Principle of Operation
MFI combines the direct imaging capabilities of digital microscopy with the precise control of microfluidics into a single instrument for automated analysis of particles or cells suspended in liquids. MFI operates by capturing images from the sample as it passes through the flow cell's sensing zone. Every particle in each image is analyzed to create a database of particle count, size, transparency and morphology (or shape). For immediate visual verification, images are displayed on the system monitor in real-time. MFI can also produce Trend Charts to monitor dynamic processes.
As a result, it offers highly quantitative particle size and count, with morphologic parameters too. Now it is possible to evaluate every possible particle type, from protein aggregates to silicone oil, and answer challenging questions about sub-visible particles. Plus MFI is the only imaging technology to offer 85% sampling efficiency, so that almost all of the sample is analyzed and the results are statistically robust.
Up until now, detecting and counting sub-visible protein aggregates in biopharmaceuticals hasn't been easy or informative. Traditional particle counters relied exclusively on particle size and/or particle concentration measurements by light scattering, light obscuration, size exclusion chromatography or other indirect methods which often miss subvisible particles (see comparison figure below). Additional particle morphology or shape analyses required filtering and inspection by manual microscopy which can often compromise the particles or interest.
MFI provides particle images in addition to size and count to allow easy characterization of particles by their unique morphology. Measuring particle shape in addition to size and concentration provides many advantages in terms of understanding the source of the particles, their physical structure and the isolation of different sub-populations which may be of interest. Many particles appear the same in terms of size, but their morphology indicates that they are very distinct from each other, as in the case of silicone oil and protein aggregates.
MFI offers a wide range of morphologic parameters which can be used to classify particles:
- Equivalent circular (or spherical) diameter – ECD
- Maximum feret diameter
- Aspect ratio
- Edge particles
MFI View System Software (MVSS) operates MFI systems and provides all data in a basic analysis format. Starting in MVSS version 4.0, multiple samples can be analyzed instantly using a variety of particle classification filters. The MFI View Analysis Suite software also provides users with the ability to create derivative parameters. A derivative parameter is formed using two of the existing morphological parameters and a mathematical operator (e.g., aspect ratio ÷ perimeter).
The figure below is representative of visible and subvisible particles detected by MFI.