Swift sampling

A Drexel University engineering professor has developed a millimetre-size cantilever biosensor that can quickly detect cells and proteins in trace samples.

The sensor could have wide applications in medical diagnostic testing, detecting contamination in food products and monitoring for biothreat agents. In medical testing, the sensor can be used to analyze the four most widely tested fluids: blood, urine, sputum and spinal fluid.

Existing conventional tests require 24 hours and a trip to a laboratory to boost the concentration of microbes in a sample to produce findings. The accurate, handheld sensor Dr. Raj Mutharasan, a Drexel chemical engineering professor, has developed over the past six years can yield findings in about 10 minutes.

No direct test for minute amounts of proteins exists on the market. A study published in the April 1, 2007, issue of Analytical Chemistry using Mutharasan’s sensor detected E. coli in ground beef at some of the lowest concentrations ever reported.

Results of a preliminary study using the device to non-invasively detect a prostate cancer biomarker in 15 minutes were recently presented by David Maraldo, a Drexel doctoral student in chemical engineering who worked with Mutharasan on the sensor, at the 96th annual meeting of the United States and Canadian Academy of Pathology.

Kishan Rijal, a Drexel doctoral student in chemical engineering, and Gossett Campbell, who received his doctoral degree in chemical engineering from Drexel in 2006, helped develop the sensor. Dr. Fernando U. Garcia, professor of pathology in the Drexel University College of Medicine, provided urine specimens to Mutharasan in testing for prostate cancer.

The sensor features a vibrating cantilever, supported at one end and coated with antibodies. The antibodies are specific to the desired target such as E. coli, anthrax or proteins that are biomarkers for diseases such as prostate cancer. When the target is present in a sample flowing past the sensor, it binds to the cantilever and changes the frequency of vibration so it can be read electronically.

The sensor affixed with antibodies against E. coli can detect as low as four cells per millilitre of solution. A voltage is applied to the ceramic layer, causing it to expand and contract, vibrating the glass sliver. The sensor detects changes in the glass sliver’s resonance frequency (the point where vibration is the greatest) and determines the presence and concentration of E. coli bacteria.

Mutharasan recently expanded the sensor’s applications to food toxins and biomarkers. A commercial prototype of the sensor is anticipated to be completed in July. Mutharasan is working with a company that has licensed Drexel’s technology to commercialise the device and expects it to be in the hands of food-safety experts soon.