We present a novel electronic circuit for a capacitive non-contact volume sensor to be used for the determination of
dispensed liquid droplets in the nanoliter range. Beside the ability of online droplet volume measurement the presented
sensor features also sensitivity to certain droplet parameters like droplet velocity, liquid type and even small droplet
deformations during the droplet's flight. The sensor principle is based on the capacitive change caused by a droplet while
it passes an open plate capacitor. In contrast to the already published results [1, 2], the presented circuit amplifies the
change of capacitance by a measurement bridge that feeds a differential amplifier. The required bridge regulation is
realised by an adjustable analogue voltage divider combined with an all-pass filter to modulate the reference signal in
phase and amplitude. The implementation of the analogue adjustment is crucial to enable the required high sensitivity.
The circuit is able to amplify changes in capacitance in the range from ▵C ≈ {0.6 to 2.7 fF} which are caused by single
droplets of volumes of V ≈ {20 to 70 nl}). The output voltage signals can reach up to Umax= 2.3V. The sensor sensitivity
to the droplet volume reaches Si = 82 mV/nl with an accuracy of ▵V = ± 4 nl. With this sensitivity even droplet
deformation occurring within the measurement capacitor can be observed as multiple signal peaks. These are caused
from lateral (towards the electrodes) and longitudinal extension of the droplet's shape that influence the effective
capacitance by ▵Cmax≈ 0.2 fF.
Liv Furuberg, Michal Mielnik, Ib-Rune Johansen, Jörg Voitel, Anja Gulliksen, Lars Solli, Frank Karlsen, Tobias Bayer, Friedhelm Schönfeld, Klaus Drese, Helen Keegan, Cara Martin, John O'Leary, Lutz Riegger, Peter Koltay
The aim of the MicroActive project is to develop an instrument for molecular diagnostics. The instrument will first be
tested for patient screening for a group of viruses causing cervical cancer. Two disposable polymer chips with reagents
stored on-chip will be inserted into the instrument for each patient sample. The first chip performs sample preparation of
the epithelial cervical cells while mRNA amplification and fluorescent detection takes place in the second chip. More
than 10 different virus markers will be analysed in one chip. We report results on sub-functions of the amplification chip.
The sample is split into smaller droplets, and the droplets move in parallel channels containing different dried reagents
for the different analyses. We report experimental results on parallel droplet movement control using one external pump
only, combined with hydrophobic valves. Valve burst pressures are controlled by geometry. We show droplet control
using valves with burst pressures between 800 and 4500 Pa. We also monitored the re-hydration times for two necessary
dried reagents. After sample insertion, uniform concentration of the reagents in the droplet was reached after respectively
60 s and 10 min. These times are acceptable for successful amplification. Finally we have shown positive amplification
of HPV type 16 using dried enzymes stored in micro chambers.
Liquid handling of volumes down to a few nanoliters is a key issue for modern bioanalytical and pharmaceutical research and industry. In this paper we present a modular dispensing device for the highly accurate delivery of liquids in the range of 10 nL - 500 nL at a precision of better than 5 % and a dosage rate up to 1000 nL/s. The reported dispensing technology is based on a fast mechanical displacement of liquid within a micromachined silicon chip (termed dosage chip). It overcomes limitations known from piezo-drop-on-demand dispensers or syringe-solenoid systems presently used in laboratory automation. The accurate and very robust multi channel system which is modularly built out of individual dispensers is able to handle a variety of different liquids simultaneously. A wide range of liquids with different physical properties can be handled with an up to now unequalled precision in that volume range. The working principle of the device as well as newest characterization results are presented.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.