2.3. Nanoribbon Biosensor

The biosensor nanoribbon system included a sensitive nanochip, which was the bottom of a 500 μL measuring cuvette, and the cuvette itself. The solution was stirred with a stirrer in a cuvette with a rotation frequency of 3000 rpm. The nanochip was a field-effect nanotransistor designed on the basis of a silicon-on-insulator structure. SOI structures were made with the implementation of a similar Smart Cut technology [28], but with a number of differences. It is known that the technology is based on hydrogen-induced transfer of silicon layers onto the handle plate. The differences were as follows: the boundary between the top silicon layer and the hidden oxide (BOX) was a glued surface, and the BOX itself, in contrast to the Smart Cut technology, was not subjected to hydrogen implantation. This approach to the SOI structure formation reduces the risk of defects in the Si/SiO₂ system, thereby ensuring the stability of the structure parameters. This method is described in more detail in [29]. The key design feature for optimizing the sensor sensitivity was epitaxial source-drains raised to 1 μm with a doping level of ~10²⁰ cm⁻³ at a density of states in a lightly doped channel of less than 10¹¹ cm⁻² eV⁻¹.

On the surface of the nanochip, there were 10 nanoribbons (Figure 1a), which were elements of 10 n-type nanotransistors. Their surfaces served as virtual shutters. SOI structures had the following characteristics: buried oxide (BOX) thickness, −300 nm; the thickness of the cut-off silicon layer, −32 nm; nanoribbon thickness (t), −32 nm, nanoribbon width (w), −3 μm, nanoribbon length (l), −10 μm, and were made according to the procedure described in [30,31]. The diameter of the nanochip sensitive zone was ~2 mm. Figure 1 shows an image of a nanoribbon surface obtained using an atomic force microscope (AFM) TITANIUM (NT-MDT, Russia) (Figure 1c), as well as an image of the nanoribbon obtained using a scanning electron microscope (SEM) S-5500 (Hitachi, Ltd., Chiyoda, Tokyo, Japan) (Figure 1d).

(a) Actual image of the nanoribbon nanochip. (b) Optical image of the surface of a nanochip with an array of nanoribbons; (c) AFM image of the nanoribbon surface obtained using a TITANIUM atomic force microscope (NT-MDT, Russia); the scan sizes are 5 × 5 µm and the resolution is 256 × 256 points. (d) SEM image of a nanoribbon obtained using a S-5500 scanning electron microscope (Hitachi, Japan). Nanoribbon measurements: nanoribbon thickness, t = 32 nm; nanoribbon width, w = 3 µm; nanoribbon length, l = 10 µm. The diameter of the nanochip sensor zone is ~2 mm.

Signal registration in digital form was carried out using a measuring unit manufactured by “Agama +” LLC (Moscow, Russia).