Name: a filter-based surface enhanced raman spectroscopic assay for rapid detection of chemical contaminants
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This material is based upon work supported by the U.S. Department of Homeland Security under Grant Award Number 2010-ST-061-FD0001 through a grant awarded by the National Center for Food Protection and Defense at the University of Minnesota. Disclaimer: The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Department of Homeland Security or the National Center for Food Protection and Defense.

1. Silver Nanoparticle Synthesis15
<ol>
	<li>Dissolve 18 mg silver nitrate in 100 ml ultrapure water (18.2 &#937;U) and vortex for 5 sec.</li>
	<li>Dissolve 27 mg sodium citrate dihydrate in 1 ml water and vortex for 5 sec.</li>
	<li>Transfer all of the prepared silver nitrate solution to a conical flask containing a stirring bar and put the flask on a magnetic hot plate. Heat the flask under vigorous stirring with a stirring speed of 700 rpm at ~350 &#176;C (setting temperature on the plate).</li>
	<li>When...

<ol>
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D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Subnanogram+detection+of+dyes+on+filter+paper+by+surface-enhanced+Raman+scattering+spectrometry.">Subnanogram detection of dyes on filter paper by surface-enhanced Raman scattering spectrometry.</a> Anal. Chem. 56 (4), 824-826 (1984).</li><li>Wu, D., Fang, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+adsorption+behavior+of+p-hydroxybenzoic+acid+on+a+silver-coated+filter+paper+by+surface+enhanced+Raman+scattering.">The adsorption behavior of p-hydroxybenzoic acid on a silver-coated filter paper by surface enhanced Raman scattering.</a> J. Colloid Interface Sci. 265 (2), 234-238 (2003).</li><li>Wigginton, K. R., Vikesland, P. 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One of the critical steps in this protocol is the Ag NPs synthesis, where uniform Ag NPs are the key for consistent results. The heating time and the concentrations of precursors must be precisely controlled. The average size of this AgNPs preparation is 80 nm, which was measured by the Zetasizer (data not shown). Another critical step is the salt aggregation where the salt concentration and aggregation time must be precisely controlled. In addition, the choice of membrane is also critical as the membrane with a smaller ...

Surface enhanced Raman spectroscopy (SERS) is a technique combining Raman spectroscopy with nanotechnology. The intensity of Raman scattering of analytes at noble metallic nano-surfaces is greatly enhanced by the localized surface plasmon resonance.1 Silver nanoparticles (Ag NPs) are by far the most widely used SERS substrates due to its high enhancement ability.2 Up to now, various synthetic methods of Ag NPs have been developed.3-6 Ag NPs can be used alone as effective SERS substrates, or combined with other materials and structures to enhance its sensitivity and/or functionality.7-11
SERS techniques have demonstrated great capacity for detection of various trace amount contaminants in food and environmental samples.12 Traditionally, there are two common ways for preparing a SERS sample: solution-based and substrate-based methods.13 The solution-based method uses NP colloids to mix with samples. Then the NP-analyte complex is collected using centrifugation, and deposited onto a solid support for Raman measurement after drying. The substrate-based method is usually applied by depositing several microliters of liquid sample onto the pre-fabricated solid substrate.14 However, neither of these two methods are effective and applicable for a large amount of sample volume. Several modifications of the SERS assays overcame the volume limits, such as the integration of a filter system15-21 or the incorporation of a microfluidic device.21-24 The modified SERS assays have shown great enhancement in sensitivity and feasibility for monitoring the chemical contaminants in large water samples.
Here we demonstrate the detailed protocol of fabrication and application of a syringe filter based SERS method to detect trace amount of pesticide ferbam and antibiotic ampicillin.

