Name: measurement of particle size distribution in turbid solutions by dynamic light scattering microscopy
Uploaded: 2017-01-09T12:30:00
Duration: 9 min 16 s
Description: Watch this Scientific Journal Video about Measurement of Particle Size Distribution in Turbid Solutions by Dynamic Light Scattering Microscopy at JoVE.com

This work has been financially supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science, and Technology (No. 25248027 to M.S.).

1. Sample Preparation
<ol>
	<li>Purification of temperature-responsive monomers
	<ol>
		<li>Dissolve 20 g of N-isopropylacrylamide (NIPA) in 100 mL of toluene.</li>
		<li>Filter the solution under suction to eliminate dust.</li>
		<li>Mix the filtrate with 500 mL of petroleum ether.</li>
		<li>Place the reaction vessel in an ice-water bath.</li>
		<li>Stir the solution until the monomers are precipitated (typically 30 min).</li>
		<li>Filter the solution under suction to obtain the precipitated monomers.</li>
		<li>Dry the monomers under reduced pressure (100 Pa) overnight.</li>
	</ol>
	</li>
	<li>Preparation of the temperature-responsive polymer solution
	<ol>
		<li>Degas 20 mL of deionized water for 1.0 min using a diaphragm pump.</li>
		<li>Dissolve 780.8 mg of the purified NIPA in 9.5 mL of degassed and deionized water.</li>
		<li>Place the reaction vessel in an ice-water bath.</li>
		<li>Shield the reaction from light by covering the apparatus with aluminum foil.</li>
		<li>Stir the solution gently for 10 min while introducing a moderate flow of Ar gas gently via a pipette tip attached to the gas cylinder with a tube.</li>
		<li>Add 11.9 &#181;L of N,N,N&#39;,N&#39;-tetramethylethylenediamine to the solution via a micropipette.</li>
		<li>Stir the solution for 1.0 min while introducing Ar gas, as mentioned in step 1.2.5.</li>
		<li>While stirring the sample, dissolve 4.0 mg of ammonium persulfate in 0.5 mL of degassed and deionized water.</li>
		<li>Mix the sample solution (from step 1.2.7) and ammonium persulfate solution (from step 1.2.8).</li>
		<li>Stir the solution for 30 s while introducing Ar gas, as mentioned in step 1.2.5.</li>
		<li>Cover the solution with aluminum foil and keep it in a refrigerator (4 &#176;C) overnight.</li>
	</ol>
	</li>
	<li>Preparation of sample mounts
	<ol>
		<li>Place 60 &#181;L of the sample solution (from step 1.2.11) in a cavity slide.</li>
		<li>Cover the solution with a circular cover glass. Be careful not to trap air bubbles.</li>
		<li>Remove excess solution using a micropipette and laboratory wipes.</li>
		<li>Seal the sample with glue. Let the glue dry at room temperature (typically 6 h).</li>
		<li>Prepare another slide filled with 0.1 wt% polystyrene latex (100-nm particle diameter) suspension by following steps 1.3.1-1.3.4. This slide is used as a standard.</li>
	</ol>
	</li>
</ol>
2. Particle Size Measurement with a Dynamic Light Scattering Microscope
<ol>
	<li>Optimization of the instrument
	<ol>
		<li>Place the polystyrene latex suspension slide (from step 1.3.5) on the stage of the inverted microscope. The cover glass side should face downward.</li>
		<li>Place a beam damper in front of the detector (an avalanche photodiode and an autocorrelator).</li>
		<li>Apply a laser beam (solid-state laser, &#955; = 488 nm, 30 mW, continuous wave) to the sample through an objective lens (10&#215;). A portion of the reflected light goes through a launch mirror of the microscope and is observed by a CCD camera mounted at the side port of the microscope (Figure 1).</li>
		<li>Adjust the height of objective lens to set the focal point at the sample suspension by shifting the height of objective lens from the low-to-high position. During this procedure, the reflected image is focused three times: at the surface of the cover glass, at the interface between the cover glass and the sample, and at the interface between the sample and the hole-slide glass. Set the focal point between the second and third points.</li>
		<li>Attenuate the scattered light intensity by changing the laser power.</li>
		<li>Introduce the scattered light into the detector by removing the beam damper in front of the detector. This unit measures the time correlation of the light intensity.</li>
		<li>Set a pinhole (&#981; = 50 &#181;m) between the microscope and the detector to achieve the confocal effect. Adjust the position of the pinhole to maximize the light intensity at the detector.</li>
		<li>Measure the time correlation function of scattered light intensity for 30 s by initiating the operation of the correlator via a computer. The measured correlation function is often expressed as g(2) (t) - 1, where t is the correlation time4 and <img alt="Equation 1" src="/files/ftp_upload/54885/54885eq1.jpg" />. Here, I(t) is the scattered light intensity at the time t and (&#8226;&#8226;&#8226;)T is time averaging. The decay time will be approximately 0.1 ms.</li>
		<li>Adjust the focal point to obtain a wide range for the initial amplitude of the time correlation function (g(2) (t = 0) - 1). 
		NOTE: The initial amplitude is strongly affected by the amount of reflected light. By moving the focal point toward the interface between the cover glass and the sample, the amount of reflected light increases. For strong light scatterers, such as polystyrene latex, the initial amplitude can be altered from 0 to 1. However, it is difficult to set the initial amplitude close to 1 for more common polymer solutions because the intensity of the reflected light is much higher than that of the scattered light.</li>
		<li>Apply the inverse Laplace transformation (using the constrained regularization program CONTIN13,14) to the obtained time correlation function to acquire the size distribution function. In cases where the initial amplitude is set to less than 0.2, the distribution function of the hydrodynamic radius will show a sharp peak around 100 nm, which is twice the actual radius (see the discussion for details).</li>
	</ol>
	</li>
	<li>Sample measurement
	<ol>
		<li>Set the stage temperature to 25 &#176;C.</li>
		<li>Place a slide prepared with poly-NIPA (PNIPA) solution (step 1.3.4) on the stage of the microscope.</li>
		<li>Measure the time correlation function of the scattered light intensity by following steps 2.1.4-2.1.8. If the initial amplitude is larger than 0.2, adjust the focal point to make the initial amplitude of the time correlation function less than 0.2 by following step 2.1.9. A small initial amplitude simplifies the analysis.</li>
		<li>Set the stage temperature to 35 &#176;C and wait until the solution turns turbid. The lower critical solution temperature (LCST) of PNIPA solution is 32 &#176;C15.</li>
		<li>Measure the time correlation function by following steps 2.1.4-2.1.8. If feasible, adjust the position of the focal point to make the initial amplitude of the time correlation function less than 0.2. For turbid solutions, their initial amplitudes tend to increase, since the intensity of the scattered light increases while that of the reflected light remains constant.</li>
		<li>Apply the inverse Laplace transformation to the obtained time correlation functions to obtain the size distribution functions. Note that the actual size is half the obtained value in cases where the initial amplitude is less than 0.2.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

