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 boiling, add all of the prepared sodium citrate solution to the conical flask immediately, and leave the solution to boil for an additional 25 min until the solution turns greenish brown, which indicates the formation of Ag NPs.</li>
	<li>Remove the flask from the hot plate and put it on another magnetic plate (do not heat) and stir O/N&#160;at the same stirring speed at RT until the mixture reaches a stable state, with a constant color and transparency. Use a UV-vis spectrometer to determine the absorbance of the prepared Ag NPs if necessary.</li>
	<li>Dilute the final mixture with ultrapure water to 100 ml.</li>
	<li>Use a Zetasizer to measure the size of the Ag NPs if necessary according to manufacturer&#39;s protocol.</li>
	<li>Transfer the Ag colloid to a sealed container and protect it from light with aluminum foil. The colloid can be stored in a refrigerator at 4-7 &#176;C for 2 months if needed.</li>
</ol>
2. Fabrication of a SERS Active Filter Membrane
<ol>
	<li>Dissolve 2.92 g sodium chloride (NaCl) in 100 ml water to make a 50 mM NaCl solution.</li>
	<li>Add 1 ml of the 5 mM NaCl solution into 1 ml of the prepared Ag NPs and mix them on a nutating mixer for 10 min at 20 rpm. This step is to aggregate the Ag NPs into Ag nanoclusters.</li>
	<li>Place a filter membrane (PVDF, 0.1 &#181;m pore size) into a filter holder, which can be attached to a syringe. The smaller pore size membrane was found more effective than the larger pore size membrane (i.e., 0.22 &#181;m) in trapping Ag nanoclusters and producing consistent signals.</li>
	<li>Load 2 ml of the prepared Ag nanoclusters into the syringe for filtration. Attach the filter holder to the syringe and manually pass the entire volume of Ag nanoclusters through the membrane at the flow rate of 1 drop/sec. The membrane traps Ag nanoclusters, forming a SERS-active filter membrane.</li>
	<li>Detach the filter membrane from the filter holder. Special caution is needed when holding the membrane on the outer rim using a pair of tweezers to ensure no damage to the membrane. Air dry for about 3 min and place membrane on a glass slide.</li>
	<li>Raman detection of the SERS substrate
	<ol>
		<li>Set the Raman instrument to a 780 nm wavelength laser with a laser power of 5 mW, exposure time of 1 sec and exposure number of 2. Set the microscopic objective to 10X. Make sure the objective on the software is set accordingly too.</li>
		<li>Place the glass slide with the membrane on top onto the platform of the Raman instrument and use the microscope to focus on the surface of the membrane.</li>
		<li>Randomly select 8-10 spots from the membrane surface and the instrument will collect them automatically in sequence. Open spectral data in manufacturer&#39;s software for analysis.</li>
	</ol>
	</li>
</ol>
3. Application of the SERS Active Filter System to Detect Chemical Contaminants
<ol>
	<li>Prepare a 10 ppb ferbam solution. 
	Caution: Ferbam is highly volatile. Use precautions (respirator and goggles) when weighing the solid.
	<ol>
		<li>Weigh 2 mg ferbam powder and dissolve it in 20 ml 50% acetonitrile (10 ml acetonitrile and 10 ml water) to make a stock solution (100 ppm). Vortex the flask for 30 sec.</li>
		<li>Take 1 ml of the 100 ppm ferbam solution in a test tube and add 9 ml 50% acetonitrile to make a 10 ppm solution. Vortex the tube for 5 sec.</li>
		<li>Take 1 ml of the 10 ppm solution in a test tube and add 9 ml 50% acetonitrile to make a 1 ppm solution. Vortex the tube for 5 sec.</li>
		<li>Take 1 ml of the 1 ppm solution in a test tube and add 9 ml 50% acetonitrile to make a 100 ppb solution. Vortex the tube for 5 sec.</li>
		<li>Take 1 ml of the 100 ppb solution in a test tube and add 9 ml 50% acetonitrile to make a 10 ppb solution. Vortex the tube for 5 sec.</li>
	</ol>
	</li>
	<li>Prepare a 1 ppm ampicillin solution.
	<ol>
		<li>Weigh 10 mg ampicillin powder and dissolve it in 100 ml water to make a 100 ppm ampicillin solution. Vortex the flask for 30 sec.</li>
		<li>Take 1 ml of the 100 ppm solution in a test tube and add 9 ml water to make a 10 ppm ampicillin solution. Vortex the tube for 5 sec.</li>
		<li>Take 1 ml of the 10 ppm solution in a test tube and add 9 ml water to make a 1 ppm ampicillin solution. Vortex the tube for 5 sec.</li>
	</ol>
	</li>
	<li>Put the filter membrane back to the filter holder, with the NP coated side facing up.</li>
	<li>Load 5 ml of one sample into a new syringe, and then attach it to the filter holder with a Ag coated membrane inside.</li>
	<li>Manually pass the entire volume of sample through the membrane at the flow rate of 1 drop/sec. Target molecules can be adsorbed and concentrated onto the NPs coated on the filter membrane.</li>
	<li>Detach filter membrane from the filter holder, air dry for about 3 min and measure the signals using the Raman instrument using the same method as described in step 2.6.</li>
	<li>Repeat step 2.2 to 2.6 to prepare another Ag-coated membrane, and follow from step 3.3 for the detection of the other sample.</li>
</ol>

