A portable, autonomous, hand-held chemical laboratory ({micro}ChemLab{trademark}) is being developed for trace detection (ppb) of chemical warfare (CW) agents and explosives in real-world environments containing high concentrations of interfering compounds. Microfabrication is utilized to provide miniature, low-power components that are characterized by rapid, sensitive and selective response. Sensitivity and selectivity are enhanced using two parallel analysis channels, each containing the sequential connection of a front-end sample collector/concentrator, a gas chromatographic (GC) separator, and a surface acoustic wave (SAW) detector. Component design and fabrication and system performance are described

Casalnuovo, Stephen A.

Frye-Mason, Gregory C

Heller, Edwin J.

Hietala, Vincent M.

Kottenstette, Richard J.

Lewis, Patrick R.

Manginell, Ronald P.

Matzke, Carolyn M.

Wong, C. Channy

FRYE-MASON,GREGORY CHARLES

HELLER,EDWIN J.

HIETALA,VINCENT M.

KOTTENSTETTE,RICHARD

LEWIS,PATRICK R.

MANGINELL,RONALD P.

MATZKE,CAROLYN M.

WONG,CHUNGNIN C.

UNT Digital Library

59/m 7?”244=Microfabricated Gas Phase Chemical Analysis SystemsGregory C. Frye-Mason, Ronald P. Mamzinell, Edwin J. Heller, Carolyn M. Matzke, Stephen A. Casalnuovo, *Vincent M. Hietal~ Richard J. Kottenstette, Patrick R. Lewis and C. Channy Wong fi% ‘oSandia National Laboratories @$*P.O. Box 5800 MS-1425, Albuquerque, NM 87185-1425.—. . tf3 &44rpmangi@sandia.govABSTRACTA portable, autonomous, hand-held chemical laboratory(pChernLabT~ is being developed for trace detection (ppb)of chemical warfhre (CW) agents and explosives in real-world environments containing high concentrations ofinterfering compounds. Microfabrication is utilized toprovide miniature, low-power components that arecharacterized by rapid, sensitive and selective response.Sensitivity and selectivity are enhanced using two parallelanalysis channels, each containing the sequentialconnection of a front-end sample collector/concentrator, agas chromatographic (GC) separator, and a surface acousticwave (SAW) detector. Component design and fabricationand system performance are described.p CHEMLAB’MChemical detection for purposes of counter-terrorismand nonproliferation is extremely challenging due to theneed for trace detection of target analytes in environmentscontaining more than 1000-fold higher concentrations ofinterferants, To address these applications, Sandia isdeveloping a hand-held (palm-top computer sized)autonomous system (pChemLabTM) for rapid (1 rein),sensitive (1-10ppb), selective detection of CW agents [1-3].The pChetnLabTM includes both gas and liquid phaseanalysis modes; the former is described here, while thelatter is the topic of reference [4]. A diagram of the systemis given in Figure 1. Each of the two analysis channelscontains a preconcentrator (PC), a GC separator and a SAWarray detector, all of which were designed andmicrofabricated at Sandia (Figure 2). Commerciallyavailable diaphragm pumps and miniature valves are used.Pattern recognition tools developed at Sandia are used toanalyze SAW array response data and identi~ detectedcompounds [5].The PC consists of a polymer-coated microhotplate [3].First, the analyte is selectively adsorbed on the coating.Then, rapid, efficient microhotplate heating (200”C in 10msec) is used to thermally desorb the