Even electrically conductive, transparent oxide layers, such as ITO, can be applied mainly because coatings within the grating coupler sensor chip. or biological weapons. Immunosensors are biosensors that use antibody-antigen interactions to provide high specificity, achieved by the molecular acknowledgement of target analytes (usually the antigens) by antibodies to form a stable complex on the surface of the system [2,3]. A wide range of transducers have been explored for immunosensing such as electrochemical, piezoelectric or optical, with variations in sensor level of sensitivity Lucidin and reproducibility [4]. In fact, it is acknowledged that to combine direct immunosensing with optical analysis is a great approach to accomplish the best level of sensitivity and selectivity [5]. With this context, evanescent field optical biosensors constitute a label free sensing instrument that steps the variance of the refractive index of the adsorbed coating Lucidin onto a chip surface and translate this variance into surface concentration of the adsorbed molecule [6]. In the field of optical label-free biosensing, the most used transducer is definitely a sensor chip with platinum surface (Surface Plasmon Resonance), which presents a relatively easy functionalization and provides information about the success of the biomolecular adsorption on the surface and the acknowledgement events [7]. Depending on the application, the possibility of choosing the material Lucidin of the active sensing surface would remain challenging. Recently, as an alternative to Surface Plasmon Resonance technique, the Optical Waveguide Spectroscopy technique, a grating coupler optical biosensor, offers emerged [8]. In this system it is possible to simulate both the refractive index switch and the thickness of the adsorbed film and its mass by numerical methods, exhibiting a very high level of sensitivity of 1 1 ng/cm2 [9]. The system retains this level of sensitivity measuring changes in the sensor surface closer than 200 nm [10]. In opposition to SPR, in the case of the grating couplers the sensing substrate is not a metallic, Rabbit Polyclonal to TR-beta1 (phospho-Ser142) but a transparent material to allow the light coupling in the waveguide. Dielectrics and conductors are normally used as elements of the sensing waveguide, but also the grating-coupler waveguide detectors can be covered using thin layers of SiO2, Ta2O5 and SiO2/TiO2 without influencing their level of sensitivity and permitting simulation of the surface properties of the material of interest [11,12]. Even electrically conductive, transparent oxide layers, such as ITO, can be applied as coatings within the grating coupler sensor chip. With such materials, the grating-coupler sensor can be combined with an electrochemical sensor, opening up new fields of applications [13]. Table 1 shows a comparison of the most common insulators. As demonstrated in the table, even though oxides are all widely used as dielectrics in Field Effect Transistors, nitride films provide a good compromise with low leakage current and low Lucidin conductivity [14]. Also, silicon nitride has been broadly exploited in optical waveguides and favored than silicon oxide, due to its high refractive index [15,16]). It also possesses a number of fabrication advantages such as the absence of undesirable impurities and the good control of the film composition and thickness. This is especially important for ultrathin layers used in optical spectroscopy measurements. Regardless of the overall performance of silicon nitride as an insulator, the aim of this work is to provide a technology that may allow quantifying the adsorption of biomolecules onto the gate of nitride-based transistors. Table 1 Properties of thin layers of various amorphous insulators.
Refractive index2.02 [16]1.46 [16]2.58 [17] 2.10 [12]2.08 [18]Leakage current (A/cm2) at 2 V1 10?15 [19]1 10?8 [19]>1 10?7 [20]9 10?8 [21] 2 10?9 [18]Dielectric constant7.5 [14] 3.9 [14]80C30 [20]26.0 [21]25.0 [18] Open in a separate window Although silicon nitride-based immunosensors.