Silver nanoparticles (AgNP) are widely used in the production of consumer products, water disinfectants, therapeutic drugs, and biomedical devices due to their antibacterial properties, but their suitability is limited by particle size. The particle size control of homogeneous AgNP and the elimination of the toxic effects of stabilizers and organic solvents present many challenges in both technology and efficiency.
Tangential flow ultrafiltration (TFU) is commonly used for the separation of proteins, viruses and cells. It is a "recycling" technique. Simply put, the feed liquid passes through a series of hollow fiber membranes with a pore size of 10kD-1000kD. Small suspended or dissolved components pass through the porous barrier with the solvent (filtrate) while the larger components are trapped (reflux). TFU can be considered a "green" technology without damaging the sample or adding additional solvent to remove excess toxic reagents or by-products. TFU can control the AgNP particle size, concentration and aggregation state very well, and it is more convenient than ultracentrifugation.
Steps:
4L latex AgNP was synthesized by Creighton method. The shape, particle size distribution, aggregation state and purity of latex particles were determined by UV-Vis spectrophotometry and Raman spectroscopy.
KrosFlo Research 2 i [KR2 i ] Tangential Flow Filtration System
Using KrosFlo to develop a particle size screening and concentration of latex AgNP using a II i tangential flow ultrafiltration system, it was carried out in three steps:
The first step :
1) Connect the MasterFlex #17 injection hose to the peristaltic pump via a hose coupling. The hose is then connected to the 50nm MidiKros assembly. Fasten the connection with a cable tie to ensure a seal. Select the hose size of the monitor control interface as 17.
2) Set the pump running direction to run counterclockwise.
3) Reduce the pump speed to less than 300ml/min and run the pump. The pump speed needs to be adjusted according to the hose used. Start the pump at a speed that is as small as possible to avoid large leaks, but it should be sufficient to allow the flow to fill the entire system. The piping connections are such that a sufficient vacuum is achieved to draw the latex from the container into the line and filter. The hose at the bottom of the filter can be connected to the top of the Y-joint in the middle of the hose.
4) Place the hose at the outlet of the filter in the container and clamp the bottom of the hose with a spring clip to start the pump operation. The vacuum created in the line begins to siphon the latex.
5) When the liquid begins to pass freely through the pipeline, stop the pump operation, add the broken part of the pipeline with a hose joint, and seal with a cable tie. Turn on the pump to run.
6) Check the pipeline for leaks. If a leak is found, adjust the fitting or retighten the tie to seal. After confirming that the line is sealed, increase the pump speed until the optimum pump speed for the selected hose is reached. Continue to filter until the liquid in the container is drained.
7) After the filtration was completed, a filtrate containing AgNP having a particle diameter of 50 nm or less was collected. The reflux can also be retained for confirmation testing.
In the first step, TFU uses a 50 nm filter (11500 px2) for particle size screening to remove AgNP and AgNP aggregates of 50 nm and above in the latex stock solution. This step also produced a small amount of concentration, which resulted in a final 3.9 L 50 nm filtrate.
The second step :
8) Flush the tubing with 2% HNO3 and ultrapure water and install the 100kD MidiKros filter as before.
9) Repeat step 3) using the 100kD MidiKros component.
10) After the filtration is complete, collect the reflux (including the tubing and the liquid in the filter). The volume is approximately 50 ml.
The second step was carried out on a larger scale, and the filtrate from the previous step was passed through a 100 kD filter (200 cm 2 ). Finally, 50 ml of reflux was obtained.
The third step :
11) Connect the MasterFlex #14 hose and 100kD MicroKros filter to the peristaltic pump and seal all connections with a cable tie. Select 14 for the hose size of the control interface and reduce the pump speed to 30 ml/min.
12) Start the filtering operation. Check the circulation loop for leaks. If a leak is found, adjust the fitting or retighten the tie to seal.
13) After confirming the pipe seal, adjust the pump speed to no more than 90ml/min.
14) After the filtration is completed, drain the residual liquid in the pipeline and the filter to stop the pump operation.
In the third step, AgNP was further concentrated, using a 100 kD filter with a smaller surface area (50 cm 2 ) to reduce the volume to 4.0 ml.
3. Inductively coupled plasma optical emission spectroscopy (ICP-OES) was used to quantitatively detect the silver content in latex AgNP, and there was almost no loss in AgNP production.
The particle size distribution of the latex AgNP was observed by transmission electron microscopy, and the final 100 kD reflux liquid was basically a non-aggregated AgNP having a particle diameter of 1-20 nm.
TFU process flow chart. An AgNP latex suspension for further analysis of the collected samples in the blue box. The samples in the vials were A) raw latex samples, B) 50 nm filtrate collected after the original latex was treated with a 50 nm filter (460 cm 2 ), C) the first 100 kD collected after reducing the volume using a 100 kD MidiKros filter (200 cm 2 ) Reflux, D) Final 100 kD reflux collected after reduction in volume using a 100 kD MicroKros filter (20 cm 2 ). The 100 kD filtrate looks close to water.
in conclusion:
TFU is a highly efficient, "green" technique for particle size screening and concentration of latex AgNPs and maintains very low particle aggregation. Since the chemical toxicity reagents and organic solvents used in the synthesis of AgNP are removed during the treatment, and the particle size dispersion of AgNP is reduced, the catalytic properties, photoelectric properties, biosensing properties and nanotoxicity can be improved, and the Applications in medicine, industry and scientific research.
In practical applications, other specifications can be selected to optimize the TFU process (filter pore size range 10kD-1000kD, membrane surface area 5.1m2-200px2, hydrophobic or hydrophilic), while monitoring process pressure or proper cleaning can improve Filter life. The charge characteristics of the particles also affect the progress of the ultrafiltration process. In addition, TFU can also be used for buffer replacement and other operations according to downstream application requirements.
However, it should be noted that if the concentration factor is too high, the stability and shelf life of the latex suspension may be lowered. At 10 ° C, the highly concentrated unfunctionalized AgNP has a shelf life of about one to two weeks. According to the actual situation, the preparation and processing parameters can be adjusted to improve product stability and shelf life.
The content of this article is the editor's translation. If there is any inconvenience, please forgive me. For details, please refer to the original text.
Original: Anders, CB, et al.. Tangential Flow Ultrafiltration: A "Green" Method for the SizeSelection and Concentration of Colloidal Silver Nanoparticles. Journal of Visualized Experiments. 2012.68.
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