<table border="0" cellpadding="0" cellspacing="0" width="604">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:211px;">Ampicillin</td>
			<td style="width:128px;">Fisher Scientific</td>
			<td style="width:136px;">BP1760-5</td>
			<td style="width:131px;">N/A</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:211px;">Ferbam</td>
			<td style="width:128px;">Chem Service</td>
			<td style="width:136px;">N-11970-250MG</td>
			<td style="width:131px;">98+%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:211px;">Silver nitrate</td>
			<td style="width:128px;">Sigma Aldrich</td>
			<td style="width:136px;">209139</td>
			<td style="width:131px;">99.0+%</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:211px;">Sodium citrate dehydrate</td>
			<td style="width:128px;">Sigma Aldrich</td>
			<td style="width:136px;">W302600</td>
			<td style="width:131px;">99+%</td>
		</tr>
		<tr height="18">
			<td height="18" style="height:19px;width:211px;">Sodium chloride</td>
			<td style="width:128px;">Sigma Aldrich</td>
			<td style="width:136px;">S7653</td>
			<td style="width:131px;">99.5+%</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:211px;">EMD Millipore Durapore PVDF Membrane Filters</td>
			<td style="width:128px;">Fisher Scientific</td>
			<td style="width:136px;">VVLP01300</td>
			<td style="width:131px;">0.10 &#181;m Pore Size, hydrophilic</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:211px;">Polycarbonate Filter Holders</td>
			<td style="width:128px;">Cole-Parmer</td>
			<td style="width:136px;">EW-29550-40</td>
			<td style="width:131px;">13 mm diameter</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Analog Vortex Mixer</td>
			<td style="width:128px;">Fisher Scientific</td>
			<td>02-215-365</td>
			<td>N/A</td>
		</tr>
		<tr height="50">
			<td height="50" style="height:51px;width:211px;">Nutating Mixers</td>
			<td style="width:128px;">Fisher Scientific</td>
			<td>05-450-213</td>
			<td style="width:131px;">N/A</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:211px;">DXR Raman spectroscope</td>
			<td style="width:128px;">Thermo Scientific</td>
			<td style="width:136px;">IQLAADGABFFAHCMAPB</td>
			<td style="width:131px;">Laser power: 1 mW Exposure time: 5 s</td>
		</tr>
	</tbody>
</table>

a filter-based surface enhanced raman spectroscopic assay for rapid detection of chemical contaminants

We demonstrate a method to fabricate highly sensitive surface-enhanced Raman spectroscopic (SERS) substrates using a filter syringe system that can be applied to the detection of various chemical contaminants. Silver nanoparticles (Ag NPs) are synthesized via reduction of silver nitrate by sodium citrate. Then the NPs are aggregated by sodium chloride to form nanoclusters that could be trapped in the pores of the filter membrane. A syringe is connected to the filter holder, with a filter membrane inside. By loading the nanoclusters into the syringe and passing through the membrane, the liquid goes through the membrane but not the nanoclusters, forming a SERS-active membrane. When testing the analyte, the liquid sample is loaded into the syringe and flowed through the Ag NPs coated membrane. The analyte binds and concentrates on the Ag NPs coated membrane. Then the membrane is detached from the filter holder, air dried and measured by a Raman instrument. Here we present the study of the volume effect of Ag NPs and sample on the detection sensitivity as well as the detection of 10 ppb ferbam and 1 ppm ampicillin using the developed assay.

The major steps of this experiment were shown in the schematic diagram (Figure 1). Figure 2 demonstrated the importance to use the optimized volume of AgNPs in the membrane coating in order to reach the maximized sensitivity. 1 ml of Ag NPs provides the strongest signal when using ferbam, as compared to 0.5 ml (insufficient coating) or 2 ml (too much coating).
We were able to detect ferbam at 10...

Watch this Scientific Journal Video about A Filter-based Surface Enhanced Raman Spectroscopic Assay for Rapid Detection of Chemical Contaminants at JoVE.com

A Filter-based Surface Enhanced Raman Spectroscopic Assay for Rapid Detection of Chemical Contaminants

A procedure for fabrication and performing the filter-based surface enhanced Raman spectroscopic (SERS) assay for the detection of chemical contaminants (i.e., pesticide ferbam and antibiotic ampicillin) is presented.

We demonstrate a method to fabricate highly sensitive surface-enhanced Raman spectroscopic (SERS) substrates using a filter syringe system that can be ...

