Design and Development of an Automated System for Isolating Rare Cells Using LabVIEW

Challenge:

Design, develop, and manufacture a tool that can detect and isolate circulating tumor cells (CTCs) or fetal cells in maternal blood for personalized treatment in oncology and noninvasive prenatal diagnosis.

Solution:

Develop a patented “lab-on-a-chip” technology that leverages the microelectronic properties of active silicon substrates to create miniature bio-laboratories that can be individually manipulated with NI embedded controllers for suspended cells.

Silicon Biosystems’ technology is based on the ability of electric fields to exert forces on neutral polarizable particles (such as cells) suspended in a liquid. According to the electrokinetic principle known as dielectrophoresis (DEP), neutral particles in a nonuniform electric field experience a force that increases the electric field strength in a spatial direction (positive) dielectrophoresis (pDEP) or decreases it in a spatial direction (negative) dielectrophoresis (nDEP). More specifically, the particle experiences either a positive or negative dielectrophoretic force due to its electrical properties, which depend on the frequency and the properties of the medium in which the particle is suspended (Figure 1).

Figure 1. Cell capture by dielectric cages

In the DEPArray system, an electric field is generated on the surface of a silicon chip (Figure 2a) that is directly connected to a microfluidic chamber in which cells are suspended. The microfluidic chamber is enclosed by the chip surface and a transparent cover tens of micrometers away from the chip surface. The surface of the active chip realizes a two-dimensional array of microcells, each of which consists of a planar electrode and an integrated logic circuit (Figure 2b). When placed in the area corresponding to the electrode, each electrode can be programmed to generate a potential well or dielectric cage. In each dielectric cage, the particles can be kept in a stable suspension state, allowing for individual analysis. Because each cell is analyzed individually, the system can perform complex fluorescence-based analysis to identify the unique characteristics that distinguish the target cell from the thousands of other contaminating cells. The target cells can be moved independently but simultaneously to a certain area of ​​the chip, where microfluidic control automatically recovers them.

Figure 2. Layout of the DEPArray chip [page]

DEPArray System

Our proprietary platform, DEPArray, is a flexible and easy-to-use advanced technology system (Figure 4). At the heart of the system is a microchip that integrates an array of 300,000 electrodes in a microfluidic circuit. The

DEPArray system uses NI hardware and software to manage high-precision mechanics, microfluidics, off-the-shelf electronics and custom tools, and vision and image processing. The workflow that the system allows the user to perform can be summarized in the following basic steps:

Load sample through microfluidic control
Acquire images in bright field and fluorescence
Analyze images
Identify and select target cells through a graphical user interface
Automatically sort identified target cells
Retrieve target cells through microfluidic control

Sample loading

Sample loading is a very delicate process. We use NI LabVIEW software to control the pump mechanism to generate the required pressure gradient to flow the sample from the inlet slot to the chip inside the microfluidic chamber. The system uses algorithms developed with the vision library of the NI Vision Development Module 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, cage the cells, and keep them suspended at all stages of the process, ensuring strong and reliable system control.

Sample analysis is performed by optically scanning the chip surface with multiple filters in both fluorescence and bright field. LabVIEW controls the chip-based processing system and captures, images, and visualizes high-resolution digital images from the microscope with micron-level precision.

Selecting Target Cells

In this step, the DEPArray system provides users with a powerful human-machine interface (HMI), developed with LabVIEW in conjunction with the Microsoft .NET framework, to classify and select target cells (Figure 3). Cells can be analyzed using different methods to verify their properties. The HMI displays a scatter plot or histogram of the analysis measurements and provides a tabular display of all measurements on the image. For each cell selected, the image captured during the analysis is also displayed, allowing the user to combine the results of the computer measurements with the morphological assessment.

Automatic Classification

In this step, based on the cell map and obstacles, LabVIEW dynamically configures the chip electrode array to individually and simultaneously move each cell of interest from its initial position to the recovery point. Digitally controlling the movement of each cell of interest enables the system to achieve high classification purity and unparalleled performance.

Retrieval

During this step, LabVIEW interacts with the peristaltic pump device to generate the required pressure gradient to move the buffer portion containing the selected cells downward in the retrieval medium (e.g., a well in a microfluidic chamber or a slide). The sorting and retrieval process can be repeated to collect multiple cells or purified groups of cells separately for genetic analysis using traditional molecular biology techniques.

Conclusion

Silicon Biosystems' technology, which leverages NI hardware and software with Sky Technology's technology, provides a means for a range of research activities, including isolating circulating tumor cells (CTCs) to study personalized treatment in oncology and identifying fetal cells in maternal blood for noninvasive prenatal diagnosis.