How do I avoid contamination?

Some batches of vials and tubes are not completely free of micron and nano-sized particles; this is particularly common in low grade, cheaper brands. Izon uses tubes and vials from Axygen. In the example shown below, similar samples were prepared in tubes from two different suppliers. Large populations of contaminants were present in one of the tubes. 
 

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Prior to the use of a new batch of consumables, Izon recommends completing the following testing protocol: 

  1. Prepare a test sample for analysis using the new consumables. This test sample should be of filtered blank electrolyte that is prepared by following typical particle preparation procedures. For example, if a sample diluted in electrolyte is typically sonicated or vortexed, then the electrolyte should be sonicated and vortexed. DO NOT add any particles into this test sample. 
  2. Select a nanopore that covers a size range for which measurements will be made using the instrument. 
  3. Set up the nanopore on the instrument using the test sample and establish a baseline current at the following settings using the Classic Capture interface: Applied stretch of 47 mm and applied voltage required to obtain a current of 100 nA.
  4. Apply a pressure of 5 mbar.
  5. Make a 30 second recording.  If a number of blockades are present in the size histogram, this indicates the presence of potentially significant contamination.
  6. Repeat Steps 2-4 for any additional nanopore size ranges that will be used with the instrument

 

Tips and recommendations

  • Some membrane filters can actually introduce particles to a solution. Izon uses Millipore's MCE membrane filters for all filtering purposes. 
  • Do NOT use filtered pipette tips. 
  • Prepare fresh electrolyte daily. Stock solution must be kept in the fridge when not in use. 
  • We highly recommend cleaning and drying the instrument parts and consumables with compressed gas (e.g. nitrogen) to ensure that all parts are completely free of particulates.
  • Place the instrument away from any air vents. Dust blown from the vent can contaminate and create an unstable baseline current. 
  • Keep a lid on samples and store glass- and plastic-ware in a closed container.
  • Clean the VPM nozzle with deionised water and dry with compressed gas before performing a measurement.