The overall goal of this filter-based Surface Enhanced Raman Spectroscopy method is to detect various target molecules at trace levels in liquid samples. Two advantages of this technique are the reduced costs in sample preparation time, more importantly, this technique provides higher sensitivity by using larger sample volumes, thus lowering the limit of detection. Generally, individuals new to this method will struggle because nano-particles may not be trapped in the pores of the membranewithout a proper aggregation step or they may not be uniformly distributed on the membraneTo begin, prepare 100 milliliters of fresh silver nitrate solution and heat it to boiling on a 350 degree Celsius hotplate with magnetic stirring at 700 RPM.Once boiling, immediately add one milliliter of freshly prepared sodium citrate solution and let the solution boil for 25 minutes. As the silver nano-particles form, the solution will turn greenish-brown. After 25 minutes, put the flask on an unheated stir plate and let it stir overnight at 700 RPM.In the morning, the mixture should be at a stable state, with a constant color and transparency. If desired, measure the absorbence of the nano-particles. Proceed by diluting the mixture with ultra-pure water to 100 milliliters.Then, use a zetasizer to measure the size of the silver nano-particles. For storage, transfer the silver nano-particles to a sealed container. Protect it from light by a foil wrap.The colloid will remain good for up to two months at four degrees Celsius. To make a SERS active filter membranefirst add one milliliter of five millimolar sodium chloride to one milliliter of prepared colloid. And mix them using a nutator at 20 RPM for 10 minutes.As the silver nano-clusters form, prepare a PVDF membranewith a zero point one micron pores. It is critical that the filter holder be completely dry and that the filter is in the correct orientation. After 10 minutes of mixing, filter the two milliliters of nano-clusters by pushing them through the membraneat a rate of about one drop per second.Push the solution through continuously without breaks. The result is a SERS active filter membraneCarefully detach the active filter membraneusing tweezers. Then, set it up to air dry for three minutes.Once dry transfer the SERS active membraneto a glass slide. Now, for Raman detection of the SERS substrate, set the instrument to a 780 nano-meter laser operating at five miliwatts. Set the exposure time to one second and the exposure strength to two.Using a 10 X subjective, focus on the sample. Make sure the software is also set to a 10 X subjective. Now, randomly select eight to 10 spots on the membraneand use the instrument to collect data from them.Then, open the spectral data in the manufacturer's software for analysis. To begin, make a serial dilution of 100 parts per million ferbam solution to obtain five milliliters of 10 parts per billion ferbam solution and 50%acitre-nitrile. Now, position the active membraneinto a filter holder with the nano-particle coating facing up.Then, load the five milliliter sample into a new syringe and attach the active filter. Now, push the sample through the filter at a continuous flow of about one drop per second. Once the solution is filtered, carefully detach the membraneand allow it to air dry for three minutes.Immediately proceed with Raman detection once the membraneis dry. Perform the data collection as before. Various volumes of silver nano-particles were tested using this method.The volume of silver nano-particles solution used to coat the membranethat provided the maximized sensitivity was one milliliter. Measuring the Raman shift shows that the SERS spectrum of 10 parts per billion of ferbam was detectable. The peak, at 1386, is due to the mixed vibration of cyanide and carbon sulfur double bond stretching and from symmetric methyl group deformation.The peak at 1516, is associated with methyl group and cyanide stretching and the peak at 561, is generated by sulfur bond stretching. A spectrum from one parts per million of ampicillin was also clearly detected. The peaks as 1594 and 1447 are from carbon double bond stretching and methylin ethyl group deformation respectively.The strong peak at 1001, is from the benzine ring vibration. The peak at 852 is associated with symmetric CNC stretching. By increasing the sample volume, the detection limit increased.The advantages of this filter based method include an adjustable volume and adjustable limit of detection. After watching this video you should have a good understanding of how to fabricate a uniform sensitive nanosubstrate using a filter membraneOnce mastered this technique can be done in 30 minutes if it is performed properly, following this procedure other methods like SEM or TEM can be performed in order to answer additional questions like the distribution of silver nano-particles on the membraneAfter its development, this technique paved the way for asserters in field of analytical chemistry to explore trace chemical targets in various food and environmental samples. Don't forget that working with pesticides and biological toxins can be extremely hazardous.A lab coat, respirator and safety goggles should always be worn while performing this procedure.