target analyte.Concentration factors of 100 for dimethyl methylphosponate (DMMP, a sarin simukmt) in air have beendemonstrated, while selectivity to xylene, a typicalinterferant, is better than 25 to 1. The microhotplate isfabricated by back-side Bosch etching, stopping on a low-stress silicon nitride membrane layer [6]. Pt heater lines aredeposited and patterned on the front side of the membrane.Sample ChemlsallyCollestIonJ Separation Selective Gas FlowConcentration Detestion Controli iSaiple RekatIve Chemkally Thhr Film Materials Patterned ExtiauetInlet Heaters on Selestlve (Stationary Phases) Materials onInsulated Adsorbent on Integrated AcousticPlatfomrs Films Channels SensorArmysFigure 1:Schematicof the gas-phase~ChemLabm.Figure2: Proceedingclockwise,a U.S. dime (18 mm dia.),PC,SAWarray detectorand GC column.GC columns are used for temporal separation ofanalytes, improving chemical discrimination. ConventionalGC systems use circular cross-section glassmicrocapilhnies, which are not easily integrated inminiature detection systems. In contras~ Bosch etching isused here to etch GC columns in silicon [7]. The high-aspect ratios afforded by this technique permit themicrofabrication of spiral columns with channels that are upto 400 pm deep and 40 pm wide separated by 40 pm thicksilicon walls. A 1 m long spiral with these typical channeldimensions fits on a -1 cmz chip. An example of amicrofabricated GC column is given in Figure 3. To formclosed channels, a Pyrex lid is anodically bonded to thesurface of the silicon substrate containing the etchedcolumns.Stationary phase coatings are deposited on the GCwalls by either conventional polymer solution techniques orsol-gel methods. The retention time of various analytes inthe stationary phase determines the temporal separation of- ...—..-.-. ~- ,, ,.,,,,. .,-T. ,. , .+ , —.— . . .. . . . . . . .rT.—Tr - -T3 . . . . _—\—-. — . . -.. . .... ,,, rr,,.~.. . ..’-.. . ...,.?’.. . . 7<.!. .--.-{ ., . ‘. —.— __ _..DISCLAIMERThis report was prepared as an account of work sponsoredby an agency of the United States Government. Neither theUnited States Government nor any agency thereof, nor anyof their employees, make any warranty, express or implied,or assumes any legal liability or responsibility for theaccuracy, completeness, or usefulness of any information,apparatus, product, or process disclosed, or represents thatits use would not infringe privately owned rights. Referenceherein to any specific commercial product, process, orservice by trade name, trademark, manufacturer, orotherwise does not necessarily constitute or imply itsendorsement, recommendation, or favoring by the UnitedStates Government or any agency thereof. The views andopinions of authors expressed herein do not necessarilystate or reflect those of the United States Government orany agency thereof.DISCLAIMERPortions of this document may be illegiblein electronic imageproduced from thedocument.products. Images arebest available original..—,~- ,..,,, ,. ..... . -’ ,.&: ,~.r---r <, z,.>,c,... . ..k.~ ----- .