Laser diode-driven lab-on-a-chip detects periodontitis pathogens

A new mobile diagnostic platform driven by a laser diode can identify the 11 most relevant periodontitis (gum inflammation that can lead to the loss of teeth) pathogens in less than 30 minutes rather than in four to six hours. Scientists at the Fraunhofer Institute for Cell Therapy and Immunology (IZI; Leipzig, Germany) have collaborated with two companies, BECIT GmbH (Wolfen Germany) and ERT-Optik (Ludwigshafen, Germany), to develop a lab-on-a-chip module called ParoChip. In the future, this will allow dentists and medical labs to prepare samples quickly and then analyze the bacteria. All steps in the process--the duplication of DNA sequences and their detection--take place directly on the platform, which consists of a disk-shaped microfluidic card that measures around six centimeters in diameter.

Dentists use sterile paper points to remove bacteria from the tooth. (Image courtesy of Fraunhofer IZI)
Dentists use sterile paper points to remove bacteria from the tooth. (Image courtesy of Fraunhofer IZI)

The analysis is conducted in a contactless and fully automated manner. Samples are taken using sterile, toothpick-shaped paper points, after which the bacteria are removed from the point and their isolated DNA injected into reaction chambers containing dried reagents. There are 11 such chambers on each card, each featuring the reagent for one of the 11 periodontal pathogens. The total number of bacteria is determined in an additional chamber via polymerase chain reaction (PCR), which allows millions of copies of even tiny numbers of pathogen DNA sequences to be made. In order to generate the extremely quick changes in temperature that are required for PCR, the disk-shaped plastic chip is attached to a metal heating block with three temperature zones and mechanically turned so it passes over these zones. This causes a fluorescent signal to be generated that is measured by a connected optical measuring device featuring a fluorescence probe, a photodetector, and a laser diode. The key benefit is that the signal makes it possible not only to quantify each type of bacterium and thus determine the severity of the inflammation, but also to establish the total number of all the bacteria combined. This enables doctors to fine-tune an antibiotic treatment accordingly.

"As the connected optical measuring system allows us to quantify bacteria, ParoChip is also suited to the identification of other bacterial causes of infection, such as food-borne pathogens or those that lead to sepsis," says Dirk Kuhlmeier, a scientist at the IZI. "Using ParoChip does away with many of the manual steps that are a necessary part of current bacteria tests. The synthetic disks can be produced cheaply and disposed of after use in the same way as disposable gloves."

Already available as a prototype, ParoChip is initially intended for use in clinical laboratories; however, it could also be used by dentists to carry out in-house analysis of patient samples in their own practice.

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