Algae Grown in Nickel Water Produce a Biochar That Detects Hydrogen Peroxide in 2 Seconds

Hydrogen peroxide occupies an unusual position in analytical chemistry. It is simultaneously a compound that industry intentionally uses in large volumes for bleaching, sterilization, and chemical synthesis, and a marker that appears involuntarily in biological systems under oxidative stress and in food and water when contamination occurs. Detecting it quickly at low concentrations therefore matters across a wide range of contexts - from clinical diagnostics measuring cellular oxidative damage to food safety monitoring to environmental testing.

Most electrochemical hydrogen peroxide sensors rely on enzymes, typically horseradish peroxidase or glucose oxidase variants, to catalyze the reaction used for detection. Enzymes are effective but fragile: they degrade over time, require controlled temperature and pH, and add cost and complexity to sensor fabrication. A study published in Biochar describes an enzyme-free alternative built from a material that did not previously exist: biochar made from marine microalgae that have been cultivated to accumulate nickel within their cells.

Biological metal enrichment rather than chemical mixing

The conventional approach to making metal-doped biochar is straightforward: produce biochar from some biomass, then treat it with a metal salt solution to deposit metal particles on or in the carbon structure. This works, but the distribution of metal particles is uneven, and the interface between particles and the carbon matrix may be poor.

The researchers took a different starting point. Marine microalgae of the species Picochlorum eukaryotum naturally accumulate metals from their growth environment. By cultivating the algae in a medium supplemented with nickel, the team caused the cells to incorporate nickel as they grew. When those cells were then converted to biochar through controlled pyrolysis - heating in a low-oxygen environment - the resulting material contained nickel nanoparticles distributed uniformly throughout the porous carbon structure, positioned where the cell biology placed them rather than deposited afterward.

"We wanted to design a sustainable sensor material using biological resources rather than fossil-based carbons," said the study's corresponding author. "Microalgae provide an ideal platform because they grow rapidly, accumulate metals naturally, and can be converted into functional carbon materials."

Detection performance

Electrodes coated with the nickel-enriched microalgae biochar were tested for hydrogen peroxide detection under several conditions. The material achieved a detection limit of 0.39 micromolar - low enough to capture clinically and environmentally relevant concentrations - with a response time of approximately two seconds. That combination of sensitivity and speed compares favorably with enzyme-based sensors, which typically require longer incubation periods and controlled conditions to function reliably.

The sensor was also tested in complex real-world sample matrices: seawater, milk, and juice. Recovery rates - the fraction of added hydrogen peroxide that the sensor correctly identifies in the presence of other dissolved compounds - were high across all three matrices. This is a significant practical requirement. A sensor that performs well in clean buffer solution but fails in food or environmental samples has limited applications. The nickel biochar sensor maintained its performance in conditions that approximate actual deployment environments.

"Our results show that biological metal enrichment during growth leads to much better catalytic performance than simply mixing metals with carbon afterward," the authors noted. "This approach opens a new route for designing functional biochar materials with controlled metal distribution."

The catalytic mechanism

The electrochemical detection relies on nickel catalyzing the oxidation of hydrogen peroxide at the electrode surface. Uniformly distributed nickel nanoparticles embedded in the porous biochar structure maximize the active surface area available for this catalytic reaction while the carbon matrix provides electrical conductivity to transfer the resulting signal. The combination is what the team describes as a consequence of biological versus chemical fabrication: cells position metals in functional arrangements that chemical deposition cannot replicate precisely.

Limitations and next steps

This work is an initial proof of concept for a specific sensor material and a specific analyte. The electrode fabrication process requires cultivating algae under controlled nickel supplementation conditions, which adds complexity compared with sensors built from commercially available carbon materials. Long-term stability testing - how the sensor performs after weeks or months of storage or repeated use - is not reported and would be needed before practical applications could be assessed.

The authors propose that the biological metal enrichment strategy could be extended to other metals and other biosensor applications by changing the cultivation medium composition. Whether other metal-algae combinations produce comparably well-distributed nanoparticles and useful catalytic properties is an empirical question that systematic follow-up work would need to address. Integration into portable or miniaturized analytical devices is identified as a future research direction but has not been demonstrated.