Specific three-dimensional inverse opal (3DIO) In2O3–CuO architecture with additional via-holes was first prepared by a simple sacrificial template method. Such specific nanostructures enable fast transport of gas molecules to the entire thin-walled sensing layers, which is very helpful for improving the sensing performance. Moreover, the mole ratio of Cu/In was controlled, ranging from 0–38.1% to adjust the hetero-contact amounts in the In2O3–CuO composites. The gas sensing properties of the as-prepared 3DIO In2O3–CuO samples were evaluated toward trace acetone, which is an important biomarker of diabetes in exhaled breath. The response of the 3DIO In2O3–CuO gas sensor with the best performance (with a mole ratio of Cu/In = 16.4%) was ∼14 to 5 ppm acetone, and had a calculated low detection limit of ∼30 ppb at 370 °C when Ra/Rg ≥ 1.2 was used as the criterion for reliable gas sensing. Besides, it also showed good selectivity, fast response (τres) and recovery (τrec) times, and stability. The enhanced gas sensing performance could be attributed to the hetero-contact effects between the different components and the specific 3DIO structure with the via-holes which provided a larger effective surface area for gas adsorption. It is believed that the as-prepared 3DIO sensor can be a promising ppb-level acetone sensor in various areas.

Hierarchical core–shell IrO2@NiO nanowires (NWs) have been designed through two simple steps, which combined electrospinning of IrO2 conductive core and chemical bath deposition growth of ultracontinuous NiO nanoflakes. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray spectrometry mapping, and X-ray photoelectron spectroscopy were employed to characterize the morphologies and structures of the as-prepared samples, and the results were also carefully compared with that of pure NiO nanoflowers and IrO2 NWs. Electrochemical studies indicate that the as-prepared core–shell IrO2@NiO NWs exhibited excellent nonenzymatic detection ability to glucose. At 0.35 V, it offered a sensitivity of 1439.4 μA mM–1 cm–2 (one order higher than pure NiO) with a wider linear range from 0.5 μM to 2.5 mM, a low detection limit of 0.31 μM (signal-to-noise ratio = 3, and moreover, good resolution in low glucose concentration, reproducibility, and long-term performance stability. Owing to the high sensitivity and performance, application of the proposed sensor in monitoring saliva glucose was also demonstrated; the results indicated that the sensor can effectively distinguish the diabetes from the healthy people and even the varying degrees of diabetic.

Analyzing the volatile organic compounds (VOCs) in exhaled breath effectively is crucial to medical treatment, which can provide a fast and noninvasive way to diagnose disease. Well-designed materials with controlled structures have great influence on the sensing performance. In this work, the ordered three dimensional inverse opal (3DIO) macroporous In2O3 films with additional via-hole architectures were fabricated and different amounts of gold nanoparticles (Au NPs) were loaded on the In2O3 films aiming at enhancing their electrical responses. The gas sensing to acetone toward diabetes diagnosis in exhaled breath was performed with different Au/In2O3 electrodes. Representatively, the best 3DIO Au/In2O3 sensor can detect acetone effectively at 340 °C with response of 42.4 to 5 ppm, the actual detection limit is as low as 20 ppb, and it holds a dynamic response of 11 s and a good selectivity. Moreover, clinical tests proved that the as-prepared 3DIO Au/In2O3 IO sensor could distinguish acetone biomarkers in human breath clearly. The excellent gas sensing properties of the Au/In2O3 electrodes were attributed to the “spillover effects” between Au and In2O3 and the special 3DIO structure. This work indicates that 3DIO Au/In2O3 composite is a promising electrode material for actual application in the monitoring and detection of diabetes through exhaled breath.

A sensitive, label-free immunosensor based on iridium oxide (IrOx, 0 ≤ x ≤ 2) nanofibers, which were synthesized through a simple one-spinneret electrospinning method, was first developed for immunoassay of the cancer biomarker α-fetoprotein (AFP). The specific wire-in-tube nanostructure could be obtained and the composition of IrOx nanofibers also could be controlled through changing the annealing temperature. The unique structure and properties of IrOx nanofibers obtained at 500 °C not only led to increased electrode surface area and accelerated electron transfer kinetics but also could provide a highly stable matrix for the convenient conjugation of biomolecules together with chitosan (CS). The good electrochemical properties of the IrOx-nanofiber-modified immunosensor allowed one to detect AFP over a wide concentration range from 0.05 to 150 ng/mL, with a detection limit of 20 pg/mL. The proposed immunosensor also has been used to determine AFP in human serum with satisfactory results. The present protocol was shown to be quite promising for clinical screening of cancer biomarkers and point-of-care diagnostics applications.Keywords: electrochemical immunosensor; electrospinning; IrOx; label-free; wire-in-tube nanostructure; α-fetoprotein

