Recombinant Komagataella phaffii cells loaded with diaphorase-mimicking nanozymes for formaldehyde detection, detoxification and electricity generation from wastewater.

Formaldehyde (FA) is a toxic, volatile compound commonly used in industry and frequently found in polluted environments. Its rapid and dependable identification is vital for both environmental assessment and health protection. Microbial biosensors enhanced with nanomaterials offer promising platforms for FA sensing due to their sensitivity, cost-efficiency, and operational simplicity. However, unstable gene expression often limits the practical application of genetically modified microorganisms. To address these challenges, we developed a hybrid biosensing system based on Komagataella phaffii yeast cells engineered to overexpress formaldehyde dehydrogenase and further enriched with a diaphorase-mimicking nanocomposite (nMoAuCo). This nanozyme exhibits both an NADH-diaphorase activity and electrocatalytic properties, enabling efficient signal transduction and intracellular enzyme delivery. The resulting amperometric biosensor revealed a broad linear range (0.02-0.18 mM) and satisfactory sensitivity (475 A⋅M-1⋅m-2) toward FA. The modified cells were also utilized as a bioanodic catalytic unit in a microbial fuel cell (MFC), achieving an open-circuit voltage of 600 mV and a peak power density of 0.3 μW⋅cm-2 at 0.5 mM FA. The functioning of such an MFC in complex samples was confirmed by the application to real wastewater. Additionally, the infused yeast cells were immobilized in alginate gel and integrated into a fluidized-bed bioreactor, resulting in a 15-fold decrease in FA concentration without the formation of harmful byproducts. Overall, the developed multifunctional platform presents a sustainable approach for FA detection, detoxification, and simultaneous bioenergy production.