The active ingredient of the ink is a pseudocapacitive spinel oxide, tin cobalt oxide with the chemical formula SnCo2O4, combined with conductive carbon nanofibers. Spinel oxides of this kind are attractive for electrochemical applications because their crystal structure offers multiple accessible oxidation states, allowing fast and reversible redox reactions at the electrode surface. In an energy storage context, this pseudocapacitive behaviour means charge is stored not only electrostatically at the interface between electrode and electrolyte, as in a conventional double-layer capacitor, but also through faradaic charge-transfer reactions that can substantially increase the amount of energy packed into a given area. The carbon nanofibers serve as a highly conductive skeletal framework that threads through the oxide particles, providing continuous pathways for electrons and helping to anchor the active material mechanically.

Screen printing was chosen as the deposition technique because it is one of the most manufacturing-friendly methods available for printed electronics. In screen printing, a viscous paste or ink is forced through a patterned mesh onto a substrate, allowing large areas to be patterned quickly with minimal material waste and without the vacuum equipment or photolithography required by conventional microfabrication. The challenge lies in formulating an ink whose rheology, viscosity, and solids loading allow clean transfer through the mesh while retaining the electrochemical activity of the functional particles. The researchers optimised the composition of the SnCo2O4 and carbon nanofiber blend, identifying a formulation designated SC-3 that delivered the best balance of conductivity, printability, and charge-storage performance.

When printed as micro-supercapacitor electrodes, the SC-3 material exhibited both pseudocapacitive and electric double-layer capacitive charge-storage mechanisms, a hybrid behaviour that combines the high power and long cycle life of double-layer storage with the higher capacitance of faradaic materials. The printed electrodes achieved an areal capacitance of 673.8 plus or minus 3.1 millifarads per square centimetre, an energy density of 93.58 plus or minus 1.5 microwatt-hours per square centimetre, and a power density of 1.353 plus or minus 3.0 milliwatts per square centimetre. These figures were reported with a relative standard deviation below one percent across three replicate measurements, indicating a high degree of reproducibility in the printing process. For microscale energy applications, where the electrode area is measured in square centimetres or less, such areal metrics are the relevant benchmarks rather than gravimetric values.

The same ink proved equally capable when deployed in sensing devices. A humidity sensor printed from the SC-3 formulation showed excellent operational stability, fast response and recovery times of 38 and 56 seconds respectively, low hysteresis of 1.46 percent, and a wide detection range spanning relative humidity values from 11 to 97 percent. Low hysteresis is a particularly important figure of merit for humidity sensors because it reflects how consistently the sensor returns to its baseline resistance after exposure to moist and dry conditions, a property that determines whether repeated measurements can be trusted without recalibration. The wide dynamic range means a single printed sensor could operate reliably in environments as different as dry indoor air and near-saturated tropical conditions.

The third application demonstrated by the team is arguably the most medically significant. When the SC-3 material was used to modify a screen-printed electrode, abbreviated SPE, the resulting electrochemical sensor exhibited excellent behaviour in detecting naproxen, a widely used non-steroidal anti-inflammatory drug. The sensor operated across a broad drug concentration range from 1 micromolar to 500 micromolar, covering concentrations relevant to both pharmaceutical quality control and environmental monitoring of waterways, where accumulated drug residues have become an emerging concern. Long-term stability testing showed that the sensor could measure naproxen reliably in tablet samples and in synthetic urine, with a relative standard deviation of 3.53 percent, plus or minus 0.72, demonstrating practical analytical performance beyond idealised laboratory conditions.

The researchers attribute the multifunctional performance to the interplay between the carbon nanofiber framework and the redox-active SnCo2O4. The nanofibers create a percolating conductive network that lowers the overall resistance of the printed film, while the spinel oxide contributes abundant active sites for both faradaic charge storage and surface reactions involved in sensing. In the humidity sensor, the oxide surface likely adsorbs water molecules and facilitates proton conduction, while in the electrochemical sensor the redox-active oxide catalyses the electron-transfer reaction of naproxen at the electrode surface. A single material satisfying these distinct physical mechanisms is what makes the platform genuinely multifunctional rather than a collection of coincidental performances.

The broader significance of the work lies in how it tackles the shortcomings of conventional standalone energy storage and sensing devices. Traditionally, a designer building a self-powered sensing node would need to integrate a supercapacitor made of one material system with a sensor made of another, often requiring incompatible deposition processes, adhesion layers, and thermal treatments. A single ink that can be printed into any of these device architectures simplifies supply chains, reduces fabrication steps, and opens the door to fully printed integrated systems in which energy storage and sensing elements are deposited side by side on the same substrate in the same manufacturing run. This is precisely the kind of process integration that printed electronics and the Internet of Things have long demanded.