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Chemistry

A Simple and Rapid Protocol for Measuring Neutral Lipids in Algal Cells Using Fluorescence

Algae are considered excellent candidates for renewable fuel sources due to their natural lipid storage capabilities. Robust monitoring of algal fermentation processes and screening for new oil-rich strains requires a fast and reliable protocol for determination of intracellular lipid content. Current practices rely largely on gravimetric methods to determine oil content, techniques developed decades ago that are time consuming and require large sample volumes. In this paper, Nile Red, a fluorescent dye that has been used to identify the presence of lipid bodies in numerous types of organisms, is incorporated into a simple, fast, and reliable protocol for measuring the neutral lipid content of Auxenochlorella protothecoides, a green alga. The method uses ethanol, a relatively mild solvent, to permeabilize the cell membrane before staining and a 96 well micro-plate to increase sample capacity during fluorescence intensity measurements. It has been designed with the specific application of monitoring bioprocess performance. Previously dried samples or live samples from a growing culture can be used in the assay.

A simple protocol to determine the neutral lipid content of algal cells using a Nile Red staining procedure is described. This time-saving technique offers an alternative to traditional gravimetric-based lipid quantification protocols. It has been designed for the specific application of monitoring bioprocess performance.

Algae are considered excellent candidates for renewable fuel sources due to their natural lipid storage capabilities. Robust monitoring of algal ...

A Method to Manipulate Surface Tension of a Liquid Metal via Surface Oxidation and Reduction

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where interfacial tension is a dominant force. A variety of methods exist for controlling the interfacial tension of aqueous and organic liquids on this scale; however, these techniques have limited utility for liquid metals due to their large interfacial tension.
Liquid metals can form soft, stretchable, and shape-reconfigurable components in electronic and electromagnetic devices. Although it is possible to manipulate these fluids via mechanical methods (e.g., pumping), electrical methods are easier to miniaturize, control, and implement. However, most electrical techniques have their own constraints: electrowetting-on-dielectric requires large (kV) potentials for modest actuation, electrocapillarity can affect relatively small changes in the interfacial tension, and continuous electrowetting is limited to plugs of the liquid metal in capillaries.
Here, we present a method for actuating gallium and gallium-based liquid metal alloys via an electrochemical surface reaction. Controlling the electrochemical potential on the surface of the liquid metal in electrolyte rapidly and reversibly changes the interfacial tension by over two orders of magnitude ( &#820;500 mN/m to near zero). Furthermore, this method requires only a very modest potential (&#60; 1 V) applied relative to a counter electrode. The resulting change in tension is due primarily to the electrochemical deposition of a surface oxide layer, which acts as a surfactant; removal of the oxide increases the interfacial tension, and vice versa. This technique can be applied in a wide variety of electrolytes and is independent of the substrate on which it rests.

We present a method to control the interfacial energy of a liquid metal in an electrolyte via electrochemical deposition (or removal) of a surface oxide layer. This simple method can control the capillary behavior of gallium-based liquid metals by tuning the interfacial energy rapidly, significantly, and reversibly using modest voltages.

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where ...

Preparation of Biopolymer Aerogels Using Green Solvents

Although the first reports on aerogels made by Kistler1 in the 1930s dealt with aerogels from both inorganic oxides (silica and others) and biopolymers (gelatin, agar, cellulose), only recently have biomasses been recognized as an abundant source of chemically diverse macromolecules for functional aerogel materials. Biopolymer aerogels (pectin, alginate, chitosan, cellulose, etc.) exhibit both specific inheritable functions of starting biopolymers and distinctive features of aerogels (80-99% porosity and specific surface up to 800 m2/g). This synergy of properties makes biopolymer aerogels promising candidates for a wide gamut of applications such as thermal insulation, tissue engineering and regenerative medicine, drug delivery systems, functional foods, catalysts, adsorbents and sensors. This work demonstrates the use of pressurized carbon dioxide (5 MPa) for the ionic cross linking of amidated pectin into hydrogels. Initially a biopolymer/salt dispersion is prepared in water. Under pressurized CO2 conditions, the pH of the biopolymer solution is lowered to 3 which releases the crosslinking cations from the salt to bind with the biopolymer yielding hydrogels. Solvent exchange to ethanol and further supercritical CO2 drying (10 - 12 MPa) yield aerogels. Obtained aerogels are ultra-porous with low density (as low as 0.02 g/cm3), high specific surface area (350 - 500 m2/g) and pore volume (3 - 7 cm3/g for pore sizes less than 150 nm).

