Making accurate measurements and tests of biomedical samples outside the laboratory often involves high costs, time delay for sample transport, and equipment that can be used only by skilled technical personnel. The ability to conduct biological analysis, pathogen identification, and patient treatment in remote locations using mobile instrumentation would help drive down healthcare costs globally.
One difficulty in developing such instruments is achieving a balance between usability and sensitivity. Until now, testing in the dairy industry has involved either sending raw milk samples out to the laboratory and waiting a week or two for results, or purchasing instruments that cost tens of thousands of dollars and would not survive in the dairy barn. To help farmers meet tough new regulatory standards, Dairy Quality, Inc., sought a highly portable product to provide fluid analysis on-site, to increase farmers' product acceptance rates and profits. Consequently, ASE Optics and Dairy Quality prototyped an iPhone-compatible fluorescence microscope for field analysis of biological fluids. The device, The Milk Guardian (see Figure 1), couples with the iPhone camera and measures cell counts per mL at a 1-micron resolution.
Figure 1. The Milk Guardian, a portable fluorescence microscope system for use in dairy farms and beyond. (Photo courtesy of Dairy Quality, Inc.)
To develop the Milk Guardian, we had to overcome several technical hurdles. The instrument needed to be pocket-sized and of low weight to be acceptable for field use, and required careful design to keep the optical components free from dirt and debris. The iPhone camera is compact in size and weight, but also has high-quality optical range, with pixel sizes of around 1.75μm, making light collection for sensitive instrumentation feasible. The small pixel size allowed us to resolve the micron sized somatic cells without a lot of magnification. The sensor in the iPhone (and other modern smartphones) has low image noise and is sensitive to very small amounts of light.
Figure 2. The Milk Guardian analyzing a sample. Green light (1) illuminates the milk sample slide (2). Propidium iodide bound to blood cells emits red fluorescent light, which imaging optics (3) relays to the iPhone camera. Software processes the image (4) to provide a somatic cell count. (Image courtesy of Dairy Quality, Inc.)
Our application uses light from an LED (with an excitation filter that narrows the wavelength range1) to excite the fluorescent molecule propidium iodide, which is bound to inactivated white blood cells and is pre-loaded on slides. The farmer dips the slide into a sample of raw milk to draw the milk into the slide mixing chambers. He then inserts the slide into the Milk Guardian, which automatically turns on the excitation source and helps push the milk into the slide viewing window. The cells appear red under the green illumination (see Figure 2). Imaging optics capture the emitted light and relay it to the iPhone camera. Software then processes the image and provides a somatic cell count for the sample. The user obtains a clear visual reading within 30 seconds, and can take immediate action to bring the quality counts back in compliance, batch to batch.2 In this application, one small dairy farmer could save $20,000 a month in production by identifying and isolating milk that does not meet quality standards.
ASE Optics and Dairy Quality see medical, environmental, and industrial applications for the design in field testing for bacteria. There are numerous biomedical uses for the technology, since healthcare faces similar challenges in analyzing samples: laboratory delays, and testing that needs to be clear and readable by technicians in the field. The instrument offers inexpensive technology that is handheld, intuitive to use, and rugged. Smartphone-compatible design could be used in sensing, measurement, and imaging in several industries, creating new markets for technology companies. ASE Optics is working to support the commercialization of the Milk Guardian for these applications. The approach is one that can be utilized in the design of opto-mechanical systems for other biomedical clients.
Christopher Cotton is general manager and founder of optical engineering services firm ASE Optics. He has more than 20 years' experience in optical system design and analysis, and specializes in laser optics. He holds an MS in Optics from the University of Rochester (1990).
1. C. T. Cotton, Molecular imaging: optical system design improves fluorescence light capture, Laser Focus World 48(7), p. 47-50, 2012.