pitt conn 2012 fi cs as invited sers talks ba assay
TRANSCRIPT
Providing Chemical Information When & Where You Need It
Pittcon 2012RTA Booth
#2110
Frank E. Inscore, Atanu Sengupta, Chetan Shende Mike Donahue, Hermes Huang,
Stuart Farquharson
Detection of single-digit Bacillus anthracis spores in ~12-min by SERS
Funding NSF
DARPA
Materials and BSL-2/3 FacilitiesProf. Sperry (Chair Cell & Molecular Biology)
Center for Biotechnology and Life SciencesUniversity of Rhode Island
The Overall Need/ProblemDetection of Bioagents
• Intentional Dispersal by Terrorist • Domestic/Military Targets• e.g. weaponized aerosols, contamination of water & food supplies• B. anthracis, Y. pestis, F. tularensis, C. botulinum A, P. hanta
Detection of Waterborne Pathogens• Unintentional Water Contamination• Domestic/Military• Cryptosporidium, Giardia, V. cholerae, Campylobacter jejuni
Detection of Foodborne Pathogens• Unintentional Food Contamination• Domestic/Military• Listeria monocytogenes, E. coli (O157:H7), Salmonella enterica
Detection of Clinical Pathogens• Unintentional Spread of Infections• Domestic/Military Hospitals• S. aureus (MERSA), Tuberculosis, AIDs
BA spores –almost perfect bioagent. Most likely to be employed by terrorist :
right size so can be inhaled – most lethal route.
RTA is developing complete package to address each of these application areas.
The Challenge & GoalDetect bioagents and pathogens
on surfaces, in aerosols, water, in biofluids, and food.(Category A agents 1st priority: Bacillus anthracis spores)
The device must provide the following:
• Sensitivity: Detect 10,000 spores Anthrax LD50 ~10,000 spores (100 ng)
• Speed: Within 15 minutes• Specificity: Identify and discriminate pathogens
(No False Positives!)• Reproducibility: Accurate and Repeatable
(No False Negatives!)
• Current methods:• DNA or RNA enumeration: (Culture growth - 24 hours)
or Polymerase Chain Reactions (PCR, >4 hours)• Test kits (limited shelf life, very high false positive rate)
The Solution: SERSInherent specificity: all chemicals (drugs/metabolites) produce a unique Raman spectrum allowing unequivocal identification (no false-positives).
Improved sensitivity: Ag and Au nanoparticle substrates used to generate SERS amplify Raman signals (increase scattering efficiency) by 1 million times or more with potential detection at sub-ppb, i.e. 10-8 M (no false-negatives).
Enhancement Factor ~ 105
SERS 1ppm DPA (aq)
RS 20,000 ppm DPA (aq)
RS 83,000 ppm DPA (KOH)
RS solid DPA
100 mW, 1-min
290 mW, 5-min
100 mW, 5-min
290 mW, 5-min
DPA (dipicolinic acid)LMC = ~ 1 ppb
1ppm DPA
83,000 ppm DPA
SERS
RS
FT-R 785 nm
ALSO, chemical contribution can provide additional 103
enhancementSub part-per-billion detection becomes possible with SERS
SERS provides
Single Molecule Detection some argue this requires enhancement factor (EF)
of 1012 -1014
Others say 105 -108
Surface-enhanced Raman Spectroscopy
Raman, although weak effect, provides molecular specificity BUT, when a molecule is within a laser induced plasmon field,
the efficiency of Raman scattering increase’s by 106 i.e. 1 million times!
Sub part-per million detection possible
h
Plasmon Field
ν
H
NH
H
H
H
N
NN
N
Ag
Surface-EnhancedRaman Photon
Commercial SERS Substrates: Benzenethiol
10-3M
10-5M
10-8M (~10ppb)
benzenethiol
RTA: LMC ~10-11M (0.01 ng/mL or 10 ppt)
Conc. EF
102
104
107
Approach: RTA SERS Patented Sampling Systems provide instant response in seconds as opposed to 30-min or more!
Metal Particle
Sol-Gel Matrix
AdsorbedMolecules
Moleculesin Solution
Laser
RamanScattering
2001: Simple SERS Sample Vials
1 10
2004: SER-Active Capillary
silver gold
2003: SERS Microplate
High Throughput Screening Extraction and Pre-ConcentrationRTA Patents
6,623,977; 6,943,031; 6,943,032; 7,312,088; 7,393,691; 7,393,692; 7,462,492; and 7,462,493
2005: SERS spin-coated Disk
2006: Functionalized Sol-Gel SERS(affords greater selectivity and sensitivity)
PC OTC
Std chromatographic media
Primary chemically selective SER-active sol-gel (SG) sub-sets developed at RTA.
