ZnO-CeO2 Hollow Nanospheres for Selective Determination of Dopamine and Uric Acid.

ZnO-CeO2 hollow nanospheres have been successfully synthesized via the hard templating method, in which CeO2 is used as the support skeleton to avoid ZnO agglomeration. The synthesized ZnO-CeO2 hollow nanospheres possess a large electrochemically active area and high electron transfer owing to the high specific surface area and synergistic effect of ZnO and CeO2. Due to the above advantages, the resulting ZnO-CeO2 hollow spheres display high sensitivities of 1122.86 µA mM-1 cm-2 and 908.53 µA mM-1 cm-2 under a neutral environment for the selective detection of dopamine and uric acid. The constructed electrochemical sensor shows excellent selectivity, stability and recovery for the selective analysis of dopamine and uric acid in actual samples. This study provides a valuable strategy for the synthesis of ZnO-CeO2 hollow nanospheres via the hard templating method as electrocatalysts for the selective detection of dopamine and uric acid.

Sequential colorimetric sensing of cupric and mercuric ions by regulating the etching process of triangular gold nanoplates.

A triangular gold nanoplate (AuNPL)-based colorimetric assay is presented for ultrasensitive determination of cupric ions (Cu2+) and mercuric ions (Hg2+) in sequence. AuNPLs were found to be etched efficiently when producing triiodide ions (I3-) by a redox reaction between Cu2+ and iodide ions (I-), leading to a change of the shape of AuNPLs from triangular to sphere along with a color change from blue to pink. In the presence of Hg2+ the etching of AuNPLs was suppressed due to the consumption of I- by the formation of HgI2. With an increase of the concentration of the Hg2+ a transformation from sphere to triangular in the shape of AuNPLs occurred with a color change from pink to blue. The evolution of AuNPLs from etching to anti-etching state by sequential addition of Cu2+ and Hg2+ was accompanied with color variations and band shifts of localized surface plasmon resonance (LSPR), allowing for visual and spectroscopic determination of Cu2+ and Hg2+ successively within 15 min. In the range 0.01-1.5 µM for Cu2+ and 0.02-3.0 µM for Hg2+, the linear relationship between the band shift values and the target ions concentration was found good (R2 > 0.996). The limit of detections (3S/k) was 19 nM for Cu2+ and 9 nM for Hg2+, respectively. The lowest visual estimation concentration was 80 nM for both Cu2+ and Hg2+ through the distinguishable color changes. This system exhibited desirable selectivity for Cu2+ and Hg2+ over other common ions tested. The method has been successfully applied to sequential determination of Cu2+ and Hg2+ in real water and food samples. Graphical abstract Scheme 1 Schematic illustration for sequential detection of Cu2+ and Hg2+ based on etching of AuNPLs.

Dual-ligand lanthanide metal-organic framework based ratiometric fluorescent platform for visual monitoring of aminoglycoside residues in food samples.

Herein, a dual-emission Eu metal-organic framework (Eu-MOF) is prepared and used as the ratiometric fluorescence probe for ultrasensitive detection of aminoglycoside antibiotics (AGs). Due to the strong hydrogen bond interactions between AGs and Eu-MOF, the blue emission is enhanced while the red emission has little fluctuation in Eu-MOF with the addition of AGs, thus a good linear relationship with the logarithm of AGs concentrations from 0.001 to 100 µg/mL can be established for quantitative analysis. Good sensitivity with the detection limit of 0.33 ng/mL for apramycin, 0.32 ng/mL for amikacin and 0.30 ng/mL for kanamycin is achieved. The proposed assay demonstrates good selectivity and applicability for determination of AGs in real milk and honey samples. The Eu-MOF materials are further fabricated as fluorescent test papers for facile visual detection. The as-established ratio fluorescence platform offers a portable and economical way for rapid monitoring AGs residues in complex food samples.

Colorimetric and visual sensing of ferrous ion by Fenton reaction-stimulated etching of triangular gold nanoplates.

In this study, a method for ultrasensitive sensing of Fe2+ based on Fenton reaction mediated etching of triangular gold nanoplates (Au NPLs) was developed. In this assay, the etching of Au NPLs by H2O2 was accelerated in the presence of Fe2+ due to the generation of superoxide free radical (O2·-) via Fenton reaction. With the concentration of Fe2+ increased, the shape of Au NPLs changed from triangular to sphere with the blue shifted localized surface plasmon resonance, accompanying a series of consecutive color changes from blue, bluish purple, purple, reddish purple and finally to pink. The rich color variations enable rapid visual quantitative determination of Fe2+ within 10 min. A good linear relationship between the peak shifts and the concentration of Fe2+ was obtained in the range of 0.035 to 1.5 µM (R2 = 0.996). Favorable sensitivity and selectivity in the presence of other tested metal ions were achieved in the proposed colorimetric assay. The detection limits (3Æ¡/k) for Fe2+ was 26 nM by UV-vis spectroscopy, and the clearly discernible concentration of Fe2+ was as low as 0.07 µM by naked eyes. The recoveries of fortified samples in pond water and serum samples ranged from 96% to 106% with interday relative standard deviations <3.6% in all cases, demonstrating the applicability of the assay for measuring Fe2+ in real samples.

