DNA and DNA–CTMA composite thin films embedded with carboxyl group-modified multi-walled carbon nanotubes

Water-resistant free-standing DNA-complexed films with antioxidant and H2O2-responsive activity

Water-insoluble DNA complexes are suitable for producing free-standing DNA films due to their low water sensitivity, which prevents their rapid degradation in aqueous environments. Here, we proposed two types of free-standing films that exhibit low dissolution rates in water: low molecular weight chitosan (LCS)-DNA films and phosphatidylcholine (PC)-cetyltrimethylammonium (CTMA)-DNA films. The structure and binding characteristics of the LCS-DNA and PC-CTMA-DNA complexes were investigated with UV-Vis spectroscopy and via the fluorescent characteristics of daunorubicin bound to them. A simple drop-casting method was then adopted for both complexes to fabricate free-standing films. An increase in antioxidant activity and water-resistance of the LCS-DNA DNA film was observed when the molar ratio of LCS to DNA was increased, but the dissolution rate of the LCS-DNA film was also dependent on the ionic strength of the dissolving solution. Fourteen days were required to dissolve the LCS-DNA film in deionized water, whereas immediate dissolution was observed in 1× phosphate-buffered saline (PBS). Deformation of the PC-CTMA-DNA film was accelerated by H₂O₂, such that the PC-CTMA-DNA film was degraded after 21 days of immersion in 1× PBS with H₂O₂. Due to the low dissolution rate in water and antioxidant activity, the free-standing LCS-DNA film should be able to store and protect embedded clinical materials, such as proteins and intercalating drugs, from moisture and enable localized delivery of treatments to designated sites. Also, the free-standing PC-CTMA-DNA film could be a biocompatible candidate for use as a membrane or sensor for detecting the levels of reactive oxygen species.

DNA foams constructed by freeze drying and their optoelectronic characteristics

The distinctive properties of DNA make it a promising biomaterial to use in nanoscience and nanotechnology. In the present study, DNA foam was fabricated into multi-dimensional shapes using a freeze drying process with liquid nitrogen and 3D printed molds. The physicochemical and optoelectronic properties of the fabricated DNA foams were investigated using Fourier transform infrared (FTIR) spectrum, X-ray photoelectron spectrum (XPS), thermogravimetric analysis (TGA), ultraviolet-visible (UV-Vis) absorption spectrum, and current-voltage (I-V) characteristics to understand the changes formed in the DNA structure and their effect on properties during the fabrication of DNA foam. The FTIR and XPS analyses confirmed that nitrogen was diffusing into the DNA structure during the DNA foam fabrication. The diffused nitrogen caused a decrease in bond lengths, strong chemical bonds, compaction of DNA structure, existence of additional carbon-nitrogen bonds, and variation in the electron density of the base elements in DNA. These changes in the DNA structure of the DNA foam were reflected in their chemical, optical, and electrical properties. Furthermore, the proper utilization of DNA foams as a template for functional materials by embedding carbon nanotubes (CNTs) and thermocolor was demonstrated.

Nanomaterial-Embedded DNA Films on 2D Frames

Recently, 3D printing has provided opportunities for designing complex structures with ease. These printed structures can serve as molds for complex materials such as DNA and cetyltrimethylammonium chloride (CTMA)-modified DNA that have easily tunable functionalities via the embedding of various nanomaterials such as ions, nanoparticles, fluorophores, and proteins. Herein, we develop a simple and efficient method for constructing DNA flat and curved films containing water-soluble/thermochromatic dyes and di/trivalent ions and CTMA-modified DNA films embedded with organic light-emitting molecules (OLEM) with the aid of 2D/3D frames made by a 3D printer. We study the Raman spectra, current, and resistance of Cu²⁺-doped and Tb³⁺-doped DNA films and the photoluminescence of OLEM-embedded CTMA-modified DNA films to better understand the optoelectric characteristics of the samples. Compared to pristine DNA, ion-doped DNA films show noticeable variation of Raman peak intensities, which might be due to the interaction between the ion and phosphate backbone of DNA and the intercalation of ions in DNA base pairs. As expected, ion-doped DNA films show an increase of current with an increase in bias voltage. Because of the presence of metallic ions, DNA films with embedded ions showed relatively larger current than pristine DNA. The photoluminescent emission peaks of CTMA-modified DNA films with OLEM_Red, OLEM_Green, and OLEM_Blue were obtained at the wavelengths of 610, 515, and 469 nm, respectively. Finally, CIE color coordinates produced from CTMA-modified DNA films with different OLEM color types were plotted in color space. It may be feasible to produce multilayered DNA films as well. If so, multilayered DNA films embedded with different color dyes, ions, fluorescent materials, nanoparticles, proteins, and drug molecules could be used to realize multifunctional physical devices such as energy harvesting and chemo-bio sensors in the near future.

