Name: insights into the interactions of amino acids and peptides with inorganic materials using single-molecule force spectroscopy
Uploaded: 2017-03-06T12:30:00
Description: Watch this Scientific Journal Video about Insights into the Interactions of Amino Acids and Peptides with Inorganic Materials Using Single-Molecule Force Spectroscopy at JoVE.com

This work was supported by the Marie Curie International Reintegration Grant (EP7). P. D. acknowledges the support of the Israel Council for Higher Education.

1. Tip Modification
<ol>
	<li>Purchase silicon nitride (Si3N4) AFM cantilevers with silicon tips (nominal cantilever radius of ~2 nm).</li>
	<li>Clean each AFM cantilever by dipping in anhydrous ethanol for 20 min. Dry at room temperature. Then treat the cantilevers by exposing them to O2 plasma for 5 min.</li>
	<li>Suspend the clean tips above (3 cm) a solution containing methyltriethoxysilane and 3-(aminopropyl) triethoxysilane in a ratio of 15:1 (v/v) in a desiccator under an inert a...

Steps 1.3, 1.4 and 1.7 in the protocol should be carried out with extensive care and in a very gentle manner. In step 1.3, the tip should not be in contact with the silane mixture and the silanization process should be carried out in an inert atmosphere (moisture free).45 This is done in order to prevent multilayer formation and because silane molecules readily undergo hydrolysis in the presence of moisture.45
In step 1.4, the temperature and tim...

The interaction between proteins and inorganic minerals leads to the construction of composite materials with distinctive properties. This includes materials with high mechanical strength or unique optical properties.1,2 For example, the combination of the protein collagen with the mineral hydroxyapatite generates either soft or hard bones for different functionalities. 3 Short peptides can also bind inorganic materials with high specificity. 4,5,6 The specificity of these peptides has been used for designing new magnetic and electronic materials,7,8,9 fabricating nanostructured materials, growing crystals, 10 and synthesizing nanoparticles.11Understanding the mechanism underlying interactions between peptides or proteins and inorganic materials will therefore allow us to design new composite materials with improved adsorptive properties. In addition, since the interphase of implants with an immune response is mediated by proteins, better understanding the interactions of proteins with inorganic materials will improve our ability to design implants. Another important area that involves proteins interacting with inorganic surfaces is the fabrication of antifouling materials.12,13,14,15 Biofouling is an undesirable process in which organisms attach to a surface. It has many detrimental implications on our lives. For example, biofouling of bacteria on medical devices leads to hospital-acquired infections. Biofouling of marine organisms on boats and large ships increases the consumption of fuel.12,16,17,18
Single-molecule force spectroscopy (SMFS), using an AFM, can directly measure the interactions between an amino acid or a peptide with a substrate.19,20,21,22,23,24,25,26 Other methods such as phage display,27,28 quartz crystal microbalance (QCM)29or surface plasmon resonance (SPR)29,30,31,32,33 measure the interactions of peptides and proteins to inorganic surfaces in bulk.34,35,36 This means that the results obtained by these methods relate to ensembles of molecules or aggregates. In SMFS, one or very few molecules are fixed to the AFM tip and their interactions with the desired substrate is measured. This approach can be expanded to study protein folding by pulling the protein from the surface. In addition, it can be used to measure interactions between cells and proteins and the binding of antibodies to their ligands.37,38,39,40 This paper describes in detail how to attach either peptides or amino acids to the AFM tip using silanol chemistry. In addition, the paper explains how to perform force measurements and how to analyze the results.

