Blood Tells Everything, Nothing Else Can

Managing chronic diseases (diabetes, autoimmune disorders, organ transplant rejection) requires frequent measurement of blood biomarkers — glucose, drug levels, inflammatory markers, immune cell counts — through venipuncture or fingerstick blood draws. No wearable or implantable system can continuously measure clinically actionable molecular biomarkers non-invasively. Existing continuous glucose monitors (CGMs) are the only commercial success, but they measure interstitial fluid (not blood), require subcutaneous insertion, and can only measure one analyte (glucose). Tear fluid contains hundreds of biomarkers that correlate with blood levels (glucose, cortisol, immunoglobulins, cytokines, drug metabolites), but no sensor technology can simultaneously measure multiple tear biomarkers continuously, at clinically relevant concentrations, without interfering with normal tear film function or vision.

Over 129 million Americans have at least one chronic disease requiring ongoing biomarker monitoring. Diabetics perform 2–4 daily fingersticks or wear CGMs; transplant patients require monthly blood draws for immunosuppressant drug levels; autoimmune patients need periodic inflammatory marker panels. A wearable tear-based monitoring system that could continuously track multiple biomarkers would enable real-time therapeutic dose adjustment (closed-loop drug delivery), early detection of disease flares, and reduced clinical visit burden. The global biosensor market exceeds $28 billion, driven by demand for continuous, non-invasive monitoring.

Smart contact lenses for glucose monitoring have been pursued by Google/Verily (project abandoned in 2018), Samsung, and multiple academic groups. The core challenge is that tear glucose concentrations are ~10× lower than blood glucose and lag behind blood levels by 10–30 minutes, making real-time glycemic control unreliable. Additionally, reflex tearing (from irritation, emotion, or wind) dilutes biomarker concentrations unpredictably. Electrochemical sensors embedded in contact lenses face biocompatibility challenges — enzyme-based sensors degrade in the tear film environment within hours, and the power requirements for continuous measurement cannot be met by current flexible battery or wireless power technology at contact lens scale. Tear collection devices (Schirmer strips, capillary tubes) are used in research but are episodic, not continuous, and tear sample volumes are tiny (5–15 μL), limiting the number of analytes measurable per collection.

A wearable tear-contact platform (punctal plug, contact lens, or conjunctival insert) with integrated multi-analyte biosensors that can: (1) continuously sample tear fluid without disrupting the tear film or causing irritation; (2) detect multiple biomarkers simultaneously at picomolar-to-nanomolar concentrations; (3) transmit data wirelessly to a smartphone or closed-loop drug delivery system; (4) maintain sensor stability and calibration for days to weeks in the ocular environment. The ARPA-H OCULAB program specifically envisions a punctal-plug-based platform (inserted into the tear drainage duct) that avoids the corneal surface, potentially solving the biocompatibility and vision-interference challenges of contact lens approaches.

A student team could characterize the correlation between tear and blood concentrations for a panel of clinically relevant biomarkers (cortisol, CRP, immunoglobulin A) using paired tear and blood samples from healthy volunteers, establishing the validation data needed for a tear-based monitoring system. An engineering team could prototype a miniaturized multi-analyte electrochemical sensor array on a flexible substrate, testing stability and sensitivity in simulated tear fluid. Relevant disciplines: biomedical engineering, analytical chemistry, ophthalmology, electrical engineering, materials science.