The study also carries implications for sustainability and cost. Tin and cobalt oxides are relatively abundant compared with some of the precious-metal catalysts used in high-end electrochemical sensors, and carbon nanofibers can be produced at scale. Because the ink is screen-printable at ambient conditions, it does not require energy-intensive vacuum deposition, and the additive nature of printing means far less material is wasted compared with etch-based patterning. The authors describe their formulation as a scalable, affordable, multifunctional conductive ink platform aimed squarely at next-generation miniaturised microelectronics, positioning it as a practical route from laboratory materials chemistry to manufacturable devices.

The research, led by Shilpa Shetty, Mohammad Saquib, Selvakumar M, and Ramakrishna Nayak at the Manipal Institute of Technology, was published open access on 11 September 2026 in Advanced Composites and Hybrid Materials, with Shetty supported by a Dr T. M. A. Pai Fellowship from the Manipal Academy of Higher Education. As wearable health monitors, environmental sensor networks, and self-powered microdevices proliferate, the demand for materials that can store energy and sense their environment within the same printed footprint will only grow. This single-ink strategy, validated across three distinct device classes with quantified performance metrics, offers a compelling template for how multifunctional materials can compress device fabrication into a single, scalable printing step.

Subject of Research: A screen-printable multifunctional conductive ink based on tin cobalt oxide decorated carbon nanofibers for energy storage and sensing devices

Article Title: A single screen-printable multifunctional active ink platform based on tin cobalt oxide decorated carbon nanofibers for energy storage and sensing applications

Article References: Shetty, S., Saquib, M., M, S., & Nayak, R. (2026). A single screen-printable multifunctional active ink platform based on tin cobalt oxide decorated carbon nanofibers for energy storage and sensing applications. Advanced Composites and Hybrid Materials. https://doi.org/10.1007/s42114-026-02070-5

Image Credits: AI Generated

DOI: 10.1007/s42114-026-02070-5

Keywords: conductive ink, screen printing, tin cobalt oxide, carbon nanofibers, micro-supercapacitors, energy storage, humidity sensor, electrochemical sensor, naproxen detection, spinel oxide, printed electronics, sensors

The appeal of biochar lies in its remarkable combination of properties. It is cheap, abundant, and derived from renewable waste biomass such as agricultural residues, wood waste, sewage sludge, and even coffee grounds. Its three-dimensional hierarchical pore structure, spanning micropores below two nanometers, mesopores between two and fifty nanometers, and macropores above fifty nanometers, creates an enormous internal surface area for capturing molecules. Its surface is naturally decorated with oxygen-containing functional groups such as hydroxyl and carboxyl moieties that bind analytes through hydrogen bonding, electrostatic attraction, and pi-pi interactions. Yet pristine biochar has a critical weakness: its electrical conductivity is often too low for high-performance electrochemical sensing, and it lacks sufficient catalytically active sites. Hybridization solves this problem by pairing biochar with conductive or catalytic partners.

The review details how the choice of synthesis route fundamentally shapes the final material. Slow pyrolysis, operating at heating rates of 0.1 to 5 degrees Celsius per minute and temperatures between 300 and 600 degrees Celsius, maximizes biochar yield and produces more ordered carbon structures. Fast pyrolysis, with heating rates up to 200 degrees per minute, favors liquid and gaseous products instead. Microwave-assisted pyrolysis delivers rapid, uniform heating and often yields higher porosity, while hydrothermal carbonization processes wet biomass in water at 180 to 250 degrees Celsius under pressure, producing hydrochar rich in oxygen functional groups but lower in conductivity. Pyrolysis temperature is the single most influential parameter: higher temperatures boost carbonization, conductivity, and surface area, but strip away the very surface groups that enable analyte interaction, forcing researchers to strike a careful balance.

Once synthesized, biochar becomes a scaffold for nanoscale building blocks of different dimensionalities. Zero-dimensional metal and metal oxide nanoparticles, including gold, silver, platinum, copper oxide, and nickel oxide, anchor onto biochar surfaces to introduce catalytic sites and accelerate electron transfer. One-dimensional structures such as carbon nanotubes and nanowires act as conductive bridges between isolated domains, reducing charge-transfer resistance. Two-dimensional materials, including graphene, reduced graphene oxide, MXenes, and metal-organic frameworks, add high porosity and broad adsorption areas. Heteroatom doping with nitrogen, sulfur, or phosphorus modulates the electronic structure and creates defect sites that enhance electrocatalytic performance. The review stresses that these components are not interchangeable: each contributes a distinct function, and rational selection should be guided by the dominant analytical bottleneck of the target pollutant rather than by simply maximizing conductivity.