The initial amplitude of the time correlation function heavily depends on the focal point, as shown in Figure 2(a). This seemingly contradicts the fact that the solution is homogeneous (except for the thin layer at the interface)8. This variation in the initial amplitude is attributed to a variation in the amount of reflected light. Partial heterodyne theory16 predicts that the initial amplitude, A, the scattered light Intensity, Is, and the reflected light intensity, Ir, satisfy the following equation1
<img alt="Equation 2" src="/files/ftp_upload/54885/54885eq2.jpg" />
This equation shows that the larger Ir becomes, the smaller A becomes. Therefore, A is reduced by setting the focal position close to the interface. The apparent diffusion constant DA can be obtained by fitting the time correlation function in the case of monodisperse solutions:
<img alt="Equation 3" src="/files/ftp_upload/54885/54885eq3.jpg" />
where <img alt="Equation 4" src="/files/ftp_upload/54885/54885eq4.jpg" />. Here, n is the refractive index of the solvent (water, 1.33), &#952; is the scattered angle (180&#176;), and&#160;&#955; is the wavelength of light (514.5 nm). Since we applied backscattering geometry, the value of q is fixed. However, this point is solved by using different wavelengths of light. Please note that any kind of continuous-wave laser source is available to construct the DLS microscope. Thanks to the small irradiated volume, the coherence factor17 is estimated to be more than 0.99 and is negligible. For polydisperse solutions, the distribution function of DA is obtained by the inverse Laplace transformation. Partial heterodyne theory also predicts that DA is not the same as the actual diffusion constant D. These two diffusion constants satisfy the following equation:
<img alt="Equation 5" src="/files/ftp_upload/54885/54885eq5.jpg" />
The diffusion constant D is converted into the hydrodynamic radius Rh using the Einstein-Stokes equation4. When A = 1, this relationship becomes DA = D. In this case, the data conversion process is the same as that for the common dynamic light scattering. The red line shown in Figure 2(b) corresponds to this case. In contrast, this relationship becomes DA = 0.5D at the limit of A &#8594; 0. Therefore, the size is estimated to be twice as large as the actual size when A is small (practically, less than 0.2), as shown by the blue line of Figure 2(b). If we know that A is significantly small, the horizontal axis can be shifted, as shown in Figure 2(c). In principle, we can convert DA into D for any value of A. In practice, however, it is better to set the initial amplitude smaller than 0.2, since the simple approximation DA &#8764; 0.5D holds true.
The prominent features of the dynamic light scattering microscope technique were demonstrated using a PNIPA solution. The conformation of PNIPA below and above the LCST has been extensively studied using small-angle neutron scattering15,18. In contrast, dynamic light scattering has not been utilized for the analysis of PNIPA above the LCST because of its turbidity19. This problem is solved by the dynamic light scattering microscope, as shown in Figures 3(a) and (b). The size of these aggregates is several &#181;m, which cannot be obtained by either small-angle X-ray/neutron scattering or conventional light scattering techniques. Time-resolved measurements using this system give information on the aggregation process during the temperature change.
The drawback of the dynamic light scattering microscope is also illustrated in Figure 3. For the result below the LCST, the time correlation function is strongly affected by the very small amount of dust present (the black lines in Figure 3). For example, the time correlation function does not decay completely, even with correlation times in the order of 1.0 s. This is because the volume irradiated with this apparatus (approximately 1.0 &#181;m) is significantly smaller than that irradiated with the usual dynamic light scattering apparatus (approximately 100 &#181;m). In cases where the intensity of scattered light is weak, the signal is obscured by the noise, such as that caused by small amounts of dust in the solution. Therefore, the three peaks shown in Figure 3(b) may not have quantitative importance although the general order of the size is meaningful. Note that such a weak scatterer can be measured by a conventional dynamic light scattering apparatus.
We have demonstrated that the dynamic light scattering microscope enables us to measure both transparent and turbid samples with the same setup. Since the optical path length in the samples is short, this technique can be applied to strong light-absorbing samples, such as carbon nanotube suspensions20. In addition, due to its high spatial resolution, this technique can be applied to biological cells. For its application to biology, this method can also be combined with other imaging techniques, such as fluorescence and Raman imaging. Thus, we believe that the dynamic light scattering microscope is a powerful tool for a wide range of research fields.

