We report the use of paper-based microfluidic devices fabricated from a novel polymer blend for the monitoring of urinary ketones, glucose, and salivary nitrite. Paper-based devices were fabricated via photolithography in less than 3 min and were immediately ready for use for these diagnostically relevant assays. Patterned channels on filter paper as small as 90 microm wide with barriers as narrow as 250 microm could be reliably patterned to permit and block fluid wicking, respectively. Colorimetric assays for ketones and nitrite were adapted from the dipstick format to this paper microfluidic chip for the quantification of acetoacetate in artificial urine, as well as nitrite in artificial saliva. Glucose assays were based on those previously demonstrated (Martinez et al., Angew Chem Int Ed 8:1318-1320, 1; Martinez et al., Anal Chem 10:3699-3707, 2; Martinez et al., Proc Nat Acad Sci USA 50:19606-19611, 3; Lu et al., Electrophoresis 9:1497-1500, 4; Abe et al., Anal Chem 18:6928-6934, 5). Reagents were spotted on the detection pad of the paper device and allowed to dry prior to spotting of samples. The ketone test was a two-step reaction requiring a derivitization step between the sample spotting pad and the detection pad, thus for the first time, confirming the ability of these paper devices to perform online multi-step chemical reactions. Following the spotting of the reagents and sample solution onto the paper device and subsequent drying, color images of the paper chips were recorded using a flatbed scanner, and images were converted to CMYK format in Adobe Photoshop CS4 where the intensity of the color change was quantified using the same software. The limit of detection (LOD) for acetoacetate in artificial urine was 0.5 mM, while the LOD for salivary nitrite was 5 microM, placing both of these analytes within the clinically relevant range for these assays. Calibration curves for urinary ketone (5 to 16 mM) and salivary nitrite (5 to 2,000 microM) were generated. The time of device fabrication to the time of test results was about 25 min.

DNA-encoded synthesis is rekindling interest in combinatorial compound libraries for drug discovery and in technology for automated and quantitative library screening. Here, we disclose a microfluidic circuit that enables functional screens of DNA-encoded compound beads. The device carries out library bead distribution into picoliter-scale assay reagent droplets, photochemical cleavage of compound from the bead, assay incubation, laser-induced fluorescence-based assay detection, and fluorescence-activated droplet sorting to isolate hits. DNA-encoded compound beads (10-μm diameter) displaying a photocleavable positive control inhibitor pepstatin A were mixed (1920 beads, 729 encoding sequences) with negative control beads (58 000 beads, 1728 encoding sequences) and screened for cathepsin D inhibition using a biochemical enzyme activity assay. The circuit sorted 1518 hit droplets for collection following 18 min incubation over a 240 min analysis. Visual inspection of a subset of droplets (1188 droplets) yielded a 24% false discovery rate (1166 pepstatin A beads; 366 negative control beads). Using template barcoding strategies, it was possible to count hit collection beads (1863) using next-generation sequencing data. Bead-specific barcodes enabled replicate counting, and the false discovery rate was reduced to 2.6% by only considering hit-encoding sequences that were observed on >2 beads. This work represents a complete distributable small molecule discovery platform, from microfluidic miniaturized automation to ultrahigh-throughput hit deconvolution by sequencing.

The ability of nitric oxide to relax smooth muscle cells surrounding resistance vessels in vivo is well documented. Here, we describe a series of studies designed to quantify amounts of adenosine triphosphate (ATP), a known stimulus of NO production in endothelial cells, released from erythrocytes that are mechanically deformed as these cells traverse microbore channels in lithographically patterned microchips. Results indicate that micromolar amounts of ATP are released from erythrocytes flowing through channels having cross sectional dimensions of 60 x 38 micron (2.22 +/- 0.50 microM ATP). Microscopic images indicate that erythrocytes, when being pumped through the microchip channels, migrate toward the center of the channels, leaving a cell-free or skimming layer at the walls of the channel, a profile known to exist in circulatory vessels in vivo. A comparison of the amounts of ATP released from RBCs mechanically deformed in microbore tubing (2.54 +/- 0.15 microM) vs a microchip (2.59 +/- 0.32 microM) suggests that channels in microchips may serve as functional biomimics of the microvasculature. Control studies involving diamide, a membrane-stiffening agent, suggest that the RBC-derived ATP is not due to cell lysis but rather physical deformation.

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of Single Mammalian Cells with Microfluidics C ells are the fundamental building blocks of life. All basic physiological functions of multicellular organisms reside ultimately in the cell. The misregulation of cellular physiology results in disease at the organism level. Thus, comprehending cell physiology is key to understanding and curing diseases. Many physiological processes can be studied using populations of cells. Others occur either on short timescales (e.g., kinase signaling cascades) or nonsynchronously (e.g., response to an external chemical gradient), so that taking a population average will not lead to an understanding of how the cellular chemistry occurs. These types of processes require single-cell analysis, and thus discretion must be exercised when deciding under which circumstances bulk versus singlecell analyses are more appropriate (1). In addition, many diseases like cancer start with a single cell; therefore, if one would like to find the rare mutations in populations of cells that herald the inception of a disease, then cells must be examined individually.Probing behavior at the single-cell level, however, is a very challenging task, primarily because of the small sample volume, the low abundance of material, and the fragile nature of the cell itself. Analyzing the contents of a single cell requires sensitive detection techniques and handling procedures that do not stress or damage it. Additionally, no proper blank exists that can be used, so truly quantitative studies are difficult. Intense interest in single-cell physiology, however, is driving the analytical and biomedical engineering fields to improve the technology for examining cells. One of the most popular and promising areas is lab-on-a-chip devices to manipulate and analyze single cells.Since Jorgenson's groundbreaking work in 1989, CE has been used to examine the contents of single cells (2-4). However, many procedures for cell injection and lysis are time-consuming, and accuracy and reproducibility rely heavily on the skill of the researcher. Furthermore, the limited number of architectures provided by microbore tubing and its relatively large volume restrict the types of processes that can be investigated. Conversely, microfluidics, or lab-on-a-chip technology, offers a versatile format in which biological cells can be analyzed.These miniaturized devices provide several analytical and operational advantages over conventional macroscale systems (5, 6). Microfluidic architectures provide precise spatial control over reagents and samples, are capable of fast analysis times, can be automated, and can precisely manipulate picoliter volumes of material without dilution. In addition, microfluidic systems are amenable to many different detection schemes, can be manufactured from many different materials at relatively low cost, allow flexibility of design, and provide the capability of integrating a series of multiple tasks (sample preparation, mixing, separation, etc.) in both serial and parallel schemes. Portable versions of these sys...