A new way for the production of biopolymer-based aerogels by carbon dioxide (CO2) induced gelation is shown. The technique utilizes pressurized carbon dioxide (5 MPa) for the production of biopolymer hydrogels and supercritical CO2 (12 MPa) to convert gels into aerogels. The only solvents needed besides CO2 are water and ethanol.

Although the first reports on aerogels made by Kistler1 in the 1930s dealt with aerogels from both inorganic oxides (silica and others) and biopolymers ...

A Novel Technique for Raman Analysis of Highly Radioactive Samples Using Any Standard Micro-Raman Spectrometer

A novel approach for the Raman measurement of nuclear materials is reported in this paper. It consists of the enclosure of the radioactive sample in a tight capsule that isolates the material from the atmosphere. The capsule can optionally be filled with a chosen gas pressurized up to 20 bars. The micro-Raman measurement is performed through an optical-grade quartz window. This technique permits accurate Raman measurements with no need for the spectrometer to be enclosed in an alpha-tight containment. It therefore allows the use of all options of the Raman spectrometer, like multi-wavelength laser excitation, different polarizations, and single or triple spectrometer modes. Some examples of measurements are shown and discussed. First, some spectral features of a highly radioactive americium oxide sample (AmO2) are presented. Then, we report the Raman spectra of neptunium oxide (NpO2) samples, the interpretation of which is greatly improved by employing three different excitation wavelengths, 17O doping, and a triple mode configuration to measure the anti-stokes Raman lines. This last feature also allows the estimation of the sample surface temperature. Finally, data that were measured on a sample from Chernobyl lava, where phases are identified by Raman mapping, are shown.

We present a technique for Raman spectroscopic analysis of highly radioactive samples compatible with any standard micro-Raman spectrometer, without any radioactive contamination of the instrument. We also show some applications using actinide compounds and irradiated fuel materials.

A novel approach for the Raman measurement of nuclear materials is reported in this paper. It consists of the enclosure of the radioactive sample in a ...

Observation and Analysis of Blinking Surface-enhanced Raman Scattering

From a single molecule at a silver nanoaggregate junction, blinking surface-enhanced Raman scattering (SERS) is observed. Here, a protocol is presented on how to prepare the SERS-active silver nanoaggregate, record a video of certain blinking spots in the microscopic image, and analyze the blinking statistics. In this analysis, a power law reproduces the probability distributions for bright events relative to their duration. The probability distributions for dark events are fitted by a power law with an exponential function. The parameters of the power law represent molecular behavior in both bright and dark states. The random walk model and the speed of the molecule across the entire silver surface can be estimated. It is difficult to estimate even when using averages, autocorrelation functions, and super-resolution SERS imaging. In the future, power law analyses should be combined with spectral imaging, because the origins of blinking cannot be confirmed by this analysis method alone.

This protocol describes the analysis of blinking surface-enhanced Raman scattering due to the random walk of a single molecule on a silver surface using power laws.

From a single molecule at a silver nanoaggregate junction, blinking surface-enhanced Raman scattering (SERS) is observed. Here, a protocol is presented on ...