Particle size is one of the most fundamental properties of colloidal and polymer solutions. Numerous techniques are used to measure the particle size. Particle sizes of 1.0 &#181;m or larger can be measured directly using an optical microscope. For smaller particles, alternative techniques, such as laser diffraction, electron microscopy, or atomic force microscopy, are used2,3. Dynamic light scattering is a commonly-used technique for the measurement of particle size distributions in solutions4. The results obtained using this technique are not derived from images of the particles but from the characteristic time of the fluctuations in scattered light intensity. These fluctuations originate from Brownian motion, which is characterized by a diffusion constant. The size distribution is obtained from the distribution of diffusion constants using the Einstein-Stokes equation. Due to its simplicity, dynamic light scattering is widely used for the routine assessment of solutions, such as paints and food colloids.
Pretreatment is required for most of the techniques used for the particle size measurement of solution samples. In the case of electron microscopy and atomic force microscopy, the sample must be analyzed under vacuum conditions. Therefore, it is difficult to observe the samples in their native forms. Furthermore, for laser diffraction and dynamic light scattering, only diluted samples that are free from multiple scattering and light absorption can be measured. To overcome this difficulty, several new techniques have been proposed for the measurement of dynamic light scattering from undiluted, concentrated solutions, such as cross-correlation spectroscopy5,6, low-coherence dynamic light scattering7,8, diffusing-wave spectroscopy9,10, and differential dynamic microscopy11,12.
We have developed a new apparatus called a dynamic light scattering microscope1. This apparatus enables us to measure turbid samples without dilution by means of a confocal optical system in which multiple scattering is eliminated using a pinhole. However, the measurement procedure and data analysis are slightly more complicated than those of commercially-available instruments. This video explains the measurement procedure and data analysis in detail using the analysis of the temperature-responsive polymer, poly(N-isopropylacrylamide), as an example.

