Color manipulation through microchip tinting for colorimetric detection using hue image analysis.

Colorimetry with microfluidic devices has been proven to be an advantageous method for in situ analyses where limited resources and rapid response for untrained users are desired. Image analysis using a small camera or cell phone can be easily incorporated for an objective readout, eliminating variations from normal differences in color perception and environmental factors during analysis. The image analysis using the parameter hue, for example, has been utilized as a highly effective, objective analysis method that correlates with the psychological way color is perceived. Hue analysis, however, is best used for colorimetric reactions that result in distinct changes from one color to a markedly different color and can be inadequate to distinguish between subtle or monotonal (colorless-to-colored) color changes. We address this with three unique color manipulation (i.e., tinting) techniques that provide greater discrimination with such color changes, thus yielding improved limits of detection for various colorimetric reactions that may have previously been limited. Tinting is invoked through dyeing the reagent substrate, colored printing the device, or colored lighting during image capture, and is shown to effectively shift the background color of the reaction detection area. Hydrogen peroxide, a constituent of peroxide-based explosives, is associated with a monochromatic color change upon reaction, and this is used to demonstrate the effectiveness of the tinting methods in improving the limit of detection from an undetectable color change to 0.1 mg mL-1.

Rapid detection of Clostridium difficile via magnetic bead aggregation in cost-effective polyester microdevices with cell phone image analysis.

Pathogen detection has traditionally been accomplished by utilizing methods such as cell culture, immunoassays, and nucleic acid amplification tests; however, these methods are not easily implemented in resource-limited settings because special equipment for detection and thermal cycling is often required. In this study, we present a magnetic bead aggregation assay coupled to an inexpensive microfluidic fabrication technique that allows for cell phone detection and analysis of a notable pathogen in less than one hour. Detection is achieved through the use of a custom-built system that allows for fluid flow control via centrifugal force, as well as manipulation of magnetic beads with an adjustable rotating magnetic field. Cell phone image capture and analysis is housed in a 3D-printed case with LED backlighting and a lid-mounted Android phone. A custom-written application (app.) is employed to interrogate images for the extent of aggregation present following loop-mediated isothermal amplification (LAMP) coupled to product-inhibited bead aggregation (PiBA) for detection of target sequences. Clostridium difficile is a pathogen of increasing interest due to its causative role in intestinal infections following antibiotic treatment, and was therefore chosen as the pathogen of interest in the present study to demonstrate the rapid, cost-effective, and sequence-specific detection capabilities of the microfluidic platform described herein.

Hematocrit analysis through the use of an inexpensive centrifugal polyester-toner device with finger-to-chip blood loading capability.

Hematocrit (HCT) measurements are important clinical diagnostic variables that help physicians diagnose and treat various medical conditions, ailments, and diseases. In this work, we present the HCT Disc, a centrifugal microdevice fabricated by a Print, Cut and Laminate (PCL) method to generate a 12-sample HCT device from materials costing <0.5 USD (polyester and toner or PeT). Following introduction from a drop of blood (finger stick), whole blood metering and cell sedimentation are controlled by centrifugal force, only requiring a CD player motor as external hardware and, ultimately, a cell phone for detection. The sedimented volume from patient blood in the HCT Disc was analyzed using a conventional scanner/custom algorithm for analysis of the image to determine a hematocrit value, and these were compared to values generated in a clinical laboratory, which correlated well. To enhance portability and assure simplicity of the HCT measurement, values from image analysis by a cell phone using a custom application was compared to the scanner. Fifteen samples were analyzed with cell phone image analysis system and were found to be within 4% of the HCT values determined in the clinical lab. We demonstrate the feasibility of the PeT device for HCT measurement, and highlight its uniquely low cost (<0.5 USD), speed (sample-to-answer <8 min), multiplexability (12 samples), low volume whole blood requirement (<3 µL), rotation speeds (<4000 rpm) needed for effective measurement as well as the direct finger-to-chip sample loading capability.