A Four-Channel Electrical Impedance Spectroscopy Module for Cortisol Biosensing in Sweat-Based Wearable Applications

A four-channel electrochemical impedance spectroscopy (EIS) analyzer module has been demonstrated on flexible chemi-impedance sensors fabricated with gold electrodes for wearable applications. The module can perform time division multiplexed (TDM) impedance measurements on four sensors at 1 kHz. In this work, we characterize the system for the detection of cortisol in an ultralow volume (1-3 µL) of perspired human sweat, sensor performance, and effects during continuous cortisol dosing and with pH and temperature variations expected on the surface of the skin that would be representative of use conditions as seen by a wearable device. Detection of cortisol was shown for concentrations of 1 pg/mL to 200 ng/mL in both synthetic and perspired human sweat, and output response reported as a change in impedance with varying cortisol concentrations. Continuous dose testing was performed to demonstrate the stability of the sensors over prolonged periods of operation for cortisol concentrations within the physiologically relevant range of 10-200 ng/mL reported in human sweat. Temperature and pH effects testing was performed for pH range 4-8 and in a temperature chamber for the clinical range reported on the surface of human skin: 25-40 °C. The cortisol sensor demonstrated stability of operation with 7.58% variability under these conditions.

Flexible Molybdenum Electrodes towards Designing Affinity Based Protein Biosensors

Molybdenum electrode based flexible biosensor on porous polyamide substrates has been fabricated and tested for its functionality as a protein affinity based biosensor. The biosensor performance was evaluated using a key cardiac biomarker; cardiac Troponin-I (cTnI). Molybdenum is a transition metal and demonstrates electrochemical behavior upon interaction with an electrolyte. We have leveraged this property of molybdenum for designing an affinity based biosensor using electrochemical impedance spectroscopy. We have evaluated the feasibility of detection of cTnI in phosphate-buffered saline (PBS) and human serum (HS) by measuring impedance changes over a frequency window from 100 mHz to 1 MHz. Increasing changes to the measured impedance was correlated to the increased dose of cTnI molecules binding to the cTnI antibody functionalized molybdenum surface. We achieved cTnI detection limit of 10 pg/mL in PBS and 1 ng/mL in HS medium. The use of flexible substrates for designing the biosensor demonstrates promise for integration with a large-scale batch manufacturing process.

Electrical nanowell diagnostics sensors for rapid and ultrasensitive detection of prostate-specific antigen

Aim: Alumina nanowell based disposable diagnostic biosensor for detecting and quantifying levels of prostate-specific antigen (PSA) from human serum has been designed, fabricated and tested. Materials & methods: The biosensors were designed by integrating nanoporous alumina membranes onto printed circuit board platforms, resulting in the generation of high-density nanowell arrays with gold base electrodes. The size and density of the nanowells were leveraged toward achieving sieving action for size-based exclusion of nonspecific molecules and size-based confinement of the target PSA molecules. Results & conclusion: We demonstrated PSA detection between 0.01 and 1000 ng/ml and detection and quantification of PSA from a 17 patient cohort validated using the Beckman Access system with >95% correlation.

Nanochannel-based electrochemical sensor for the detection of pharmaceutical contaminants in water

Effective real-time monitoring is the key to understanding and tackling the issue of pharmaceutical contamination of water. This research demonstrates the utility of an alumina nanochannel-based electrochemical sensor platform for the detection of ibuprofen in water derived from various sources. Our results indicate that the sensor is highly sensitive with a limit of detection at 0.25 pg mL(-1). The novel sensor described here has potential for application as a simple, rapid, inexpensive and highly reliable method for real-time environmental water quality assessment.