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Updated: May 29, 2026
A Microfluidic Chip for the Versatile Chemical Analysis of Single Cells
Published on: October 15, 2013
Human tear protein analysis enabled by an alkaline microfluidic homogeneous immunoassay
1Graduate Program in Bioengineering, The University of California, Berkeley-University of California, San Francisco, Berkeley, California 94720, United States.
Insights
This study introduces a novel microfluidic immunoassay for rapid, noninvasive tear protein analysis. The assay accurately quantifies lactoferrin, a biomarker for Sjögren
Area of Science:
- Biomedical Engineering
- Analytical Chemistry
- Ophthalmology
Background:
- Tear protein analysis offers potential for diagnosing ocular and systemic diseases noninvasively.
- Current methods for tear protein measurement face challenges in speed, quantity, and specificity.
- Sjögren's syndrome (SS) diagnosis relies on invasive procedures and lacks sensitive tear-based biomarkers.
Purpose of the Study:
- To develop the first microfluidic homogeneous immunoassay for rapid, quantitative, and specific tear protein biomarker detection.
- To optimize an assay for lactoferrin (Lf), a key biomarker for Sjögren's syndrome, in human tear fluid.
- To establish a protocol for eluting proteins from Schirmer strips for on-chip analysis.
Main Methods:
- Development and optimization of a homogeneous electrophoretic immunoassay on a microfluidic chip.
- Utilized <1 μL of human tear fluid for assay development.
- Characterized assay performance including accuracy, specificity, and limit of detection; developed protein elution protocol from Schirmer strips.
Main Results:
- Achieved rapid quantification of lactoferrin in <5 seconds at clinically relevant concentrations.
- The on-chip assay demonstrated accuracy within 15% of ELISA, specificity (<15% nonspecific signal), and a lower limit of detection of 3 ± 2 nM Lf.
- Successfully related on-chip measured Lf concentrations to ocular surface concentrations.
Conclusions:
- This work presents a first-in-kind, translatable microfluidic assay for Sjögren's syndrome diagnostics using tear fluid.
- The developed assay expands the capabilities of electrophoretic immunoassays for diverse protein targets.
- This advancement provides a crucial tool for rapid tear protein measurements, benefiting both basic research and clinical medicine.
Abstract:
The ability to probe the protein content of human tear fluid has enormous potential for deepening our understanding of ocular and systemic disease pathology and enabling novel noninvasive tear-based diagnostic technologies. To overcome current challenges in tear proteomic measurements, we report on the first microfluidic homogeneous immunoassay capable of making rapid, quantitative, and specific measurements of endogenous tear protein biomarkers in human tear fluid. Lactoferrin (Lf) is a tear-specific biomarker for Sjögren's syndrome (SS), a serious systemic autoimmune disease currently diagnosed through rudimentary volumetric and surface chemistry measurements and an invasive lip biopsy. We detail optimization of a homogeneous electrophoretic immunoassay for Lf in <1 μL of tear fluid at clinically relevant concentrations. In particular, we present assay development details and a final assay that enables quantification of Lf in <5 s in a clinically relevant range for SS diagnostics. Characterization suggests the on-chip assay is accurate to within 15% of ELISA, specific (<15% nonspecific signal), and with a lower limit of detection of 3 ± 2 nM Lf in human tear matrix. Additionally, we develop and characterize a protocol for eluting proteins from nitrocellulose Schirmer strips, the clinical de facto standard for tear collection and storage. We relate on-chip measured Lf concentrations back to ocular surface concentrations for the first time to our knowledge. Taken in sum, this work details important steps toward (1) expanding the set of proteins quantified by electrophoretic immunoassays to encompass a wider range of isoelectric points than has been reported, (2) creating a first-in-kind translatable assay with clinical relevance to SS diagnostics, and (3) expanding the analytical toolkit available for rapid tear protein measurements, as is relevant to the advancement of basic research and clinical medicine.
