Mimicking an Enzyme-Based Colorimetric Aptasensor for Antibiotic Residue Detection in Milk Combining Magnetic Loop-DNA Probes and CHA-Assisted Target Recycling Amplification

A mimicking-enzyme-based colorimetric aptasensor was developed for the detection of kanamycin (KANA) in milk using magnetic loop-DNA-NMOF-Pt (m-L-DNA) probes and catalytic hairpin assembly (CHA)-assisted target recycling for signal amplification. The m-L-DNA probes were constructed via hybridization of hairpin DNA H1 (containing aptamer sequence) immobilized magnetic beads (m-H1) and signal DNA (sDNA, partial hybridization with H1) labeled nano Fe-MIL-88NH₂-Pt (NMOF-Pt-sDNA). In the presence of KANA and complementary hairpin DNA H2, the m-L-DNA probes decomposed and formed an m-H1/KANA intermediate, which triggered the CHA reaction to form a stable duplex strand (m-H1-H2) while releasing KANA again for recycling. Consequently, numerous NMOF-Pt-sDNA as mimicking enzymes can synergistically catalyze 3,3′,5,5′-tetramethylbenzidine (TMB) for color development. The aptasensor exhibited high selectivity and sensitivity for KANA in milk with a detection limit of 0.2 pg mL^–1 within 30 min. The assay can be conveniently extended for on-site screening of other antibiotics in foods by simply changing the base sequence of the probes

Cellulose-Based Composite Macrogels from Cellulose Fiber and Cellulose Nanofiber as Intestine Delivery Vehicles for Probiotics

Cellulose-based composite macrogels made by cellulose fiber/cellulose nanofiber (CCNM) were used as an intestine delivery vehicle for probiotics. Cellulose nanofiber (CNF) was prepared by a 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation system, and the carboxyl groups in CNF acted as pore size and pH responsibility regulators in CCNMs to regulate the probiotics loading and controlled release property. The macrogel presented a porosity of 92.68% with a CNF content of 90%, and the corresponding released viable <i>Lactobacillus plantarum</i> (<i>L. plantarum</i>) was up to 2.68 × 10⁸ cfu/mL. The porous structure and high porosity benefited <i>L. plantarum</i> cells to infiltrate into the core of macrogels. In addition, the macrogels made with high contents of CNF showed sustainable release of <i>L. plantarum</i> cells and delivered enough viable cells to the desired region of intestine tracts. The porous cellulose macrogels prepared by a green and environmental friendly method show potential in the application of fabricating targeted delivery vehicles of bioactive agents