Microfluidic immunoassays as rapid saliva-based clinical diagnostics

doi:10.1073/pnas.0607254104

Microfluidic immunoassays as rapid saliva-based clinical diagnostics

^†Biosystems Research Department, Sandia National Laboratories, Livermore, CA 94550; and
^§Michigan Center for Oral Research, School of Dentistry, University of Michigan, Ann Arbor, MI 48106

Edited by Robert H. Austin, Princeton University, Princeton, NJ, and approved January 11, 2007 (received for review August 21, 2006)

Abstract

At present, point-of-care (POC) diagnostics typically provide a binary indication of health status (e.g., home pregnancy test strip). Before anticipatory use of diagnostics for assessment of complex diseases becomes widespread, development of sophisticated bioassays capable of quantitatively measuring disease biomarkers is necessary. Successful translation of new bioassays into clinical settings demands the ability to monitor both the onset and progression of disease. Here we report on a clinical POC diagnostic that enables rapid quantitation of an oral disease biomarker in human saliva by using a monolithic disposable cartridge designed to operate in a compact analytical instrument. Our microfluidic method facilitates hands-free saliva analysis by integrating sample pretreatment (filtering, enrichment, mixing) with electrophoretic immunoassays to quickly measure analyte concentrations in minimally pretreated saliva samples. Using 20 μl of saliva, we demonstrate rapid (<10 min) measurement of the collagen-cleaving enzyme matrix metalloproteinase-8 (MMP-8) in saliva from healthy and periodontally diseased subjects. In addition to physiologically measurable indicators of periodontal disease, conventional measurements of salivary MMP-8 were used to validate the microfluidic assays described in this proof-of-principle study. The microchip-based POC diagnostic demonstrated is applicable to rapid, reliable measurement of proteinaceous disease biomarkers in biological fluids.

Footnotes

^‡To whom correspondence should be addressed at:
Sandia National Laboratories, P.O. Box 969, MS 9292, Biosystems Research Department, Livermore, CA 94550.
E-mail: aeherr{at}sandia.gov
Author contributions: A.E.H., A.V.H., D.J.T., and A.K.S. designed research; A.E.H., A.V.H., D.J.T., and H.M.T. performed research; A.E.H., A.V.H., D.J.T., J.S.B., and W.V.G. contributed new reagents/analytic tools; A.E.H. and H.M.T. analyzed data; and A.E.H. and A.K.S. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS direct submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0607254104/DC1.
Abbreviations:

POC,

point-of-care;

μCEI,

microchip electrophoretic immunoassay;

MMP-8,

matrix metalloproteinase-8;

αMMP-8*,

fluorescently labeled mAb to MMP-8;

BSA*,

fluorescently labeled BSA;

LIF,

laser-induced fluorescence.
Freely available online through the PNAS open access option.