Biomedical Engineering Reference
In-Depth Information
rapidly open the valve. The valve can then be held open for longer pulses, or
indefinitely, using a lower 'hold' voltage (
8 V).
An advantage of this approach to reagent jetting is the ability to precisely
meter nanoliter-scale volumes of fluid. Typical syringe pump based liquid
handling instruments operate in the microliter to milliliter range and are in-
appropriate for arraying or high throughput applications at smaller volumes.
Conversely, the picoliter scale quantities dispensed with thermal or piezo-
based techniques are too small to effectively deliver volumes in the nanoliter
range. To increase or alter the delivery volume using these techniques, mul-
tiple dispenses are necessary. Even at high actuation rates, such an approach
is too time consuming [16]. With solenoid-based dispensers, volumes ranging
from a few nanoliters to several microliters can be rapidly delivered [17]. Flow
through the valve is dependent on a number of parameters, including the ap-
plied pressure, valve opening time, fluid viscosity, and nozzle dimensions. The
valve opening time is the easiest variable to control and can be modulated by
simply changing the duration of the hold voltage. The linear relation between
dispensed volume and valve opening time is shown in Fig. 4.4.
Several fluid dispensing devices based on solenoid valve technology have
been described [17-19]. The technology is relatively simple to implement, en-
abling the construction of custom instruments for desired applications. Com-
mercial systems based on solenoid valve technology are available from Carte-
∼
Fig. 4.4.
Graph of the volume ejected as a function of valve pulse width for a
solenoid-based reagent jet. A linear relation between the dispensed volume and valve
opening time is observed. A pressure head of 10 psi and a nozzle of 125
µ
m inner
diameter was used. The volumes were determined by weighing the sum of 1000
dispensing events
