Overview
This video demonstrates a technique to detect bacterial contaminants in food and water samples using nanosensors. The target pathogenic bacteria are detected through a combination of magnetic relaxation and fluorescence emission modalities.
Protocol
1. Rapid Detection of E. coli O157:H7 using MFnS
- Spike various PBS solutions (1X, pH 7.4, 300 µL) with increasing amounts of the 10-6 bacterial stock, resulting in CFU ranges from 1-100. Add a consistent amount of MFnS (100 µL) to these solutions.
- Create one baseline solution that contains only PBS (1X, pH 7.4, 300 µL) and MFnS (100 µL).
- Incubate solutions for 30 min at 37 °C and then allow them to cool to room temperature.
- Transfer individual solutions to the magnetic relaxometer (0.47 Tesla) and record changes in relaxation times (T2) relative to the CFUs in each solution.
- To record changes in T2 values, begin by measuring the T2 value of the baseline solution that contains only PBS and MFnS.
- Place the solution in the magnetic relaxometer. Open the respective software, select the "T2 relaxation" setting, and press "measure."
- Following the collection of the baseline T2, measure the T2 values of the additional solutions that were spiked with various concentrations of bacteria.
Note: The change in T2 is equivalent to baseline T2 subtracted from the spiked T2.
- To record changes in T2 values, begin by measuring the T2 value of the baseline solution that contains only PBS and MFnS.
- Remove samples from the magnetic relaxometer and centrifuge the tubes at 2880 x g for 10 min.
- Decant the supernatant and resuspend bacterial pellets in 100 µL of PBS (1X, pH 7.4).
- Add 80 µL of each resuspension to a 96-well plate and record fluorescence intensities at 595 nm.
Note: Testing can be repeated using different solvents, including lake water, milk, and others, as described in the results section.
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Materials
Name | Company | Catalog Number | Comments |
Ferrous Chloride Tetrahydrate | Fisher Scientific | I90-500 | |
Ferric Chloride Hexahydrate | Fisher Scientific | I88-500 | |
Ammonium Hydroxide | Fisher Scientific | A669S-500 | |
Hydrochloric Acid | Fisher Scientific | A144S-500 | |
Polyacryllic Acid | Sigma-Aldrich | 323667-100G | |
EDC | Thermofisher Scientific | 22980 | |
NHS | Fisher Scientific | AC157270250 | |
Anti-E. coli O111 antibody | Sera care | 5310-0352 | |
Anti-E. coli O157:H7 antibody [P3C6 | Abcam | ab75244 | |
DiI Stain | Fisher Scientific | D282 | |
Nutrient Broth | Difco | 233000 | |
Freeze-dried E. coli O157:H7 pellet | ATCC | 700728 | |
Magnetic Relaxomteter | Bruker | mq20 | |
Zetasizer | Malvern | NANO-ZS90 | |
Plate Reader | Tecan | Infinite M200 PRO | |
Magnetic Column | QuadroMACS | 130-090-976 | |
Centrifuge | Eppendorf | 5804 Series | |
Centrifuge (accuSpin Micro 17) | Fisher Scientific | 13-100-676 | |
Floor Model Shaking Incubator | SHEL LAB | SSI5 | |
Analytical Balance | Metler Toledo | ME104E | |
Digital Vortex Mixer | Fisher Scientific | 02-215-370 | |
Open-Air Rocking Shaker | Fisher Scientific | 02-217-765 |