Electro-polymerization of Nafion perfluorinated resin and 3,4-ethylenedioxythiophene (EDOT) with two different surfactants yielded nanoscale improved surface coatings on carbon fiber microelectrodes. Increased sensitivity and good selectivity for sensing sub-second release of dopamine, serotonin and adenosine in the presence of large concentrations of ascorbic acid and DOPAC was demonstrated. Two different surfactants were used during electro-polymerization: sodium dodecyl sulfate or sodium dodecyl benzene sulfonate. With the improved nanoscale coatings, the dopamine signal is increased by 4X-9X, while the serotonin signal is increased by 4X, and the adenosine signal is increased by 3X compared to bare carbon. We measured the highest sensitivity of ∼ 34 nA/μM (5X increase from the bare carbon fiber) with the EDOT:Nafion and sodium dodecyl benzene sulfonate. Dopamine selectivity can be achieved using the full voltammetry curves with respect to ascorbic acid, serotonin and adenosine using distinguishing features of the voltammograms, such as differences in reduction or oxidation potentials and with respect to DOPAC using lower signals. Serotonin can be distinguished from dopamine by the difference in reduction potentials. Furthermore, a shift toward less positive potentials for the adenosine oxidation was observed with the coated carbon fibers. The novel surface coated electrodes can potentially improve in vivo measurements.

Simultaneous access to different biofluids enables an accurate analysis of multiple analytes, leading to a precision diagnosis and appropriate medication. Additionally, establishing a relationship between various markers in different biofluids and their correlation to biomarkers in blood allows the development of an algorithmic approach, which aids non-invasive diagnosis through single parameter monitoring. However, the main bottleneck that exists in multiple biofluid analyses for its clinical implementation is the requirement of an advanced microfluidic coupled device design, which empowers simultaneous collection and monitoring. To tackle this challenge, an epidermal wearable bio-fluidic patch that facilitates simultaneous on-demand extraction, sampling, and storage of sweat and interstitial fluid (ISF) together with monitoring of their corresponding counterions is presented. The clean room free development of a biofluidic patch is realized through 3D integration of laser patterned optimized microfluidic structures, a low-cost screen-printed stimulation module, and a potentiometric chloride (Cl⁻) and calcium (Ca²⁺) ion sensing module for adequate dual biofluid sampling and analysis. The developed Cl⁻ and Ca²⁺ ion-selective sensors exhibit good repeatability, selectivity, acceptable stability, and sensitivity. The proof-of-concept demonstration of the fabricated patch for simultaneous dual-sampling, storage, and monitoring of the sweat Cl⁻ and ISF Ca²⁺ on a healthy volunteer during different periods of the day leverages its potential in real-time personalized healthcare clinical usages. Furthermore, the patch's electronic interface and use of wireless transmission facilitates a point-of-care non-invasive lab-on-skin application for monitoring the health status of individuals.