+ and Tb3+ into SDNA, such differences could be extended up to ~1.36, ~1.44 and ~1.28 times larger than SDNA, respectively. Structural deformation and alteration (from double-stranded to single-stranded DNA) of FS-SDNA, FS-Au NP-SDNA, FS-Cu2+-SDNA and FS-Tb3+-SDNA occurred at 93, 115, 102 and 100 °C, respectively. Finally, viscoelastic characteristics of FS-SDNA thin films were completely changed by passing α-transition (i.e., glass transition) temperature of 173 °C. Glass transition temperatures were not visible for FS-NM-SDNA thin films since measured temperature range was only up to 200 °C. Decrease of β-transition temperature and increase of water evaporation and structure deformation temperatures of FS-NM-SDNA were revealed due to intercalation and electrostatic interaction (non-specific interaction and entropic force) between Cu2+/ Tb3+ (Au NP) and SDNA. Consequently, this resulted in enhanced thermo-mechanical stabilities of FS-NM-SDNA thin films than those of FS-SDNA thin films.
acquired by analysis of third and fourth peaks placed at ~93 and ~173 °C, respectively. Interestingly, suppression and peak shifts of E″ were observed for FS-NM-SDNA thin films, indicating significant differences in transition behavior compared to FS-SDNA. Finally, graphs of tan δ (corresponded to E''/E′) for FS-SDNA and FS-NM-SDNA thin films were obtained. Results shown in Fig. 4c provided clues of the overall dynamic mechanical behavior of materials. Although glass transition temperature (i.e., transition temperature between glassy state and semicrystalline/rubbery state) might be obtained by a peak having maximum temperature of tan δ, glass transition temperatures of FS-NMSDNA thin films were hardly acquired within measured temperature range up to 200 °C. At temperatures of over 200 °C, samples started to show severe damage by burning. Fig. 5a–c illustrate differences of E′, E″ and tan δ per unit temperature which provided the number of transitions (obtained by finding temperatures having zero differences) and significant slope changes (by counting number of local extrema of differences) of dynamic modulus and tangent of phase angle. From temperature-dependent E′ difference of FS-SDNA thin films, two zero differences and two local extrema could be found at 40, 115 °C and −13, 90 °C which corresponded to local extrema and extreme slope changes of E′, respectively. Although E′ differences of FS-Cu2+-SDNA showed similar trend as FS-SDNA, FS-Au NP-SDNA showed roughly constant E′ differences. This meant that magnitudes of E′ change in measured range of temperature were minute and negligible. E″ and tan δ differences of FS-SDNA and FS-NM-SDNA thin films at a given unit temperature are shown in Fig. 5b and c. Differences of E″ for FS-Au NP-SDNA thin films were relatively small compared to those for FS-SDNA thin films. This meant that the amount of energy loss during deformation of thin films having Au NPs was independent of temperature. Interestingly, no significant differences of tan δ were observed. This indicated ratios of E″ and E′ along the whole range of measured temperatures were not much different. β-transition, water evaporation, structural deformation and αtransition temperatures for FS-SDNA and FS-NM-SDNA thin films obtained from E″ are shown in Fig. 5d. As the temperature of the system increased from low temperature, localized motion of chemical bonds within DNA molecules occurred such as bending and stretching (e.g., vibration mode of deoxyribose moiety, C–N and C]C stretching in cytosine). When temperature of the system reached to β-transition temperature, collective motion of DNA molecules was allowed due to expansion of free-space within films which then generated toughness to the system by absorbing thermal energy. As the system absorbed more
4. Conclusions We fabricated free-standing pristine SDNA (FS-SDNA) and nanomaterial-embedded SDNA (FS-NM-SDNA) thin films by casting method 5
Journal of Physics and Chemistry of Solids 135 (2019) 109104
S. Yoo, et al.
and studied their tensile properties (i.e., stress-strain and Young's modulus) and dynamic mechanical properties (i.e., temperature-dependent storage modulus (E′), loss modulus (E″) and tangent of phase angle (tan δ)). When stress-strain curves and Young's moduli of FSSDNA, FS-Au NP-SDNA, FS-Cu2+-SNDA and FS-Tb3+-SDNA thin films were examined, stresses of all FS-NM-SDNA thin films were increased rapidly than FS-SDNA thin films with increasing strain. Young's moduli of FS-NM-SDNA thin films were also significantly enhanced than those of FS-SDNA. This might be due to the doping of various NMs in water contents. Dynamic mechanical analysis (i.e., E′, E″ and tan δ) of FSSDNA and FS-NM-SDNA thin films as a function of temperature were also investigated in order to understand stiffness and structural stabilities of samples at a given temperature. When NMs were embedded into SDNA, slight increase in E′ and peak shifts were observed. This implied that FS-SDNA thin films with NMs showed relatively higher thermal rigidity and stability than FS-SDNA thin films due to their enhancement in binding affinities between SDNA duplexes and NMs. Noticeable peaks in E″ were assigned to characteristic transition temperatures of FS-SDNA and FS-NM-SDNA such as β-transition, water evaporation, structural deformation and α-transition. To obtain information of overall dynamic mechanical behaviors of FS-SDNA and FSNM-SDNA thin films, tan δ (corresponded to E''/E′) was also measured. Interestingly, β-transition temperatures of FS-NM-SDNA thin films were decreased whereas evaporation and structural deformation temperatures were increased compared to those of pristine SDNA thin films owing to the presence of binding affinities between NMs and SDNA in FS-NM-SDNA thin films. Accordingly, NM embedment into SDNA thin films significantly enhanced thermo-mechanical stabilities. Finally, differences in E′, E″ and tan δ per unit temperature were analysed by finding temperatures having zero differences and counting the number of local extrema of differences to better understand the transition mechanism. Our results might be very useful for constructing functional material-doped DNA thin films. They are also helpful for understanding thermo-mechanical properties that are very important for real devices and sensors used in piezoelectric materials and flexible substrates.
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