(698d) Ultrasensitive Quantification of Pesticide Contamination and Drift Using Silica Particles with Encapsulated DNA

The impact of pesticides and other potentially harmful and environmentally applied chemicals on ecosystems and human health are a constant issue of an ongoing public and scientific debate. Besides undeniable benefits, some pesticides also pose risks to human health and environment. For some agricultural practices, contamination with certain pesticides needs to be reduced or completely avoided. One prominent example is organic farming that does not rely on synthetic pesticides. As a consequence, there is a urgent need to develop tools that are able to universally quantify trace amounts of pesticides enabling the evaluation of contamination, drift and persistence on non-treated areas or in the environment.

Recently, we have developed a bioinspired tracer particles in our lab, silica particles with encapsulated DNA (SPED).[1] SPED consist of short deoxyribonucleic acid (DNA) tags having a length of ~100 base pairs. These DNA tags are incorporated into a chemically inert spherical silica capsule in the nano- to submicron size range (100 â?? 250 nm) and are thus protected from degradation even under irradiation and harsh radical or heat treatments. The DNA label can be selectively released from the silica using fluoride chemistry and quantified with matching primers/probes using real-time polymerase chain reaction (qPCR), a widely-applied, specific and ultra-sensitive technique for DNA analysis. Under ideal conditions, SPED can be quantified down to a 1 ppt (ng/L) range.[2] SPED have already been successfully applied in tagging oil products, food, activated sludge, or ecological food webs.[3-6] They pose no risk to the environment, and could be readily extracted and quantified from many environmental or biological matrices.

Here, we would like to present our recent findings of using SPED as an ultrasensitive environmental tracer tool for pesticides and show that SPED fulfill the above mentioned requirements of an ideal tracer tool.[7] SPED could be incorporated and robustly recovered from a large range of pesticides. In field experiments on obstacle-free fields and in an apple orchard, pesticide deposits down to 1 nL cm^-2 could be quantified after spraying a SPED-labeled test liquid containing 5.8 ppm (mg L^-1) SPED. Based on the analysis of the SPED distribution, wind and field-related patterns were clearly traceable. Due to their low material costs and enormous number of available different DNA tags, SPED cannot only be employed to identify and elucidate pesticide drift patterns down to ultra-low concentrations, but also allow cost-effective multiplexing experiments. Additionally, SPED could be also used as a unique chemical barcode for pesticides and other environmentally applied chemicals, helping, e.g., to identify the source of a contaminating pesticide. Misuse of pesticides could be therefore better investigated and prosecuted. Overall, the use of SPED improves and simplifies pesticide drift assessments for agricultural or environmental protection purposes, thus facilitating the use of new agricultural techniques and decreasing pesticide-related safety risks.

[1] Paunescu, D.; Puddu, M.; Soellner, J. O. B.; Stoessel, P. R.; Grass, R. N. Reversible DNA encapsulation in silica to produce ROS-resistant and heat-resistant synthetic DNA 'fossils'. Nature Protocols 2013, 8, 2440-2448.
[2] Paunescu, D.; Mora, C. A.; Querci, L.; Heckel, R.; Puddu, M.; Hattendorf, B.; Günther, D.; Grass, R. N. Detecting and number counting of single engineered nanoparticles by digital particle polymerase chain reaction. ACS Nano 2015, 9, 9564-72.
[3] Puddu, M.; Paunescu, D.; Stark, W. J.; Grass, R. N. Magnetically recoverable, thermostable, hydrophobic DNA/silica encapsulates and their application as invisible oil tags. ACS Nano 2014, 8, 2677-2685.
[4] Bloch, M. S.; Paunescu, D.; Stoessel, P. R.; Mora, C. A.; Stark, W. J.; Grass, R. N. Labeling milk along its production chain with DNA encapsulated in silica. Journal of Agricultural and Food Chemistry 2014, 62, 10615-10620.
[5] Grass, R. N.; Schälchli, J.; Paunescu, D.; Soellner, J. O. B.; Kaegi, R.; Stark, W. J. Tracking trace amounts of submicrometer silica particles in wastewaters and activated sludge using silica-encapsulated DNA barcodes. Environmental Science & Technology Letters 2014, 1, 484-489.
[6] Mora, C. A.; Paunescu, D.; Grass, R. N.; Stark, W. J. Silica particles with encapsulated DNA as trophic tracers. Molecular Ecology Resources 2015, 15, 231-241.
[7] Mora, C. A.; Schärer, H.-J.; Oberhänsli, T.; Ludwig, M.; Stettler, R.; Stoessel, P. R.; Grass, R. N.; Stark, W. J. Ultrasensitive Quantification of Pesticide Contamination and Drift Using Silica Particles with Encapsulated DNA. Environmental Science & Technology Letters 2016, 3, 19-23.