SAMPLE PREPARATION AND DETECTION OF PATHOGENS IN FOOD
AND BLOOD BY ACOUSTOPHORESIS
B. Ngamsom,
1
M.J. Lopez-Martinez,
1
J.C. Raymond,
2
P. Broyer,
3
P. Patel,
2
and N. Pamme
1*
1
The University of Hull, Department of Chemistry, Cottingham Road, Hull, HU6 7RX, UK
2
bioMérieux, Marcy ľ Etoile, 69280 FRANCE and
3
bioMérieux, Grenoble, 38024 FRANCE
ABSTRACT
We report on-chip continuous flow acoustophoresis for sample preparation and detection of
pathogenic microorganisms from food and blood. The continuous depletion of undesirable particles from
the sample is demonstrated, whilst high levels of viable pathogens are retrieved for downstream analysis.
KEYWORDS: Sample preparation, Acoustophoresis, Pathogen detection
INTRODUCTION
Current tests for microbiological contamination of food involve mashing up a sample in a filter bag
with an enrichment broth using a ‘Stomacher’. The filtrate with pathogenic cells is further processed
using lengthy cultural techniques or more rapid tests based on molecular biology. A major limitation is
interference attributed to the complex matrices (particulates, turbidity, inhibitors, colour). Manual
techniques based on immunomagnetic separation, centrifugation and filtration have been used with
varying degrees of success [1]. Acoustophoresis has been applied for the separation of particles/cells
based on size, density and compressibility; most studies have reported the focusing of desired particles
into a central stream, away from the original sample [2-5]. Here, acoustophoresis was employed for
separating complex pathogen containing food and blood matrices from undesirable particles by focusing
these into a central stream, rendering a “cleaner” sample still containing pathogenic cells (fig. 1a).
THEORY
The principle of acoustophoresis is based on a radiation force (F
r
):
)
4
sin( ) , ( )
2
(
2
0
x
p V
F
m p
r
(1)
where (,) is the acoustic contrast factor, a function of density and compressibility of the particle
relative to the surrounding medium. At a given pressure amplitude (p
0
) and wavelength (), the
radiation force is proportional to particle volume (V
p
) [2]. This principle was applied here for the
separation of unwanted particles from pathogenic cells from food/blood matrices. Debris particles
(10-100 µm) experience a larger radiation force and get focused into the pressure node in the
separation channel, exiting via the central outlet whilst the less affected pathogenic cells (ca. 1 µm)
will remain within the sample stream (fig. 1a).
Figure 1: (a) Separation of larger debris particles from pathogens by acoustophoresis. (b) Design of
acoustophoresis chip. (c) Photo of the device, with the piezoelectric transducer attached to the top.
978-0-9798064-7-6/µTAS 2014/$20©14CBMS-0001 1190
18th International Conference on Miniaturized
Systems for Chemistry and Life Sciences
October 26-30, 2014, San Antonio, Texas, USA