ICREA Research Professor Arben Merkoci and colleagues report a paper-based sensor for detection of cadmium (Cd2+) in water at record levels of sensitivity, in latest issue of Analytical Chemistry.
The sensor is cheap, portable and easy-to-use, making it a potentially ideal replacement for the costly, large time-consuming and complicated equipment traditionally employed for metal detection in water, and enabling water analysis in remote locations with limited resources
Reporting in the latest issue of Analytical Chemistry a team of researchers from ICN, the Universitat Autonoma de Barcelona and Tulane University (New Orleans, USA) have described a new, portable, low-cost and easy to use sensor for detecting the heavy metal cadmium (as Cd2+) in drinking water (“All-integrated and highly sensitive paper-based device with sample treatment platform for Cd2+ immunodetection in drinking waters”).
Water pollution continues to cause health and environmental problems globally, meaning that much of the world’s population does not have regular access to clean drinking water. Unfortunately, water analysis usually involves bulky and complex equipment, a dedicated laboratory and trained technicians, which are out of reach for most developing nations and which make field detection nearly impossible, especially in remote areas. Thus, there is a pressing need for affordable, easy to use devices for on-site water testing.
Now, ICREA Research Professor and ICN Group Leader Arben Merkoci, doctoral student Adaris López Marzo and colleagues have created a paper-based sensor that employs an immunoassay and gold nanoparticles to detect Cd2+, a common pollutant whose presence in drinking water has been linked to various health problems, including kidney and liver malfunction, and cardiovascular diseases.
The functionalised paper strip, which measures about 6 x 0.7 cm (l x w), changes from pink to white in the presence of Cd2+. The intensity of the colour band corresponds to the concentration of Cd2+, which Merkoci and colleagues quantified by scanning the band with a RapidScan® reader.
The team then validated the device using real water samples, for which it offered the highest sensitivity ever reported for detection of metals using paper-based sensors: a Limit of Detection (LOD) of 0.1 ppb and a Limit of Quantification (LOQ) of 0.4 ppb. This LOD is 50 times lower than the legally permissible limit for Cd2+ in drinking water. They also tested their device by testing recovery using spiked samples (achieving a recovery rate of nearly 100%) and by comparing their results to those obtained using standard methods, such as inductively-coupled plasma emission spectroscopy (ICPES).
The Cd2+ in water is selectively detected through a two-step immunochemical reaction whereby the free ionic species conjugates to free EDTA on the first of two reaction pads in the sensor (this first pad also contains free ovalbumin, which is used to capture other metal ion species to mask background signals). The Cd-EDTA complex then competes with pre-formed complex of Cd-EDTA-BSA-gold nanoparticles for binding to same sites in the monoclonal antibody 2A8G15.
“We are confident that our new sensor could be particularly useful for routine screening of drinking water samples or for testing industrial process streams, especially in developing countries, where heavy-metal concentrations tend to be high,” affirms Prof Merkoci, “and that this technology could easily be extended to other analytes of interest.”
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