——... J-the analytes arriving at the SAW detector array. The twochannels of the pChemLabTMcan be optimized for differentanalytes by placing different coatings on each GC (as wellas on each PC and SAW, if needed). Alternatively,channels can be optimized for detection of the sameanalyte, providing redundancy and decreasing false alarmrates (Figure 4),Figure3: Cross-sectionSEM of a GC column fabricated in siliconby Bosch etching.. .350-3oo-$ 250-C0% 2oo-2150-100”50.0’ 10 10 30 40TIm~O(sec)50Figure4 Elutiontimesfor two microfabricatedGC columns,onewith a polar coating,the other a non-polarcoating. Peakreorderingprovidesconfirmationof results.SAW delav lines can be used as sensitive mass detectorsand can provi~e chemically selective detection when coatedwith sorbent materials [8]. Decreasing the SAW devicearea increases the operating frequency, fl and dramaticallyimproves the mass sensitivity (the mass detection limit isproportional to I/f 3, assuming that noise is linear in f).Therefore. SAW sensors are ideal candidates for,miniaturized sensors as their sensitivity improves withminiaturization.SAW devices were micro fabricated by patterning goldinterdigitated transducers (IDT) on a quartz substrate. ThepChemLabTMemploys a four-element SAW array in eachgas analysis channel. A centrally located input IDT inhiatesan acoustic wave in the substrate. Four smaller output IDTsdetect the acoustic wave. The paths, or delay lines,between the input IDT and three of the outputs are coatedwith different materials; the fourth delay line serves as areference. As analytes are adsorbed on the three sensordelay lines, the velocity of the SAW is altered as is itsphase relative to the reference. GaAs-based electronics areused to provide DC outputs proportional to the SAW phase.An example of the collective performance of a PC, GCand SAW array is given in Figure 5.500EJ o-: .1000\ /\ —BSP3:-1500- \ \~—W275 a&-zooo -IiDEHP~ -2500- — DMMP SOminSimukmt—-3000Win Simulmt im wbv—ltxJpFbv0.5 0.75 1 1.25Time (mIn)Figure 5: SAWresponseto a mixtureof DMMP and DEHPafterpassing though microfabricated PC and GC components. Delaylines were coated with ethyl cellulose (ETcell), an H-bond acidmodified polymer (BSP3) and a cyano-modified polysiloxane(OV275).CONCLUSIONSTheuseof microfabricated components in trace-level,gas-phase detection of chemical wari%re agent simukmtshas been demonstrated. The gas-phase analysis subsystemof Sandia’s pChemLabw incorporates micro fabricatedpreconcentrators, GC columns and SAW array detectors.Current work is focused on system-level optimization.ACKNOWLEDGEMENTSSandia is a multiprogram laboratory operated by SandiaCorporation, a Lockheed Martin Company, for the UnitedStates Department of Energy under contract DE-AC04-94AL85000. The authors would like to thank Jay Grate ofPacific Northwest National Lab for the BSP polymer.REFERENCES[1] G.C. Frye-Mason, et. al., p-TAS’98, Bar@ Canada,October 12-16,1998, p477.[2] S.A. Casalnuovo, et. al., 1999 IEEE InternationalFrequency Control Symposium, Besrmgon, France, April12-16,1999.[3] RP. Manginell, et. al., International Conference onModeling and Simulation of Microsystems, April 19-21,San Juan, Puerto Rico, p663.[4] D.W. Arnold, et. al., #TAS’98, Banff, Canada, October12-16,1998, P435.[5] G.C. Osbourn, et. al., Accounts of Chemical Research,31 (1998) 297.[6] R.P. Manginell, et. al., 1998 SPIE Micromachining andMicro fabrication Conference, Santa Clara, CA, September20-22, 1998, p269.[7] C.M. Matzke, et. al., ibid, p262.[8] D.S. Ballantine, et. al., Acoustic Wave Sensors: Theorv,Desire, and Phvsico-Chemical Amiications, San Diego,Academic Press, 1997, Chpt. 3.