<table border="0" cellpadding="0" cellspacing="0" width="591">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="76">
			<td height="76" style="height:76px;width:216px;">N-isopropylacrylamide, 98%</td>
			<td style="width:89px;">Tokyo Chemical Industry Co., Ltd.</td>
			<td style="width:119px;">I0401</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="76">
			<td height="76" style="height:76px;width:216px;">toluene, 99%</td>
			<td style="width:89px;">Wako Pure Chemical Industries, Ltd.</td>
			<td style="width:119px;">201-01876</td>
			<td></td>
		</tr>
		<tr height="76">
			<td height="76" style="height:76px;width:216px;">petroleum ether, distillation temperature 30 ~ 60 &#176;C</td>
			<td style="width:89px;">Wako Pure Chemical Industries, Ltd.</td>
			<td style="width:119px;">169-22565</td>
			<td></td>
		</tr>
		<tr height="57">
			<td height="57" style="height:57px;width:216px;">N,N,N&#39;,N&#39;-tetramethylethylenediamine, 99%</td>
			<td style="width:89px;">Sigma</td>
			<td style="width:119px;">T9281</td>
			<td></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;width:216px;">ammonium persulfate, 98%</td>
			<td style="width:89px;">Sigma</td>
			<td style="width:119px;">248614</td>
			<td></td>
		</tr>
		<tr height="57">
			<td height="57" style="height:57px;width:216px;">polystyrene latex suspension, 1 wt%</td>
			<td style="width:89px;">Duke Scientific Corporation</td>
			<td style="width:119px;">3500A</td>
			<td></td>
		</tr>
		<tr height="57">
			<td height="57" style="height:57px;width:216px;">argon</td>
			<td style="width:89px;">Koike Sanso Kogyo Co., Ltd.</td>
			<td style="width:119px;"></td>
			<td>purity &#62; 99.999 vol.%</td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;width:216px;"></td>
			<td style="width:89px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="57">
			<td height="57" style="height:57px;width:216px;">cavity slide</td>
			<td style="width:89px;">Matsunami Glass Ind.,Ltd.</td>
			<td style="width:119px;">83-0336</td>
			<td></td>
		</tr>
		<tr height="57">
			<td height="57" style="height:57px;width:216px;">inverted microscope</td>
			<td style="width:89px;">Nikon Instech Co., Ltd.</td>
			<td style="width:119px;">ECLIPSE Ti-U</td>
			<td></td>
		</tr>
		<tr height="38">
			<td height="38" style="height:38px;width:216px;">Thermo Plate</td>
			<td style="width:89px;">Tokai Hit CO.,Ltd</td>
			<td style="width:119px;">TP-108R-C</td>
			<td></td>
		</tr>
		<tr height="38">
			<td height="38" style="height:38px;width:216px;">Ar-Kr ion laser</td>
			<td style="width:89px;">Spectra-Physics</td>
			<td style="width:119px;">Stabilite 2018</td>
			<td></td>
		</tr>
		<tr height="57">
			<td height="57" style="height:57px;width:216px;">avalanche photodiode</td>
			<td style="width:89px;">ALV-GmbH</td>
			<td style="width:119px;">ALV-High Q.E. Avalanche Photo Diode</td>
			<td></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;width:216px;">correlator</td>
			<td style="width:89px;">ALV-GmbH</td>
			<td style="width:119px;">ALV-5000/EPP</td>
			<td></td>
		</tr>
	</tbody>
</table>

