I am making CS nano-particles through ionic gelation method, where I use Tripoly phosphate (TPP) as a cross linker. I dissolve my chitosan in 1% Acetic acid solution with 0.5% Tween 80 as a dispersant and TPP in water. No matter what ever parameter I change (Chitosan concentration, TPP concentration, Chitosan solution pH, Stirring rate), the average particle size always remain in the range of (20-17 nm). I was just wondering if any one out there in the learned community has ever faced the similar situation Or am I doing some thing wrong or may be I am looking at some thing else. I measure the particle average size via nano Zeta sizer through making the serial dilutions of the colloidal nano suspensions after confirming the reference latex particle size (As suggested by the Malvern in their SOP). I will greatly appreciate your intellectual help, enlightenment and guidance in this matter.
I have no expertise relevant to your specific problem but long experience with physico-chemical rate process phenomena. It sounds to me as if your method is a one-shot, go or no-go process. Over a wide range of conditions, it either produces your nano particles or it doesn't. Kind of like many simple precipitation phenomena. Do you want bigger particles? If so, it seems likely that you will have to devise a secondary step that will make your particles coalesce, analogous to e.g. sintering and grain-growth phenomena at the micrometer scale. If you want smaller particles, I have no suggestions.
Dear Daniels, thanks for your reply and kind suggestions. In fact am interested in small size particles some where between 40-50 nm in size.
Dear Amira Hanafy, Thanks for your answer. I did try the different concentrations of chitosan from 0.05% to 1.0%. The TPP concentrations were varied from 0.21 mg/ml to 6.72 mg/ml. I did the mixing of ingredients on a magnetic stirrer with various stirring rates (200 rpm to 1000 rpm). The pH of chitosan solutions were varied from 4-5.9.
I did overnight mixing of chitosan and tween-80 (0.5%) in 1% Acetic acid through magnetic stirring at 600 rpm and then adjusted the desired pH of chitosan solution between 4 and 5.9. After that I made up the required volume as per the final desired % of chitosan solution. After that while stirring on the magnetic stirrer, I added TPP drop by drop into the chitosan solution and let it stir overnight at room temperature. Next morning I made serial dilutions from the suspension and estimated the average zeta size of the particles through DLS on nano zetasizer 90S.
Dear Amira, thanks for your technical insight on this issue. I usually get colloidal dispersion as the solution turns to homogenous light milky immediately after I add TPP to the chitosan solution, but I do not find any aggregates in the solution, which tends to settle down. As per your suggestion, I will reduce the mixing time of CS and TPP down to one hour from overnight. My chemicals are all brand new. I hope I must be able to solve this mystery. Secondly, I will try to measure particle size at 3-5 time dilution.
Dear Rajesh,
I am agree with Amira's advice on overnight stirring of CS and TPP solution. Because you are using ionic gelation method for the fabrication of NPs, due to ionic cross-linking the mechanical strength of NPs remains low. So if you left it overnight on stirrer might be chances of disintegration of NPs.
TPP is hygroscopic so if problems with TPP then use new one.
I am surprise with NPs size range and this also increasing my doubt of NPs disintegration.
Feel free for further discussion.
Dear Lalit,
Thanks for your technical input to this problem. My TPP is brand new and free flowing. There is no problem with the moisture. When I measure the particle size on to nano sizer after overnight stirring, I get just one very narrow peak and the correlogram of the measurement is well with in the range (0.8-0.9). More over pdi value is 0.09-0.118 at 1000 X dilution. So I am kind of thinking that logically speaking, if there would have been disintegration of the particles, the correlogram value will fluctuate, pdi will be very much off limit >0.5 as well as due to aggregation, there could be settling of the particles which I did not observe at all. More over, I measured the particle size even up to 120 days after storage at 4C in the refrigerator. There was technically no change in the size of the particles. If there would have been any disintegration of the particles, Zeta sizer would have not passed the sample at all.
Did you analysed the size and shape of NPs via SEM,TEM and AFM techniques?
Hi Rajesh,
You can not receive nano chitosan with that size by your way. They could not be so small as you say (17-20 nm). Usually, they are around 100 nm by that way. You may have wrong way to measure size. Only less than 10 percent nanochitosan formed by you way, other part is nomal chitosan. I have recommend you as follows:
1- Low speed of stirring needs increased much higher. You can combine with ultra-sonic equipment.
2- No need TWEEN adding.
3- Need pH controlling by NaOH adding.
4- Need remove chitosan by centrifuging before size measure.
5- Use of acrylic acid as alternative for higher nano yield.
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