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In this work, WO3 films were synthesized by glancing angle deposition (GLAD) and conventional planar deposition respectively. By depositing Pt on WO3 by GLAD, the NO2 sensitivity of WO3 films were significantly improved. The structural characteristics and NO2 sensing properties of the films were investigated in order to establish the enhancement mechanism. The results show WO3 films prepared by GLAD have porous nanorod-like structure, and isolated Pt clusters are distributed on WO3. The nanostructured Pt/WO3 films show high sensitivity to NO2 at 150 °C, detecting as low as 80 ppb NO2 with a response of 1.23. Meanwhile, the films also exhibit high NO2 selectivity against NH3, CO, acetone and ethanol. The excellent NO2 sensing properties of the Pt/WO3 films can be explained due to large specific surface area of nanorod-like WO3, catalysis of Pt and Schottky barriers at interfaces. The reliable Pt/WO3 nanostructure prepared by GLAD could be potentially applied in low-temperature, highly sensitive NO2 sensor for micro-electro-mechanical system (MEMS).

A homogeneous porous Co3O4-ZnO nanomaterial (Zn-CoOx) was successfully fabricated by precipitation-annealing route. The as-prepared Zn-CoOx exhibited good response, reliable reversibility and good selectivity towards alcohols, which attributed to the porous structure and p-n heterojunction formed between Co3O4 and ZnO. In particular, the different Fermi levels of Co3O4 and ZnO leaded to a further increase the depth of the space charge layer, which improved the gas sensitivity of the material from 10% to 480%. Besides, the continuous Co3O4 leaded to a relatively lower operating temperature and resistance. This material preparation method and bimetallic oxides could be widely used in the research and development of metal oxide gas sensitive materials and sensors.

Co3O4 is a promising p-type semiconductor for ethanol detection. In this work, ethanol detection sensors were fabricated with nanostructured Co3O4, which exhibited higher selectivity and lower operating temperature. The Co3O4 was synthesised using ZIF-67 as a sacrificial precursor. The T400-Co3O4 that was obtained by calcining ZIF-67 at 400 °C showed the best sensing performance. Its response to 100 ppm ethanol vapor was 221.99 at a low optimal operating temperature (200 °C). Moreover, T400-Co3O4 achieved a low detection limit (1 ppm), remarkable repeatability, and higher selectivity compared to ammonia, carbon monoxide, acetone, hydrogen, methane, methanol, and nitrogen dioxide. The enhanced sensing performance was mainly attributed to three factors: (1) the adsorption/desorption of active adsorbed oxygen molecules (e.g. O− and O2−) and abundant oxygen vacancies, which increased the number of active sites; (2) the catalytic activity of Co3+, which greatly increased the reaction route and decreased the activation energy; and (3) the effective diffusion of gas molecules, which increased the effect of collisions between gas molecules and the material surface. This work provides an effective means to fabricate sensitive ethanol gas sensors with low energy consumption.

Semiconductors are widely used as basic materials in commercial ethanol detection sensors. In this work, SnO2 sensors were modified by a Co doping method to obtain Co-SnO2 for gaseous ethanol detection. For investigating the best sensing performance and elucidating the underlying catalytic mechanism, the effects of the Co/Sn feed ratio and calcination temperature during sample preparation were examined. The sample with a Co/Sn feed molar ratio of 1.0 calcined at 500 °C (D3-Co-SnO2) possessed better ethanol sensitivity than other samples. The best response to 100 ppm gaseous ethanol (i.e., ratio of sensor resistance in air to that in ethanol) was 105.2 at an operating temperature of 350 °C. More importantly, D3-Co-SnO2 achieved a low detection limit of 1 ppm and apparently higher selectivity over various gases (e.g., acetone, hydrogen, methane, etc.). The enhanced sensing performance was attributed to (1) the incorporation of Co atoms, which increased the number of oxygen vacancies and active sites; (2) the catalytic activity of Co(III) and Co(II), which changed the reaction process; and (3) the suitable pore size, which led to effective diffusion of the gas molecules.

A molecularly imprinted magnetic sensor with electroluminescent tags (MIP-ECL sensor) was developed for ultrasensing diethylstilbestrol (DES). A strategy is exploited to enhance ECL emission of the [Ru(bpy)3]2 +-tripropyl amine (TPrA) system by CdTe@ZnS quantum-dots (QDs) through energy transfer. Magnetically molecularly imprinted nanoparticles (MMIPs NPs) based on Fe3O4@SiO2 carriers are artificial, easily reproducible, and could replace easily inactivated first antibodies for capturing more DES molecules. Functionalized bio-conjugates of single antibody-CdTe@ZnS (Ab-CdTe@ZnS) are for the first time loaded on signal labels of Ru(bpy)32 +-doped silica nanocomposites (Ru@SiO2) for signal amplification. The final bio-conjugated signal probes are denoted as Ab-DES/CdTe@ZnS–Ru@SiO2. MMIPs beads that have captured antigens are bio-conjugated with antibody-labeled luminescent probes by specific immunoreactive reaction, and then the luminescent immunocomplex generates ECL signal on the magnetic electrode. The logarithm of ECL intensities depend linearly on the logarithm of DES concentrations in the range from 4.8 × 10− 4 to 36.0 nM with a detection limit of 0.025 pM. This novel assay is much more sensitive than other MIP sensors, and achieves lower cost and more enhanced stability than other immunosensors. The sensor is significantly potential and has been applied to DES detection in actual environment.

A novel molecularly imprinted electrochemiluminescence (MIP-ECL) sensor was fabricated for diethylstilbestrol (DES), which exploited the strategy of specific identification by molecularly imprinted polymers (MIPs) instead of expensive biomolecules. Core-shell quantum-dots (QDs) of CdTe@ZnS were utilized to enhance ECL emission. The sensor was assembled as a solid-state electrode by immobilizing CdTe@ZnS/reduced-graphene oxide (r-GO) composite on a glassy carbon electrode (GCE) surface, and then being covered with MIPs film with specific cavities. The fabricated sensor (denoted as MIP/CdTe@ZnS/r-GO/GCE) was based on the obstruction of ECL signals by DES molecules enriched on MIP film. The ECL intensity of the QDs-K2S2O8 system was reduced when the DES molecules were selectively rebound onto the MIP film by molecularly imprinted solid phase extraction (MISPE). Accordingly, the logarithm of the quenched ECL intensity versus the logarithm of the DES concentration was in a good linear relationship over a wide range from 1.8 × 10− 3 to 25.0 nmol/L with the limit of detection (LOD) of 0.25 pmol/L (S/N = 3). The sensor also exhibits excellent selectivity with fast response and good accuracy. Lake water and milk samples were assayed by this sensor, and the recoveries ranging from 92.2%–108.3% were obtained.