measurement of particle size distribution in turbid solutions by dynamic light scattering microscopy

A protocol for measuring polydispersity of concentrated polymer solutions using dynamic light scattering is described. Dynamic light scattering is a technique used to measure the size distribution of polymer solutions or colloidal particles. Although this technique is widely used for the assessment of polymer solutions, it is difficult to measure the particle size in concentrated solutions due to the multiple scattering effect or strong light absorption. Therefore, the concentrated solutions should be diluted before measurement. Implementation of the confocal optical component in a dynamic light scattering microscope1 helps to overcome this barrier. Using such a microscopic system, both transparent and turbid systems can be analyzed under the same experimental setup without a dilution. As a representative example, a size distribution measurement of a temperature-responsive polymer solution was performed. The sizes of the polymer chains in an aqueous solution were several tens of nanometers at a temperature below the lower critical solution temperature (LCST). In contrast, the sizes increased to more than 1.0 &#181;m when above the LCST. This result is consistent with the observation that the solution turned turbid above the LCST.

Time correlation functions of scattered light intensity for a polystyrene latex suspension (particle radius: 50 nm) were measured at different focal points, as shown in Figure 2(a). These correlation functions were converted into the distribution functions of the hydrodynamic radius by the inverse Laplace transformation (refer to Figure 2(b) and (c)). Using the same procedure, the time correlation functions and distribution functions of the hydrodynamic radius of the PNIPA solution were obtained at 25 &#176;C and 35 &#176;C, respectively. Figures 3(a) and (b) show the time correlation functions of the scattered light intensity and the corresponding size distribution functions of the PNIPA solution below (25 &#176;C) and above (35 &#176;C) the LCST. The size distribution functions were obtained by the inverse Laplace transformation followed by the correction of the partial heterodyne. The average hydrodynamic radius below the LCST is several tens of nanometers, which is typical for polymer solutions. In contrast, the hydrodynamic radius above the LCST is about 1.0 &#181;m. This result is consistent with the fact that the solution is turbid above the LCST. The red and blue lines in Figure 3 represent the size distribution of PNIPA solutions obtained immediately after and 20 min after the solution became turbid, respectively. Figure 3(b) clearly indicates the growth of the aggregation.
<img alt="Figure 1" src="/files/ftp_upload/54885/54885fig1.jpg" /> 
Figure 1. Schematics of the dynamic light scattering microscope. Pinhole (PH), beam splitter (BS), polarizer (Pol), and avalanche photodiode (APD). <a href="http://cloudflare.jove.com/files/ftp_upload/54885/54885fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/54885/54885fig2.jpg" /> 
Figure 2. Representative results for a polystyrene latex suspension. (a) Time correlation functions of the scattered light intensity for the polystyrene latex suspension. The nominal radius is 50 nm and the concentration is 0.1 wt%. Two datasets were obtained from different scattering points. (b), (c) Corresponding size distribution functions for the polystyrene latex suspension obtained by the inverse Laplace transformation of (a). The red line corresponds to the time correlation function whose initial amplitude is approximately 1.0, and the blue line corresponds to that with an initial amplitude that is approximately 0.2. The horizontal axis was calculated without (b) and with (c) considering the effect of partial heterodyning (PHD) when A &#60;&#60; 1. <a href="http://cloudflare.jove.com/files/ftp_upload/54885/54885fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/54885/54885fig3.jpg" /> 
Figure 3. Representative results for a PNIPA solution. (a) Time correlation functions of scattered light intensity for the PNIPA solution. (b) Corresponding size distribution functions for the PNIPA solution obtained by the inverse Laplace transformation of (a). The horizontal axis was calculated considering the effect of partial heterodyning for each data set. The black line represents the data obtained at 25 &#176;C. The red line represents the data obtained just after the solution turned turbid (35 &#176;C). The blue line represents the data obtained after a 20-min measurement of the red line. <a href="http://cloudflare.jove.com/files/ftp_upload/54885/54885fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

