Microfluidic Sample Compartmentalization for Biomolecular Concentration Quantification Using a Nanopore Sensor.

Determination of the concentration of a biomolecule in a sample is a fundamental measurement in analytical chemistry and central to many diagnostic applications. Solid-state nanopores (ssNPs) stand out as leading candidates to quantify biomolecules due to their capacity to achieve label-free electrical detection with single-molecule resolution. Often, the concentration of a biomolecular sample is estimated in relation to the ssNP capture rate, that is, the number of molecules translocated by the nanopore per unit time. However, this method poses challenges due to variability in capture rates, which have proven difficult to control experimentally. In this work, we introduce a microtrap, that is, a microfluidic device with an integrated nanopore sensor, that leverages sample compartmentalization in known pL volumes allowing direct molecule counting and eliminating the need for capture rate calibration. We demonstrate direct quantification of pico- to nanomolar concentrations of double-stranded DNA (dsDNA) and green fluorescent protein (GFP) molecules in minutes and without the need for calibration of the nanopore sensor capture rate. Moreover, we demonstrate the ability to preconcentrate the biomolecular sample by real-time tuning of the microtrap volume, which can be used to reduce the measurement time and to lower the detection limit.