<ol>
	<li>Albrecht, M. G., Creighton, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anomalously+intense+Raman+spectra+of+pyridine+at+a+silver+electrode.">Anomalously intense Raman spectra of pyridine at a silver electrode.</a> J. Am. Chem. Soc. 99 (15), 5215-5217 (1977).</li><li>Schatz, G. C., Young, M. A., Van Duyne, R. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Electromagnetic mechanism of SERS. Surface-enhanced Raman scattering. , 19-45 (2006).</li><li>Matijevic, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+and+properties+of+uniform+size+colloids.">Preparation and properties of uniform size colloids.</a> Chem. Mater. 5 (4), 412-426 (1993).</li><li>Nickel, U., zu Castell, A., P&#246;ppl, K., Schneider, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+silver+colloid+produced+by+reduction+with+hydrazine+as+support+for+highly+sensitive+surface-enhanced+Raman+spectroscopy.">A silver colloid produced by reduction with hydrazine as support for highly sensitive surface-enhanced Raman spectroscopy.</a> Langmuir. 16 (23), 9087-9091 (2000).</li><li>Khanna, P. K., Subbarao, V. V. V. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanosized+silver+powder+via+reduction+of+silver+nitrate+by+sodium+formaldehydesulfoxylate+in+acidic+pH+medium.">Nanosized silver powder via reduction of silver nitrate by sodium formaldehydesulfoxylate in acidic pH medium.</a> Mater. Lett. 57 (15), 2242-2245 (2003).</li><li>Henglein, A., Giersig, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Formation+of+colloidal+silver+nanoparticles:+capping+action+of+citrate.">Formation of colloidal silver nanoparticles: capping action of citrate.</a> J. Phys. Chem. B. 103 (44), 9533-9539 (1999).</li><li>Sun, X., Li, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Colloidal+carbon+spheres+and+their+core/shell+structures+with+noble-metal+nanoparticles.">Colloidal carbon spheres and their core/shell structures with noble-metal nanoparticles.</a> Angew. Chem. Int. Edit. 43 (5), 597-601 (2004).</li><li>Lu, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Seed-mediated+growth+of+large,+monodisperse+core-shell+gold-silver+nanoparticles+with+Ag-like+optical+properties.">Seed-mediated growth of large, monodisperse core-shell gold-silver nanoparticles with Ag-like optical properties.</a> Chem. Commun. (2), 144-145 (2002).</li><li>Aslan, K., Wu, M., Lakowicz, J. R., Geddes, C. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluorescent+core-shell+Ag@SiO2+nanocomposites+for+metal-enhanced+fluorescence+and+single+nanoparticle+sensing+platforms.">Fluorescent core-shell Ag@SiO2 nanocomposites for metal-enhanced fluorescence and single nanoparticle sensing platforms.</a> J. Am. Chem. Soc. 129 (6), 1524-1525 (2007).</li><li>Lu, Y., Yin, Y., Li, Z. Y., Xia, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+and+self-assembly+of+Au@+SiO2+core-shell+colloids.">Synthesis and self-assembly of Au@ SiO2 core-shell colloids.</a> Nano. Lett. 2 (7), 785-788 (2002).</li><li>Link, S., Wang, Z. L., El-Sayed, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Alloy+formation+of+gold-silver+nanoparticles+and+the+dependence+of+the+plasmon+absorption+on+their+composition.">Alloy formation of gold-silver nanoparticles and the dependence of the plasmon absorption on their composition.</a> J. Phys. Chem. B. 103 (18), 3529-3533 (1999).</li><li>He, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+Detection+of+Ricin+in+Milk+Using+Immunomagnetic+Separation+Combined+with+Surface+Enhanced+Raman+Spectroscopy.">Rapid Detection of Ricin in Milk Using Immunomagnetic Separation Combined with Surface Enhanced Raman Spectroscopy.</a> J. Food. Sci. 76 (5), N49-N53 (2011).</li><li>Zheng, J., He, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface-Enhanced+Raman+Spectroscopy+for+the+Chemical+Analysis+of+Food.">Surface-Enhanced Raman Spectroscopy for the Chemical Analysis of Food.</a> Compr. Rev. Food. Sci. F. 13 (3), 317-328 (2014).</li><li>He, L., Haynes, C. L., Diez-Gonzalez, F., Labuza, T. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+detection+of+a+foreign+protein+in+milk+using+IMS-SERS.">Rapid detection of a foreign protein in milk using IMS-SERS.</a> J. Raman. Spectrosc. 42 (6), 1428-1434 (2011).</li><li>Wei, W. Y., White, I. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+simple+filter-based+approach+to+surface+enhanced+Raman+spectroscopy+for+trace+chemical+detection.">A simple filter-based approach to surface enhanced Raman spectroscopy for trace chemical detection.</a> Analyst. 137 (5), 1168-1173 (2012).</li><li>Cheng, M. L., Tsai, B. C., Yang, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Silver+nanoparticle-treated+filter+paper+as+a+highly+sensitive+surface-enhanced+Raman+scattering+(SERS)+substrate+for+detection+of+tyrosine+in+aqueous+solution.">Silver nanoparticle-treated filter paper as a highly sensitive surface-enhanced Raman scattering (SERS) substrate for detection of tyrosine in aqueous solution.