1) The document describes a microfluidic device and method for detecting substances of forensic significance like papaverine and noscapine using surface-enhanced Raman spectroscopy (SERS). 2) The microfluidic device is fabricated using soft lithography techniques and assembled to control the flow of analyte, silver nanoparticles, and lithium chloride solutions. 3) The detection method works by merging the three input fluids within the microchannel, allowing diffusion-driven aggregation of silver nanoparticles around analyte molecules and producing a SERS signal that is mapped with a laser.

1. Detection of Substances of Forensic Significance Using
Microfluidics and SERS
Valentina Hallefors1, Rustin Mirsafavi1,2, Carl Meinhart1,3, Martin Moskovits1,4
1UC Santa Barbara, 2BMSE, 3Department of Mechanical Engineering, 4Department of Chemistry and Biochemistry
TRACKING THE SOURCE OF HEROIN
1
•Create silicon wafer with mold pattern using lithographic
techniques
2
•Pour PDMS on mold and cure to create channel design
3
•Clean PDMS chip and glass slides with ethanol to prepare
for bonding using UV/ozone
4
•Assemble parts and install inlets and outlets
Papaverine and noscapine are two opium alkaloids commonly used to track
the source of heroin by law enforcement agents. Papaverine can be found in
the opium poppy and is vital in locating the source of pre-manufactured
heroin. Noscapine, which survives the manufacturing process, is useful in
identifying the origin of seized drugs as it is found in street heroin[1].
RESULTS
5
•Load device with LiCl, AgNPs, and analyte
6
•Apply vacuum to outlet to initiate flow
7
•Secure device inside microscope and locate region of
intersection between fluids
8
•Map region with laser 4-5 times in intervals of 2.5 minutes
DEVICE FABRICATION
RUNNING THE ASSAY
SERS AND MICROFLUIDICS
Raman spectroscopy uses the interaction of light with molecules to identify
molecular structures based on their discriminant vibrational modes, yielding
a unique Raman signature for each molecular type. Surface-enhanced Raman
spectroscopy (SERS) utilizes the surface plasmons on silver nanoparticles
(AgNPs) to amplify the Raman signal by a factor of 1010, providing a sensitive
tool suitable for small quantity detection. Microfluidics allows for precise
control and manipulation over small volumes of fluid. The devices are
configured so as to create a laminar flow at the point of intersection between
the salt, analyte, and AgNPs. This yields a purely diffusion-driven process
that aids the aggregation of the AgNPs and interaction between these
particles and the analyte. A mapping of the region of optimal aggregation
with a laser yields a SERS spectra of the analyte molecule.
Figure 1[2]: Surface plasmons
greatly enhance the Raman signal.
Figure 2[2] : Aggregation of the silver
nanoparticles around the analyte creates
SERS hot spots.
REFERENCES
Our future goal is to detect the presence and
concentrations of noscapine and papaverine in
complex media. The concentration of a substance is
related to the area under the peaks of its SERS
spectra. By collecting further experimental data with
a broader range of concentrations (0.1-100 μM), we
can constrain this relationship and apply it to
determine unknown concentrations.
Figure 3[2] : The device is loaded
with 20 μL of 0.2 M LiCl,
20 nm AgNP, and analyte.
A 633 nm laser is used to map a
section of the microchannel where
the three input fluids have merged.
Figure 4: A background signal is present in all data and likely originates from the citrate in the AgNP solution.
FUTURE WORK
ACKNOWLEDGEMENTS
Thank you to the Institute for Collaborative
Biotechnologies (ICB) and the AIM
Photonics program for funding this research.
(100 μM)
(100 μM)
[1] Denooz R, Dubois N, Charlier C (2005). "[Analysis of two year heroin seizures in the Liege
area]". Revue médicale de Liège (in French). 60 (9): 724–8. PMID 16265967.
[2] Andreou C, Mirsafavi R, Moskovits M, Meinhart CD (2015). Detection of low concentrations of
ampicillin in milk. The Analyst. 140: 5003-5. PMID 26087055.