AFM. Group 1 : Assisstant : PRASHAN. Romain LAVERRIERE Tatiana PACHOVA

Transcription

1 2012 AFM Assisstant : PRASHAN Group 1 : Romain LAVERRIERE (romainl0@etu.unige.ch) Tatiana PACHOVA (pachova0@etu.unige.ch)

2 Table of content: 1 Abstract Introduction Methodology [1] CD Analysis DVD Analysis Determination of tip s dimension Ferritin molecular mass determination Results [2] CD Analysis DVD Analysis Determination of tip s dimension Ferritin molecular mass determination Discussion Conclusion References

3 1 Abstract During this experimentation, CD and DVD surface have been analysed with AFM spectrometry. The following results were found (Table 1): Table 1: CD & DVD data CD DVD Pit width (nm) Pit depth (nm) Capacity Mo 4.42 Go Then, by the analysis of gold nanoparticles, tip s radius has been determined as to be nm. Finally, the molecular mass of ferritin was obtained as to be kda. 2 Introduction Atomic force spectrometry (AFM) is based on the molecular repulsive force. When the tip arrive very close to a surface, there is a repulsive interaction which and maintain the tip to few nanometres above the surface without touching it. Thus, by moving the tip across the surface, we can obtain the topology by measuring the elevation of the tip. The software can easily make a virtual picture from the collected data, which is very useful for further analysis. 3 Methodology [1] 3.1 CD Analysis A small piece of CD (1x1 cm), previously separated of its protecting layer with adhesive tape, is fixed on a metallic plate under the AFM tip. Then, using the software, the tip is approached very near the sample s surface and the shape is analysed. With the data, we can easily calculate the average depth and width of the pits, and finally estimated the storage capacity of the CD. 3.2 DVD Analysis The same manipulations as for the CD have been followed. 3.3 Determination of tip s dimension A small piece of mica is fixed using adhesive tape in a centrifugal machine. Then, 7-8 drops of PEI are dropped on it and the centrifugal machine is turned on to dry it. Afterwards, 3 drops of gold nanoparticles solution are dropped on the mica. Once again, the piece is dried by the centrifugation. The piece of mica containing gold nanoparticles is placed under the AFM tip and the dimension of the tip is determined. 3.4 Ferritin molecular mass determination The same manipulations as for the determination of tip s dimension have been followed. 3

4 4 Results [2] 4.1 CD Analysis Using the software, which gives a virtual image of the topology (Image 1), 10 random pits have been measured (depth and width). The results are shown bellow (table 2). Figure 1: CD topography Table 2: CD pits measurements # pit Width (nm) Depth (nm) Mean SD Then, the storage capacity of CD is calculated: Table 3: CD Capacity Area/pit (nm2) Area of CD (nm2) 8.605E+15 Number of pits Capacity (Bits) E+9 Capacity (Mo)

5 4.2 DVD Analysis As for the CD, 10 random pits have been measured. The results are the following: Figure 2: DVD topography Table 4: DVD pits measurments # pit Width (nm) Height (nm) Mean SD Then, the storage capacity of the DVD is calculated and gives the following: Table 5: DVD capacity Area/pit (nm2) Area of DVD (nm2) 8.605E+15 Number of pits Capacity (Bits) Capacity (Go)

6 4.3 Determination of tip s dimension Again, 10 measurements of gold nanoparticles have been done done. From the apparent length and the height, one is able to find the dimension of the tip by the following equation: The results are the following: R!"# = l!""! 8h Figure 3: Gold nanoparticles topography Table 6: tip's radius L app. (nm) H (nm) R tip (nm) Mean SD Ferritin molecular mass determination Finally, 10 measurements of ferritin have been done from the picture (Figure 4). Knowing the dimension of the tip, the apparent length of ferritin and its height, one can find its real dimension from the following equation: R!"##$%$& = 1 2 l!""! 8 R!"# h 6

7 Then, the molecular volume and furthermore the mass can be determinate by this relation: V = πh 2R!"#! 8 + h! 6 Figure 4: Ferritin topography Table 7: Ferritin molecular weight L App. (nm) Height (nm) Base radius (nm) V (nm3) m (g) MW (kg/mol) E E E E E E E E E E Mean E SD The molecular weight as found for the ferritin is kda. 7

8 5 Discussion The results for the calculation of CD and DVD capacity are quite good. Errors can be found as the measurements are done approximately. For the gold nanoparticles, the tip s radius found seems to be too high. That could be provided by the fact that gold forms aggregates, which can be very large. Since the tip s radius seems to be too high, it s not a surprise to found a huge molecular weight for the ferritin. Besides of the error on the tip, we can also add the fact the ferritin was stocked with water, which can considerably increase the apparent molecular weight. 6 Conclusion The AFM spectrometry seems to work very well but only if analytes have been prepared perfectly, which can be verified by the picture provided by the software. We can clearly see that in the very good results of CD & DVD storage capacity in opposite of the determination of ferritin molecular weight which need the preparation of analytes. 7 References [1] M. Borkovec, TP_AtomicSpectroscopy_rev2012, Travaux pratiques de chimie analytique / Chimistes et Biochimistes 3ème année, 2012 [2] M. Borkovec, Error Analysis Introduction, Travaux pratiques de chimie analytique / Chimistes et Biochimistes 3ème année,