</a> Anal. Chim. Acta. 708 (1), 89-96 (2011).</li><li>Fierro-Mercado, P. M., Hern&#225;ndez-Rivera, S. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+sensitive+filter+paper+substrate+for+SERS+trace+explosives+detection.">Highly sensitive filter paper substrate for SERS trace explosives detection.</a> Int. J. Spectrosc. 2012, 716527 (2012).</li><li>Tran, C. 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. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gold-coated+polycarbonate+membrane+filter+for+pathogen+concentration+and+SERS-based+detection.">Gold-coated polycarbonate membrane filter for pathogen concentration and SERS-based detection.</a> Analyst. 135 (6), 1320-1326 (2010).</li><li>Berthod, A., Laserna, J. J., Winefordner, J. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+by+surface+enhanced+Raman+spectroscopy+on+silver+hydrosols+and+silver+coated+filter+papers.">Analysis by surface enhanced Raman spectroscopy on silver hydrosols and silver coated filter papers.</a> J Pharm Biomed Anal. 6 (6), 599-608 (1988).</li><li>Ackermann, K. R., Henkel, T., Popp, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+Online+Detection+of+Low-Concentrated+Drugs+via+a+SERS+Microfluidic+System.">Quantitative Online Detection of Low-Concentrated Drugs via a SERS Microfluidic System.</a> ChemPhysChem. 8 (18), 2665-2670 (2007).</li><li>Walter, A., M&#228;rz, A., Schumacher, W., R&#246;sch, P., Popp, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Towards+a+fast,+high+specific+and+reliable+discrimination+of+bacteria+on+strain+level+by+means+of+SERS+in+a+microfluidic+device.">Towards a fast, high specific and reliable discrimination of bacteria on strain level by means of SERS in a microfluidic device.</a> Lab. Chip. 11 (6), 1013-1021 (2011).</li><li>Lee, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fast+and+sensitive+trace+analysis+of+malachite+green+using+a+surface-enhanced+Raman+microfluidic+sensor.">Fast and sensitive trace analysis of malachite green using a surface-enhanced Raman microfluidic sensor.</a> Anal. Chim. Acta. 590 (2), 139-144 (2007).</li><li>Guo, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+Silver+Nanoparticles+in+Antimicrobial+Products+Using+Surface-Enhanced+Raman+Spectroscopy+(SERS).">Analysis of Silver Nanoparticles in Antimicrobial Products Using Surface-Enhanced Raman Spectroscopy (SERS).</a> Environ. Sci. Technol. 49 (7), 4317-4324 (2015).</li><li>Narayanan, V. A., Begun, G. M., Stokes, D. L., Sutherland, W. S., Vo-Dinh, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Normal+Raman+and+surface+enhanced+Raman+scattering+(SERS)+spectra+of+some+fungicides+and+related+chemical+compounds.">Normal Raman and surface enhanced Raman scattering (SERS) spectra of some fungicides and related chemical compounds.</a> J. Raman. Spectrosc. 23 (5), 281-286 (1992).</li><li>Kang, J. S., Hwang, S. Y., Lee, C. J., Lee, M. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=SERS+of+dithiocarbamate+pesticides+adsorbed+on+silver+surface;+thiram.">SERS of dithiocarbamate pesticides adsorbed on silver surface; thiram.</a> Bull. Korean. Chem. Soc. 23 (11), 1604-1610 (2002).</li><li>Li, Y. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+and+sensitive+in-situ+detection+of+polar+antibiotics+in+water+using+a+disposable+Ag-graphene+sensor+based+on+electrophoretic+preconcentration+and+surface-enhanced+Raman+spectroscopy.">Rapid and sensitive in-situ detection of polar antibiotics in water using a disposable Ag-graphene sensor based on electrophoretic preconcentration and surface-enhanced Raman spectroscopy.</a> Biosens. Bioelectron. 43, 94-100 (2013).</li><li>Clarke, S. J., Littleford, R. E., Smith, W. E., Goodacre, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+monitoring+of+antibiotics+using+Raman+and+surface+enhanced+Raman+spectroscopy.">Rapid monitoring of antibiotics using Raman and surface enhanced Raman spectroscopy.</a> Analyst. 130 (7), 1019-1026 (2005).</li><li>Zheng, J., Pang, S., Labuza, T. P., He, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Semi-quantification+of+surface-enhanced+Raman+scattering+using+a+handheld+Raman+spectrometer:+a+feasibility+study.">Semi-quantification of surface-enhanced Raman scattering using a handheld Raman spectrometer: a feasibility study.</a> Analyst. 138 (23), 7075-7078 (2013).</li><li>Zheng, J., Pang, S., Labuza, T. P., He, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+surface-enhanced+Raman+scattering+detection+using+a+handheld+and+a+bench-top+Raman+spectrometer:+A+comparative+study.">Evaluation of surface-enhanced Raman scattering detection using a handheld and a bench-top Raman spectrometer: A comparative study.</a> Talanta. 129, 79-85 (2014).</li></ol>

