This Small Business Innovation Research Phase I project focuses on commercializing dip-stick tests for detection of heavy metals (lead, uranium, copper, mercury) in water, where the appearance of a red line on the test strip will indicate the presence of a contaminant. Heavy metal contamination in water poses a serious health concern and their easy detection is essential for fast and effective removal. Currently established detection methods use sophisticated, expensive instrumentation and skilled operators. There exists the need for spot test kits for low cost, real time and on-site detection for wide range of contaminants. ANDalyze proposes to make highly sensitive and specific dip-stick tests using recent advances in biotechnology and nanotechnology. A special class of metal-specific DNA sequences, called DNAzymes will be functionalized with gold nanoparticles and dried on lateral flow devices (test strips) to make dip-stick sensors for heavy metals, similar in format to the home pregnancy test kits.
The broader impact of this research is that these dip-stick tests are an ideal solution for easy, on-site water quality testing in homes, schools, hospitals and industries, instead of sending water samples to analytical labs where it can often take more than 2 weeks to get back results. This provides a significant advantage to a user who can start any remediation process sooner upon detection of contaminants, thereby reducing their adverse impacts. These tests are particularly valuable in developing countries where access to instrumentation or money for sophisticated analytical tests may be limited.
Trace levels of heavy metals, such as lead, mercury, uranium, cadmium often contaminate our water resources due to natural and human activities. These metals are toxic at very low parts-per –billion levels. Currently, when water is tested, a sample is taken, and sent to an analytical lab for analysis. This is expensive and can take up to two weeks to get results during which time significant damage may have been done by consuming the contaminated water. There are a few spot test kits which are available commercially for detection of heavy metals in water, however they are often difficult to use or do not meet the EPA requirements. Thus there exists the need for a general technology for on-site, real time and low cost detection of heavy metal pollutants. The NSF – SBIR Phase I project was for development of easy-to-use, qualitative dip-stick sensors for heavy metals, namely lead, uranium, mercury, copper in water using a new technology that uses DNA as the main sensor component. For each target contaminant, a specific DNA sequence is isolated in the laboratory which is sensitive and specific for that target. This DNA is then linked to red colored-gold nanoparticles and this forms the sensor. This is dried on lateral flow devices to make dip-stick tests that are similar to the commonly used home pregnancy test kits. When the test strip is dipped into a solution containing the target contaminant, two red lines are seen on the strip, whereas if the contaminant is not present, only one red line is seen (see picture). In the duration of this project, for all the listed metals, we were able to test different DNA constructs and buffer conditions to select optimum conditions for making the tests. We tested the sensitivity, detection range and specificity of the sensors. The lead dip-stick showed the best performance during the scope of this project; with a detection limit of ~20 ppb (EPA maximum contaminant level in drinking water for lead is 15 ppb). Tests for uranium, mercury and copper showed positive results when the metal is present and negative results in the absence of metal; however improvement in sensitivity is required. We were successful in demonstrating the feasibility of this approach and continue the development and commercialization of these sensors.