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In this study, we integrated genetic detection for polymerase chain reaction (PCR) with microfluidics technology for the detection of peanut DNA. A cross-junction microchannel was used to induce emulsion droplets of water in oil for PCR on a chip. Compared with the single-phase flow, the emulsion droplet flow exhibited a 7.24% lower evaporation amount and prevented air bubble generation. PCR results of the droplet microfluidic PCR chip for peanut DNA fragment detection was verified by comparison with a commercial PCR thermal cycler and increased fluorescence intensity in SYBR Green reagent-based PCR. Moreover, PCR on the microfluidic PCR chip was successful for sesame, Salmonella spp., and Staphylococcus aureus. The droplet microfluidic PCR device developed in this study can be applied for peanut detection in the context of food allergy.

Mushroom tyrosinase was immobilized on modified polystyrene- polyamino styrene (PSNH) and polymethylchloride styrene (PSCL)-to produce L-DOPA from L-tyrosine. Glutaraldehyde was used as an activating agent for the PSNH to immobilize the tyrosinase, and 10% (w/v) glutaraldehyde was optimal in conferring the highest specific activity (11.96 U/g) to the PSNH. Methylchloride on the PSCL was directly linked with the tyrosinase, and 1.5 mmol of Cl/g was optimal in attaining the specific activity of 17.0 U/g. The temperature and optimal acidity were, respectively, 60 degrees C and pH 5.5 for the PSNH, and 70 degrees C and pH 3.0 for the PSCL. In a 50-mL batch reactor working over 36 h, the L-DOPA production rate at 30 degrees C was 1.44 mg/(L x h) for the PSNH and 2.33 mg/(L x h) for the PSCL. The production rate over 36 h was 3.86 mg/(L x h) for the PSNH at 60 degrees C and 5.54 mg/(L x h) for the PSCL at 70 degrees C. Both of the immobilized enzymes showed a remarkable stability with almost no change in activity after being stored wet. The operational stability study indicated a 22.4% reduction in L-DOPA production for the PSNH and an 8.63% reduction for the PSCL over seven runs (each run was for 144 h at 30 degrees C) when the immobilized enzymes were used under turnover conditions. The immobilized tyrosinase was more stable on the PSCL than on the PSNH.