The authors have nothing to disclose.

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 pore size was found more effective to trap Ag nanoclusters. For the particular membrane used in this study, there is a front and back side where the front side must be placed up in the holder to connect the syringe. If it was placed down, the coating was much less effective. Avoiding bubbles when passing through the membrane is another key to a successful coating.
For troubleshooting of this assay, the following steps are recommended. If no or little signal is detected, check for the following causes. The main cause could be the Ag NPs are not aggregated enough to be trapped in the pores of the filter membrane. Increasing the salt concentration and/or incubation time can enhance the aggregation. Otherwise, check that the backside of the filter membrane is facing up and that the volume or concentration of sample loaded on to the membrane is not too low. If the signal of the target molecule is not consistent, check for the following causes: the size distribution of the Ag NPs may be too broad or the NPs are not evenly distributed on the membrane, probably due to too much aggregation of NPs or too fast passing through the membrane.
Compared with our previous data on using Ag dendrites as SERS substrate,30-31 the sensitivity of this filter-based SERS assay is much higher on ferbam detection. This is due to the advantage of the filter-based system, which can flow large amount of sample, so that more analyte molecules are concentrated onto the SERS substrate. Another advantage of using the filter-based system over the solution-based method is the ease of operation and fieldable measurement, as no centrifugation is needed to collect the NP-analyte complex. The limitation of this method is it cannot be used for complex liquid matrices such as milk directly, as the complex components can block the membrane pores. Pretreatment is needed to remove interfering components before passing the membrane.
In summary, we demonstrate a simple and sensitive filter-based SERS assay, which could be applied to the detection of contaminants or adulterations in liquid food matrix and environmental samples. To further push the limit of detection, optimization of the parameters, such as NP sizes and amount, salt concentration, sample volume and instrument parameters is needed.