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Measurement of Particle Size Distribution in Turbid Solutions by Dynamic Light Scattering Microscopy

A protocol for the direct measurement of particle size distribution in concentrated solutions using dynamic light scattering microscopy is presented.

A protocol for measuring polydispersity of concentrated polymer solutions using dynamic light scattering is described. Dynamic light scattering is a ...

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Quantitative and Qualitative Examination of Particle-particle Interactions Using Colloidal Probe Nanoscopy

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Colloidal probe nanoscopy can be used within a variety of fields to gain insight into the physical stability and coagulation kinetics of colloidal systems and aid in drug discovery and formulation sciences using biological systems. The method described within provides a quantitative and qualitative means to study such systems.

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Dynamic Electrochemical Measurement of Chloride Ions

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Dynamic measurement of chloride ions is presented. Transition time of an Ag/AgCl electrode, during a chronopotentiometric technique, can give the concentration of chloride ions in electrolyte. This method does not require a stable conventional reference electrode.

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver ...

Dissolution Dynamic Nuclear Polarization Instrumentation for Real-time Enzymatic Reaction Rate Measurements by NMR

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The sensitivity enhancement provided by dissolution dynamic nuclear polarization (DNP) enables following metabolic processes in real time by NMR and MRI. The characteristics and performances of a dedicated dissolution DNP setup designed for study enzymatic reactions are discussed.

The main limitation of NMR-based investigations is low sensitivity. This prompts for long acquisition times, thus preventing real-time NMR measurements of ...

Fabrication and Testing of Photonic Thermometers

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We describe the process of fabrication and testing of photonic thermometers.

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Nanosponge Tunability in Size and Crosslinking Density

We describe a protocol for the synthesis of linear polyesters containing pendant epoxide functionality and their incorporation into a nanosponge with controlled dimensions. This approach begins with synthesis of a functionalized lactone which is key to the pendant functionalization of the resulting polymer. Valerolactone (VL) and allyl-valerolactone (AVL) are then copolymerized using ring-opening polymerization. Post-polymerization modification is then used to install an epoxide moiety on some or all of the pendant allyl groups. Epoxy-amine chemistry is employed to form nanoparticles in a dilute solution of both polymer and small molecule diamine crosslinker based on the desired nanosponge size and crosslinking density. Nanosponge sizes can be characterized by transmission electron microscopy (TEM) imaging to determine the dimension and distribution. This method provides a pathway by which highly tunable polyesters can create tunable nanoparticles, which can be used for small molecule drug encapsulation. Due to the nature of the backbone, these particles are hydrolytically and enzymatically degradable for a controlled release of a wide range of hydrophobic small molecules.

This article describes a process for tuning the size and crosslinking density of covalently crosslinked nanoparticles from linear polyesters containing pendant functionality. By tailoring synthesis parameters (polymer molecular weight, pendant functionality incorporation, and crosslinker equivalents), a desired nanoparticle size and crosslinking density can be achieved for drug delivery applications.

We describe a protocol for the synthesis of linear polyesters containing pendant epoxide functionality and their incorporation into a nanosponge with ...

