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Excessive intake and emission of nitrite will cause serious harm to the ecosystem and human health. Herein, the AuNPs/Co(OH)2 nanocomposites with a unique three-dimensional (3D) hierarchical structure are designed and synthesized for the detection of nitrite. Wheatear-like cobalt hydroxide (Co(OH)2) is synthesized on carbon cloth (CC) by hydrothermal method. Flower bud-like gold nanoparticles (AuNPs) are electrodeposited on Co(OH)2. By integrating the common advantages of AuNPs and Co(OH)2 such as enlarged specific surface area, significantly increased active sites, high conductivity, and 3D hierarchical structure, the proposed AuNPs/Co(OH)2/CC electrode shows excellent nitrite sensing properties, with the linear range of 0.625–3387.5 μM, the limit of detection (LOD) of 0.1 μM, and high sensitivity of 2475.5 μA mM−1 cm−2. Moreover, the sensor can measure nitrite content in sausages with high recoveries, indicating its feasibility in practical application. This work guides the reasonable design of 3D hierarchical nanomaterials and the construction of high-performance sensing interfaces.

Graphene based metal nanocomposites are widely used in electrochemical glucose sensors for their prominent synergistic effects. Many reviews have been reported to summarize and compare the two types of synthetic technologies that post immobilization and in situ growth for preparing these nanocomposites. However, these comparisons and evaluations are almost based on the nanomaterials comprised of different components. Based on rationally selecting β-cyclodextrins as the common functional reagents, we have innovatively synthesized two novel graphene based metal nanocomposites composed of the identical ingredients through the developed post immobilization method and new one-step electrodeposition in situ growth approach respectively. After optimized the key parameters to ensure the optimal synthesis conditions were provided, we have further performanced the systematically comparative study on properties of the two nanocomposites from many aspects, so as to scientifically evaluate the two synthesis technologies. Glucose sensors based on the two resultant nanocomposites have been fabricated successfully, both of them showed high response ability. Sensitivity of the sensor modified by the nanocomposite synthesized through in situ growth was improved 3–8 times, demonstrated this strategy is more effective. Our work would provide guidelines to synthesize graphene based metal nanocomposites which has potential applications in electroanalysis.

In this paper, a self-supported electrode for nitrite detection was obtained by loading ferrous selenide nanorods on carbon cloth (FeSe NR/CC) via in situ synthesis. The morphology and chemical composition of the FeSe NR/CC were characterized using scanning electron microscope (SEM), X-ray diffractogram (XRD), and X-ray photoelectron spectroscopy (XPS). Owing to the synergistic effect between FeSe nanorods and carbon cloth, the rich redox active sites, and the lower transferring resistance, the binder-free and self-supported sensor based on FeSe NR/CC exhibits a wide linear relationship from 0.625 μM to 6775.5 μM, a fast-current response of 3 s, and a high sensitivity of 1107.7 μA mM−1 cm−2. The detection limit of the FeSe NR/CC was evaluated as 0.07 μM and the developed sensor displays excellent selectivity, stability, and reproducibility. Additionally, the as-prepared sensor has been successfully applied to detect nitrite in pickled vegetable samples, proving its feasibility for practical applications. Therefore, the self-supported and binder-free electrode proposed in this study could be used as a highly efficient and cost-effective electrochemical nitrite sensing device to achieve rapid quantitative detection of nitrite in food samples.

A simple and novel immunochromatographic assay (ICA) was developed for specific and sensitive determination of ochratoxin A (OTA) employing microorganism (MO) as reducers and carriers. In this work, microorganism loaded gold nanoparticles (MO@AuNPs) composites were synthesized by reacting Yeast/Lactobacillus (LAB) with HAuCl4 via biosorption and subsequent bioreduction. The synthesis conditions (pH and reaction time) and main parameters (morphology, diameter and functional groups) of MO@AuNPs were investigated. Owing to the large sizes (about 2 μm) and high adsorption abilities of MO@AuNPs, the few antibodies were labeled, resulting a lower detection limit for ICA. After optimization, the linear detection of OTA using MO@AuNPs-based immunoassay ranged from 0.1 to 1.6 ng/mL, and the visual limit of detection (vLOD) was 0.1 ng/mL, which was nearly 8-fold lower than traditional AuNPs-ICA. Meanwhile, the proposed strategy also possessed high specificity for OTA against other mycotoxins. The applicability of the platform was successfully assessed through the detection of OTA in rice, corn, ginger and green bean samples. The results indicated that these creative sensing elements are promising alternatives and bring an innovative inspiration for biological detections.