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		<tr height="173">
			<td height="173" style="height:173px;width:164px;">Silicon nitride (Si3N4) AFM cantilevers with silicon tips</td>
			<td style="width:147px;">Bruker (Camarilo, CA, USA)</td>
			<td style="width:64px;"></td>
			<td style="width:264px;">MSNL10, nominal cantilevers radius ~2 nm&#160;</td>
		</tr>
		<tr height="106">
			<td height="106" style="height:106px;width:164px;">Methyltriethoxysilane&#160;</td>
			<td style="width:147px;">Acros Organics (New Jersey, USA)</td>
			<td style="width:64px;"></td>
			<td style="width:264px;">For Silaylation of the AFM tip&#160;</td>
		</tr>
		<tr height="106">
			<td height="106" style="height:106px;width:164px;">3-(Aminopropyl) triethoxysilane</td>
			<td style="width:147px;">Sigma-Aldrich (Jerusalem, Israel)</td>
			<td style="width:64px;"></td>
			<td style="width:264px;">Used for tip modification&#160;</td>
		</tr>
		<tr height="106">
			<td height="106" style="height:106px;width:164px;">Triisopropylsilane</td>
			<td style="width:147px;">Sigma-Aldrich (Jerusalem, Israel)</td>
			<td style="width:64px;"></td>
			<td style="width:264px;">Used for tip modification</td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:164px;">N-Ethyldiisopropylamine</td>
			<td style="width:147px;">Alfa-Aesar (Lancashire, UK)</td>
			<td style="width:64px;"></td>
			<td style="width:264px;">Used for tip modification</td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:164px;">Triethylamine</td>
			<td style="width:147px;">Alfa-Aesar (Lancashire, UK)</td>
			<td style="width:64px;"></td>
			<td style="width:264px;">Used for tip modification</td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:164px;">Piperidine</td>
			<td style="width:147px;">Alfa-Aesar (Lancashire, UK)</td>
			<td style="width:64px;"></td>
			<td style="width:264px;">Used for tip modification</td>
		</tr>
		<tr height="232">
			<td height="232" style="height:232px;width:164px;">Fluorenylmethyloxycarbonyl-PEG-N-hydroxysuccinimide&#160; (Fmoc-PEG-NHS)</td>
			<td style="width:147px;">Iris Biotech GmbH (Deutschland, Germany)</td>
			<td style="width:64px;"></td>
			<td style="width:264px;">Used as the covalent flexible linker&#160; (MW = 5000 Da)</td>
		</tr>
		<tr height="253">
			<td height="253" style="height:253px;width:164px;">2-(1H-benzotriazol-1-yl)-1,1,3,3,-tetramethyluronium hexafluorophosphate (HBTU)</td>
			<td style="width:147px;">Alfa Aser (Heysham, England)</td>
			<td style="width:64px;"></td>
			<td style="width:264px;">Used as a coupling reagent.&#160;</td>
		</tr>
		<tr height="148">
			<td height="148" style="height:148px;width:164px;">N-methyl-2-pyrrolidone (NMP)</td>
			<td style="width:147px;">Acros Organics (New Jersey, USA)</td>
			<td style="width:64px;"></td>
			<td style="width:264px;">Used as Solvent in Tip modification procedure</td>
		</tr>
		<tr height="148">
			<td height="148" style="height:148px;width:164px;">DMF (dimethylformamide)</td>
			<td style="width:147px;">Merck (Darmstadt, Germany)</td>
			<td style="width:64px;"></td>
			<td style="width:264px;">Used as Solvent in Tip modification procedure</td>
		</tr>
		<tr height="106">
			<td height="106" style="height:106px;width:164px;">Trifluoro acetic acid (TFA)</td>
			<td style="width:147px;">Merck (Darmstadt, Germany)</td>
			<td style="width:64px;"></td>
			<td style="width:264px;"></td>
		</tr>
		<tr height="106">
			<td height="106" style="height:106px;width:164px;">Acetic anhydride</td>
			<td style="width:147px;">Merck (Darmstadt, Germany)</td>
			<td style="width:64px;"></td>
			<td style="width:264px;"></td>
		</tr>
		<tr height="106">
			<td height="106" style="height:106px;width:164px;">Peptides</td>
			<td style="width:147px;">GL Biochem (Shanghai, China).</td>
			<td style="width:64px;"></td>
			<td style="width:264px;"></td>
		</tr>
		<tr height="106">
			<td height="106" style="height:106px;width:164px;">Phenylalanine and Tyrosine&#160;</td>
			<td style="width:147px;">Biochem (Darmstadt, Germany)&#160;</td>
			<td style="width:64px;"></td>
			<td style="width:264px;"></td>
		</tr>
		<tr height="240">
			<td height="361" rowspan="7" style="height:361px;width:164px;">30% TiO2 dispersion in the mixture of solvent 2-(2-Methoxyethoxy) ethanol (DEGME) and Ethyl 3-Ethoxypropionate (EEP)</td>
			<td rowspan="7" style="width:147px;">Applied Vision Laboratories (Jerusalem, Israel)</td>
			<td rowspan="7" style="width:64px;"></td>
			<td rowspan="7" style="width:264px;">(30%) in the mixture of solvent 2-(2 Methoxyethoxy) ethanol (DEGME) and Ethyl 3-Ethoxypropionate (EEP)</td>
		</tr>
		<tr height="20">
		</tr>
		<tr height="20">
		</tr>
		<tr height="20">
		</tr>
		<tr height="20">
		</tr>
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		</tr>
		<tr height="21">
		</tr>
		<tr height="148">
			<td height="148" style="height:148px;width:164px;">Mica substrates</td>
			<td style="width:147px;">TED PELLA, INC. (Redding, California, USA)</td>
			<td style="width:64px;"></td>
			<td style="width:264px;">9.9 mm diameter</td>
		</tr>
	</tbody>
</table>

insights into the interactions of amino acids and peptides with inorganic materials using single-molecule force spectroscopy

The interactions between proteins or peptides and inorganic materials lead to several interesting processes. For example, combining proteins with minerals leads to the formation of composite materials with unique properties. In addition, the undesirable process of biofouling is initiated by the adsorption of biomolecules, mainly proteins, on surfaces. This organic layer is an adhesion layer for bacteria and allows them to interact with the surface. Understanding the fundamental forces that govern the interactions at the organic-inorganic interface is therefore important for many areas of research and could lead to the design of new materials for optical, mechanical and biomedical applications. This paper demonstrates a single-molecule force spectroscopy technique that utilizes an AFM to measure the adhesion force between either peptides or amino acids and well-defined inorganic surfaces. This technique involves a protocol for attaching the biomolecule to the AFM tip through a covalent flexible linker and single-molecule force spectroscopy measurements by atomic force microscope. In addition, an analysis of these measurements is included.

