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Question: Literature Review on the Topic of Surface Modifications with a Purpose of Depositing Lipids. Answer: Introduction It is very difficult to study complex natural cell membrane due to their native states. Lipids with the simpler model system are hence admirable for studying biomolecule interaction as well as the particular role of the component of the membrane. The suitable choice of the model will highly depend on the method employed for the scrutiny(Ottova-Leitmannova, 2015). Every model selected will have both disadvantage and advantage. The bilayers of lipids can be made on the solid support through using multiple methods including Langmuir-Blodgett (LB) and LS (Langmuir Scaefer ). This method can be done in situ but LS and LB methods will need deposition of just a monolayer at a time by the help of Langmuir fil balance. This method is preferred for the bilayer deposition having a specific and controlled asymmetric leaflet composition. The most common method of preparing model cellular membrane is (DIBB) Droplet Interface Bilayer method. In this technique, the lipid bilayer is made from two water droplets which are submerged in oil and also coated with a monolayer of lipids. This can be either control, asymmetric or symmetric each droplet composition bilayer tailoring can be realized(Lemons, 2012). In addition, the solution on either side of the membrane is able to be controlled permitting for studies of the interactions in the membrane and specific bimolecular. This technique was employed recently to reconstitute bilayer of lipids from the total extract of model cell membrane known as Escharia coli. Surface Sensitive Methods To Study Supported Lipid Bilayers And MolecularInteractions With Them Quartz crystal microbalance with dissipation. The inherent properties of the piezoelectric quartz can be keenly analyzed using QCM-D to trigger oscillation in the sensor, this will respond by deforming immediately when an external voltage is subjected to it(Ratner, 2012). The standing shear waves will be developed in the two gold electrodes due to the application of the alternating voltage. The shear wave will decay into the liquid having the characteristic length of decay. This length is always taken as 250nm, this for the crystal which is immersed in a pure water hence, this will give a perfect range of detection for the QCM-D. A solvent will be identified as a mass which is coupled with a mean thickness conforming to ?L. Where ?L is taken as the density of the liquid. The length of decay will vary with the following equation(Auernhammer, 2011). ; where nL is the absolute density of the liquid. Hence, if the solvent is exchanged with another one having higher viscosity, it will trigger an increase in the mean thickness detected by the crystal. The principle for the operation of QCM.D is based on the relationship between the change in frequency and the change in mass of sensor crystal. For such setup, if a change in mass is taken as m and change in frequency is taken as f, then from the simple Sauerbrey relationship m=-C* f/n. where C is the material specific Saurbray constant which is given as C=tg*?q/f0 and n is the harmonic number. Tq is the thickness of the quartz while ?q is the density of the quartz(Rotello, 2014). QCM-D basically records the wet adsorbed and not the dry ones since other optical techniques like ellipsometry, reflectometry and surface plasmon will do. This can be evident as an asset of the QCM-D method because it includes a tool needed for complementary info for the adsorbed layer in several liquid environments and also in combination with other surface sensitive methods(Smentkowski, 2011). The following diagrams show principle in dissipation and frequency change in the QCM-D. Fig 1: Dissipation Fig 2: Signals generated from a soft vesicle layer. AFM and the setup for imaging under continuous flow conditions. For AFM, the topology can be envisaged thru the interaction of resulting force on the tip upon scanning the surface and a sharp tip. Through scanning the surface in the pattern of the raster as well as sensing the position of laser beam sensor(Iglic, 2013). Depending on the material and the reason for the study, the AFM is operated in several modes like contact, tapping or noncontact mode. Zasadzinski used lipid AFM imaging on a lipid layer in 1991, these lipid bilayers were 1,2- dimyristoyl-sn-glycero-3-phosphoethanolamine, from that date a plethora of membrane scrutiny has been done using AFM. The below diagrams shows how AFM utilizes the interatomic forces amid a sharp tip and a surface. Fig 3. a) shows AFM utilizes interatomic forces b) Shows the optimized AFM AFC setup based on gravity. Neutron reflection This is the very powerful method employed for studying thin adsorbed layer because it gives more info on the structural features in the direction which is orthogonal to the interface having a resolution with few Angstrom(Crdenas, 2012). The sketch of a neuron beam impinging on the surface is shown below; Fig4: a) shows neuron beam sketch b) shows neuron scattering in a silicon block and c) shows simulated reflectivity curve. Formation Of Supported Lipid Bilayers By Vesicle Fusion, The Case For Single Component And Fluid Lipid Systems QCM-D is a highly sensitive method more so for the viscous layer which has a large amount of water. This shows a reason QCM-D has become a stronghold for learning the formation of SLB through vesicle formation. But AFM excels for in-plane imaging for morphology in the layer of adsorbed having lateral resolution to few nm and Angstrom resolution in the x-axis orientation. NR is as well very sensitive to the buried interface but less sensitive to a diffuse water-rich structure like vesicle. References Auernhammer, G. (2011). Surface and Interfacial Forces - From Fundamentals to Applications. Hawaii: Springer Science Business Media. Crdenas, M. (2012). Understanding the formation of supported lipid bilayers via vesicle fusionA case that. Hawaii: American Vacuum Society. Iglic, A. (2013). Advances in Planar Lipid Bilayers and Liposomes. Manchester : Academic Press. Lemons, J. (2012). Biomaterials Science: An Introduction to Materials in Medicine. Manchester : Academic Press. Ottova-Leitmannova, A. (2015). Advances in Planar Lipid Bilayers and Liposomes, Volume . Stoke : Gulf Professional Publishing. Ratner, B. (2012). Biomaterials Science: An Introduction to Materials in Medicine. Chicago : Elsevier. Rotello, V. (2014). Nanoparticles: Building Blocks for Nanotechnology. Chicago: Springer Science Business Media. Smentkowski, V. S. (2011). Surface Analysis and Techniques in Biology. London: Springer Science Business Media.