Microfabricated Gas Phase Chemical Analysis Systems

A portable, autonomous, hand-held chemical laboratory ({mu}ChemLab{trademark}) is being developed for trace detection (ppb) of chemical warfare (CW) agents and explosives in real-world environments containing high concentrations of interfering compounds. Microfabrication is utilized to provide miniature, low-power components that are characterized by rapid, sensitive and selective response. Sensitivity and selectivity are enhanced using two parallel analysis channels, each containing the sequential connection of a front-end sample collector/concentrator, a gas chromatographic (GC) separator, and a surface acoustic wave (SAW) detector. Component design and fabrication and system performance are described

(- b , 59/@99-zL7d3eMicrofabricated Gas Phase Chemical Analysis SystemsGregory C. FryeMaso@ Ronald P. Man~inelI, Edwin J. Heller, Carolyn M. Matzke, Stephen A. Casalnuovo,Vincent M. Hietala, Richard J. Kottenstette, Patrick R. Lewis and C. Channy Wong~q~~==!r~~~Sandia National LaboratoriesP.O. Box 5800 MS-1425, Albuquerque, NM 87185-1425rprnangi@sandia.gov AU6 18 f$~g-,ABSi’RACTA portable, autonomous, hand-held chemical laboratory(~ChemLabT~ is being developed for trace detection @pb)of chemical warfhre (CW) agents and explosives in real-world environments containing high concentrations ofinterfming compounds. Microihbrication is utilized toprovide miniature, low-power components that arecharacterized by rapi~ sensitive and selective response.Sensitivity and selectivity are enhanced using two parallelanalysis channels, each containing the sequentialconnection of a front-end sample collector/concentrator, agas chromatographic (GC) separator, and a surfhce acousticwave (SAW) detector. Component design and t%bricationand system performance are described.p CHEMLWChemical detection for purposes of counter-terrorismand nonproliferation is extremely chalknging due to theneed for trace detection of target analytes in environmentscontaining more than 1000-fold higher concentrations ofinterferants. To address these application% Sandm isdeveloping a hand-held (palm-top computer sized)autonomous system (pChemLabTM) for rapid (1 rein),sensitive (1-10ppb), selective detection of CW agents [1-3].The pChemLabw includes both gas and Iiquid phaseanalysis modeq the former is described here, while thelatter is the topic of reference [4]. A diagram of the systemis given in Figure 1. Each of the two analysis channelscontains a preconcentrator (PC), a GC separator and a SAWarray detector, all of which were designed andmicrotlbricated at Sandia (Figure 2). Commerciallyavailable diaphragm pumps and miniature valves are used.Pattern recognition tools developed at Sandia are used toanalyze SAW array response data and identifi detectedcompounds [5].The PC consists of a poIymer-coated microhotplate [3].First, the artalyte is selectively adsorbed on the coating.Then, rapi~ efficient microhotplate heating (200”C in 10msec) is used to thermally desorb the target analyte.Concentration t%ctors of 100 for dimethyl methylphosponate (DMMP, a sarin simukmt) in air have beendemonstrated, while selectivity to xylene, a typicalinterferant, is better than 25 to L The microhotplate isfabricated by back-side Bosch etching, stopping on a low-stress silicon nitride membrane layer [6]. Pt heater limesaredeposited and patterned on the front side of the membrane.Sa&ple Re’alstlve Chemkslly Thin Film Matmials Patterned Es&metInlet Heatem on Salestlve (Stetlona~ Phases) MaterIele onIneulated Adsorbent on kitegretod AmustIcPlatforms Films Channels SensorArmyaFigure 1:Schematicof the gas-phasepChemLabw.Figure2 Proceedingclockwise,a U.S. dime (18 nun dia.), PC,SAWarray detectorand GC column.GC columns are used for temporal separation ofanalytes, improving chemical discrimination. ConventionalGC systems use circular cross-section glassmicrocapilktries, which are not easily integrated inminiature detection Vstems. In contra% Bosch etching isused here to etch GC columns in silicon [7]. The high-aspect ratios afforded by this technique permit themicrofhbrication of spiral cohunns with channels that are upto 400 pm deep and 40 pm wide separated by 40 pm thicksilicon walls. A 1 m long spiral with these typical channeldimensions fits on a -1 cmz chip. An example of amicroihbricated GC column is given in Figure 3. To formclosed channels, a Pyrex lid is anodically bonded to thesurt%ce of the silicon substrate containing the etchedCohlnlns.Stationary phase coatings are deposited on the GCwalls by either conventional polymer solution techniques orsol-gel methods, The retention time of various analytes inthe stationary phase determines the temporal separation of——— —. -—. . .DISCLAIMERThis report was prepared as an account of work sponsoredby an agency of the United States