Figure 1 exhibits the tip modification procedure. In the first step, a plasma treatment changes the surface of the silicon nitride tip. The tip presents OH groups. These groups will then react with the silanes. At the end of this step, the surface of the tip will be covered by free -NH2 groups. These free amines will then react with Fmoc -PEG-NHS, a covalent linker. The Fmoc group of the PEG linker is removed by pipyridine, a deprotecting reagent. Finally, the ...

Watch this Scientific Journal Video about Insights into the Interactions of Amino Acids and Peptides with Inorganic Materials Using Single-Molecule Force Spectroscopy at JoVE.com

Insights into the Interactions of Amino Acids and Peptides with Inorganic Materials Using Single-Molecule Force Spectroscopy

Here we present a protocol to measure the force of interactions between a well-defined inorganic surface and either peptides or amino acids by single-molecule force spectroscopy measurements using an atomic force microscope (AFM). The information obtained from the measurement is important to better understand the peptide-inorganic material interphase.

The interactions between proteins or peptides and inorganic materials lead to several interesting processes. For example, combining proteins with minerals ...

The overall goal of the single-molecule force spectroscopy technique is to determine the adhesion force and nature of interactions between amino acids or peptides with different surfaces. This matter can help answer key questions in the area of surface chemistry and be used for the development of new composites and chordates. The main advantage of this technique is that it provides information on interaction between the desired molecule and surfaces at the single molecule level.To begin, purchase silicon nitride AFM cantilevers equipped with silicon tips with a nominal cantilever radius of two nanometers. Mount the tip on the holder. Clean each of the AFM cantilevers by dipping them into ethanol for 20 minutes and then dry them at room temperature.Next, place the tips into a plasma chamber and treat the cantilevers by exposing them to oxygen plasma for five minutes. Prepare a solution containing 15 parts methyltriethoxysilane and one part three amino propyltriethoxysilane and suspend the canitlevers three centimeters above the solution while under an inert atmosphere. It is important that the tips and the holder do not touch the silane mixture.In addition, the silane is highly moisture sensitive, and therefore these tips need to be carried out in an inert atmosphere. Once sealed, connect the desiccator to a vacuum pump and apply a vacuum for two hours to form a mono-layer of the two types of mixed silane compounds on the surface of the cantilevers. Carefully remove the tips and place them onto a hot plate preheated to 70 degrees Celsius.Leave the tips to dry for 10 minutes. Cool the tips at room temperature before immersing them in a solution of Fmoc-PEG-NHS for one hour at room temperature. Next, dip the tips into chloroform for five minutes and then into DMF for an additional five minutes.After incubation in DMF, de-protect the Fmoc groups of the attached PEG molecules by dipping the tips into 20%piperidine solution in DMF for 30 minutes. Again, dip the tips in DMF for four minutes and then in N-Methyl-2-pyrrolidone for an additional four minutes. To couple amino acids onto the tips, immerse the for one and a half hours into an amino acid coupling solution with a total concentration of 30 millimolar and five milliliters of N-Methyl-2-pyrrolidone.To protect the remaining free or unreactant PEG residues by the acetyl group, dip the tips for 30 minutes in a 0.65 molar mixture of four parts acetic anhydride and one part diisopropylethylamine and N-Methyl-2-pyrrolidone. Then sequentially dip the peptide amino acid functionalized tips for four minutes each into NMP, chloroform, 50%ethanol and water before finally drying the tip in air. Attach the desired test surface to a metallic holder of the AFM with commercially available epoxy.Then, place the metallic holder into the glass holder of the AFM, which is shaped as a small petri dish. Fill the glass holder with TRIS buffer. And then place the metallic holder on the AFM stage below the tip holder.Next, mount the AFM tip on the AFM's optic glass. Place the optic glass block in the AFM head. And put the AFM head on the stage.Next, calibrate the AFM cantilevers with spring constants ranging from 10 to 30 piconewtons per nanometer. A typical force measurement results in a force distance curve like those shown here. The first peek indicates non-specific interactions between the tip and the surface and the second peek refers to the specific adhesion event.From several hundred force distance curves, it is possible to construct a histogram by plotting the number of adhesion events versus force. Applying a Gaussian fit on these histograms will determine the most probable force. After watching this video, you should have a good understanding of how to chemically modify AFM tips with amino acids or peptides and how to perform single-molecule force spectroscopy using AFM.

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