Simple, catalytic DNA biosensors for effective detection of heavy metals & other diverse analytes based on color changes

 

Researchers at the University of Illinois at Urbana-Champaign have developed a new technology capable of effectively detecting and quantifying metal ions in a sample by color changes. Accurate, versatile, and inexpensive, this technology uses the catalytic DNA-directed assembly of gold nanoparticles and its associated color changes to determine the presence and concentration of a particular metal ion. The sensor works like a pH paper and yet can detect a diverse range of analytes.

This catalytic DNA (DNAzyme) based biosensor technology can be used to detect and quantify metal ions such as lead, based on a simple blue-to-red color change. This method combines the high sensitivity and selectivity of DNAzymes with the convenience of gold nanoparticle-based detection. The technology allows for semi-quantitative and quantitative detection of metal ions in both high and low concentrations. DNA has recently been found to catalyze a variety of chemical and biological reactions.

Catalytically active DNA are isolated through in vitro selection. The in vitro selection method can be customized to select DNAzymes that are active in the presence of any chosen substance (target analyte). Active DNAzymes can cleave another piece of DNA in the presence of the target analyte used in the in vitro selection. The piece of DNA being cleaved by DNAzymes can be used as a linker for DNA-tagged gold nanoparticles.

Gold nanoparticles aggregated by DNA linkers have a blue color. Once the DNA linkers are cleaved by DNAzymes, the formation of blue nanoparticle aggregates is inhibited, and a red color of separated gold nanoparticles results. The fraction of DNA linkers cleaved by DNAzymes in a certain time is governed by the concentration of the target analyte. Thus, from the color of the resulting nanoparticle aggregates, blue, purple or red, the concentration of the target analyte can be quantified.

This technology has been demonstrated for lead detection and quantification, and is generally applicable for detection of a wide range of other analytes. The detection limit of a lead sensor is already at or below the limit set by the federal agencies. A unique feature of the DNAzyme-nanoparticle sensor is that the dynamic range for detection can be varied easily by using an inactive variant of the DNAzyme. This feature is extremely important for practical application because the concentration of the target analytes is often unknown. Sensors with adjustable sensitivity range such as these are suitable for point-of-use application to detect chemical and biological terrorism agents.

Applications

  • Consumer Market: such as home-based toxic metal detection and quantification kits, including lead, mercury, arsenic and chromium, in a similar way that pH is monitored.
  • Environmental Monitoring: This technology can be applied for on-site real-time environmental monitoring of water resources and soil, etc.
  • Industrial Process Monitoring: This technology can be applied for on-site real-time monitoring of toxic metal ions in industrial process as well as in waste water management.
  • Medical Laboratory Diagnostics: for the analysis of both beneficial and toxic metal ions.
  • Developmental Biology and Clinical Toxicology: This technology can be used to monitor metal ion spatial distribution and transportation simultaneously.

Benefits

  • Selective: Catalytic DNA is stable, selective, and extremely sensitive; therefore there is little to no interference from other ions
  • Inexpensive and Simple To Use: Does not require expensive or complicated equipment, colorimetric detection will allow for use in private homes
  • Versatile: This technology can be developed to detect any metal ions, including Magnesium, Calcium, Manganese, Zinc, Cobalt, Copper, Lead, Mercury, Arsenic, Chromium and Cadmium, as well as other diverse analytes such as chemical and biological warfare agents.
  • Tunable: The sensitivity range can be tuned so that the sensors can detect and quantify a wide range of concentrations of the target analytes without false positive or false negative results.