A novel, sensitive, and selective electrochemical sensor based on oxime-functionalized gold nanoparticles (AuNPs) and nitrogen-doped graphene (NG) composites (NG/AuNPs) was developed for the direct electrochemical detection of dimethoate, a non-electroactive organophosphorus pesticide (OP). 2-(4-Mercaptobutoxy)-1-naphthaldehyde oxime (MNO), a new organic molecule containing –SH and oxime synthesized by our group, was decorated onto electrodes through the S–Au bond between –SH of MNO and AuNPs. NG/AuNPs were modified on the electrode to provide acting sites for MNO and to amplify current response. The results indicated that the reduction current of MNO was increased, and the selectivity, sensitivity, and stability of the sensor were improved. Dimethoate was detected by using MNO as an electroactive probe through the nucleophilic substitution between oxime and dimethoate. Under optimal conditions, the sensor displayed a linear range from 1 × 10−12 to 4 × 10−8 M with a low detection limit of 8.7 × 10−13 M (S/N = 3). Results indicated that the sensor was successfully applied to detect dimethoate in water, tomato, and orange samples. Interference study analyses were investigated using the prepared electrode, which exhibited an acceptable result.

Molecularly imprinted membrane-zinc porphyrin-mathacrylate(MIM-Zn-MAA), a dual read-out sensor based on a molecularly imprinted membrane, was developed to recognize and detect dimethyl methylphosphonate (DMMP) as an intermediate molecule of organophosphorus pesticides. The membranes were prepared via thermal polymerization of two functional monomers(zinc porphyrin and mathacrylate) on the surface of a glass slide functionalized with ethylene glycol dimethacrylate and azobisisobutyronitrile. The morphology of the as-synthesized MIM-Zn-MAA was determined with scanning electronic microscopy. The composite membranes exhibited macrovoid morphologies, which were affected by the functional monomers. These membranes were selectively adsorbed onto the template molecule and displayed higher adsorbing capacity toward DMMP compared with their structural analogs. Changes in the fluorescent spectra were qualitatively and quantitatively monitored via fluorescence photometry. Difference maps were also obtained using colorimetry before and after the reaction between MIM-Zn-MAA and DMMP at various concentrations. The maps showed a wide linear range varying from 0.1 µmol/L to 10 mmol/L with a low detection limit of 0.1 µmol/L. These preliminary results demonstrate that the as-fabricated dual read-out sensor displays good sensitivity and selectivity toward DMMP, indicaing its considerable potential in DMMP detection in real applications.

Glassy carbon electrodes (GCEs) modified with l-cysteine (l-cys)/gold nanoparticles (AuNPs)/nitrogen-doped graphene (NG) composite were prepared to fabricate a novel electrochemical sensor for lead. AuNPs were uniformly dispersed into NG and l-cys was successfully decorated on AuNPs through the S–Au bond. The l-cys/AuNPs/NG exhibited a well-distributed nanostructure and high responsivity toward Pb(II). The results indicated that l-cys/AuNPs/NG/GCE exhibited the highest peak current, reflecting that the l-cys/AuNPs/NG composites showed the best response signal toward Pb2+. Under optimized conditions, a linear relationship between the current intensity and Pb2+ concentration was obtained in a range of 0.5–80 μg L−1 with a detection limit of 0.056 μg L−1 (S/N = 3). The analytical interference procedure and practical application were investigated using the prepared electrode, which exhibited an acceptable result.

A new type of graphene-Co3O4 functionalized porphyrin was synthesized and used for selective and sensitive detection of methyl parathion (MP). Co3O4 nanoparticles were firstly modified onto graphene oxide sheets and the porphyrin/Co3O4/graphene nanocomposites were then synthesized by self-assembly decoration of anion porphyrin on Co3O4-modified graphene sheets by π–π stacking. By dexterously controlling the electrochemical reduction variables and optimizing the electrode preparation parameters, with the satisfactory conductivity, strong adsorption toward MP, the developed novel sensor fabricated with the as-synthesized nano-assembly for determination of MP shows some satisfactory properties such as a wide linear concentration range (from 4.0 × 10−7 M to 2.0 × 10−5 M), low detection limit (1.1 × 10−8 M), favorable repeatability, long-time storage stability, and satisfactory anti-interference ability. It also had high precision for the real sample analysis, which indicated the good perspective for field application.

•SPIONs are coated with the novel compounds DDNP-carboxyl derivative.•We described a facile chemical method to functionalize the surface of SPIONs.•They show superparamagnetic and high relaxivity.Superparamagnetic iron oxide nanoparticles (SPIONs) have been proposed for use in magnetic resonance imaging as versatile ultra-sensitive nanoprobes for Alzheimer's disease imaging. In this work, we synthetized an efficient contrast agent of Alzheimer's disease using 1,1-dicyano-2-[6-(dimethylamino)naphthalene-2-yl]propene (DDNP) carboxyl derivative to functionalize the surface of SPIONs. The DDNP-SPIONs are prepared by conjugating DDNP carboxyl derivative to oleic acid-treated SPIONs through ligand exchange. The structure, size distribution and magnetic property were identified by IR, TGA–DTA, XRD, TEM, Zetasizer Nano and VSM. TEM and Zetasizer Nano observations indicated that the DDNP-SPIONs are relatively mono-dispersed spherical distribution with an average size of 11.7 nm. The DDNP-SPIONs were then further analyzed for their MRI relaxation properties using MR imaging and demonstrated high T2 relaxivity of 140.57 s− 1Fe mM− 1, and the vitro experiment that DDNP-SPIONs binding to β-Amyloid aggregates were then investigated by fluorophotometry, the results showed that the combination had induced the fluorescence enhancement of the DDNP-SPIONs and displayed tremendous promise for use as a contrast agent of Alzheimer's disease in MRI.