DNAzyme-Amplified Electrochemical Biosensor Coupled with pH Meter for Ca2+ Determination at Variable pH Environments

For more than 50% of multiparous cows, it is difficult to adapt to the sudden increase in calcium demand for milk production, which is highly likely to cause hypocalcemia. An electrochemical biosensor is a portable and efficient method to sense Ca²⁺ concentrations, but biomaterial is easily affected by the pH of the analyte solution. Here, an electrochemical biosensor was fabricated using a glassy carbon electrode (GCE) and single-walled carbon nanotube (SWNT), which amplified the impedance signal by changing the structure and length of the DNAzyme. Aiming at the interference of the pH, the electrochemical biosensor (GCE/SWNT/DNAzyme) was coupled with a pH meter to form an electrochemical device. It was used to collect data at different Ca²⁺ concentrations and pH values, and then was processed using different mathematical models, of which GPR showed higher detecting accuracy. After optimizing the detecting parameters, the electrochemical device could determine the Ca²⁺ concentration ranging from 5 μM to 25 mM, with a detection limit of 4.2 μM at pH values ranging from 4.0 to 7.5. Finally, the electrochemical device was used to determine the Ca²⁺ concentrations in different blood and milk samples, which can overcome the influence of the pH.

Fibres and films made from DNA and CTMA-modified DNA embedded with gold nanorods and organic light-emitting materials

The scaffolding of deoxyribonucleic acid (DNA) makes DNA molecules effective templates for hosting various types of nanomaterials. Recently, electrospun fibres formed by a variety of polymers have begun to see use in a number of applications, such as filtration in energy applications, insulation in thermodynamics and protein scaffolding in biomedicine. In this study, we constructed electrospun fibres and thin films made of DNA and cetyltrimethylammonium chloride (CTMA)-modified DNA (CDNA) embedded with dyes, organic light-emitting materials (OLEMs), and gold nanorods (GNRs). These materials provide significant advantages, including selectivity of dimensionality, solubility in organic and inorganic solvents, and functionality enhancement. In addition, coaxial fibres made of CDNA were constructed to demonstrate the feasibility of constructing relatively complex fibres with an electrospinner. To determine the basic physical characteristics of the fibres and thin films containing GNRs and OLEMs, we conducted current measurements, photoluminescence (PL) measurements, X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible (UV-Vis) spectroscopy. The currents in DNA and CDNA were found to exhibit Ohmic behaviour, while the PL emission could be controlled by OLEMs. In addition, the XPS provided the chemical configuration of samples, and the UV-Vis spectra revealed the plasmon resonance of GNR. Due to their simple fabrication and enhanced functionality, these DNA and CDNA fibres and thin films could be used in various devices (e.g., filters or blocking layers) and sensors (e.g., gas detectors and bio sensors) in a number of industries.

Enhanced performance of an electrochemical aptasensor for real-time detection of vascular endothelial growth factor (VEGF) by nanofabrication and ratiometric measurement

Achieving a biosensing interface without baseline drift caused by variables in matrix samples is essential for real-time detection of analytes. In this study, we developed a molecular beacon based electrochemical aptasensor to realize the ratiometric signal quantification of VEGF in serum by surface modification of nanocomposites of graphene oxide/methylene blue (GO/MB) and AuNPs followed by the attachment of ferrocene-labeled aptamer (aptamer-Fc) against VEGF. The presence of VEGF can trigger the configuration change of aptamer-Fc, resulting in the redox probe Fc being far away from the electrode surface to attenuate the electrochemical communication between electrode and Fc. Meanwhile, signal of MB also decreased due to the impediment of aptamer-Fc to electron transfer passage. The achieved GC-rGO/MB-AuNPs-aptamer-Fc sensing interface was successfully used for the sensitive detection of VEGF in real-time with a linear detection range 2-500 pg mL^-1 and detection limit of 0.1 pg mL^-1 based on ratiometric dual signal (Fc and MB) read-out. It was observed loading MB and AuNPs to the GO based sensing interface was favorable to enhance the analytical performance in terms of sensitivity and capability to effectively eliminate background interference. This electrochemical aptasensor provides a universal and reliable biosensing platform which is potential for real-time and sensitive tracking of various cytokines in vivo.

