Tuning DNA adsorption affinity and density on metal oxide and phosphate for improved arsenate detection.

Arsenic (As) contamination in groundwater presents a major health and environmental concern in developing countries. Typically, As is found in two oxidation states. Most chemical tests for inorganic arsenic are focused on As(III), and few have been developed for As(V). We are interested in developing biosensors for As(V) based on its similarity with phosphate. Building upon previous work involving DNA-capped Fe3O4 nanoparticles for As(V) detection, we investigated two other nanomaterials: CeO2 and CePO4 in terms of DNA adsorption and As(V) induced DNA desorption. Fluorescently labeled DNA is physically adsorbed to the surface sites on the nanoparticle surface via its phosphate backbone. In the cases of CeO2 and Fe3O4, the fluorescence was quenched due to electron transfer, whereas for the insulating CePO4, no quenching was observed. Arsenate, being similar to phosphate, can also bind to the surface of the nanoparticles and displace the DNA, increasing the fluorescence signal. The length and sequence of DNA were systematically studied. Using this method, CeO2 performed significantly better than Fe3O4, lowering the detection limit by almost 10-fold. In addition, for CeO2 and CePO4, using shorter DNA was more effective for As(V) detection than using the longer DNA since they both adsorb DNA more tightly than Fe3O4 does. Overall, CeO2 has the best performance since it has an intermediate adsorption affinity of DNA, while CePO4 adsorbs DNA too strongly.