Key Parameters That Determine the Magnitude of the Decrease in Current in Nanopore Blockade Sensors

Optical Nanopore Blockade Sensors for Multiplexed Detection of Proteins

Enduring challenges for quantitative analysis in nanopore sensing are the detection of low biomarker concentrations in reasonable time frames and the detection of multiple biomarkers in the same sample. Herein we report an optical blockade nanopore sensor strategy that can detect more than a protein at femtomolar concentrations in rapid time (approximately 12 min). This is done using a nanopore array functionalized with an aptamer that can bind to two different but related target proteins. The assay then monitors two different colors of fluorescent particles modified with antibodies specific to the protein of interest, as they block the nanopores using a wide-field microscope. By distinguishing specific and nonspecific blockade events for each nanoparticle based on whether they can be easily pulled out of the nanopores using an electric field, we can simultaneously quantify the concentrations of vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) down to femtomolar concentrations.

Nanopore Blockade Sensors for Quantitative Analysis Using an Optical Nanopore Assay

Nanopore sensing is a popular biosensing strategy that is being explored for the quantitative analysis of biomarkers. With low concentrations of analytes, nanopore sensors face challenges related to slow response times and selectivity. Here, we demonstrate an approach to rapidly detect species at ultralow concentrations using an optical nanopore blockade sensor for quantitative detection of the protein vascular endothelial growth factor (VEGF). This sensor relies on monitoring fluorescent polystyrene nanoparticles blocking nanopores in a nanopore array of 676 nanopores. The fluorescent signal is read out using a wide-field fluorescence microscope. Nonspecific blockade events are then distinguished from specific blockade events based on the ability to pull the particles out of the pore using an applied electric field. This allows the detection of VEGF at sub-picomolar concentration in less than 15 min.

Understanding and modelling the magnitude of the change in current of nanopore sensors

Nanopores are promising sensing devices that can be used for the detection of analytes at the single molecule level. It is of importance to understand and model the current response of a nanopore sensor for improving the sensitivity of the sensor, a better interpretation of the behaviours of different analytes in confined nanoscale spaces, and quantitative analysis of the properties of the targets. The current response of a nanopore sensor, usually called a resistive pulse, results from the change in nanopore resistance when an analyte translocates through the nanopore. This article reviews the theoretical models used for the calculation of the resistance of the nanopore, and the corresponding change in nanopore resistance due to a translocation event. Models focus on the resistance of the pore cavity region and the access region of the nanopore. The influence of the sizes, shapes and surface charges of the translocating species and the nanopore, as well as the trajectory that the analyte follows are also discussed. This review aims to give a general guidance to the audience for understanding the current response of a nanopore sensor and the application of this class of sensor to a broad range of species with the theoretical models.