Band gap, dielectric constant, and susceptibility of DNA layers as controlled by vanadium ion concentration

Deoxyribonucleic acid (DNA) doped with transition metal ions shows great versatility for molecular-based biosensors and bioelectronics. Methodologies for developing DNA lattices (formed by synthetic double-crossover tiles) and DNA layers (used by natural salmon) doped with vanadium ions (V3+), as well as an understanding of the physical characteristics of V3+-doped DNA nanostructures, are essential in practical applications in interdisciplinary research fields. Here, DNA lattices and layers doped with V3+ are constructed through substrate-assisted growth and drop-casting methods. In addition, enhanced physical characteristics such as the band gap energy, work function, dielectric constant, and susceptibility of V3+-doped DNA nanostructures with varying V3+ concentration ([V 3+ ]) are investigated. The critical concentration ([V 3+ ]C ) at a given amount of DNA was predicted based on an analysis of the phase transition of DNA lattices from crystalline to amorphous with specific [V 3+ ]. Generally, the [V 3+ ]C provided crucial information on the structural stability and extremum physical characteristics of V3+-doped DNA nanostructures due to the optimum incorporation of V3+ into DNA. We obtained the optical absorption spectra for energy band gap estimation; Raman spectra for identifying the preferential coordination sites of V3+ in DNA; x-ray photoelectron spectra to examine the chemical state, chemical composition, and functional groups; and ultraviolet photoelectron spectra to estimate the work function. In addition, we addressed the electrical properties (i.e. current, capacitance, dielectric constant, and storage energy) and magnetic properties (magnetic field-dependent and temperature-dependent magnetizations and susceptibility) of DNA layers in the presence of V3+. The development of biocompatible materials with specific optical, electrical, and magnetic properties is required for future applications because they must have designated functionality, high efficiency, and affordability.

Large-Scale Fabrication of Copper-Ion-Coated Deoxyribonucleic Acid Hybrid Fibers by Ion Exchange and Self-Metallization

It has been a challenge to achieve deoxyribonucleic acid (DNA) metallization and mass production with a high quality. The main aim of this study was to develop a large-scale production method of metal-ion-coated DNA hybrid fibers, which can be useful for the development of physical devices and sensors. Cetyltrimethylammonium-chloride-modified DNA molecules (CDNA) coated with metal ions through self-metallization exhibit enhanced optical and magnetic properties and thermal stability. In this paper, we present a simple synthesis route for Cu²⁺-coated CDNA hybrid fibers through ion exchange followed by self-metallization and analyze their structural and chemical composition (by X-ray diffraction (XRD), high-resolution field emission transmission electron microscopy (FETEM), and energy-dispersive X-ray spectroscopy (EDS)) and optical (by ultraviolet (UV)-visible absorption, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopies (XPS)), magnetic (by vibrating-sample magnetometry), and thermal (by a thermogravimetric analysis) characteristics. The XRD patterns, high-resolution FETEM images, and selected-area electron diffraction patterns confirmed the triclinic structure of Cu²⁺ in CDNA. The EDS results revealed the formation of Cu²⁺-coated CDNA fibers with a homogeneous distribution of Cu²⁺. The UV-vis, FTIR, and XPS spectra showed the electronic transition, interaction, and energy transfer between CDNA and Cu²⁺, respectively. The Cu²⁺-coated CDNA fibers exhibited a ferromagnetic nature owing to the presence of Cu²⁺. The magnetization of the Cu²⁺-coated CDNA fibers increased with the concentration of Cu²⁺ and decreased with the increase in temperature. Endothermic (absorbed heat) and exothermic (released heat) peaks in the differential thermal analysis curve were observed owing to the interaction of Cu²⁺ with the phosphate backbone.