DNA nanostructures doped with lanthanide ions for highly sensitive UV photodetectors

Deoxyribonucleic acid (DNA) and lanthanide ions (Ln(3+)) exhibit exceptional optical properties that are applicable to the development of nanoscale devices and sensors. Although DNA nanostructures and Ln(3+) ions have been investigated for use in the current state of technology for more than a few decades, researchers have yet to develop DNA and Ln(3+) based ultra-violet (UV) photodetectors. Here, we fabricate Ln(3+) (such as holmium (Ho3+), praseodymium (Pr3+), and ytterbium (Yb3+))-doped double crossover (DX)-DNA lattices through substrate-assisted growth and salmon DNA (SDNA) thin films via a simple drop-casting method on oxygen (O-2) plasma-treated substrates for high performance UV photodetectors. Topological (AFM), optical (UV-vis absorption and FTIR), spectroscopic (XPS), and electrical (I-V and photovoltage) measurements of the DX-DNA and SDNA thin films doped with various concentrations of Ln(3+) ([Ln(3+)]) are explored. From the AFM analysis, the optimum concentrations of various Ln(3+) ([Ln(3+)](o)) are estimated (where the phase transition of Ln(3+)-doped DX-DNA lattices takes place from crystalline to amorphous) as 1.2 mM for Ho3+, 1.5 mM for Pr3+, and 1.5 mM for Yb3+. The binding modes and chemical states are evaluated through optical and spectroscopic analysis. From UV-vis absorption studies, we found that as the [Ln(3+)] was increased, the absorption intensity decreased up to [Ln(3+)](o), and increased above [Ln(3+)]. The variation in FTIR peak intensities in the nucleobase and phosphate regions, and the changes in XPS peak intensities and peak positions detected in the N 1 s and P 2p core spectra of Ln(3+)-doped SDNA thin films clearly indicate that the Ln(3+) ions are properly bound between the bases (through chemical intercalation) and to the phosphate backbone (through electrostatic interactions) of the DNA molecules. Finally, the I-V characteristics and time-dependent photovoltage of Ln(3+) doped SDNA thin films are measured both in the dark and under UV LED illuminations (lambda(LED) = 382 nrn) at various illumination powers. The photocurrent and photovoltage of Ln(3+)-doped SDNA thin films are enhanced up to the [Ln(3+)](o) compared to pristine SDNA due to the charge carriers generated from both SDNA and Ln(3+) ions upon the absorption of light. From our observations, the photovoltages as function of illumination power suggest higher responsivities, and the photovoltages as function of time are almost constant which indicates the stability and retention characteristics of the Ln(3+)-doped SDNA thin films. Hence, our method which provides an efficient doping of Ln(3+) into the SDNA with a simple fabrication process might be useful in the development of high-performance optoelectronic devices and sensors.