Veeradasan Perumal

‘Spotted Nanoflowers’: Gold-seeded Zinc Oxide Nanohybrid for Selective Bio-capture

Hybrid gold nanostructures seeded into nanotextured zinc oxide (ZnO) nanoflowers (NFs) were created for novel biosensing applications. The selected ‘spotted NFs’ had a 30-nm-thick gold nanoparticle (AuNP) layer, chosen from a range of AuNP thicknesses, sputtered onto the surface. The generated nanohybrids, characterized by morphological, physical and structural analyses, were uniformly AuNP-seeded onto the ZnO NFs with an average length of 2–3 μm. Selective capture of molecular probes onto the seeded AuNPs was evidence for the specific interaction with DNA from pathogenic Leptospirosis-causing strains via hybridization and mis-match analyses. The attained detection limit was 100 fM as determined via impedance spectroscopy. High levels of stability, reproducibility and regeneration of the sensor were obtained. Selective DNA immobilization and hybridization were confirmed by nitrogen and phosphorus peaks in an X-ray photoelectron spectroscopy analysis. The created nanostructure hybrids illuminate the mechanism of generating multiple-target, high-performance detection on a single NF platform, which opens a new avenue for array-based medical diagnostics.

pH Measurement using in house fabricated interdigitated capacitive transducer

Microelectronics technologies have contributed a lot of facilities to fabricate small scale devices especially in biological and medical fields where the full advantage in development of transducers and sensors which are capable of characterizing bio-species. The research about the characterisation of fabricated electrode transducer using biomolecule detection technique has been studied to understand the important relationship between the transducer and the structure which leads to high sensitivity and selectivity. This paper mainly illustrate regarding the fabrication process of Interdigitated capacitive sensor (IDC) based sensor for bio-molecular detection process. We have applied conventional photolithography technique by using metal deposited on silicon substrate to fabricate a microelectrode transducer and employed as electrochemical microelectrode sensors to measure the bio-molecules electrical characteristics. IDC mask is designed by using auto-cad software which tailors for detection of bio substance which is extremely small scale in size. IDC mask is patterned transfer on sample by using conventional lithography process which the parameters are critically adjusted to ensure that the pattern transfer process occur with minimal defects. The fabricated sensor will be further validated through electrical and morphological characteristic. The morphological characterizations were carried out using High power microscope (HPM), Atomic force microscope (AFM) and a Scanning electron microscope (SEM). The electrical measurements were carried out using Dielectric analyser (DA) and a source meter. Capacitance test and impedance test is taken with various pH solution to observe the response of the sensor with different pH values. Purchased pH buffer solutions which varied from pH1 to pH12 are dropped on the microelectrode and the effect on it is investigated for the application in pH measurement. This research has proven that increase in pH value from acidic to alkaline is proportional with capacitance. The measured values of capacitance with respect to each pH concentrations applied during the measurements were repeatable and reproducible.

Thickness Dependent Nanostructural, Morphological, Optical and Impedometric Analyses of Zinc Oxide-Gold Hybrids: Nanoparticle to Thin Film

The creation of an appropriate thin film is important for the development of novel sensing surfaces, which will ultimately enhance the properties and output of high-performance sensors. In this study, we have fabricated and characterized zinc oxide (ZnO) thin films on silicon substrates, which were hybridized with gold nanoparticles (AuNPs) to obtain ZnO-Aux (x = 10, 20, 30, 40 and 50 nm) hybrid structures with different thicknesses. Nanoscale imaging by field emission scanning electron microscopy revealed increasing film uniformity and coverage with the Au deposition thickness. Transmission electron microscopy analysis indicated that the AuNPs exhibit an increasing average diameter (5–10 nm). The face center cubic Au were found to co-exist with wurtzite ZnO nanostructure. Atomic force microscopy observations revealed that as the Au content increased, the overall crystallite size increased, which was supported by X-ray diffraction measurements. The structural characterizations indicated that the Au on the ZnO crystal lattice exists without any impurities in a preferred orientation (002). When the ZnO thickness increased from 10 to 40 nm, transmittance and an optical bandgap value decreased. Interestingly, with 50 nm thickness, the band gap value was increased, which might be due to the Burstein-Moss effect. Photoluminescence studies revealed that the overall structural defect (green emission) improved significantly as the Au deposition increased. The impedance measurements shows a decreasing value of impedance arc with increasing Au thicknesses (0 to 40 nm). In contrast, the 50 nm AuNP impedance arc shows an increased value compared to lower sputtering thicknesses, which indicated the presence of larger sized AuNPs that form a continuous film, and its ohmic characteristics changed to rectifying characteristics. This improved hybrid thin film (ZnO/Au) is suitable for a wide range of sensing applications.

