Single Nanoparticle Translocation Through Chemically Modified Solid Nanopore

Abstract

The nanopore sensor as a high-throughput and low-cost technology can detect single nanoparticle in solution. In the present study, the silicon nitride nanopores were fabricated by focused Ga ion beam (FIB), and the surface was functionalized with 3-aminopropyltriethoxysilane to change its surface charge density. The positively charged nanopore surface attracted negatively charged nanoparticles when they were in the vicinity of the nanopore. And, nanoparticle translocation speed was slowed down to obtain a clear and deterministic signal. Compared with previous studied small nanoparticles, the electrophoretic translocation of negatively charged polystyrene (PS) nanoparticles (diameter ~100 nm) was investigated in solution using the Coulter counter principle in which the time-dependent nanopore current was recorded as the nanoparticles were driven across the nanopore. A linear dependence was found between current drop and biased voltage. An exponentially decaying function (t d ~ e (-v/v0) ) was found between the duration time and biased voltage. The interaction between the amine-functionalized nanopore wall and PS microspheres was discussed while translating PS microspheres. We explored also translocations of PS microspheres through amine-functionalized solid-state nanopores by varying the solution pH (5.4, 7.0, and 10.0) with 0.02 M potassium chloride (KCl). Surface functionalization showed to provide a useful step to fine-tune the surface property, which can selectively transport molecules or particles. This approach is likely to be applied to gene sequencing.

Keywords: Chemical surface modifications; Nanopore; Polystyrene nanoparticles.

Fig. 1

Schematic representation of Si₃N₄ chips and SEM. a electrical measurement setup. b Si₃N₄ chips. c–f modified chips were carried out in the nanofluid developed in our lab to investigate their electrical properties. g SEM of PS microspheres (~100 nm). h Si₃N₄ nanopore

Fig. 2

Characterization of functionalized nanopores. a FESEM images functionalized with 3-APTES. b, c EDS measurements: before the functionalization (–OH), functionalized with 3-APTES. d I–V curves: black before the functionalization (–OH), red functionalized with 3-APTES

Fig. 3

Translocation events. a PS microsphere translocation through chemically modified nanopores. b PS microsphere translocation through bare nanopores

Fig. 4

Histogram and linear relationship. a–d histograms of normalized count and current blockade at various voltages at 0.02 M KCl. e voltage dependency of current blockade at 0.02 M KCl

Fig. 5

Histogram and functional relationship. a–d histograms of normalized count and duration time at various voltages at 0.02 M KCl. e an exponentially decaying function (t _d  ~ e ^−v/v0) for the dwell time dependent on the voltage at 0.02 M KCl

Fig. 6

Scatter plots. a–d two dimensional scatter plots of amplitude versus event duration of PS translocation experiments at 0.02 M KCl under different voltage

Fig. 7

Typical translocation event. a three typical current traces. b the process of event translocation

Fig. 8

Events and the frequency of types. a–d interactions between the nanopores wall of the chemical modification in different degrees. e the frequency histogram of type of events under different biased voltage

Fig. 9

Particle translocation by pH tuning. a Translocations of particle through amine-functionalized solid-state nanopores at pH 5.4, b pH 7.0, c pH 10.0. d the histogram of translocation time and Gaussian fitting at pH 7.0