Solid-State Nanopore Sensors

We fabricate conic nanopores using ion-track and laser-assisted pulling technologies. We are particularly interested in various non-equilibrium ion flux phenomena, such as rectification and stick-slip dynamics, related to ion and molecular transport across such pores. We explain the rectification and rectification inversion phenomena by ion enrichment and depletion phenomena inside and outside such asymmetric pores due to conductivity and field gradients that dominate at different voltages and pore selectivity. For weakly selective negatively charged pores, intra-pore ion transport controls the current and internal ion enrichment/depletion (shown in Fig(a)) at positive/reverse biased voltage (current enters/leaves through the tip, respectively), which is responsible for current rectification. For strongly selective negatively charged pores under positive bias, the current can be reduced by external field focusing and concentration depletion at the tip at low ionic strengths and high voltages, respectively. These external phenomena produce a rectification inversion for highly selective pores at high (low) voltage (ionic strength) shown in Fig(b). We exploit such inner and outer ion enrichment and depletion phenomena to enhcance nanoparticle aggregation for plasmonic hotspots, to concentrate analyte on a biochip, to detect the presence of oppositely charged biomolecules and to slow down the translocation of small molecules like miRNA and proteins for more precise enumeration and identification. For example, we are able to slow down the translocation time of 20B miRNA to 100 ms, which is 100 times longer than its duplex counterpart (Fig C).

Related Publications

Ion Logical Circuits

We have built an integrated fluid phase ionic logic circuit by integrating existing ionic capacitors, nanopore resistors, bipolar membrane ion diodes and a unique nonlinear ion memristor, all for strong physiological electrolytes. The ion memristor is based on a non-equilibrium anodic oxidation reaction of a silicon microelectrode in an aqueous solution. It shows a stable pinched hysteretic current-voltage characteristic, that can be utilized to synthesize fluid-based memory arrays with on-off logic components. By integrating ion memristors with micro/nanofluidic systems, together with crossbar logic, ionic NAND/NOR gates and latches with high speeds can be made. We use these ionic logic components to activate, read individual ion current based sensors while store and retrieve intermediate values in multiple sensor arrays, reducing the complexity of operating micro/nanofluidic system. We envision that excitable, bistable and oscillatory ionic circuits that mimic neurons in the human body can also be built. Direct integration with neuron cells without intermediate metallic or semiconductor circuits is also planned.

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Asymmetric Nanopore Continuous Fractionation of Nanocarriers

We are developing a high-yield exosome isolation and fractionation technology that has far higher yield than ultra centrifugation UC, excluded volume precipitation Exoquick and size exclusion chromatography qEV. We asymmetrically wet etch ion-track nanoporous membranes so that the filtering tip end, with tunable diameter from 10 nm to 500 nm, dominates the flow resistance. This reduces the total shear in the nanofluidic pore by order of magnitude and hence minimizes exosome lysing and fusion in nanofiltration and in UC.