Patents: 6623977, 6943031, 6943032, 7312088, 7393691, 7393692, 7462492, 7462493, 7713914
Chem. Type Metal cap/ 800 µ Analyte Selectivity M
SG1 SG2
polar - negativenon-polar - negative
Agsilversilver
SG3 more non-pol - neg. silverSG6 very polar - neg. Ag
SG1-PDMSSG2-PEGSG2-PDMSSG3-PDMS
less polar - neg.less non-polar - neg.more non-pol - neg.very non-pol - neg.
Agsilversilversilversilver
SG4 very polar-positive Au
R&D: SERS Lab-On-ChipDifferent wafer, glass and plastic LOC designs
RTA’s SERSID - Trace Chemical Analyzer’s for Field and Lab Use2010
Providing Chemical Information When & Where You Need It
2011
Preliminary Analysis: Raman SpectroscopyB. cereus
B. subtilis
B. anthracis
CaDPA
Core Wall(proteins-cysteine,
)Ca dipicolinateCortex
(peptidoglycan)
Exosporium
Spore Coat
DNARibosomes
C CO O
O ON
2-
Ca 2+
J. Raman Spectrosc., 35, 82-86 (2004); Spectrosc., (2005)
Caveat: no consensus spectra in literature.Variability: growth/media conditions.Limitations: sensitivity/sample issues.
Portable 1064 nm system: Chem ID, Hazmat & Hoax Material Analyzer
Preliminary Analysis: Surface-Enhanced Raman Spectroscopy
Appl Spec, 58, 351 (2004)
IJHSES, 20, 12-18 (2007)
US Patent: 7713914 B2
SPIE, 5585, 53-57 (2005)
BC in DDA (78C) ~2-min
BC in DDA (22C) ~60-min
BC in AA (22C) ~2-min
BC in 0.02M HNO3 (heat+sonicate) ~10-min
BC spores in nasal mucusin AA
BC spores in saliva in AA
BC spores0.03 mg/mL(aq)
80 mW 785nm 1-min BS 0.01 mg/mL (aq) 80 mW 785nm 1-min
BS 0.01 mg/mL (aq) 160 mW 785nm 1-min
* *
Area is 0.2 mm x 0.2 mmDepth is 0.1 mm
Volume = 0.004 mm3
= 4 nL
Microscope Cell Counting: Counting Grid
Average for 10 grids = 87 spores
87 spores/4 nl=21,725/microL
This Image = 60 spores
Microscope Image: Quantifying Spores in Counting Chamber
Diluted by 10=2200 spores/microL
IJHSES, 20, 12-18 (2007)Bioterrorism, S. Morse, Ed., ISBN 978-953-307-636-2 (2012)
220 spores in actual volume measured
SERS: sensitivity great! 220 Spores detected ~2-min!
100 pg/microL (ppb) DPA in AA reference spectrum
220 BC spores with AA on SG1PDMS
1 spore = 10 pg, DPA =10% spore weight
Internal AA Reference
IJHSES, 20, 12-18 (2007)
*
*
Problem: need both high specificity & sensitivity
10^9 spores/mL + AABC
BS
BAS
RSDPA (s)
Na2DPA (s)
CaDPA (s)
SERS 1 mg/mLDPA (aq)
Na2DPA (aq)
CaDPA (aq)
The Proposal: SERS-Active Capture AssayIncorporate Molecular Recognition Elements for Specificity
Target SpecificMolecular
Recognition Elements
Ag Nanoparticles
Sol-Gel Layer
Glass Surface
Pathogens
16
Dipicolinic acid25 ppm B.
cereus
cysS-Ag
No DPA signature!
250 ppm
B. subtilis
spectrum same as before adding BS
Patent Application: (2011)
Proof of Concept:NSF (July 2008)
IJAC (March 2012)SPIE (March 2012)
Peptide-Functionalized Silver Sol-gel • Ag nanoparticles immobilized within porous sol-gel in a glass capillary were successfully functionalized
with a short peptide that specifically binds Bacillus anthracis spores.• Peptide functionalization and spore binding are verified by SERS. • The functionalized spectrum dominated by sulfur of the pep-cys-Ag bond (660 cm-1 ).