Color Spot Test As a Presumptive Tool for the Rapid Detection of Synthetic Cathinones

Synthetic cathinones are a large class of new psychoactive substances (NPS) that are increasingly prevalent in drug seizures made by law enforcement and other border protection agencies globally. Color testing is a presumptive identification technique indicating the presence or absence of a particular drug class using rapid and uncomplicated chemical methods. Owing to their relatively recent emergence, a color test for the specific identification of synthetic cathinones is not currently available. In this study, we introduce a protocol for the presumptive identification of synthetic cathinones, employing three aqueous reagent solutions: copper(II) nitrate, 2,9-dimethyl-1,10-phenanthroline (neocuproine) and sodium acetate. Small pin-head sized amounts (approximately 0.1-0.2 mg) of the suspected drugs are added to the wells of a porcelain spot plate, and each reagent is then added dropwise sequentially before heating on a hotplate. A color change from very light blue to yellow-orange after 10 min indicates the likely presence of synthetic cathinones. The highly stable and specific test reagent has the potential for use in the presumptive screening of unknown samples for synthetic cathinones in a forensic laboratory. However, the nuisance of an added heating step for the color change result limits the test to laboratory application and decreases the likelihood of an easy translation to field testing.

Here we present a simple, inexpensive, and selective chemical spot test protocol for the detection of synthetic cathinones, a class of new psychoactive substances. The protocol is suitable for use in various areas of law enforcement that encounter illicit material.

Synthetic cathinones are a large class of new psychoactive substances (NPS) that are increasingly prevalent in drug seizures made by law enforcement and ...

Gold Nanoparticle Modified Carbon Fiber Microelectrodes for Enhanced Neurochemical Detection

For over 30 years, carbon-fiber microelectrodes (CFMEs) have been the standard for neurotransmitter detection. Generally, carbon fibers are aspirated into glass capillaries, pulled to a fine taper, and then sealed using an epoxy to create electrode materials that are used for fast scan cyclic voltammetry testing. The use of bare CFMEs has several limitations, though. First and foremost, the carbon fiber contains mostly basal plane carbon, which has a relatively low surface area and yields lower sensitivities than other nanomaterials. Furthermore, the graphitic carbon is limited by its temporal resolution, and its relatively low conductivity. Lastly, neurochemicals and macromolecules have been known to foul at the surface of carbon electrodes where they form non-conductive polymers that block further neurotransmitter adsorption. For this study, we modify CFMEs with gold nanoparticles to enhance neurochemical testing with fast scan cyclic voltammetry. Au3+ was electrodeposited or dipcoated from a colloidal solution onto the surface of CFMEs. Since gold is a stable and relatively inert metal, it is an ideal electrode material for analytical measurements of neurochemicals. Gold nanoparticle modified (AuNP-CFMEs) had a stability to dopamine response for over 4 h. Moreover, AuNP-CFMEs exhibit an increased sensitivity (higher peak oxidative current of the cyclic voltammograms) and faster electron transfer kinetics (lower &#916;EP or peak separation) than bare unmodified CFMEs. The development of AuNP-CFMEs provides the creation of novel electrochemical sensors for detecting fast changes in dopamine concentration and other neurochemicals at lower limits of detection. This work has vast applications for the enhancement of neurochemical measurements. The generation of gold nanoparticle modified CFMEs will be vitally important for the development of novel electrode sensors to detect neurotransmitters in vivo in rodent and other models to study neurochemical effects of drug abuse, depression, stroke, ischemia, and other behavioral and disease states.

In this study, we modify carbon-fiber microelectrodes with gold nanoparticles to enhance the sensitivity of neurotransmitter detection.

For over 30 years, carbon-fiber microelectrodes (CFMEs) have been the standard for neurotransmitter detection. Generally, carbon fibers are aspirated into ...

A Two-Step Pyrolysis-Gas Chromatography Method with Mass Spectrometric Detection for Identification of Tattoo Ink Ingredients and Counterfeit Products

Tattoo inks are complex mixtures of ingredients. Each of them possesses different chemical properties which have to be addressed upon chemical analysis. In this method for two-step pyrolysis online coupled to gas chromatography mass spectrometry (py-GC-MS) volatile compounds are analyzed during a first desorption run. In the second run, the same dried sample is pyrolyzed for analysis of non-volatile compounds such as pigments and polymers. These can be identified by their specific decomposition patterns. Additionally, this method can be used to differentiate original from counterfeit inks. Easy screening methods for data evaluation using the average mass spectra and self-made pyrolysis libraries are applied to speed up substance identification. Using specialized evaluation software for pyrolysis GS-MS data, a fast and reliable comparison of the full chromatogram can be achieved. Since GC-MS is used as separation technique, the method is limited to volatile substances upon desorption and after pyrolysis of the sample. The method can be applied for quick substance screening in market control surveys since it requires no sample preparation steps.

