Dr. Melanie Rudolph Profile

Dr. Melanie Rudolph

at Univ of Arizona

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Proceedings Article | 2 May 2019 Paper

Printable transistors for wearable sweat sensing

Melanie Rudolph, Jonathan Harris, Erin Ratcliff

Proceedings Volume 11020, 110200N (2019) https://doi.org/10.1117/12.2518890

KEYWORDS: Electrodes, Polymers, Transistors, Sensors, Field effect transistors, Metals, Platinum, Biosensing, Ions, Polymer thin films

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Human performance monitoring (HPM) devices for sweat sensing in both civilian and military uses necessitate chemical sensors with low limits of detection, rapid read out times, and ultra-low volumes. Electronic and electrochemical sensing mechanisms for biomarker identification and quantification are attractive for overall ease of use, including robust, portable, fast readout, and simple operation. Transistors have the high signal gain required to sense low concentrations (μM to pM) at low volumes (μL to nL) in real-time (<1 minute), metrics not achievable by benchtop analytical techniques. Two main challenges currently prohibit the realization of transistor-based biosensors: i) the need for printed devices for low-cost, disposable sensors; and ii) the need to overcome diminished sensitivity in high ionic strength solutions. In this proof-of-concept work, we demonstrate organic electrochemical transistors (OECT) as a promising low cost, printable device platform for electrochemical detection of biomarkers in high ionic strength environments. This work focuses on how the materials choice and functionality impacts the electrochemical and sensor and transducer performance and determining the feasibility of reducing the size of the sensor to nanoliter volume detection. Initial studies target dopamine. Detection limits for simple electrochemical approaches using platinum or glassy carbon electrodes remain relatively high (~ 1-10 ng/mL or 50 nM). Using an OECT, we demonstrate an initial detection level of dopamine at ~ 10 pg/mL achieved without any selective binding modifications to the gate electrode at gate voltages below 1 V.

Proceedings Article | 2 May 2019 Paper

Predicting limits of detection in real-time sweat-based human performance monitoring

Melanie Rudolph, Jonathan Harris, Erin Ratcliff

Proceedings Volume 11020, 110200O (2019) https://doi.org/10.1117/12.2518885

KEYWORDS: Sensors, Adsorption, Electrodes, Molecules, Diffusion, Microfluidics, Active sensors, Advanced distributed simulations, Chemical elements, Field effect transistors

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Sweat-based human performance monitoring devices offer the possibility of real-time emotional and cognitive awareness in both civilian and military applications. Broad applicability and point of use necessitate non-invasive, printable, flexible, wearable chemical sensors with low power consumption. Sweat fluidics must enable movement of sweat across the sensor compartment within 1 minute to assure only fresh sweat is at the chemical sensor. The sensor material should have reaction kinetics to capture a sufficient number of target molecules for quantification in real-time (< 1minute). Chemical selectivity is critical in complex biofluids such as sweat, which may be comprised of 800+ biomarkers. Given these constraints, there continues to be significant technological barriers for translation from laboratory-based proof-of-concept demonstrations and scalable manufacturing of devices. Using finite element simulations, we focus on determining which sweat flow geometry and chemical capture dynamics are best suited to meet temporal performance requirements. Two common sensing approaches are compared and contrasted: bio-recognition chemical adsorption events and electrochemical detection. Responsivity of both mechanisms is shown to be highly dependent on fluid dynamics, analyte capture efficiency, analyte concentration, and reaction kinetics. Key metrics of temporal response and capture efficiency will be discussed for a number of state of the art electronic sensor materials, with a focus on the validity of printable platforms.

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