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A "Janus particle" refers to the production of two materials in a single system and shows a difference in physical characteristics, and two surfaces participate in the formation with different chemistries. This research generated the Janus using a hybrid of zinc oxide (ZnO) and gold (Au) on the sensor surface toward making high‐performance DNA sensors. The Janus ZnO/Au‐textured film was synthesized via the one‐step sol–gel method, which involves a suitable ratio of a mixture of ZnO sol seed solution. The synthesized Janus ZnO/Au‐textured film undergoes a low‐temperature aqueous hydrothermal route to synthesize quasi‐one‐dimensional nanowires. The average grain size in the Janus ZnO/Au nanotextured wire was 41.60 nm. The fabricated nanotextured wire was further optimized by tuning the thickness and characterized by XRD and high‐resolution microscopy. Electrical characterization was conducted on the Janus ZnO/Au nanotextured wire coupled with an interdigitated electrode sensor to detect the specific leptospirosis DNA strand. The generated device is capable of detecting lower DNA concentration at 1 × 10–13 M with a sensitivity of 8.54 MΩ M–1 cm–2. The high performance is attained on linear concentrations of 10–6–10–13 M with the determination coefficient, "I = 135437.63C−3609.07" R2 = 0.9551. A potential strategy is proposed as a base for developing different high‐performance sensors. [ABSTRACT FROM AUTHOR]

The authors describe an impedimetric nanosensor for aptamer-mediated detection of ATP. A triangular junction of polysilicon substrate is used as a transducer. The aptamer was immobilized on the substrate via biotin-streptavidin interaction. ATP can be detected by this method in the 10 to 100 nM concentration range at room temperature and estimated the signal to noise ratio above the range of 3σ. It was applied to the detection of ATP in 1:1000 diluted human urine. The desired transducer is highly reproducible and specific. It is selective over closely related molecules such as guanosine triphosphate, cytidine triphosphate and uridine triphosphate. The method is perceived to represent a valuable tool for the diagnosis for infections and inflammations. The novelties shown in this study compared to other sensors are, consumption of low sample volume (~ 1 μl), non-invasive and suitable with AC and DC currents. [ABSTRACT FROM AUTHOR]

The authors describe an electrochemical method for the determination of the blood clotting factor IX (FIX). A nanogapped dielectrode (with a < 100 nm junction) was modified with antibody against FIX, and the resulting system was characterized by both impedance spectroscopy and voltammetry. In order to attain the improved sensitivity, gold nanoparticles were electrostatically attached to FIX. The current to voltage (I-V) measurement was carried out from 1 V to 5 V, where the entire calibration plot with 5 V was taken. This results in a limit of detection as low of 1 pM, which is much lower compared to the real concentration of FIX (87 nM) in human blood serum. The analytical range extends from 1 pM to 0.1 μM. The electrode is highly specific over other serum proteins. [ABSTRACT FROM AUTHOR]

This article describes a sensitive impedimetric method for the determination of human blood coagulation factor IX protein (FIX) which is present in extremely low concentration in serum. An interdigitated electrode (IDE) whose surface was layered with zinc oxide was modified with two kinds of probes. One is an antibody, the other an aptamer against FIX. A comparative study between anti-FIX aptamer and anti-FIX antibody showed the aptamer to possess higher affinity for FIX. A sandwich aptamer assay was worked out by using the FIX-binding aptamer on the surface of the IDE. It has a detection limit as low as 10 pM which makes it 4 to 30-fold more sensitive than any other method reported for FIX. Moreover, to practice detection in clinical samples, FIX was detected from the human blood serum by spiking. In our perception, the sensitivity of the ZnO-modified IDE presented here makes it a promising tool for sensing clinically relevant analytes that are present in very low (sub-pM) concentrations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Human chorionic gonadotropin (hCG), a glycoprotein hormone secreted from the placenta, is a key molecule that indicates pregnancy. Here, we have designed a cost-effective, label-free, in situ point-of-care (POC) immunosensor to estimate hCG using a cuneated 25 nm polysilicon nanogap electrode. A tiny chip with the dimensions of 20.5 × 12.5 mm was fabricated using conventional lithography and size expansion techniques. Furthermore, the sensing surface was functionalized by (3-aminopropyl)triethoxysilane and quantitatively measured the variations in hCG levels from clinically obtained human urine samples. The dielectric properties of the present sensor are shown with a capacitance above 40 nF for samples from pregnant women; it was lower with samples from non-pregnant women. Furthermore, it has been proven that our sensor has a wide linear range of detection, as a sensitivity of 835.88 μA mIU-1 ml-2 cm-2 was attained, and the detection limit was 0.28 mIU/ml (27.78 pg/ml). The dissociation constant Kd of the specific antigen binding to the anti-hCG was calculated as 2.23 ± 0.66 mIU, and the maximum number of binding sites per antigen was Bmax = 22.54 ± 1.46 mIU. The sensing system shown here, with a narrow nanogap, is suitable for high-throughput POC diagnosis, and a single injection can obtain triplicate data or parallel analyses of different targets. [ABSTRACT FROM AUTHOR]

The performance of sensing surfaces highly relies on nanostructures to enhance their sensitivity and specificity. Herein, nanostructured zinc oxide (ZnO) thin films of various thicknesses were coated on glass and p-type silicon substrates using a sol-gel spin-coating technique. The deposited films were characterized for morphological, structural, and optoelectronic properties by high-resolution measurements. X-ray diffraction analyses revealed that the deposited films have a c-axis orientation and display peaks that refer to ZnO, which exhibits a hexagonal structure with a preferable plane orientation (002). The thicknesses of ZnO thin films prepared using 1, 3, 5, and 7 cycles were measured to be 40, 60, 100, and 200 nm, respectively. The increment in grain size of the thin film from 21 to 52 nm was noticed, when its thickness was increased from 40 to 200 nm, whereas the band gap value decreased from 3.282 to 3.268 eV. Band gap value of ZnO thin film with thickness of 200 nm at pH ranging from 2 to 10 reduces from 3.263eV to 3.200 eV. Furthermore, to evaluate the transducing capacity of the ZnO nanostructure, the refractive index, optoelectric constant, and bulk modulus were analyzed and correlated. The highest thickness (200 nm) of ZnO film, embedded with an interdigitated electrode that behaves as a pH-sensing electrode, could sense pH variations in the range of 2-10. It showed a highly sensitive response of 444 μAmM-1cm-2 with a linear regression of R2 =0.9304. The measured sensitivity of the developed device for pH per unit is 3.72μA/pH. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]