Gold nanorod embedded novel 3D graphene nanocomposite for selective bio-capture in rapid detection of Mycobacterium tuberculosis

Tuberculosis (TB) is a chronic and infectious airborne disease which requires a diagnosing system with high sensitivity and specificity. However, the traditional gold standard method for TB detection remains unreliable with low specificity and sensitivity. Nanostructured composite materials coupled with impedimetric sensing utilised in this study offered a feasible solution. Herein, novel gold (Au) nanorods were synthesized on 3D graphene grown by chemical vapour deposition. The irregularly spaced and rippled morphology of 3D graphene provided a path for Au nanoparticles to self-assemble and form rod-like structures on the surface of the 3D graphene. The formation of Au nanorods were showcased through scanning electron microscopy which revealed the evolution of Au nanoparticle into Au islets. Eventually, it formed nanorods possessing lengths of ~ 150 nm and diameters of ~ 30 nm. The X-ray diffractogram displayed appropriate peaks suitable to defect-free and high crystalline graphene with face centered cubic Au. The strong optical interrelation between Au nanorod and 3D graphene was elucidated by Raman spectroscopy analysis. Furthermore, the anchored Au nanorods on 3D graphene nanocomposite enables feasible bio-capturing on the exposed Au surface on defect free graphene. The impedimetric sensing of DNA sequence from TB on 3D graphene/Au nanocomposite revealed a remarkable wide detection linear range from 10 fM to 0.1 µM, displays the capability of detecting femtomolar DNA concentration. Overall, the novel 3D graphene/Au nanocomposite demonstrated here offers high-performance bio-sensing and opens a new avenue for TB detection.

Diagnosing human blood clotting deficiency

There are different clotting factors present in blood, carries the clotting cascade and excessive bleeding may cause a deficiency in the clotting Diagnosis of this deficiency in clotting drastically reduces the potential fatality. For enabling a sensor to detect the clotting factors, suitable probes such as antibody and aptamer have been used to capture these targets on the sensing surface. Two major clotting factors were widely studied for the diagnosis of clotting deficiency, which includes factor IX and thrombin. In addition, factor IX is considered as the substitute for heparin and the prothrombotic associated with the increased thrombin generation are taking into account their prevalence. The biosensors, surface plasmon resonance, evanescent-field-coupled waveguide-mode sensor, metal-enhanced PicoGreen fluorescence and electrochemical aptasensor were well-documented and improvements have been made for high-performance sensing. We overviewed detecting factor IX and thrombin using these biosensors, for the potential application in medical diagnosis.

DC magnetron sputtered TiO 2 thin film as efficient hole blocking layer for perovskite solar cell

The ultra-thin film of metal oxide were fabricated via DC-magnetron sputtering to acts as the hole blocking layer. The traditional dye absorption material were replaced by the fourth generation light harvesting material, the CH<inf>3</inf>NH<inf>3</inf>PbI<inf>3</inf> which deemed to reach the PV efficiency limit. The complete conversion of PbI<inf>2</inf> into CH<inf>3</inf>NH<inf>3</inf>PbI<inf>3</inf> crystal structure vital in lowering the internal series resistance. With this new light harvesting material were used able to achieve 7.75% efficiency via sequential two step deposition of perovskite.

Template-assisted growth of highly oriented 3D graphene pH sensor towards new avenues for biosensor

In recent times, the high flexibility and exceptional electrical conductivity of free-standing monolithic 3D graphene has attracted considerable attention in the field of electronic sensor development for real time sensing. In this work, we have synthesized free-standing monolithic 3D graphene through chemical vapor deposition (CVD) using nickel foam as a sacrificial template for pH sensing. The surface and structural morphology were characterized by scanning electron microscopy and Raman spectroscopy. The results show a highly oriented and defect free monolithic 3D graphene which imitates the nickel template surface and the 3D graphene microporous structure firmly retained its structure even after Ni template etching. The voltage versus current and resistance corresponding to pH (pH-4 to pH-10) at constant current of 1μA are detailed in delineated graphs. It shows a linear regression of R = (211.90 −13.67pH) and a measured sensitivity of 13.67 Ω/pH for the developed 3D graphene device. The synthesized 3D graphene paves a way for the development of highly sensitive, selective and flexible sensing platform which presents a new avenue for biosensor development.

Fabrication and characterization of metal microwire transducer for biochip application

Microwire makes good sensors because their small dimensions which enhance their sensitivity. To be useful, microelectrode sensors must be integrated with electronic capable of processing those signal. In this research, we demonstrated a method to fabricated and characterize metal microwire device for biosensing application. Using conventional photolithography technique and other experimental techniques, we developed a reliable procedure for producing aluminium wires with micron-scale features. Significantly, in micro fabrication the critical dimension (CD) of wafers in photolithography is the most important parameter that determines the final performance of devices. Hence, it is paramount to have high resolution, high sensitivity and precise alignment to successfully transfer the original pattern to wafer. The process was optimized by control the spin speed for photoresist (PR) coating, spin time, post exposure bake time, developer concentration ratio, hard bake and aluminium etch time so as to achieve the possible fabrication process and get the expected microwire size. The process begins with the photoresists coating and spinning at 3000 rpm to form a thin and uniform layer. Subsequently, the PR coated substrates were exposed to UV light for 10s. After the alignment and exposure, the substrate were developed using the resists developer with 25:10 ratio in which 25 parts of developer and 10 parts of deionized water. Eventually, the post exposure bake and hard bake time were optimized for a better throughput on the pattern transfer process. The aluminium microwire has been successfully fabricated with the contact pads. The wires range in thickness from 1 μm-4μm to achieve a resistivity as low as possible for nano range limit of detection. This microelectrodes transducer will be eventually used as biomolecule detection kit. The fabricated microwire was morphologically characterized using Atomic force microscope (AFM), Scanning electron microscope (SEM), High power microscope (HPM). Besides that, the electrical properties of the fabricated aluminium microwire were studied using source meter.