The researchers used tailor-made printable inks stencil-printed as serpentine patterns on regular purple nitrile powder-free exam gloves to create stretchable, yet robust conductive circuits. The thumb is used as a sample collection surface and only sports a printed stretchable carbon disk to ensure the adhesion of analyte residues.
At the tip of the index, part of an electrochemical cell is printed, immobilizing the enzyme organophosphorus hydrolase (OPH) capped with a conductive semi-solid gel matrix (covering an enzymatic OPH/Nafion layer) for analyte diffusion from the collection pad towards the OPH enzyme layer on the working electrode. The enzyme reacts to the presence of organophosphate (OP) compounds, also known as nerve agents for their high neurotoxicity.
When a wearer of the glove swipes the thumb on a surface (for example that of a fruit) to test for the presence of OP compounds, closing the fingers to reach the tip of the index with the sample collection pad of the thumb completes the electrochemical cell.
The electrochemical detection is carried out using a wireless Bluetooth-based portable miniaturized potentiostat attached on the back of the hand. The biocatalytic OPH hydrolysis reaction produces p-nitrophenol which can be detected through scanning-potential square-wave voltammetry (SWV). The voltammetric results can then be displayed on a smartphone or any other connected mobile device.
This glove-based electrochemical biosensor has been developed as a wearable point-of-use and real-time screening tool for defense and food security applications. The glove and its sensing circuit were tested to prove the resilience and compliance of the printed traces against extreme mechanical deformations, bending and stretching up to 50% without impacting the biosensor results.
In all, the sensing finger (index) relies on three different layers of elastic inks printed on the nitrile glove surface. A silver layer (Ag/AgCl particles combined with Ecoflex elastomeric material) is used both as the reference electrode and the serpentine connections along the finger down to the third knuckle (where an adjustable ring bandage connects the glove to a hand-held potentiostat).
A second flexible layer made of a modified carbon ink (with an elastomeric styrene-isoprene co-polymer for stretchability) forms the working and counter electrodes, and a third transparent flexible and stretchable insulator layer covers the serpentine connections (while exposing the sensing area and square contact pads). The sample collection area on the thumb finger is much simpler, with a single printed circular pad of a stretchable carbon ink.
The researchers envisage that such a glove-embedded printable biosensor system could be extended to multiplexed chemical detection, with different reaction cells designed across different finger tips (to be successively probed with the thumb pad) or to address different detection requirements.
Such a glove could be produced at scale, to be cheap and disposable, for the real-time on-site screening of chemical threats for military, forensic, consumer protection and food safety applications.
This work was supported by the Defense Threat Reduction Agency Joint Science and Technology Office for Chemical and Biological Defense. For more, see “Wearable Flexible and Stretchable Glove Biosensor for On-Site Detection of Organophosphorus Chemical Threats.”
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