A spherical iron oxide precursor was prepared using a solvothermal method, and then treated thermally at 400 • C to obtain α-Fe 2 O 3 nanoparticles. The structures and morphology of the as-obtained products were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The results showed that the diameter of the α-Fe 2 O 3 nanoparticles was approximately 500 nm. In addition, we formed the α-Fe 2 O 3 nanoparticles into a thick film as a gas sensor and performed a gas sensing test. When the working temperature was set at 250 • C, the α-Fe 2 O 3 nanoparticle displayed very good selectivity and high sensitivity for trimethylamine (TMA). The minimum detection was as low as 1 ppm, and the response value for 100 ppm TMA gas was 27.8. Taken together, our findings illustrated that the α-Fe 2 O 3 nanoparticles could be used as a gas-sensitive material to test the freshness of fish.

Fluorescent detection is a practical kind of methods to use in heavy metal ions detection technology. Carbonized Polymer Dots (CPDs) is good carbon-like material with low toxicity, green, ion-response. In this work, we successfully synthesized a yellowing fluorescent CPDs from folic acid. The luminescence intensity of CPDs decreased with the increase of copper ion content, and the detection limit was 0.44ppm.

Ferrocene (Fc) is an organometallic compound of sandwich structure. As the anticancer and excellent electrical activities, ferrocene and its derivatives have many applications in electrochemical monitoring [1-3]. Hydrogen peroxide (HP), with strong permeability and oxidation properties, is the product of many peroxidase catalyzed reaction, and it is widely used in medical and cosmetic fields, even for food bleaching by some illegal merchants which may cause healthy problem. In this study, the polyelectrolyte multilayer films containing ferrocene-derived polymer assembling by sol-gel process [4] was introduced to HP determination as a sensor.