DNA-magnetic Particle Binding Analysis by Dynamic and Electrophoretic Light Scattering

Isolation of DNA using magnetic particles is a field of high importance in biotechnology and molecular biology research. This protocol describes the evaluation of DNA-magnetic particles binding via dynamic light scattering (DLS) and electrophoretic light scattering (ELS). Analysis by DLS provides valuable information on the physicochemical properties of particles including particle size, polydispersity, and zeta potential. The latter describes the surface charge of the particle which plays major role in electrostatic binding of materials such as DNA. Here, a comparative analysis exploits three chemical modifications of nanoparticles and microparticles and their effects on DNA binding and elution. Chemical modifications by branched polyethylenimine, tetraethyl orthosilicate and (3-aminopropyl)triethoxysilane are investigated. Since DNA exhibits a negative charge, it is expected that zeta potential of particle surface will decrease upon binding of DNA. Forming of clusters should also affect particle size. In order to investigate the efficiency of these particles in isolation and elution of DNA, the particles are mixed with DNA in low pH (~6), high ionic strength and dehydration environment. Particles are washed on magnet and then DNA is eluted by Tris-HCl buffer (pH = 8). DNA copy number is estimated using quantitative polymerase chain reaction (PCR). Zeta potential, particle size, polydispersity and quantitative PCR data are evaluated and compared. DLS is an insightful and supporting method of analysis that adds a new perspective to the process of screening of particles for DNA isolation.

This protocol describes the synthesis of magnetic particles and evaluation of their DNA-binding properties via dynamic and electrophoretic light scattering. This method focuses on monitoring changes in particle size, their polydispersity and zeta potential of particle surface which play major role in binding of materials such as DNA.

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Microfluidic Chips for In Situ Crystal X-ray Diffraction and In Situ Dynamic Light Scattering for Serial Crystallography

This protocol describes fabricating microfluidic devices with low X-ray background optimized for goniometer based fixed target serial crystallography. The devices are patterned from epoxy glue using soft lithography and are suitable for in situ X-ray diffraction experiments at room temperature. The sample wells are lidded on both sides with polymeric polyimide foil windows that allow diffraction data collection with low X-ray background. This fabrication method is undemanding and inexpensive. After the sourcing of a SU-8 master wafer, all fabrication can be completed outside of a cleanroom in a typical research lab environment. The chip design and fabrication protocol utilize capillary valving to microfluidically split an aqueous reaction into defined nanoliter sized droplets. This loading mechanism avoids the sample loss from channel dead-volume and can easily be performed manually without using pumps or other equipment for fluid actuation. We describe how isolated nanoliter sized drops of protein solution can be monitored in situ by dynamic light scattering to control protein crystal nucleation and growth. After suitable crystals are grown, complete X-ray diffraction datasets can be collected using goniometer based in situ fixed target serial X-ray crystallography at room temperature. The protocol provides custom scripts to process diffraction datasets using a suite of software tools to solve and refine the protein crystal structure. This approach avoids the artefacts possibly induced during cryo-preservation or manual crystal handling in conventional crystallography experiments. We present and compare three protein structures that were solved using small crystals with dimensions of approximately 10-20 &#181;m grown in chip. By crystallizing and diffracting in situ, handling and hence mechanical disturbances of fragile crystals is minimized. The protocol details how to fabricate a custom X-ray transparent microfluidic chip suitable for in situ serial crystallography. As almost every crystal can be used for diffraction data collection, these microfluidic chips are a very efficient crystal delivery method.

Microfluidic Chips for In Situ Crystal X-ray Diffraction and In Situ Dynamic Light Scattering for Serial Crystallography

This protocol describes in detail how to fabricate and operate microfluidic devices for X-ray diffraction data collection at room temperature. Additionally, it describes how to monitor protein crystallization by dynamic light scattering and how to process and analyze obtained diffraction data.

This protocol describes fabricating microfluidic devices with low X-ray background optimized for goniometer based fixed target serial crystallography. The ...

