Due to the effect of an electrical double layer within the fluid channel, the behavior of nanofluid is observed to be significantly different compared with its microfluidic counterparts.
The electrical potential then modifies the concentration of ion species, resulting in an asymmetric current-voltage characteristic for the current through the pipet.
Transport of ions in the electrolyte can be adjusted by tuning the pH value in a dilute ionic solution, or by introducing an external electrical potential to change the surface charge density of the wall.
The transistor can be turn on or off by an external electrical signal, allowing the control of ionic fluids in a nano-scaled channel.
For electrolyte solution in a channel with a macro- or micro-scaled radius, surface charges at the wall attract counterions and repel co-ions due to electrostatic force.
The dimension of the electrical double layer is determined by the Debye length in this system, which is typically much smaller than the channel radius.
Therefore, it is possible to manipulate the flow of ions inside the nanochannel by introducing surface charges on the wall or by applying an external electrical potential.
Because a higher concentration leads to a shorter Debye length for the electrical double layer at the channel wall.
In this case, the flow of positive charges passing through the channel is not favorable, resulting in a decrease in ionic current.
[11][12] A nanofluidic field-effect transistor can be made of silica nanotubes with an oxide as the dielectric material between the metal gate electrode and the channel.
[14] This concept is an analogy to the structure of a metal-oxide semiconductor field-effect transistor (MOSFET) in electronic circuits.
There is possibility to achieve a nanofluidic circuitry, which is capable of logic operation and manipulation for ionic particles.
Since the conductance of ionic current flow is controlled by the gate voltage, using a material with high dielectric constant as the wall of the channel is desired.
This device could be deemed as the building blocks for ionic counterpart of the electronic field-programmable gate array.
The surface charge at the channel wall can be modified using chemical methods, by changing the electrolyte concentration or pH value.
Nanofuidic triode is a three-terminal double junction nanofluidic device composed of positive-charged alumina and negative-charged silica nanochannels.
When surface charges present at the wall of a channel of micro-scaled width, counterions are attracted and co-ions are repelled by electrostatic force.
This region penetrate into solution to a certain distance called Debye length until the electric potential decays to the bulk value of neutrality.
Because they are built using the same manufacturing technology, it is possible to make a nanofluidic system with digital integrated circuit on a single chip.
Top-down methods are the conventional processes utilized in the IC industry and Microelectromechanical systems research.
A typical method of top-down fabrication includes photolithography to define the geometry of channels on a substrate wafer.
Other technologies to fabricate nano-channels include surface micromachining with sacrificial layers, nano-imprinting lithography, and soft-lithography.
For these structures to be utilized as nanofluidic devices, the interconnection between nano-channels and microfluidic systems becomes an important issue.
[21] An important advantage of micro- and nano-scaled systems is the small amount of sample or reagent used in analysis.
In many cases, nanofluidic devices are integrated within a microfluidic system to facilitate logic operation of fluids.
The future of nanofluidic systems will be focused on several areas such as analytical chemistry and biochemistry, liquid transport and metering, and energy conversion.
A system with solely nanofluidic devices standalone is impractical because it would requires a large driving pressure to make fluids flow into the nano-channel.
[22] Nanofluidic devices are powerful in their high sensitivity and accurate manipulation of sample materials even down to a single molecule.
Nevertheless, the drawback of nanofuidic separation systems is the relatively low sample throughput and its result in detection.
In the application for large molecule, clogging is a concern because the small size of the nanochannel makes it easy to happen.