Piezoelectric Sensor Detects Bacterial Toxins and Certain Cancers

A tiny vibrating cantilever sensor could soon help doctors and field clinicians quickly detect harmful toxins, bacteria, and indicators of some cancers from small samples of blood or urine.

Cantilever sensor technology detects its minute targets using a method that is similar to a springboard bouncing with the movements of a diver. The board-or cantilever in this application–vibrates at a higher frequency when the diver jumps off and his or her mass is removed. Conversely, the vibration frequency of a cantilever would decrease when weight is added to it. Measuring the difference in frequency of mass-free versus mass-loaded vibrations allows scientists to detect cells or DNA, in samples.

Scientists from Drexel University (Philadelphia, PA, USA) are in the process of refining the sensor technology that they developed to measure samples at the cellular level into an accurate method for quickly detecting traces of DNA in liquid samples.

Lead researcher Dr. Raj Mutharasan, a professor in Drexel's College of Engineering explained that the group's application of lead zirconate titanate (PZT) to current piezoelectric-excited cantilever sensor technology has created a way to conduct more sensitive and timely tests for DNA. This DNA test will allow for quick identification of harmful cells and bacteria.

"I equate this new technology to authorities trying to catch a criminal using latent fingerprints rather than a mug shot," Mutharasan said. "It is more precise, selective, and sensitive. With the PZT sensor we can potentially detect DNA derived from a much smaller number of pathogens and in a much shorter period of time than current methods."

Because PZT sensors are completely controllable, Dr. Mutharasan's group has discovered high-order vibration modes in certain designs that are sensitive to very small mass changes, on the order of one-billionth of a microgram, in liquid samples. "Such high sensitivity enables us to measure biological molecules at a million-fold more sensitive than what is currently feasible," Dr. Mutharasan said.

The advantage of the cantilever sensor is that double-stranded DNA can be unwound by vibrating the sensor at the proper frequency. This essential step for replication can cut a typical detection process, which could take several hours, down to less than an hour.

The PZT sensor enables testing of samples in liquids and at room temperature. Therefore, scientists can foresee applications in detecting food and water contamination, as well as use in the medical field.

Already the PZT sensor has successfully detected DNA indicators for prostate cancer in urine samples, toxin-producing genes in pathogenic Escherichia coli and an identifying gene of malaria-causing Plasmodium falciparum in patient blood samples.

The technology is still likely to be three-to-five years from becoming commercially available for medical and environmental uses according to Dr. Mutharasan.

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