Elemental-sensitive Detection of the Chemistry in Batteries through Soft X-ray Absorption Spectroscopy and Resonant Inelastic X-ray Scattering

Energy storage has become more and more a limiting factor of today's sustainable energy applications, including electric vehicles and green electric grid based on volatile solar and wind sources. The pressing demand of developing high-performance electrochemical energy storage solutions, i.e., batteries, relies on both fundamental understanding and practical developments from both the academy and industry. The formidable challenge of developing successful battery technology stems from the different requirements for different energy-storage applications. Energy density, power, stability, safety, and cost parameters all have to be balanced in batteries to meet the requirements of different applications. Therefore, multiple battery technologies based on different materials and mechanisms need to be developed and optimized. Incisive tools that could directly probe the chemical reactions in various battery materials are becoming critical to advance the field beyond its conventional trial-and-error approach. Here, we present detailed protocols for soft X-ray absorption spectroscopy (sXAS), soft X-ray emission spectroscopy (sXES), and resonant inelastic X-ray scattering (RIXS) experiments, which are inherently elemental-sensitive probes of the transition-metal 3d and anion 2p states in battery compounds. We provide the details on the experimental techniques and demonstrations revealing the key chemical states in battery materials through these soft X-ray spectroscopy techniques.

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Obtention of Giant Unilamellar Hybrid Vesicles by Electroformation and Measurement of their Mechanical Properties by Micropipette Aspiration

Giant vesicles obtained from phospholipids and copolymers can be exploited in different applications: controlled and targeted drug delivery, biomolecular recognition within biosensors for diagnosis, functional membranes for artificial cells, and development of bioinspired micro/nano-reactors. In all of these applications, the characterization of their membrane properties is of fundamental importance. Among existing characterization techniques, micropipette aspiration, pioneered by E. Evans, allows the measurement of mechanical properties of the membrane such as area compressibility modulus, bending modulus and lysis stress and strain. Here, we present all the methodologies and detailed procedures to obtain giant vesicles from the thin film of a lipid or copolymer (or both), the manufacturing and surface treatment of micropipettes, and the aspiration procedure leading to the measurement of all the parameters previously mentioned.

The goal of the protocol is to reliably measure membrane mechanical properties of giant vesicles by micropipette aspiration.

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Application of Voltage in Dynamic Light Scattering Particle Size Analysis

Dynamic light scattering (DLS) is a common method for characterizing the size distribution of polymers, proteins, and other nano- and microparticles. Modern instrumentation permits measurement of particle size as a function of time and/or temperature, but currently there is no simple method for performing DLS particle size distribution measurements in the presence of applied voltage. The ability to perform such measurements would be useful in the development of electroactive, stimuli-responsive polymers for applications such as sensing, soft robotics, and energy storage. Here, a technique using applied voltage coupled with DLS and a temperature ramp to observe changes in aggregation and particle size in thermoresponsive polymers with and without electroactive monomers is presented. The changes in aggregation behavior observed in these experiments were only possible through the combined application of voltage and temperature control. To obtain these results, a potentiostat was connected to a modified cuvette in order to apply voltage to a solution. Changes in polymer particle size were monitored using DLS in the presence of constant voltage. Simultaneously, current data were produced, which could be compared with particle size data, to understand the relationship between current and particle behavior. The polymer poly(N-isopropylacrylamide) (pNIPAM) served as a test polymer for this technique, as pNIPAM's response to temperature is well-studied. Changes in the lower-critical solution temperature (LCST) aggregation behavior of pNIPAM and poly(N-isopropylacrylamide)-block-poly(ferrocenylmethyl methacrylate), an electrochemically active block-copolymer, in the presence of applied voltage are observed. Understanding the mechanisms behind such changes will be important when trying to achieve reversible polymer structures in the presence of applied voltage.

Here, a protocol to apply voltage to solution during dynamic light scattering particle size measurements with the intent to explore the effect of voltage and temperature changes on polymer aggregation is presented.

Dynamic light scattering (DLS) is a common method for characterizing the size distribution of polymers, proteins, and other nano- and microparticles. ...