This article describes a prototype system for quantifying bioassays, and for exchanging the results of the assays digitally with physicians located off-site. The system uses paper-based microfluidic devices for running multiple assays simultaneously, camera phones or portable scanners for digitizing the intensity of color associated with each colorimetric assay, and established communications infrastructure for transferring the digital information from the assay site to an offsite laboratory for analysis by a trained medical professional; the diagnosis then can be returned directly to the healthcare provider in the field. The microfluidic devices were fabricated in paper using photolithography, and were functionalized with reagents for colorimetric assays. The results of the assays were quantified by comparing the intensities of the color developed in each assay with those of calibration curves. An example of this system quantified clinically relevant concentrations of glucose and protein in artificial urine. The combination of patterned paper, a portable method for obtaining digital images, and a method for exchanging results of the assays with off-site diagnosticians offers new opportunities for inexpensive monitoring of health, especially in situations that require physicians to travel to patients (e.g., in the developing world, in emergency management, and during field operations by the military) to obtain diagnostic information that might be obtained more effectively by less valuable personnel.

A new acoustic sensor geometry, the magnetic acoustic resonant sensor (MARS), is described. The device comprises a circular 0.5-mm-thick resonant plate fabricated from a wide variety of nonpiezoelectric materials and coated on the underside with a 2.5-microm-thick aluminum film. Harmonic radial shear waves over at least a 2 orders of magnitude frequency range can be induced in the resonant plate by enhanced magnetic direct generation using a noncontacting rf coil and NdFeB magnet. Mass loading with adherent aluminum films produced frequency changes of 106 Hz/nm (40.8 Hz/ng-mm(-2)), while contact with viscous fluids resulted in maximum changes of 15 446 Hz/cP. At an operating frequency of 50 MHz, the device detected viscosity changes as low as 0.0006 cP. The adsorption of proteins such as human IgG and the binding of a complementary antigen, goat anti-human IgG, on the upper nonmetallized surface of the device has been monitored with a detection limit of approximately 75 ng/mL. The binding of substrates and allosteric effectors to glycogen phosphorylase b has provided evidence that the device is very sensitive to viscoelastic changes in adsorbed proteins. The MARS device generates radial shear acoustic waves over a broad bandwidth that are unaffected by the conductivity of the solution. These results suggest that simple metal, glass, crystalline, or polycrystalline plates can be used as a new type of tunable acoustic immunosensor.

A magnetic acoustic resonator sensor was silanized with octadecyltrichlorosilane in order to produce a hydrophobic surface. Confirmation of the presence of the silane film was obtained from quantitative X-ray photoelectron spectroscopy and from measurement of advancing water contact angle. Frequency shifts for operation of the device in water, compared with air, were much smaller than for bare, untreated sensors. This result is consistent with analogous experiments conducted with the thickness-shear mode acoustic wave sensor. Atomic force microscopy showed that the cavities (depth, 2.9 nm; width, 11 nm) present on the bare surface numbered about 2860 per square micrometer. The calculated frequency shift associated with cavity-trapped water for the hydrophilic sensor was about half the value found by experimental measurement, assuming all similarsized cavities on the hydrophobic device are filled with gas. Furthermore, since the cavities on the latter surface were largely filled by silane the level of supposed trapped gas was much reduced, leading to a gross overestimate of the possible air to water shift in frequency. The results of this work confirm that an alternative explanation for surface free energy effects connected to acoustic device responses is required.

No abstract