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Flow cell appearance
The flow cell is a disposable element of the sequencing platform that provides the fluidic interface between the nanopores and the electrodes, allowing the user’s sample to be analysed.
The flow cell is composed of: a moulded plastic fluidic chamber and retainer, a fluidic gasket, and the sensor chip containing a printed circuit board (PCB) and an application specific integrated circuit (ASIC).
The flow cell dimensions are 92.4 mm x 28.0 mm x 5.8 mm; on the upper side all the ports and sensor chip are visible. The flow cell clips into the MinION Mk1B, Mk1C or GridION device.
The fluidics of the flow cell are described below. The sensor array is where the sequencing chemistry happens. The array is made up of 512 sensing wells, each designed to collect sequencing data through a single nanopore.
The flow cell itself is designed with a number of distinct areas. These areas include: the priming port, SpotON port, sensor array, waste channel, and two waste ports. Sample can be added directly onto the nanopore array via the SpotON port. The volume of the main chamber area over the sensor array is 100 μl, while the waste can hold 2 ml.
Flow cell valves
The path of the liquid through the flow cell is regulated by two valves: one immediately downstream of the priming port, and the other between the end of the array and the waste chamber (valves shown in the diagram below in red). The flow cells are shipped with the priming port covered and both valves closed.Waste chamber
The waste chamber has a total capacity of 2 ml and is accessible when the valve at the end of the array is open. Waste port 2 allows excess sample to be removed with a pipette if, for instance, the flow cell is topped up mid-run. -
Storage buffer
The flow cell has three compartments: the common electrode reservoir which is separated from the bulk by a diffusion barrier, the bulk which is separated from the individual wells by a membrane, and the individual wells. The flow cells are shipped with the storage buffer (yellow) in all three compartments to maintain osmotic balance. The storage buffer contains salt and the standard redox couple that enables current to run through the nanopore. The storage buffer also contains a QC DNA molecule that gives a distinct signal which helps to identify functional pores during Platform QC.
Before library loading, the flow cell is flushed with Priming mix (a mixture of RBF and nuclease-free water, shown as blue), which displaces the storage buffer from the bulk compartment.