Sensing the electrical activity of single ion channels with top-down silicon nanoribbons

Using top-down fabricated silicon nanoribbons, we measure the opening and closing of ion channels alamethicin and gramicidin A. A capacitive model of the system is proposed to demonstrate that the geometric capacitance of the nanoribbon is charged by ion channel currents. The integration of top-down nanoribbons with electrophysiology holds promise for integration of electrically active living systems with artificial electronics.

shown in figure S2(g, h). Therefore, we believe that there is a negative shift of the threshold voltage after the SLBs formed. A DPhPC lipid contains one positive charge and one negative charge, however, the positive charge at the head group is closer to silicon nanoribbon surface when the SLBs form, thus possibly resulting in the negative shift of the threshold voltage. A layer-by-layer polyelectrolyte deposition experiment (figure S3 and S4) was performed to obviously show this trend. Figure S2. Depletion curves of a silicon nanoribbon device with the threshold voltage of ~ 0 V before (a, d) and after lipid bilayer deposition (b, e) and after lipid bilayer removal by SDS washing (c, f) in KCl solutions with varied concentrations and pH Values. Another silicon nanoribbon device with the threshold voltage of ~ 0.5 V was represented in (g, h) to show the negative shift of threshold voltage.

Layer by layer polyelectrolyte deposition:
In order to confirm our interpretation of the voltage shift, we performed layer by layer polyelectrolyte deposition. PSS and PDDA were dissolved in MES buffer (10 mM, 50 mM NaCl, pH=6.0) at a concentration of 1 µg/mL. Similar results were reported by us on graphene in ref. [13] and by another group on silicon in ref. [11].
The figures below show the change in the surface potential (calculated as the change in drain current normalized by the device transconductance) upon sequential additions of charged polymers PSS and PDDA.

Fluorescence imaging and fluorescence recovery after photobleaching (FRAP)
The FRAP analysis was performed to evaluate the lateral diffusion of SLB on silicon nanoribbons. The diffusion coefficient, D, can be determined by the equation: D = 0.224 r 2 /t1/2, in which r is the radius of the photobleached area, and t1/2 is the time required to achieve 50% fluorescence intensity recovery. Silicon nanoribbon arrays were used in this study instead of single nanoribbon devices. A representative experiment is shown below. Fluorescence images of a sample spot with a diameter of about 29 µm were recorded before ( figure S5(a)), immediately after ( figure S5(b)), and 276 seconds (figure S5(c)) after photobleaching. According to the FRAP recovery curve shown below, the diffusion coefficient D of ~0.71 µm 2 s -1 were calculated for LR-DHPE in the SLB with the mobile fraction F of ~92%.

Capacitance calculations:
In order to compare the capacitance of solution double layer, dielectric layer and the silicon channel, we use the following calculations to roughly estimate their capacitances.

Yield and statistics:
The experiments were performed a total of 10 times. Of these, current spikes were observed 6 times.