This method for two-step pyrolysis online coupled to gas chromatography with mass spectrometric detection and data evaluation protocol can be used for multi-component analysis of tattoo inks and discrimination of counterfeit products.

Tattoo inks are complex mixtures of ingredients. Each of them possesses different chemical properties which have to be addressed upon chemical analysis. ...

Preparation of Nanoparticles for ToF-SIMS and XPS Analysis

Nanoparticles have gained increasing attention in recent years due to their potential and application in different fields including medicine, cosmetics, chemistry, and their potential to enable advanced materials. To effectively understand and regulate the physico-chemical properties and potential adverse effects of nanoparticles, validated measurement procedures for the various properties of nanoparticles need to be developed. While procedures for measuring nanoparticle size and size distribution are already established, standardized methods for analysis of their surface chemistry are not yet in place, although the influence of the surface chemistry on nanoparticle properties is undisputed. In particular, storage and preparation of nanoparticles for surface analysis strongly influences the analytical results from various methods, and in order to obtain consistent results, sample preparation must be both optimized and standardized. In this contribution, we present, in detail, some standard procedures for preparing nanoparticles for surface analytics. In principle, nanoparticles can be deposited on a suitable substrate from suspension or as a powder. Silicon (Si) wafers are commonly used as substrate, however, their cleaning is critical to the process. For sample preparation from suspension, we will discuss drop-casting and spin-coating, where not only the cleanliness of the substrate and purity of the suspension but also its concentration play important roles for the success of the preparation methodology. For nanoparticles with sensitive ligand shells or coatings, deposition as powders is more suitable, although this method requires particular care in fixing the sample.

A number of different procedures for preparing nanoparticles for surface analysis are presented (drop casting, spin coating, deposition from powders, and cryofixation). We discuss the challenges, opportunities, and possible applications of each method, particularly regarding the changes in the surface properties caused by the different preparation methods.

Nanoparticles have gained increasing attention in recent years due to their potential and application in different fields including medicine, cosmetics, ...

Direct Comparison of Hyperspectral Stimulated Raman Scattering and Coherent Anti-Stokes Raman Scattering Microscopy for Chemical Imaging

Stimulated Raman scattering (SRS) and coherent anti-Stokes Raman scattering (CARS) microscopy are the most widely used coherent Raman scattering imaging technologies. Hyperspectral SRS and CARS imaging offer Raman spectral information at every pixel, which enables better separation of different chemical compositions. Although both techniques require two excitation lasers, their signal detection schemes and spectral properties are quite different. The goal of this protocol is to perform both hyperspectral SRS and CARS imaging on a single platform and compare the two microscopy techniques for imaging different biological samples. The spectral focusing method is employed to acquire spectral information using femtosecond lasers. By using standard chemical samples, the sensitivity, spatial resolution, and spectral resolution of SRS and CARS in the same excitation conditions (i.e., power at the sample, pixel dwell time, objective lens, pulse energy) are compared. The imaging contrasts of CARS and SRS for biological samples are juxtaposed and compared. The direct comparison of CARS and SRS performances would allow for optimal selection of the modality for chemical imaging.

This paper directly compares the resolution, sensitivity, and imaging contrasts of stimulated Raman scattering (SRS) and coherent anti-Stokes Raman scattering (CARS) integrated into the same microscope platform. The results show that CARS has a better spatial resolution, SRS gives better contrasts and spectral resolution, and both methods have similar sensitivity.

Stimulated Raman scattering (SRS) and coherent anti-Stokes Raman scattering (CARS) microscopy are the most widely used coherent Raman scattering imaging ...