Translating these materials into working sensors requires equally careful electrode engineering. The authors survey five main strategies. Layer-by-layer assembly offers precise control over film thickness and the spatial distribution of active sites, though excessive multilayers can increase interfacial resistance. Electrochemical deposition grows catalytic nanostructures directly on the electrode with excellent electrical contact, allowing particle density and morphology to be tuned through deposition potential and time. Homogeneous pre-mixed casting remains the most common laboratory method, dispersing biochar hybrids in solvent with polymeric binders before drop-casting. Screen-printing and 3D printing promise scalable manufacturing of disposable electrodes and complex architectures with programmable porosity. Finally, bulk modification of carbon paste electrodes distributes the electroactive material throughout the electrode volume, allowing a fresh surface to be regenerated by simple polishing when fouling occurs, an advantage for continuous monitoring in chemically complex matrices.

The sensing mechanism itself follows an elegant sequence. Contaminants first diffuse from the bulk solution into the porous biochar network, where they are enriched through adsorption interactions. The hybrid components then accelerate electron-transfer kinetics by providing conductive pathways and electrocatalytically active sites, converting the accumulated analyte into amplified electrochemical signals with improved sensitivity and lower detection limits. This capture-to-transduction logic is illustrated by striking examples from the recent literature. A walnut-shell biochar electrode coated with electropolymerized poly-tyrosine simultaneously detected cadmium, lead, copper, and mercury ions in water and soil samples. Oxygen-vacancy-engineered nickel cobalt oxide nanorods grown on coconut-shell biochar achieved highly sensitive lead detection, with the hybrid interface dramatically outperforming either component alone.

Pesticide sensing showcases a second design principle. For electroactive compounds such as carbendazim, a biochar and reduced graphene oxide nanocomposite couples local analyte enrichment with improved signal transport, with the hybrid producing higher oxidation currents than either material individually. For weakly responsive pesticides like malathion, catalytic activation becomes essential: a ternary nanocomposite of graphitic carbon nitride, copper oxide, and derived biochar exhibited the smallest peak separation, lowest charge-transfer resistance, and highest stripping current among tested electrodes. A porous biochar decorated with nano-zero-valent iron detected glyphosate through a combination of porous diffusion, electrostatic attraction, and hydrogen bonding, with the iron domains serving as electron-transfer-active centers. The authors note, however, that real-matrix validation, fouling resistance, and repeated-use stability remain underexamined across much of this literature.

Pharmaceuticals and emerging contaminants push the field toward matrix-reliability engineering. A sludge-derived biochar and graphite conductive ink, printed on transparency sheets using nail polish as a binder, detected the antibiotic imipenem in environmental samples, with biochar loading optimized as a genuine design variable that lowered charge-transfer resistance. A 3D-printed electrode combining acrylonitrile butadiene styrene waste, graphite, and rice husk biochar monitored levofloxacin in river and supply water after simple dilution. For plastic-associated chemicals, a zinc oxide and biochar nanohybrid detected bisphenol A in water, while a magnetite-activated biochar sensor targeted tetrabromobisphenol A. PFAS and microplastics remain frontier challenges: biochar can capture these persistent pollutants effectively, but converting that capture into a measurable electrochemical signal requires recognition layers and transduction elements that are only beginning to be developed. Early work has shown biochar electrodes detecting roughly 100-nanometer polystyrene microplastics, hinting at what may become possible.

Looking ahead, the review identifies biochar-based conductive inks as a potential game-changer. A biochar ink developed for malathion detection produced a current response roughly ten times higher than graphite-based electrodes, attributed to greater active-site availability, enhanced interfacial charge transfer, and higher hydrophilicity. If conductivity, dispersion stability, and printability can be reliably optimized, such inks could offer a sustainable alternative to commercial graphene and carbon nanotube formulations for screen-printed and flexible devices. The authors also call for artificial intelligence and machine learning to predict how feedstock, pyrolysis conditions, and modification strategies shape material properties, and for computational screening of hybrid compositions before synthesis. The central challenges remain reproducibility, given the intrinsic variability of biochar, and the gap between laboratory demonstrations and field deployment in wastewater, agricultural runoff, and seawater. But the trajectory is clear: a material once valued simply for making soil fertile may soon stand guard over the world’s water, one electron at a time.

Subject of Research: Biochar-based hybrid nanocomposites for electrochemical sensing of environmental contaminants

Article Title: Advanced functional biochar-based hybrid nanocomposites for electrochemical sensing platforms in environmental monitoring

Article References: Poorahong, S., Naorungroj, S., Jesadabundit, W., Thangphatthanarungruang, J., Promphet, N., Darayen, J., Wonsawat, W., Boctor, J. N. T., Murphy, D. V., Ozer, T., Chailapakul, O., & Jampasa, S. (2026). Advanced functional biochar-based hybrid nanocomposites for electrochemical sensing platforms in environmental monitoring. Discover Electrochemistry, 3(1), Article 72. https://doi.org/10.1007/s44373-026-00158-7

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00158-7

Keywords: biochar, electrochemical sensors, nanocomposites, environmental monitoring, heavy metals, pesticides, PFAS, graphene, metal-organic frameworks, conductive ink, pyrolysis, water pollution