Optoelectronic properties of DNA thin films implanted with titania nanoparticle-coated multiwalled carbon nanotubes

Rendering the unique features of individual nanoscale constituents into macroscopic thin films remains technologically challenging; the engineering of these constituents habitually compromises their inherent properties. Efficient, environmentally benign, and biodegradable DNA and cetyltrimethyl-ammonium chloride-modified DNA (DNA-CT) thin films (TFs) implanted with titania nanoparticle-coated multiwalled carbon nanotubes (MCNT-TiO2) are prepared by a drop-casting technique. The energy dispersive X-ray spectroscopy studies of DNA and DNA-CT TFs with MCNT-TiO2 identifies various elements (C, O, N, P, Na, and Ti) via quantitative microanalysis. The X-ray photoelectron, Raman, Fourier-transform infrared (FTIR), and UV-visible absorption spectra show changes in the chemical compositions and functional groups associated with binding energies, enhancement of characteristic MCNT-TiO2 Raman bands, and intensity changes and peak shifts of the FTIR and UV-Vis-NIR absorption bands, respectively. The PL spectra indicate an energy transfer in the measured samples, and the quenching of PL indicates a decrease in the recombination efficiency. Lastly, we measure the conductivity, which increased with an increasing concentration of MCNT-TiO2 in the DNA and DNA-CT TFs due to the better connectivity of MCNT-TiO2. By using these materials, the optoelectronic properties of DNA and DNA-CT TFs implanted with MCNT-TiO2 are easily tunable, enabling several engineering and multidisciplinary science applications, such as photonics, electronics, energy harvesting, and sensors

Morphological and Optoelectronic Characteristics of Double and Triple Lanthanide Ion-Doped DNA Thin Films

Double and triple lanthanide ion (Ln³⁺)-doped synthetic double crossover (DX) DNA lattices and natural salmon DNA (SDNA) thin films are fabricated by the substrate assisted growth and drop-casting methods on given substrates. We employed three combinations of double Ln³⁺-dopant pairs (Tb³⁺–Tm³⁺, Tb³⁺–Eu³⁺, and Tm³⁺–Eu³⁺) and a triple Ln³⁺-dopant pair (Tb³⁺–Tm³⁺–Eu³⁺) with different types of Ln³⁺, (i.e., Tb³⁺ chosen for green emission, Tm³⁺ for blue, and Eu³⁺ for red), as well as various concentrations of Ln³⁺ for enhancement of specific functionalities. We estimate the optimum concentration of Ln³⁺ ([Ln³⁺]_O) wherein the phase transition of Ln³⁺-doped DX DNA lattices occurs from crystalline to amorphous. The phase change of DX DNA lattices at [Ln³⁺]_O and a phase diagram controlled by combinations of [Ln³⁺] were verified by atomic force microscope measurement. We also developed a theoretical method to obtain a phase diagram by identifying a simple relationship between [Ln³⁺] and [Ln³⁺]_O that in practice was found to be in agreement with experimental results. Finally, we address significance of physical characteristicscurrent for evaluating [Ln³⁺]_O, absorption for understanding the modes of Ln³⁺ binding, and photoluminescence for studying energy transfer mechanismsof double and triple Ln³⁺-doped SDNA thin films. Current and photoluminescence in the visible region increased as the varying [Ln³⁺] increased up to a certain [Ln³⁺]_O, then decreased with further increases in [Ln³⁺]. In contrast, the absorbance peak intensity at 260 nm showed the opposite trend, as compared with current and photoluminescence behaviors as a function of varying [Ln³⁺]. A DNA thin film with varying combinations of [Ln³⁺] might provide immense potential for the development of efficient devices or sensors with increasingly complex functionality

Identifying Fibrillization State of Aβ Protein via Near-Field THz Conductance Measurement

Progressive Alzheimer's disease is correlated with the oligomerization and fibrillization of the amyloid beta (Aβ) protein. We identify the fibrillization stage of the Aβ protein through label-free near-field THz conductance measurements in a buffer solution. Frequency-dependent conductance was obtained by measuring the differential transmittance of the time-domain spectroscopy in the THz range with a molar concentration of monomer, oligomer, and fibrillar forms of the Aβ protein. Conductance at the lower frequency limit was observed to be high in monomers, reduced in oligomers, and dropped to an insulating state in fibrils and increased proportionally with the Aβ protein concentration. The monotonic decrease in the conductance at low frequency was dominated by a simple Drude component in the monomer with concentration and nonlinear conductance behaviors in the oligomer and fibril. By extracting the structural localization parameter, a dimensionless constant, with the modified Drude-Smith model, we defined a dementia quotient (DQ) value (0 < De < 1) as a discrete metric for a various Aβ proteins at a low concentration of 0.1 μmol/L; DQ = 1.0 ± 0.002 (fibril by full localization, mainly by Smith component), DQ = 0.64 ± 0.013 (oligomer by intermixed localization), and DQ = 0.0 ± 0.000 (monomer by Drude component). DQ values were discretely preserved independent of the molar concentration or buffer variation. This provides plenty of room for the label-free diagnosis of Alzheimer's disease using the near-field THz conductance measuremen