SERS ofBA specific peptide
cys-Ag
Cys
tein
e-A
g
Pept
ide
AgSol-Gel
Glass Capillary Wall
wash
pictures are not to scale
pep-cys-Ag
tf = 0.5-72 hrs Use Immediately or Seal (stable >6-months) functionalize
Assay: Spore Capture: Incubation and WashA 5-step SERS assay was successfully developed.
Pept
ide
AgSol-Gel
Glass Capillary Wall
Spor
e
1) Draw 10 µL sample into a peptide functionalized capillary, wait 5-15 minutes.
2) Perform washes to minimize non-specific interactions (40 sec)3) Treat sol-gel capture matrix with new proprietary reagent wash (10-sec)4) Perform additional treatment using AA wash (10-sec)
sol-gel & spore treatmentscleaning washes
washes applied after spore incubation:minimize non-specific interactions within capture matrix
whiletreatments amplify spore signal via DPA enhancement
incubation
5) Place capillary in Raman analyzer, measure spectrum (1 minute).
Spore Detection & Sensitivity: SERSA 5-step SERS assay for BA was successfully developed.
(also similar BC and BS assays)
Sensitivity:10 spore spectrum!
NO False Negatives!
1/100th of 1000 spores/mL sample is in capillary
measuret = 60 seconds
Total Assay: 7-17 mindepends on spore incubation time
(5-15 min)
Spore Assay SpecificityA 5-step SERS assay for BA was successfully developed.
1/100th of 10000 BA spores/mL sample is in capillary
Selectivity:BA 100 spore assay challenged:
10-100X [higher] BC, BM, & BS.NO False Positives!
BA-S BCBMBS
Spore Assay RepeatabilityA 5-step SERS assay for BA was successfully developed.
1/100th of 10000 spores/mL sample is in capillary
Repeatability:100 BA spores - 12 for 12
Capillaries!No False Negatives!
Reproducibility Assessed: ROC Curve Analysis15-min incubation K=4.8
5-min incubation K=2.3
50/50 probability line
Concentration Number of Capillaries
Mean 1007 Peak Height
Standard Deviation
Mean Standard Deviation (σ)
K Value
Blank (BC,BM,BS) 9 0.1 0.02 0.18
104 BAS (5-min) 12 0.52 0.4 2.3104 BAS (15-min) 3 0.96 0.12 4.8
Goal is a 95% confidence level (bioagent concentration that can be detected 95% of time). Determine K-value (indicates a statistically significant separation between a true and false response).
K > 3.29 meet Army’s requirement (of 95% probability of detection & 5% probability of false alarm).
Since some non-specificity of other Bacillus spores with sol-gel, use of BC blank as opposed to water blank is more realistic!
BA Assay Goal: IMPROVE PERFORMANCE
ACCOMPLISHED!New Silver Sol-Gel Chemistry
New Additional Post-Functionalization Wash New Spore Incubation Time 10-min @95% Confidence
Concentration Number of Capillaries
Mean 1007 Peak Height
Standard Deviation
Mean Standard Deviation (σ)
K Value
Blank (105 BC) 7 0.02 0.0161 0.047104 BAS (10-min) 7 0.181 0.078 3.43
Concentration Number of Capillaries
Mean 1007 Peak Height
Standard Deviation
Mean Standard Deviation (σ)
K Value
Blank (Water) 5 0.025 0.0064 0.037104 BAS (10-min) 7 0.181 0.078 4.19
Specific goal of this ROC analysis: determine if modifications reduce spore incubation time from 15 to 10 min, without compromising sensitivity & specificity of the assay, i.e. detecting 10,000 BAS spores with 95% specificity (K value greater than 3.29).
~12-min, Assay Specificity: 98.5%
~12-min, Assay Specificity: 96%
This clearly indicates that the non-specific interaction of BC with the BA assay substrate is around 2.5%. (∆=4%-1.5%)
No False Positives/Negatives
t = 10-min + 40-sec + 20-sec + 60-sec = 12-min
K = 3.43
K = 4.19
Executive Summary
Proposed device (SERS analyzer/BA assay) provides the following:
• Sensitivity: Detect < 10,000 BA spores (as low as 10 BA-S spores)• Speed: Less than 15 minutes (within 12 minutes)
• Specificity: Identify and discriminate BA (against BC, BS, BM)(No False Positives!)
• Reproducibility: Accurate and Repeatable (95% confidence 100 spores)(No False Negatives!)
Possible assay time = 8.5-min + 40-sec + 20-sec + 30-sec = 10-min!
Complete publication for BA assay (ames and sterne) pending (2012).Assay validation at US Army Edgewood facilities (June 2012)