Complex biological fluids without
pretreatment, separation, or
purification impose stringent limitations on the practical deployment
of label-free plasmonic biosensors for advanced assays needed in point
of care applications. In this work, we present an enzyme-free plasmonic
neurotransmitter dopamine biosensor integrated with a microfluidic
plasma separator. This integrated device allows the in-line separation
of plasma directly from the bloodstream and channels it to the active
detection area, where inorganic cerium oxide nanoparticles function
as local selective dopamine binding sites through strong surface redox
reaction. A thorough understanding and engineering of the nanoparticles
is carried out to maximize its dopamine sensitivity and selectivity.
We obtain detection of dopamine at 100 fM concentration in simulated
body fluid and 1 nM directly from blood without any prior sample preparation.
The detection selectivity is found to be at least five-times higher
compared to the common interfering species. This demonstration shows
the feasibility of the practical implementation of the proposed plasmonic
system in detection of variety of biomarkers directly from the complex
biological fluids.
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