Stable electrical, morphological and optical properties of titanium dioxide nanoparticles affected by annealing temperature

Different TiO2 synthesization processes give different properties. Most of researches in material studies only focus on the morphological and optical properties of TiO2 while lacking in the effort of achieving stable electrical properties of the material. In engineering, stable electrical properties are vital in order to develop a device. Moreover, current technology needs more nanostructure application to enhance the performance of devices. In this paper, TiO2 nanoparticle was synthesized by sol–gel method using 1:0.1:9 ratios of titanium isopropoxide:acetic acid:ethanol, respectively. This synthesized TiO2 was able to respond in extremely small and consistent electrical reading (nanoampere). This metal oxide is good enough to be used as a material to develop ultra-high sensitive biosensor. Annealing process on the TiO2 film was able to improve its’ electrical conductivity. The three layers TiO2 coating were annealed at 400, 500, 600 and 700 °C and the surface morphologies, structural also electro-optical properties were studied using FESEM, XRD, UV–Vis and Keithley 6485 picoammeter. The XRD pattern shows the presence of stable anatase and rutile structures even at low temperature, whereas FESEM shows that annealingtemperature affects the particle size. The optical band gap of TiO2 thin films decreases from 3.74 to 3.34 eV as the annealing temperature increases. The current-to-voltage characteristics show that the conductivity decreases as the annealing temperature varies from 400to 700 °C. The output measurements indicated an improvement in electrical properties with annealing temperature

Titanium Dioxide Nanoparticle-Based Interdigitated Electrodes: A Novel Current to Voltage DNA Biosensor Recognizes E. coli O157:H7

Nanoparticle-mediated bio-sensing promoted the development of novel sensors in the front of medical diagnosis. In the present study, we have generated and examined the potential of titanium dioxide (TiO2) crystalline nanoparticles with aluminium interdigitated electrode biosensor to specifically detect single-stranded E.coli O157:H7 DNA. The performance of this novel DNA biosensor was measured the electrical current response using a picoammeter. The sensor surface was chemically functionalized with (3-aminopropyl) triethoxysilane (APTES) to provide contact between the organic and inorganic surfaces of a singlestranded DNA probe and TiO2 nanoparticles while maintaining the sensing system’s physical characteristics. The complement of the target DNA of E. coli O157:H7 to the carboxylate- probe DNA could be translated into electrical signals and confirmed by the increased conductivity in the current-to-voltage curves. The specificity experiments indicate that the biosensor can discriminate between the complementary sequences from the base-mismatched and the non-complementary sequences. After duplex formation, the complementary target sequence can be quantified over a wide range with a detection limit of 1.0 x 10- 13M. With target DNA from the lysed E. coli O157:H7, we could attain similar sensitivity. Stability of DNA immobilized surface was calculated with the relative standard deviation (4.6%), displayed the retaining with 99% of its original response current until 6 months. This high-performance interdigitated DNA biosensor with high sensitivity, stability and non-fouling on a novel sensing platform is suitable for a wide range of biomolecular interactive analyses

Interdigitated electrode fabrication process.

<p>Nine steps were followed to complete the fabrication of this device under room temperature.</p

Experimental set-up of picoammeter for the TiO₂ nanoparticle-based DNA biosensor.

<p>Current responses show ability of the device to retain the same output current after hybridization and dehybridization of 1 μM targeted DNA.</p

Steps were used for picoammeter-TiO₂ nanoparticle DNA biosensor.

<p>(a) Sensing surface. The device has sensing zone that uniformly covered with TiO₂ nanoparticles on top of the fabricated aluminum electrodes. (b) Three steps involved in the measurements. It includes dropping of sample, drying the droplet and measuring the current response.</p

Preparation of sensing surface.

<p>(a) Schematics of the DNA immobilization and hybridization process. This resistive DNA biosensor with titanium dioxide nanoparticles enhances the current signal that eliminates PCR. (b) SEM image of interdigitated electrodes. The average gap size between two aluminum finger-shaped electrodes is 16 μm.</p

Responses on the sensing surface.

<p>(a) Current response of the 10 μM probe of <i>E</i>. <i>coli</i> O157:H7 ssDNA concentration measured over 8 months. Inset shows the corresponding histogram of the peak current values on a sensor for 8 months.(b) Current responses of different target DNA hybridized on the 10 μM probe DNA. These results proved the ability of the fabricated device to differentiate the positive and negative controls. (c)Current to voltage curves of the complemented target DNA concentrations. Inset shows the current values of different target DNA concentrations over the range 1E-12, 10E-12, 1E-9, 10E-9, 1E-6 and 10E-6 M. (d) Average current measurements of three different targeted DNA concentrations, 1 pM, 1 nM and 1 μM. The corresponding histogram shows the current values after 5 hybridization cycles.</p

Current responses of different target DNA hybridized on the 10 μM probe DNA.

<p>The target DNA was from the lysed <i>E</i>. <i>coli</i> O157:H7. Different concentrations of target DNA were tested.</p

Geometrical Characterisation of TiO₂-rGO Field-Effect Transistor as a Platform for Biosensing Applications

The performance of the graphene-based field-effect transistor (FET) as a biosensor is based on the output drain current (Id). In this work, the signal-to-noise ratio (SNR) was investigated to obtain a high-performance device that produces a higher Id value. Using the finite element method, a novel top-gate FET was developed in a three-dimensional (3D) simulation model with the titanium dioxide-reduced graphene oxide (TiO2-rGO) nanocomposite as the transducer material, which acts as a platform for biosensing application. Using the Taguchi mixed-level method in Minitab software (Version 16.1.1), eighteen 3D models were designed based on an orthogonal array L18 (6134), with five factors, and three and six levels. The parameters considered were the channel length, electrode length, electrode width, electrode thickness and electrode type. The device was fabricated using the conventional photolithography patterning technique and the metal lift-off method. The material was synthesised using the modified sol–gel method and spin-coated on top of the device. According to the results of the ANOVA, the channel length contributed the most, with 63.11%, indicating that it was the most significant factor in producing a higher Id value. The optimum condition for the highest Id value was at a channel length of 3 µm and an electrode size of 3 µm × 20 µm, with a thickness of 50 nm for the Ag electrode. The electrical measurement in both the simulation and experiment under optimal conditions showed a similar trend, and the difference between the curves was calculated to be 28.7%. Raman analyses were performed to validate the quality of TiO2-rGO