Digital Microfluidic Method for Protein Extraction by Precipitation

Analytical Chemistry. Jan, 2009  |  Pubmed ID: 19117460

We present the first microfluidic method for extracting proteins from heterogeneous fluids by precipitation. The new method comprises an automated protocol for precipitation of proteins onto surfaces, rinsing the precipitates to remove impurities, and resolubilization in buffer for further analysis. The method is compatible with proteins representing a range of different physicochemical properties, as well as with complex mixtures such as fetal bovine serum and cell lysate. In all cases, the quantitative performance (measured using a fluorescent assay for % recovery) was comparable to that of conventional techniques, which are manual and require more time. Thus, this work represents an important first step in efforts to develop fully automated microfluidic methods for proteomic analyses.

Droplet-scale Estrogen Assays in Breast Tissue, Blood, and Serum

Science Translational Medicine. Oct, 2009  |  Pubmed ID: 20368154

Estrogen is a key hormone in human reproductive physiology, controlling ovulation and secondary sexual characteristics. In addition, it plays an important role in the pathogenesis of breast cancer. Indeed, estrogen receptor antagonists and aromatase inhibitors (which block estrogen biosynthesis) are primary drugs used for treatment and prevention in at-risk populations. Despite its importance, tissue concentrations of estrogen are not routinely measured because conventional techniques require large samples of biopsies for analysis. In response to this need, we have developed a digital microfluidic method and applied it to the extraction and quantification of estrogen in 1-microliter samples of breast tissue homogenate (as would be collected with fine-needle aspiration), as well as in whole blood and serum. This method may be broadly applicable to conditions requiring frequent analysis of hormones in clinical samples (for example, infertility and cancer).

Multilayer Hybrid Microfluidics: a Digital-to-channel Interface for Sample Processing and Separations

Analytical Chemistry. Aug, 2010  |  Pubmed ID: 20670000

Microchannels can separate analytes faster with higher resolution, higher efficiency and with lower reagent consumption than typical column techniques. Unfortunately, an impediment in the path toward fully integrated microchannel-based laboratories-on-a-chip is the integration of preseparation sample processing. In contrast, the alternative format of digital microfluidics (DMF), in which discrete droplets are manipulated on an array of electrodes, is well-suited for carrying out sequential chemical reactions such as those commonly employed in proteomic sample preparation. We recently reported a new paradigm of "hybrid microfluidics," integrating DMF with microchannels for in-line sample processing and separations. Here, we build on our initial efforts, introducing a second-generation hybrid microfluidic device architecture. In the new multilayer design, droplets are manipulated by DMF in the two-plate format, an improvement that facilitates dispensing samples from reservoirs, as well as droplet splitting and storage for subsequent analysis. To demonstrate the capabilities of the new method, we implemented an on-chip serial dilution experiment, as well as multistep enzymatic digestion. Given the myriad applications requiring preprocessing and chemical separations, the hybrid digital-channel format has the potential to become a powerful new tool for micro total analysis systems.

Let's Get Digital: Digitizing Chemical Biology with Microfluidics

Current Opinion in Chemical Biology. Oct, 2010  |  Pubmed ID: 20674472

Digital microfluidics (DMF) has recently emerged as a popular technology for a wide range of applications in chemical biology. In DMF, nL-mL droplets containing samples and reagents are controlled (i.e., moved, merged, mixed, and dispensed from reservoirs) by applying a series of electrical potentials to an array of electrodes coated with a hydrophobic insulator. DMF is distinct from microchannel-based fluidics as it allows for precise control over multiple reagent phases (liquid and solid) in heterogeneous systems with no need for complex networks of microvalves. Here, we review the state-of-the-art in DMF as applied to a wide range of applications in chemical biology, including proteomics, enzyme assays and immunoassays, applications involving DNA, cell-based assays, and clinical applications.

Synchronized Synthesis of Peptide-based Macrocycles by Digital Microfluidics

Angewandte Chemie (International Ed. in English). Nov, 2010  |  Pubmed ID: 20715231

Folded Emitters for Nanoelectrospray Ionization Mass Spectrometry

Rapid Communications in Mass Spectrometry : RCM. Dec, 2010  |  Pubmed ID: 21072798

Electrospray ionization (ESI) has revolutionized mass spectrometry (MS), providing a facile method for the ionization of macromolecules for analysis by mass. The development of nanoESI-MS has further extended the utility of ESI-MS, permitting the analysis of small-volume samples with enhanced sensitivity over conventional ESI-MS. Traditional nanoESI-MS experiments use pulled-glass capillary emitters, which are expensive to purchase and require specialized instruments and training to fabricate in-house. Furthermore, these emitters suffer from problems including clogging, sample contamination, and irreproducible spray stability. Here, we report a new emitter for nanoESI-MS, made by folding small pieces of polyimide tape. In comparison with conventional pulled-glass capillary emitters, the new emitters are inexpensive and simple to make. Their low cost makes them disposable after a single use, such that sample contamination or clogging is never a problem. Emitter performance has been evaluated for diverse analytes encompassing a large mass range, including small molecules, peptides, proteins, and synthetic polymers. In all cases, the performance is similar to that of pulled-glass capillary emitters, with the advantages of low cost, ease of use, and disposability.

A Digital Microfluidic Method for in Situ Formation of Porous Polymer Monoliths with Application to Solid-phase Extraction

Analytical Chemistry. May, 2011  |  Pubmed ID: 21524096

We introduce the marriage of two technologies: digital microfluidics (DMF), a technique in which droplets are manipulated by application of electrostatic forces on an array of electrodes coated by an insulator, and porous polymer monoliths (PPMs), a class of materials that is popular for use for solid-phase extraction and chromatography. In this work, circular PPM discs were formed in situ by dispensing and manipulating droplets of monomer solutions to designated spots on a DMF device followed by UV-initiated polymerization. We used PPM discs formed in this manner to develop a digital microfluidic solid-phase extraction (DMF-SPE) method, in which PPM discs are activated and equilibrated, samples are loaded, PPM discs are washed, and the samples are eluted, all using microliter droplets of samples and reagents. The new method has extraction efficiency (93%) comparable to that of pipet-based ZipTips and is compatible with preparative sample extraction and recovery for on-chip desalting, removal of surfactants, and preconcentration. We anticipate that DMF-SPE may be useful for a wide range of applications requiring preparative sample cleanup and concentration.

A Digital Microfluidic Method for Dried Blood Spot Analysis

Lab on a Chip. Oct, 2011  |  Pubmed ID: 21869989

Blood samples stored as dried blood spots (DBSs) are emerging as a useful sampling and storage vehicle for a wide range of applications. Unfortunately, the surging popularity of DBS samples has not yet been accompanied by an improvement in automated techniques for extraction and analysis. As a first step towards overcoming this challenge, we have developed a prototype microfluidic system for quantification of amino acids in dried blood spots, in which analytes are extracted, mixed with internal standards, derivatized, and reconstituted for analysis by (off-line and in-line) tandem mass spectrometry. The new method is fast, robust, precise, and most importantly, compatible with automation. We propose that the new method can potentially contribute to a new generation of analytical techniques for quantifying analytes in DBS samples for a wide range of applications.