Translume’s glass flow cells can be equipped with nozzles. This provides a means to surround a fluid of interest with a sheath. Nozzle-equipped chips are often used when encapsulating particles or in microflow cytometry.
Typically, the base microfluidic channel has a Y-shape layout. The fluid of interest feeds from the middle input channel into the main common channel through an integrated nozzle – this forms the “core”. The two input arm side channels converge at the nozzle to form the sheath that surrounds the core.
Nozzle-equipped flow cells are made of three layers, a design which provides an optically-clear view of the microfluidic channels from both the top and bottom. All elements are made from fused silica glass. Integrated optics, to monitor the microfluidic channel, can be added to the flow cell.
We offer glass flow cells with integrated nozzles on a custom basis. Some common geometries are briefly described below. If you do not find what you are looking for below, we will be happy to work with you, investigate and prepare new design elements specific to your needs.
2” x 1” is the most common size, but we can work with larger or smaller substrates if desired.
The thickness of the central fused silica glass layer is typically 500-µm (We have occasionally worked with other central layer thicknesses). The top and bottom fused silica glass layers can be either 250-µm or 500-µm thick.
Microfluidic Channel Size
The channel height must be equal to the middle layer thickness (i.e. typically 500-µm). The channel width can be varied over a wide range.
We can provide a variety of nozzle shapes, with inner diameter ranging from 25-µm upwards to the limit imposed by the channel width. Nozzles with output inner diameter smaller than 25-µm can also be fabricated, but their cross-sections are not as circular as that of larger nozzles.
The nozzle outside shape and its length can be adjusted to fit your application, as illustrated below.
Hydrodynamic Focusing Chamber
In order to provide hydrofocusing on all sides (i.e. reduction of the core width and height), the nozzle needs to be inserted into a purposed-shape chamber. The combination nozzle and hydro-focusing chamber can be designed to minimize the size of the core stream at a given point. Note that even when using a focusing chamber, hydrofocusing is still strongly dependent on the pressure applied to the core and the sheath. Typically, best results are obtained at relatively low pressures (in the 0 to 1.5 psi range).
Nozzles can be nested (daisy-chained) as shown below. Nested nozzles can provide special functionalities, such as multilayer-encapsulation.
Most importantly, glass flow cells with a dual nested nozzle provide better hydrofocusing than single-nozzle flow cells.
As shown here the first nozzle provides the initial flow hydro-focusing of the core stream. In order to avoid flow instabilities and core distortion (especially unwanted vertical elongation), the hydro-focusing (compression ratio), associated with this first nozzle, is relatively mild.
For some cases this may be all that is needed. However for more demanding application a nested nozzle arrangement can provide additional compression.
The output of the first nozzle is combined with additional sheath before entering in a second nozzle.
This second nozzle provides a highly symmetrical geometry to further compress the fluid.
At the exit of the second nozzle, additional sheath volume surrounds the compressed liquid to prevent lateral expansion.
This nested design provides three-dimensional compression and stable output. In this last image the flow is shown approximately 2-millimeters downstream of the second nozzle.
Combined flow: 4.5 ml/min
pressure sheet: 2.5 PSI
pressure core: 2.8 PS