The Center is working to develop a continuous flow microspotter for the deposition of high quality spots of DNA, proteins, cells, sugars, lipids, and other biomolecules. The spotter can be used for doing multi-step chemistry on a chip and sequential deposition. Due to the ability of the spotter to individually address each spot, crosstalk is minimized and background signals reduced. The technology is being developed by Wasatch Microfluidics for:
- DNA chips
- Protein chips
- Lipid chips
- Sugar chips
- Cell chips
- Sequential deposition
The Continuous Flow Microspotter. The CFM operates by flowing solution over individual microarray sites through microchannel “loops” molded into the silicone polymer PDMS (Polydimethylsiloxane). The spotting face is pressed against a substrate to create a seal. Small openings on the face allow the solution to make contact with the surface (see Figure 1). The CFM can be used to sequentially flow different samples or reagents through the channels. Therefore, it can be used to perform surface modifications, deposit biomolecules, carry out wash steps and deliver reagents, during which time each spot is kept isolated from surrounding spots and the atmosphere. To scale the technology for high-throughput, many flow loops are placed next to one another in a thin layer, followed by stacking many layers together, creating a device that can address hundreds or thousands of sites on a rectangular array.
Strengths of the Technology. The strengths of the technology include:
- Massively parallel fluid handling—can deliver many reagents simultaneously to unique array locations.
- Capture from complex samples—can selectively capture and concentrate from heterogeneous solutions with high sensitivity if the surface is activated to capture the molecule of interest.
- Isolation from the atmosphere—each spot is isolated in microchannels during deposition and testing.
- Isolation from surrounding spots—each spot is isolated from surrounding spots, decreasing background noise and cross contamination.
- Chemical reactions on a spot—can conduct chemical reactions or binding assays by running reagents in succession.
- Recapture of precious samples—solutions are recirculated into the original sample wells.
- Small sample sizes—dead volumes in the microchannels range from 10 to 30 nL. The current sample wells are cylindrical and require at least ten microliters. In future designs, smaller, cone shaped wells will be used to dramatically reduce this amount.
- Flexible design and prototyping—design configurations (channel geometry, orifice size, spot morphology, number of channel loops) can be readily adjusted to optimize parameters of interest.
- Scalability—the current design allows scaling to hundreds or thousands of flow loops without a significant increase in complexity of assembly and operation.
- Inexpensive material, high volume manufacturing compatible—disposable devices can be produced in high volume with hot embossing or injection molding.
The CFM as a Point-of-Care Diagnostic Tool. As a future diagnostic tool, the CFM has a significant advantage over microtiter plate and microarray ELISAs, in that dedicated microarray printing or fluid handling robotics are not necessary. All fluid handling and deposition is conducted directly within the disposable CFM print head. A small pumping device is needed to circulate the fluids, but this can be accomplished with an inexpensive handheld or small desktop unit. Integration of optics could allow for immediate detection and quantification of results. Contamination would not be of concern, because fluids only contact the interior of the disposable CFM device and not the dedicated pumping and sensing equipment. For a point-of-care (POC) device, assay performance will be further simplified by merging multiple wells with each flow loop, thereby allowing capture agents, buffers and other fluids to be pre-loaded and stored within the disposable CFM head. Thus, the insertion of patient samples would be the only step required of a physician or lab technician.