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Challenge: Design, develop, and manufacture a tool capable of detecting and isolating circulating tumor cells (CTCs) or fetal cells from maternal blood. The former supports research into personalized oncology treatments, and the latter supports noninvasive prenatal diagnosis.
Solution: A patented technique called "chip laboratory" was developed. It leverages the microelectronic properties of an active silicon substrate to create micro-scale biological workstations and uses NI embedded controllers to operate suspended cells individually.
Silicon Biosystems' technique is based on the ability of electric fields to exert forces on neutral polarizable particles suspended in a liquid, such as cells. According to the electrodynamic principle known as dielectrophoresis (DEP), a neutral particle in a nonuniform electric field experiences forces that move it toward regions of increasing field intensity in positive dielectrophoresis (pDEP) or toward regions of decreasing intensity in negative dielectrophoresis (nDEP). More specifically, particles experience pDEP or nDEP depending on their electrical properties, which are a function of frequency and of the properties of the suspending medium.
In the DEPArray system, the electric field is generated at the surface of a silicon chip, which interfaces directly with the microfluidic chamber containing the cell suspension. The microfluidic chamber is enclosed by the chip surface and a transparent cover located tens of micrometers above the chip. The active chip surface implements a two-dimensional array of microcells, each consisting of planar electrodes and integrated logic circuitry. When placed above a given electrode region, each electrode can be programmed to generate a potential well or dielectrophoretic cage. Within each dielectrophoretic cage, particles can be held in stable suspension for individual analysis. Because each cell is analyzed individually, the system supports complex fluorescence-based analyses that can identify features distinguishing target cells from thousands of contaminating cells. Target cells can be moved independently, and also simultaneously, to a region of the chip where microfluidic control enables their automated recovery.
DEPArray System
The DEPArray platform is a flexible system. The core of the system is a microchip that integrates an array of 300,000 electrodes within a microfluidic circuit.
DEPArray uses NI hardware and software to manage precision mechanical systems, microfluidics, off-the-shelf electronics and custom tooling, as well as vision and image processing. The user workflow is summarized in the following basic steps:
- Load the sample via microfluidic control
- Acquire images in brightfield and fluorescence
- Analyze images
- Identify and select target cells through a graphical user interface
- Automatically classify identified target cells
- Recover target cells via microfluidic control
Sample Loading
Sample loading is a very precise process. NI LabVIEW software controls pump devices to generate the required pressure gradients so that the sample flows from the inlet well onto the chip inside the microfluidic chamber. The system uses algorithms developed with the NI Vision Development Module libraries to automatically monitor and control the loading process.
Capture and Analysis
Once the sample is loaded onto the chip, LabVIEW controls all I/O lines to configure the electrode array, trap cells in cages, and keep them suspended during all stages of the workflow to ensure robust system control.
Sample analysis is performed by optically scanning the chip surface using multiple filters for fluorescence and brightfield. LabVIEW controls the processing system that holds the chip and performs capture and image processing with micrometer-level precision, producing visualizable high-resolution digital images from the microscope.
Selecting Target Cells
At this step, the DEPArray system provides a human-machine interface (HMI) developed with LabVIEW and the Microsoft .NET framework to classify and select target cells. Cells can be analyzed using different approaches to validate their properties. The HMI displays scatter plots or histograms of analysis measurements and provides a list view of all measurements for the images. For each selected cell, the images captured during analysis are displayed so users can combine computed measurements with morphological assessment.
Automatic Classification
In this step, LabVIEW dynamically configures the chip electrode array based on the cell map and obstacles so that each cell of interest can be moved individually and simultaneously from its initial position to the recovery point. Digitally controlling each cell's movement yields high classification purity and consistent performance.
Recovery
During recovery, LabVIEW interacts with peristaltic pump devices to generate the required pressure gradients so that the buffer containing selected cells flows from the recovery region (for example, a trap or a slide) downstream. The classification and recovery process can be repeated to collect multiple individual cells or multiple purified cell groups for downstream genomic analysis using conventional molecular biology techniques.
Conclusion
Silicon Biosystems' technology, together with NI hardware and software and Sky Technology's techniques, provides methods for research aimed at isolating circulating tumor cells for personalized oncology studies and for identifying fetal cells in maternal blood for noninvasive prenatal diagnosis.
