Microalgae-derived cellulose/inorganic nanocomposite rattle-type microspheres as an advanced sensor for pollutant detection

Abstract The versatility of rattle-type microspheres is tightly correlated with the composition and morphology. Exploring advanced rattle-type microspheres with simultaneous controllable composition and micro/nanostructures via novel designed and regulated strategies may have great advantages for performing complex tasks. Herein, cellulose/inorganic hybrid rattle-type microspheres, produced using microalgae as natural chemical reservoirs, microreactors and matrix, is reported. By adjusting only pH and temperature, rattle-type microspheres with simultaneously controllable mesoporous outer shells (19.4 to 46.3 nm) and multicomponent nanocores (i.e., Ca5(PO4)3OH and Fe3O4/MgFe2O4) are obtained using microalgae as single-source precursors. Especially, the rattle-type microspheres-mediated immunosensor shows ultrahigh sensitivity for the detection of trace microcystin-LR in complex real water samples with a limit of quantitation of 0.05 ng/mL, which is a 10-fold improvement compared with conventional enzyme linked immunosorbent assays. Enhancement of the sensitivity is due to the tailorability and functionality in both the hollow shells and the cores of the rattle-type microspheres. The finely controlled pore-size, void space and natural carboxyl groups of the shell are beneficial for enzymes loading and for bio-conjugation. The cores contain magnetite and hydroxyapatite nano-particles, which can be utilised for magnetic separation and for anchoring more enzymes, resulting in considerable signal amplification. This work opens up a new and green route for the construction of rattle-type microspheres with tunable compositions and porosities, which makes it a flexible platform for various applications in immunoassay, biosensors, enrichment and separation of target substances, drug-delivery, and environmental remediation.