Government. Neither theUnited States Government nor any agency thereof, nor anyof their employees, make any warranty, express or implied,or assumes any legal liability or responsibility for theaccuracy, completeness, or usefulness of any information,apparatus, product, or process disclosed, or represents thatits use would hot infringe privately owned rights. Referenceherein to any specific commercial product, process, orservice by trade name, trademark, manufacturer, orotherwise does not necessarily constitute or imply itsendorsement, recommendation, or favoring by the UnitedStates Government or any agency thereof. The views andopinions of authors expressed herein do not necessarilystate or reflect those of the United States Government orany agency thereof..—— _ . . . -..—,. ———. —DISCLAIMERPortions of this document may be illegiblein electronic image products. Images areproduced from the best available originaldocument..,, . _,=._ >m.-,,-+.m.--,. .,> . . . ..1... - -— -r ,- .>... ., ~.y- - --- ,.. — .the analytes arriving at the SAW detector array. The twochannels of the ~ChemLabm can be optimized for differentanalytes by placing different coatings on each GC (as wellas on each PC and SAW, if needed). Alternatively,channels can be optimized for detection of theJ sameanalyte, providing redundancy and decreasing IMse alarmrates (Figure 4).Figure3: Cross-section SEMof a (3C column fabricated in siliconby Bosch etching.350-3oo -ij 250-0g 2oo-Ix150-100”50-,.xy!m. .0’ Io 10 30llm~~sec)40 soFigure 4 Elution times for two microlbbricated GC columns, onewith a pohmcoating the other a non-pokr coating. Peakreordering provides confirmation of results.SAW delay lines can be used as sensitive mass detectorsand can provide chemically selective detection when coatedwith sorbent materials [8]. Decreasing the SAW devicearea increases the operating frequency, ~ and dramaticallyimproves the”mass sensitivity (the mass detection limit isproportional to I/f 3, assumrng that noise is linear in ~.Therefore, SAW sensors are ideal candidates forminiaturized sensors as their .sensitivi& improves withminiaturization.SAW devices were microihbricated by patterning goldinterdigitated transducers (T.DT)on a quartz substrate. ThepChemLabW employs a four-element SAW array in eachgas analysis channel. A centrally located input IDT initiatesan acoustic wave in the substrate, Four smaller outmtt IDTsdetect the acoustic wave. The paths, or del;y lines,between the input LDT and three of the outputs are coatedwith different materials the fourth delay line serves as a.reference, As analytes are adsorbed on the three sensordelay lines, the velocity of the SAW is altered as is itsphase relativeto the reference. GaAs-basedelectronicsareused to provideDC outputsproportionalto the SAW phase.An example of the collective performance of a PC, GCand SAW array is given in Figure 5.!0::.1000\g -1500-=-2000 -8Z -2500- — DMMP SOmin Siam —-3000$zdn SImtisnt—Ioopfbv0.5 0.76 1 1.25Tim (rein)F&e 5: SAWresponseto a mixtureof DMMPand DEHPafterpassingthoughmicrot%bricatedPC and GC components. Delaylines were coated with ethyl cellulose (ETcell), an H-bond acidmodified polymer (BSP3) and a cyano-modified pcdysiloxane(OV275).CONCLUSIONS‘l%e use of microtkbricated components in trace-level,gas-phase detection of chemical wart%re agent simukmtshas been demonstrated. The gas-phase analysis subsystemof Sandia’s pcheniabm incorporates microfhbricatedpreconcentrators, GC cohunqs and SAW amay detectors.Current work is thcused on system-level optimization.AC.KNOWLEDGEMIINTSSandia is a multiprogram laboratory operated by SandiaCorporation, a Lockheed Martin Company, for the UnitedStates Department of Energy under contract DE-AC04-94AL85000. The authors would Sie to think Jay Grate ofPacific Northwest National Lab for the BSP polymer.RI!XERENCES[1] G.C. Frye-Mason, et. al., #-TAS’98, Ban5 CanatiOctober 12-16,1998, P477.[2] S.A. Caszdnuovo, et. al., 1999 IEEE InternationalFrequency Control Symposium, Besanqm, France, April12-16,1999.[3] RP. Manginell, et. al., International Con@v’ence onModeling and Simulation of Microgwtems, April 19-21,San Juan, plKXtO Rico, P663.[4] D.W. Arnoldj et. al., wTAS’98, Banfi Canah October12-16, 1998, p435.[5] G.C. OsboW et. al., Accounts of Chemical Research,31 (1998) 297.[6] R.P. Manginell, et. al., 1998 SPIE hiicromachining andMicrofabrication Conference, Santa Clara, CA September20-22,1998, p269.[7] C.M. Matzke, et. al., ibid, p262.[8] D.S. Ballantine, e~ al., Acoustic Wave Sensors: Theow,Desire and Physico-Chemical Applications, San Diego,Academic Press, 1997, Chpt. 3..--:, ,.%,-~T-. “. , ., .. . , ..<..,~ .—, .. .J.:, :-. ,, GJJ.. ... - . . .. . . V?,.,,.f :.!; . ,, :. .-,,, ,, ~ ,.,,:.:.~ , ~,.., . ——. —.. .

Microfabricated Gas Phase Chemical Analysis Systems

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