Vincent R. Hill, Blake A. Simmons, and James E. Amburgey

OBJECTIVES:

The goal of this study was to demonstrate that insulator-based dielectrophoresis (iDEP) could be used to efficiently capture and recover diverse microbes from large-volume drinking water samples that were concentrated using ultrafiltration.

BACKGROUND:

Research has shown that ultrafiltration (UF) can be an effective technique for simultaneously concentrating viruses, bacteria, and parasites in large-volume samples of drinking water. However, UF results in sample concentrates of ~150 mL or more, which are too large for sensitive detection of pathogens using many techniques. The iDEP technology has the potential to be an efficient technique for further concentrating and separating microbes in ultrafilter concentrates.

HIGHLIGHTS:

The iDEP devices used in this project were effective for trapping and separating bacteria (E. coli and B. subtilis spores) and parasites (C. parvum and G. lamblia) in deionized (DI) water, non-concentrated tap water, and 10-L UF-concentrated tap water samples. A “dilution-ultrafiltration” procedure was developed to reduce water sample conductivity values to below a threshold needed for successful use of the iDEP device. Although capture efficiencies were high (92 percent and higher), microbial recovery efficiencies for the iDEP technique were 18-26 percent for Bacillus subtilis and 27-36 percent for Cryptosporidium parvum in UF-concentrated samples.

APPROACH:

Polymeric iDEP devices were fabricated for this project. Four microbes were used in the study: Escherichia coli, Cryptosporidium parvum oocysts, Bacillus subtilis spores, and Giardia lamblia cysts. Water sample volumes for ultrafiltration (UF) were 10-L; for iDEP they were 1-3 mL. The effect of hydrodynamic flow on trapping voltage (V) in iDEP devices was determined for each microbe. Microbe trapping voltages and microbe separation were determined using DI water, non-concentrated tap water, and ultrafiltration-concentrated tap water. The effect of Joule heating on iDEP devices processing moderate conductivity water samples was investigated. A “dilution-UF” procedure was developed to reduce water sample conductivity values to below the threshold needed for successful use of the iDEP devices. Microbe recovery using dilution-UF and iDEP was studied.

RESULTS/FINDINGS:

The polymeric iDEP devices fabricated for this project were found to be effective for trapping bacteria and oo(cysts) at reasonable applied voltages (1500 V and lower), but were not effective for trapping viruses. Development of a virus-specific iDEP device was beyond the scope and budget of the project. The iDEP devices were effective for trapping and separating E. coli, B. subtilis spores, C. parvum oocysts, and G. lamblia cysts in DI water, non-concentrated tap water, and 10-L UF-concentrated tap water samples. However, processing problems were encountered for the iDEP devices when processing water samples having conductivity values of 70 µS/cm and higher. A “dilution-UF” procedure was effective for reducing water sample conductivity values to below 70 µS/cm. Recovery efficiencies for the dilution-UF procedure were high when using 1.5-μm microspheres (85−93 percent recovery), B. subtilis spores (70-100 percent), and C. parvum oocysts (81−87 percent). Capture efficiencies for the iDEP devices were also high (92 percent and higher), but microbial recovery efficiencies were relatively low (18-26 percent for Bacillus subtilis 27-36 percent for Cryptosporidium parvum) in UF-concentrated samples. Additional research on the physical engineering of iDEP devices for drinking water processing, including devices for virus capture, is warranted and would likely lead to improved microbe recovery performance.

IMPACT:

Sample procedure development: The research performed for this project will be helpful for facilitating the continued development of dielectrophoresis-based devices for capture and recovery of diverse microbes in drinking water samples. The iDEP technology can be a powerful tool for recovering target microbes and separating them from other microbes, but its application to drinking water (especially for viruses) requires additional research. The dilution-UF procedure was found to be effective for recovering microbes from water samples and for producing water concentrates of sufficiently low conductivity for processing with iDEP devices.

PARTICIPANTS:

Contra Costa Water District

Centers for Disease Control and Prevention

Sandia National Laboratories