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 ppb level and ampicillin at 1 ppm with great signal intensity by the developed filter-based SERS assay (Figure 1). The SERS spectrum of ferbam exhibits distinct characteristic peaks at 10 ppb. The peak at 1,386 cm-1 is from the mixed vibration of CN and C=S stretching, and symmetric CH3 deformation. The peak at 1,516 cm-1 is associated with CH3 and CN stretching. The peak at 561 cm-1 is generated by SS streching.25-27 The spectrum of 1 ppm ampicillin was also clearly detected. The peak at 1,594 cm-1 and 1,447 cm-1 are from C=C stretching and CH3/CH2 deformation, respectively. The strong peak at 1,001 cm-1 is from the benzene ring vibration. The peak at 852 cm-1 is associated with symmetric CNC stretching.28-29 The experimental time for analyzing one sample is less than 20 min including the fabrication of SERS-active filter membrane with pre-synthesized Ag NPs.
With increasing sample volume, we can further increase the detection limit, as shown in Figure 4. We observed an increase of peak intensity when increasing the sample volume. This is the advantage of the filter based method as the volume is adjustable and the limit of detection is also adjustable.
<img alt="Figure 1" src="/files/ftp_upload/53791/53791fig1.jpg" /> 
Figure 1. A schematic diagram of filter SERS assay. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53791/53791fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/53791/53791fig2.jpg" /> 
Figure 2. SERS spectra of 5 ml 100 ppb ferbam passing through the membranes coated by different amount of Ag NPs. From top to bottom: 0.5 ml Ag colloid with 0.5 ml NaCl, 1.0 ml Ag with 1.0 ml NaCl, 1.5 ml Ag with 1.5 ml NaCl, respectively. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53791/53791fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/53791/53791fig3.jpg" /> 
Figure 3. SERS spectra of ferbam and ampicillin on Ag NPs coated filter membrane. From top to bottom: control of 50% acetonitrile, 10 ppb ferbam, control of water, 1 ppm Ampicillin, respectively. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53791/53791fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/53791/53791fig4.jpg" /> 
Figure 4. SERS spectra of different volumes of 100 ppb ferbam on Ag NPs coated filter membrane. From top to bottom: 3 ml ferbam, 5 ml ferbam, 7 ml ferbam, 9 ml ferbam, respectively. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53791/53791fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

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 ...

a-filter-based-surface-enhanced-raman-spectroscopic-assay-for-rapid

Nanyang Technological University

Research

JoVE Journal

Chemistry

9.3K Views.  University of Massachusetts Amherst. 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.

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

Preparation of Hydrophobic Metal-Organic Frameworks via Plasma Enhanced Chemical Vapor Deposition of Perfluoroalkanes for the Removal of Ammonia

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high surface area microporous materials, such as metal-organic frameworks (MOFs), unique challenges present themselves for PECVD treatments. Herein the protocol for development of a MOF that was previously unstable to humid conditions is presented. The protocol describes the synthesis of Cu-BTC (also known as HKUST-1), the treatment of Cu-BTC with PECVD of perfluoroalkanes, the aging of materials under humid conditions, and the subsequent ammonia microbreakthrough experiments on milligram quantities of microporous materials. Cu-BTC has an extremely high surface area (~1,800 m2/g) when compared to most materials or surfaces that have been previously treated by PECVD methods. Parameters such as chamber pressure and treatment time are extremely important to ensure the perfluoroalkane plasma penetrates to and reacts with the inner MOF surfaces. Furthermore, the protocol for ammonia microbreakthrough experiments set forth here can be utilized for a variety of test gases and microporous materials.

Herein the procedures for plasma enhanced chemical vapor deposition of perfluoroalkanes on microporous materials such as metal-organic frameworks to enhance their stability and hydrophobicity are described. Furthermore, breakthrough testing of milligram quantities of samples is described in detail.

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high ...

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 ...

Preparation of Highly Porous Coordination Polymer Coatings on Macroporous Polymer Monoliths for Enhanced Enrichment of Phosphopeptides

We describe a protocol for the preparation of hybrid materials based on highly porous coordination polymer coatings on the internal surface of macroporous polymer monoliths. The developed approach is based on the preparation of a macroporous polymer containing carboxylic acid functional groups and the subsequent step-by-step solution-based controlled growth of a layer of a porous coordination polymer on the surface of the pores of the polymer monolith. The prepared metal-organic polymer hybrid has a high specific micropore surface area. The amount of iron(III) sites is enhanced through metal-organic coordination on the surface of the pores of the functional polymer support. The increase of metal sites is related to the number of iterations of the coating process.
The developed preparation scheme is easily adapted to a capillary column format. The functional porous polymer is prepared as a self-contained single-block porous monolith within the capillary, yielding a flow-through separation device with excellent flow permeability and modest back-pressure. The metal-organic polymer hybrid column showed excellent performance for the enrichment of phosphopeptides from digested proteins and their subsequent detection using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The presented experimental protocol is highly versatile, and can be easily implemented to different organic polymer supports and coatings with a plethora of porous coordination polymers and metal-organic frameworks for multiple purification and/or separation applications.

A procedure for the preparation of porous hybrid separation media composed of a macroporous polymer monolith internally coated by a high surface area microporous coordination polymer is presented.

We describe a protocol for the preparation of hybrid materials based on highly porous coordination polymer coatings on the internal surface of macroporous ...

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. ...