In this work, novel upconversion lanthanide oxyfluoride (LnOF:Yb3+, Er3+, Ln = La, Y, Gd) inverse opal photonic crystals (IOPCs) were successfully fabricated by the sol–gel method combined with polymethylmethacrylate (PMMA) template technique and the modulation of the photonic stop band (PSB) on the green emissions 2H11/2/4S3/2 → 4I15/2 for Er3+ ions were systemically studied under 980 nm excitation. The results showed that the LaOF IOPCs (annealed at 500 °C) were of cubic phase while GdOF and YOF matrices were of rhombohedral phase, and the LaOF IOPCs demonstrated more efficient upconversion luminescence (UCL) than GdOF and YOF due to the phase transition. In contrast to the ground reference (REF) samples, strong suppression of UCL was observed in the IOPCs while the PSB overlapped with the 2H11/2/4S3/2 → 4I15/2 lines. Furthermore, the spontaneous decay rates (SDRs) of 2H11/2/4S3/2 → 4I15/2 were suppressed in the IOPCs, independent of the location of the PSB. In LaOF IOPCs, the decay time constants of 4S3/2 → 4I15/2 were increased by as much as 9 times in contrast to the corresponding REFs. It was also significant to observe that in the IOPCs the local thermal effect was greatly suppressed. In addition, broadband UCL extending into the visible range was observed in LnOF:Yb3+, Er3+ REF samples under high excitation power, and the origin was identified by electron paramagnetic resonance (EPR) spectroscopy.

CuO nanoparticles (NPs) based graphene oxide (CuO/GO) composites with different CuO NPs loading amount as well as pure CuO NPs with different hydrothermal temperatures were synthesized using a hydrothermal method. Transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Raman spectroscopy were employed to characterize the morphology and structures of our samples. The influence of hydrothermal temperature, GO sheet, and loading amount of CuO on particle size and structure of CuO was systemically investigated. The nonenzymatic biosensing properties of CuO/GO composites and CuO NPs toward glucose were studied based on glassy carbon electrode (GCE). The sensing properties of CuO NPs were improved after loading on GO sheets. The CuO/GO composites with saturated loading of the CuO NPs exhibited the best nonenzymatic biosensing behavior. It exhibited a sensitivity of 262.52 μA mM–1 cm–2 to glucose with a 0.69 μM detection limit (S/N = 3) and a linear range from 2.79 μM to 2.03 mM under a working potential of +0.7 V. It also showed outstanding long term stability, good reproducibility, excellent selectivity, and accurate measurement in real serum sample. It is believed that CuO/GO composites show good promise for further application on nonenzymatic glucose biosensors.Keywords: composite; CuO; glucose detection; graphene; hydrothermal procedure;

Inverse opals (IO), as a special kind of macroporous material with large surface to volume ratio and ordered layer structure, have great application potential in highly sensitive gas sensing area. In this paper, macroporous SnO2 IO were synthesized by a simply PMMA template method and their porous sizes were controlled ranging of 140–400 nm. The performance of the SnO2 IO sensors to formaldehyde (HCHO) gas was systemically studied. The results indicated that the sensing properties of the SnO2 IO sensors to HCHO were highly improved than the traditional sensors, depending strongly on the porous sizes. The response of the SnO2 IO sensors increased gradually with the increase of porous size. The response of the optimum SnO2 sensor was as high as 629 for 100 ppm HCHO gas detection and the practical detection limit was as low as 10 ppb, which was one of the best levels for the detection of HCHO gas. And more, they also demonstrated fast response dynamics and long time stability.

In this work, novel upconversion lanthanide oxyfluoride (LnOF:Yb3+, Er3+, Ln = La, Y, Gd) inverse opal photonic crystals (IOPCs) were successfully fabricated by the sol–gel method combined with polymethylmethacrylate (PMMA) template technique and the modulation of the photonic stop band (PSB) on the green emissions 2H11/2/4S3/2 → 4I15/2 for Er3+ ions were systemically studied under 980 nm excitation. The results showed that the LaOF IOPCs (annealed at 500 °C) were of cubic phase while GdOF and YOF matrices were of rhombohedral phase, and the LaOF IOPCs demonstrated more efficient upconversion luminescence (UCL) than GdOF and YOF due to the phase transition. In contrast to the ground reference (REF) samples, strong suppression of UCL was observed in the IOPCs while the PSB overlapped with the 2H11/2/4S3/2 → 4I15/2 lines. Furthermore, the spontaneous decay rates (SDRs) of 2H11/2/4S3/2 → 4I15/2 were suppressed in the IOPCs, independent of the location of the PSB. In LaOF IOPCs, the decay time constants of 4S3/2 → 4I15/2 were increased by as much as 9 times in contrast to the corresponding REFs. It was also significant to observe that in the IOPCs the local thermal effect was greatly suppressed. In addition, broadband UCL extending into the visible range was observed in LnOF:Yb3+, Er3+ REF samples under high excitation power, and the origin was identified by electron paramagnetic resonance (EPR) spectroscopy.