Innovative biochip holds promise for cheap, portable HIV testing

The team at Penn State University designed a device which can focus particles or cells in a single stream and perform three different optical assessments of each cell. They believe it represents a major step towards low cost flow cytometry chips for clinical diagnosis in hospitals, clinics and in the field. "HIV is diagnosed based on counting CD4 cells," said Tony Jun Huang, associate professor of engineering, science and mechanics at Penn State. "90% of the diagnoses are done using flow cytometry." Flow cytometers use a laser light to illuminate cells and produce three optical signals. Processing these signals allows diagnosticians to identify individual cells in a mixed cell population and track the progression of HIV, cancer and other diseases. The current method uses a delicate three dimensional flow cell that is difficult to manufacture, with machines needing multiple lenses and mirrors for optical alignment. The researchers created an approach they say requires only a one layer, two dimensional flow cell and no optical alignment. "Current machines are very expensive costing $100,000," said Huang. "Using our innovations, we can develop a small one that could cost about $1000." The device uses a technique called microfluidic drifting which moves all the cells into a horizontal line, then forces them into single file to pass through a microlaser beam. The team says its chip can be mass produced by moulding and standard lithographic processes. "The optical fibres are automatically aligned once inserted into the chip, therefore requiring no bulky lenses and mirrors for optical alignment," said Huang. "Our machine is small enough that it can be operated by battery, which makes it usable in Africa and other remote locations." The researchers tested the device using commercially available, cell sized fluorescent beads. They are now testing the device with actual cells.