Nanofluidic devices prepared by an atomic force microscopy-based single-scratch approach

Abstract

Nanofluidic chips with different numbers of nanochannels were fabricated based on a commercial AFM system using a single-scratch approach. The electrical characterization and enzymatic reactions at the nanoscale were demonstrated using the obtained chips. The effects of the number of nanochannels and the solution concentration on the measured electric current were investigated. The influence of the hydrodynamic convection generated from the induced inflow at the end of the nanochannel on the ion transport through the nanochannel was also studied. Moreover, the enzymatic reactions for trypsin towards poly-l-lysine (PLL) or thrombin were conducted with a nanofluidic chip to investigate the reaction specificity between trypsin and PLL. Results show that the electric current change during the experimental process could be used as a label-free indicator to detect the enzymatic activity.

Fig. 1. (a) Schematic diagram of the nanochannel fabrication, (b) SEM micrograph of diamond coated AFM tip, (c) AFM image, and (d) the cross-section of the nanochannel fabricated with a normal load of 20 μN and velocity of 3 μm s⁻¹.

Fig. 2. (a) Schematic diagram of nanofluidic chip, (b) electric current measurement results of chips I and II, (c) an equivalent electrical circuit of chips I and II that comprised of resistors, and (d) electric current measurement results for concentration of KCl from 0.1 to 100 mM.

Fig. 3. (a) Schematic diagram of the flow in a nanofluidic chip and (b) electric current measurement results for hydrodynamic inflow of KCl from 0 to 70 nL min⁻¹. The inset display the measurement results for hydrodynamic inflow from 0 to 35 nL min⁻¹.

Fig. 4. Schematic diagram of the experimental processes for the reaction between trypsin and polylysine. (a) Original PDMS nanochannel surface, (b) PLL coating on the nanochannel surface, (c) trypsin reacted with PLL, and (d) the cleaved substrate and trypsin were removed. Electric current measurement results for reaction between PLL and (e) trypsin and (f) thrombin.