Synthesis of Cu₂CdSnS₄ quaternary alloy nanostructures for dengue serotype-2 DNA biosensor applications

The relentless research and development in new materials holds the key towards continuous technological advancement especially for DNA biosensor. For this purpose, Cu₂CdSnS₄ (CCTS) quaternary alloy nanostructure which regards low-cost, earth-abundant elements and defects free has received a lot of attention recently. It possesses numbers of merits including high optical absorption coefficient(> 104 cm-1) , suitable energy band gap (1.4- 1.5 eV), high power conversion efficiency, p-type conductivity, high hole mobility and enhanced sensitivity of DNA biosensor. Therefore, the aim of this study is to enhance the optical and electrical properties of CCTS quaternary alloy nanostructures to be used in different applications such as optoelectronics and dengue DNA biosensor. CCTS quaternary alloy nanostructures have been synthesized thereafter deposited on different types of substrates using effective-cost and simple spin coating technique. The optical, structural, morphological, topographical and electrical properties of CCTS have been investigated using varied substrates namely Si, Si0₂ and GaN to choose the best one to be utilized in different applications. It was found for optoelectronics; the optical band gap was increased from 1.29 eV to 1.31 eV with changing annealing temperature from room temperature to 500 °C. XRD results have revealed that with ultrasonic samples have more peaks than without ultrasonic ones. The morphological and topographical images have proved that high annealing temperature helps to produce more consistent thin fitm due to increasing of grain size. The reflection spectra for with ultrasonic samples are 10% lower than without ultrasonic ones which means that using ultrasonic in synthesizing CCTS will enhance the absorption capabilities of CCTS. The best study in terms of different properties was with ultrasonic at 400 oc. Moreover, the calculated band gap was increased from 1.25 eV to 1.28 eV and lattice constants were decreased from (a=5.26 A, c=10.52 A) to (a=5.23 A, c= 10.46 A) with increasing copper concentration from 0. 2 M to 1 M. Also, the morphological and topographical studies indicate the superiority of 0.6 M than the other copper concentrations in terms of consistency and homogeneity. As far as our work on biosensor development is concerned, the electrical characterization of Ag interdigitated electrodes which were deposited on SiJSi02/CCTS has found a proportional relationship between the current and voltage whereas, capacitance and impedance have displayed an inverse relationship with frequency. The surface of Si/Si0₂/CCTS was functionalized by using a procedure consists from three steps and they are the surface modification using APTES, EDC and NHS followed by DNA probe immobilization and then the hybridization of six different DNA targets (100 fM, 1 pM, 10 pM, 100 pM, 1 nM and 10 nM). The calculated sensitivity of the biosensor was 24.2 ~ nM-1 cm- 2. Whilst the calculated limit of detection (LOD) and limit of quantitation (LOQ) were 16.9 and 56.3 nM, respectively. The demonstrated results have shown that using CCTS quaternary alloy nanostructures in the fabrication of dengue serotype-2 DNA biosensor is considered as a novel approach due to effective-cost fabrication, simple fabrication procedure, and high sensitivity.