Programmable electrodes integrated into wearable devices enable selective molecular detection in complex formulations such as cosmetics and skincare products.
(Nanowerk Spotlight) Detecting specific chemicals in complex mixtures remains a persistent scientific challenge. When multiple compounds exist together – as in cosmetics, pharmaceuticals, or biological fluids – traditional sensors fail to distinguish individual molecules, often detecting everything simultaneously and producing muddled results.
“The most exciting outcome of our work is developing programmable, screen-printed, flexible porous electrodes that selectively enhance or suppress electrochemical signals through a scalable, low-cost surface engineering strategy,” explains Professor Jeerapan. “This is the first report demonstrating how anodization combined with acid-induced porosity can systematically tailor the electrochemical behavior of flexible printed electrodes.”
Traditional electrochemical sensors face a fundamental problem: they detect everything at once. The Thai researchers took a radically different approach by engineering the electrode surface itself to perform filtering.
Their three-step process begins with screen-printing a special ink containing carbon nanotubes, graphene, and sodium hydrogen carbonate particles onto a flexible substrate. Next, acid treatment dissolves the sodium hydrogen carbonate, creating a highly porous structure with 214% greater surface area than conventional electrodes. Finally, electrochemical anodization at precisely controlled voltages (1.75-2.25V) introduces oxygen-containing functional groups that create a negatively charged surface.
This surface engineering transforms how the electrode interacts with different molecules:
Neutral and positively charged molecules (like hydroquinone or ruthenium complexes) receive an “ON” signal – their detection is enhanced by up to 880%, depending on the analyte, compared to standard electrodes
Negatively charged molecules (like salicylic acid or iron complexes) receive an “OFF” signal – their detection is actively suppressed due to electrostatic repulsion.
“What makes our approach powerful is that we can program these ON/OFF states by adjusting the anodization conditions,” explains Dr. Natcha Rasitanon, co-author of the study. “We discovered that applying specific voltages creates the perfect balance of surface functionality for maximum selectivity.”
Concept of screen-printed porous nanocomposite electrode and its applications. (A) Fabrication of screen-printed porous nanocomposite electrode prepared by acid treatment and anodization, including SEM images of (1) CNT electrode, (2) PCNT2.0 electrode, (3) the photo of PCNT2.0 electrode on a flexible substrate, and (4) the illustration of selective effect toward positively charged, neutral, and negatively charged analytes on the surface of the PCNT2.0 electrode. (B–C) Conceptual illustration comparing (B) the CNT electrode surface and (C) the PCNT2.0 electrode surface. The illustrations show the oxidation reactions of HQ and SA, and the reduction reactions of hexaammineruthenium(III) ion ([Ru(NH3)6]3+) and hexacyanoferrate(III) ion ([Fe(CN)6]3−) on their respective surfaces, with conceptual SWV responses. The PCNT2.0 electrode demonstrates enhanced sensitivity and selective rejection in the SWV responses. (D) Illustration of a flexible PCNT2.0 electrode printed on a wearable glove for on-finger electrochemical detection, revealing analytical responses to a sample containing HQ and SA. (E) Flexible porous glucose biosensor relying on adsorbed HQ redox mediator and surface-coated glucose oxidase (GOx) enzyme biomolecules, enabling amperometric glucose detection. (Image: Reprinted from DOI:10.1021/acssensors.4c03519, CC BY)
The Electrostatic Filtering Mechanism
The science behind this selectivity lies in the surface charge created during anodization. By precisely controlling the electrochemical oxidation process, the researchers introduced oxygen-containing groups that impart a negative charge to the electrode surface.
“At pH 7, hydroquinone remains neutral while salicylic acid becomes negatively charged due to its carboxylic group,” explains lead author Adisak Pokprasert. “This creates an electrostatic interaction where neutral hydroquinone can freely approach the electrode surface, while negatively charged salicylic acid is repelled.”
This effect is dramatically demonstrated in the hydroquinone-to-salicylic acid detection ratio, which improves from less than 1 in conventional electrodes to over 10 in the engineered porous electrodes. The team verified this selective behavior using various electrochemical techniques and model compounds with different charges.
For practical wearable applications, the electrodes must maintain performance under repeated bending and flexing. The team conducted extensive mechanical testing, demonstrating that their electrodes maintain consistent electrical resistance and electrochemical performance even after 100 bending cycles at angles ranging from 45° to 180°.
“This mechanical resilience is crucial for wearable sensors that need to conform to body movements,” notes Professor Jeerapan. “Our electrodes maintain their selective detection capabilities even under significant mechanical stress.”
To demonstrate real-world utility, the researchers integrated their electrodes into a wearable glove platform. By touching skincare products with the glove, users could immediately detect regulated compounds like hydroquinone, even in the presence of salicylic acid – a capability not possible with conventional sensors that would be confused by the mixture.
Beyond Skincare: Enhanced Biosensing Applications
The enhanced surface properties also proved valuable for biosensing applications. The researchers showed that their porous surface dramatically improved the adsorption of hydroquinone redox mediators used in glucose biosensors.
“When we compared conventional electrodes with our engineered porous electrodes in glucose sensing, we observed a 3662% increase in current response,” says Professor Jeerapan. “This massive enhancement stems from our electrode’s ability to better immobilize both the redox mediator and the enzyme needed for glucose detection.”
This improvement demonstrates how the technology’s benefits extend beyond simple chemical detection to more complex biosensing systems.
Advantages Over Current Technology
Several competing approaches exist for selective electrochemical detection, but they typically involve additional components or processing steps:
Selective membranes add bulk and reduce flexibility
“Our approach relies solely on surface engineering of the electrode material itself,” explains Professor Jeerapan. “By programming the inherent surface properties, we achieve selectivity without adding complexity.”
Future Directions and Challenges
While the technology shows immediate promise for skincare product analysis and glucose monitoring, the researchers are already working on expanding its capabilities.
“We’re now focusing on programming the electrodes to detect different combinations of molecules by fine-tuning the anodization parameters,” says Professor Jeerapan. “The goal is a system where users can adjust selectivity for different applications by simply changing the surface programming.”
Challenges remain in optimizing stability for long-term use and scaling up manufacturing, but the fundamental approach demonstrates that programmable surfaces can transform how electrochemical sensors interact with complex samples. This ability to selectively amplify desired signals while suppressing interference represents a critical advancement that could enable more reliable chemical monitoring in fields ranging from healthcare to environmental testing.
“What excites me most is how this approach fundamentally changes what’s possible with printed electrochemical sensors,” concludes Professor Jeerapan. “Instead of designing separate sensors for each application, we’re moving toward universal platforms that can be programmed for different detection needs – similar to how software can reprogram hardware for different functions.”
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