Siloxane coatings for surfaces are essential in many scientific and industrial applications. We describe a straightforward gas-phase evaporation technique in inert atmosphere and introduce a practical and reliable silanization protocol adaptable to different silane types. The primary aim of depositing ultrathin siloxane films on surfaces is to enable a reproducible and homogenous surface functionalization without agglomeration effects during the layer formation. To realize high-quality and large-area coatings, it is fundamental to understand the reaction conditions of the silanes, the process of the siloxane layer formation, and the possible influence of the substrate morphology. We used three typical silane types to exemplify the potential and versatility of our process: aminopropyltriethoxysilane, glycidoxypropyltrimethoxysilane, and 1 H,1 H,2 H,2 H-perfluorooctyl-trichlorosilane. The ultrathin siloxane layers, which are generally difficult to characterize, were precisely investigated with high-resolution surface-characterization methods to verify our concept in terms of reproducibility and coating quality. Our results show that this gas-phase evaporation protocol is easily adaptable to all three, widely used silane types also enabling a large-area upscale.

Silicon nanowires (SiNW) are highly sensitive to biomolecules. In some publications, changes of SiNW conductance in relation to their concentration levels are displayed. Upon binding, biomolecule charges change the surface potential and, thereby, the SiNW conductance. We discussed earlier that SiNWs can be regarded as long-channel, ion-sensitive field-effect transistors (ISFETs). The choice of a stable working point is important and defines the SiNW conductance. The common detection principle is based on the shift in threshold voltage. Regardless of conductance change or threshold voltage shift, relative values are related to biomolecule concentrations. However, potentiometric detection suffers from Debye screening of biomolecule charges by counter ions of the test solution. This makes biosensing in physiological buffer solutions difficult if not impossible. In this report, a method for impedance sensing with SiNWs, which was earlier used for ISFET devices is introduced. This method gains comparable results to potentiometric sensing. The change of interface impedance is indirectly linked with the biomolecule charges. In addition, the dielectric property of the interface layer plays an important role. At elevated frequencies, our method can be regarded as an alternative mechanism similar to dielectric spectroscopy at low frequencies. Thereby, Debye screening does no longer dominate the recordings.Nowadays, the detection of DNA is essential and indispensable in biomedicine. There are many scientific applications, in which the identification of the base pair sequence is crucial. Applications can be found in criminology, i.e., forensics, [1][2][3] determination of gene mutations in plants, [4][5][6] DNA detection in biotechnology, [7][8][9] and in the detection of different, genetically predetermined diseases in medicine. [10][11][12] Within all these applications, the possibility of a fully electronic, labelfree DNA detection is getting more and more interesting to provide a quick and reliable readout. This is especially needed in forensics to convict a perpetrator and in medicine for the fast diagnosis of diseases so that the patient can immediately be medicated or operated. Moreover, a swift DNA detection is desired for biological warfare agents. [13] Since the first publication of Piet Bergveld and coworkers in 1970, [14] ion-sensitive field-effect transistors (ISFETs) are applied as biosensors for biomolecules, such as DNA, [15][16][17][18][19] enzymes, [20][21][22] and proteins. [23][24][25] Furthermore, it was shown that it is also possible to record cellular signals with ISFETs. [26][27][28] In the past decades, the application of silicon nanowires (SiNWs) attracted more and more attention in terms of extracellular recordings [29][30][31] and biomolecule sensing, like the detection of DNA immobilization, [32] hybridization, [33] and single nucleotide polymorphism [34][35][36] as well as antibody-antigen interactions. [37,38] In an earlier publication, we discussed that our silicon nanowire devices can be rega...

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Sensors for label‐free biomolecule detection using ion‐sensitive field‐effect transistor (ISFET) arrays working in a liquid environment offer great opportunities for fast diagnostics of diseases and other point‐of‐care applications. In the last decades, ISFET‐based sensors with progressively improved sensitivity, robustness, and diversity of detected biomolecules were described. However, a reliable, miniaturized electronic readout for such sensors is one of the main demands in the field. In this work, we developed a handheld readout system for biomolecule sensing with ISFET arrays, which can measure four channels simultaneously and can be used for a wide range of ISFET devices from microsized ISFETs to silicon nanowire transistor arrays. The hardware was built around a 32‐bit PIC microcontroller. A user‐friendly software written in LabVIEW communicates with the hardware to record and to display the measurement results. After a simple calibration, the error of the handheld system was below 5% in comparison with a standard semiconductor parameter analyzer. For the first applications, pH sensing and deoxyribonucleic acid (DNA) immobilization and hybridization events were successfully measured with our ISFET sensors. Our readout system in combination with our top‐down fabricated sensor devices has the potential to bring the ISFET sensors closer to the point‐of‐care testing in near future.

631 3724 5313 † Both authors contributed equally.Silicon nanowire field-effect transistors (SiNW-FETs) are offering a label-free sensing of DNA molecules based on the detection of the biomolecules' charges. Typically, the charge accumulation at the solid-liquid interface is leading to a change in surface potential of the device. In other works, this effect is usually displayed as change in conductance of the nanowires. In this paper, we show that our topdown processed SiNW-FET devices can be regarded as longchannel, ion-sensitive field-effect transistor devices (ISFETs) and that their electronic characteristics can be fitted by an advanced MOSFET model taking narrow channel effects into account. In DNA experiments, changes in threshold voltage upon immobilization of capture DNA and hybridization with complementary target DNA were recorded as reported before. The signal amplitudes were scaling with different concentrations of electrolyte buffer as known from the commonly used Poisson-Boltzmann theory. In reports from other groups, the sensitivity of SiNW-FETs was reported to be superior compared to ISFETs and scaling effects were observed with smaller wires having higher sensitivities. From our experiments, it seems that the immobilization of the DNA to the wire structure is leading to two effects: firstly, the threshold voltage is changing, leading to a shift in the transistors' transfer characteristics similar to what was described for ISFET devices. In addition, upon DNA binding, a general increase in charge carrier density inside the nanowire is leading to an enhanced conductance. We assume that the latter effect is scaling with nanowire dimensions, while the surface effect is typically constant for all sensor structures.