Here we use a polyurethane tunable nanopore integrated into a resistive pulse sensing technique to characterize nanoparticles surface chemistry via the measurement of particle translocation velocities, which can be used to determine the zeta potential of individual nanoparticles.
The overall goal of this procedure is to characterize the surface chemistry of nano particles using tunable resistant post sensing, or TRPS, and determine the zeta potential of the material. This is demonstrating by characterizing DNA modified nano particles. This method can help answer key questions in the characterization of nanomaterials and the development of bioassay.
The main advantage of this technique is that you can complete particle by particle analysis. Each DNA particle signal is translated into a zeta potential measurement, providing a complete picture of the sample being analyzed. The oldest method could provide insight into the characterization of materials.
It can also be applied to other applications, such as the development of bioassay for the detection of cells, viruses, DNA, and proteins. Generally, individual new to this method will struggle because it's not a simple inject the samp and then wait for the answer. There is some input from the scientist needed.
To begin this procedure, vortex streptavidin coated particles for 30 seconds before sonication for two minutes at 80 watts to assure mono dispersity. Dilute the streptavidin coated particles one in one hundred in PBST buffer to achieve a resulting concentration of one times ten to the nine particles per milliliter. Then vortex the particles for 30 seconds.
Based on a binding capacity of 4, 352 picomols per milligram at the appropriate concentration of DNA to the particles for resulting concentrations of 10, 20, 30, 40, 47, 95, 140, and 210 nanomolar. After vortexing the samples for 10 seconds, place them on a rotary wheel at room temperature for 30 minutes to allow the DNA to bind to the particle surfaces via a streptavidin biotin interaction. Once the captured DNA has been added and incubated with the particles, remove the excess DNA and solution via magnetic separation by placing the samples onto a magnetic rack for 30 minutes.
Following this, remove the supernatant, taking care not to disturb the newly formed cluster of particles, closest to the magnet. Then replace the supernatant with the same volume of fresh PBST buffer. Now add the required amount of target DNA to each sample to ensure the maximum possible target binding was reached.
Vortex the samples for 10 seconds. And place them on the rotary wheel at room temperature for 30 minutes. Once the hybridization is complete, remove the excess target DNA via magnetic separation by placing the samples onto the magnetic rack for 30 minutes.
Next remove the supernatant, taking care not to disturb the newly formed cluster of particles, closest to the magnet. Then replace the supernatant with the same volume of fresh PBST buffer. After repeating the previous steps for duplicate samples, place the samples on the rotary wheel at room temperature for 16 hours to investigate DNA hybridization times.
At this point, plug in a TRPS instrument into a computer system with software in place. Using calipers, measure the distance between the outside of two parallel jaws. Type the distance in the stretch field in the instrument settings tab and click on calibrate stretch underneath the tab.
Following this, laterally fit a polyurethane nanopore membrane of appropriate sizing for analysis onto the jaws with the nanopore ID number facing upward. Then stretch the jaws to the stretch required for analysis using the stretch adjustment handle on the side of the instrument. Place 80 microliters of PBST buffer in the lower fluid cell beneath the nanopore, ensuring there are no bubbles present that may affect the measurement.
Now click the upper fluid cell into place and add 40 microliters of buffer, ensuring there are no bubbles present. Then place a faraday cage over the system and apply an external pressure as described in the text protocol. After placing 40 microliters of the calibration particles into the upper fluid cell, complete a TRPS measurement at three applied voltages.
Alter the voltage by clicking on the plus and minus buttons on the voltage scale in the instrument settings tab in the software. Check that the three voltages return the appropriate background currents. And ensure that at the medium voltage, the calibration particles produce an average blockade magnitude of at least 0.3 nanoamperes.
Once the conditions outlined in the text protocol have been achieved, start the run by clicking start in the software in the data acquisition tab. To complete the measurement, click stop in the data acquisition tab and save the data file. Wash the system by replacing the calibration particles with 40 microliters with PBST buffer into the upper fluid cells several times.
And applying various pressures until no more blockade events are present, ensuring there are no residual particles and no cross contamination. After the appropriate baseline current is achieved, replace the electrolyte in the upper fluid cell with 40 microliters of sample. Start the sample run by clicking start in the data acquisition tab.
Record a minimum of 500 particles and ensure the run time is a minimum of 30 seconds. To complete the measurement, click stop in the data acquisition tab and save the data file. An example of size and zeta potential analysis of streptavidin coated particles with no modifications and streptavidin coated particles saturated with single stranded DNA on the surface is shown here.
Although both samples were of a similar size, the zeta potential was significantly different and much larger when DNA was functionalized onto the particle surface. The size and zeta potential data exhibited for samples with the lowest an highest concentrations of DNA hybridized to the streptavidin coated particles is displayed here. A larger zeta potential value is recorded for particles hybridized with a higher concentration of DNA.
The change in zeta potential measured for capture probed DNA only, a fully complementary DNA target, a middle binding DNA target, an end binding DNA target, and an overhanging DNA target is shown here. Once mastered, this technique can be done in 20 minutes if it is performed properly. While attempting this procedure it's important to remember to thoroughly wash a nanopole between each calibration and sample to ensure there is no cross contamination between samples and prevent any nanopole blocking.
After its development, this technique paved the way for researchers in the field of biosenses to explore protein-protein and protein-DNA interactions in multiplex assays. After watching this video you should have a good understanding of how to obtain zeta potential using TRPS and prepare DNA modified particles for bioassays.