A sensitive fluorescence nanoplatform for monitoring benzoyl peroxide in food using carbon dots coupled with glutathione capped gold nanoparticles as FRET probe.

Herein, a sensitive fluorescence nanoplatform for benzoyl peroxide (BPO) detection is constructed from carbon dots (CDs) and glutathione capped gold nanoparticles (GSH-AuNPs). The fluorescence of CDs is first quenched due to the fluorescence resonance energy transfer (FRET) effect in the presence of GSH-AuNPs, and then effectively recovered when adding BPO. The detection mechanism lies in the aggregation of AuNPs in a high salt background due to oxidation of GSH caused by BPO, thus the amount of BPO is reflected by the variations of the recovered signals. The linear range and detection limit in this detection system is found to be 0.05-200 µM (R2 = 0.994) and 0.1 µg g-1 (3σ/K), respectively. Several possible interferents with high concentration show little influence on BPO detection. The proposed assay exhibits good performance for BPO determination in wheat flour and noodles, demonstrating its applicability for facile monitoring BPO additive amount in real foods.

Silver ions involved fluorescence "on-off" responses of gold nanoclusters system for determination of carbendazim residues in fruit samples.

Herein, a fluorescence "on-off" system was developed for monitoring carbendazim (CBZ) residues in fruit samples, based on glutathione-gold nanoclusters (GSH-Au NCs) and silver ions (Ag+). First, the fluorescence intensity of GSH-Au NCs was greatly enhanced (turn on) with aggregation-induced emission enhancement (AIEE) effect in the presence of Ag+, then fluorescence quenching occurred (turn off) with adding CBZ by the chelation between CBZ and Ag+. The quenching degree was well linearly dependent on CBZ concentration covering from 0.5 to 20 µM. Moreover, the GSH-Au NCs-Ag+ system exhibited superior selectivity towards CBZ and was sensitive for the determination of CBZ in apple and orange juices with a low detection limit of 0.12 µM. The recoveries of CBZ spiked in fruit samples ranged from 81.0 % to 111.4% with the relative standard deviations less than 6.6%, demonstrating its great potential for monitoring CBZ residues in fruit samples.

Lanthanum ions assisted non-enzymatic ratiometric fluorescence probe for monitoring fenthion residues in agro-product samples.

In this work, a La3+ assisted glutathione-capped gold nanoclusters and carbon dots (GSH-Au NCs/CDs) nanoplatform for sensitive detection of fenthion (FEN) is fabricated. The fluorescence response of GSH-Au NCs significantly increases due to aggregation-induced emission enhancement (AIEE) effect induced by La3+, which is further enhanced with adding FEN due to the coordination between La3+ and FEN. Taking the fluorescence intensity of CDs as the signal background, the ratiometric fluorescence of GSH-Au NCs and CDs has a good linear relationship with the FEN concentration from 0.01 to 1.10 µg mL-1, and detecting FEN exhibits a good sensitivity at a low detection limit of 6.74 ng g-1. The La3+ assisted GSH-Au NCs/CDs nanoplatform demonstrates desirable selectivity and applicability for monitoring trace level of FEN in fruit and vegetable samples. The non-enzymatic strategy by taking advantage of successive AIEE of GSH-Au NCs has a great potential for facile screening organophosphate pesticides in agro-products.

An investigation of template anchoring strategy for molecularly imprinting materials based on nanomagnetic polyhedral oligomeric silsesquioxanes composites.

A template anchoring strategy for high performance molecularly imprinting materials (MI-materials) was displayed in the present work, which involved efficient usage of template molecules with the aid of functional monomer grafted on the support. The imprinting polymerization process was carried out on the surface of carboxyl functionalized Fe3O4@POSS (Fe3O4@POSS-COOH) anchoring with tetracycline templates as a demonstration. In this strategy, Fe3O4@POSS-COOH was first prepared via a simple copolymerization between methacrylic acid (MAA) and the residual end vinyl groups of Fe3O4@POSS. The carboxyl groups immobilized on Fe3O4@POSS surface can drive tetracycline templates into the formed polymer layers through hydrogen interactions between tetracycline and the functionalized monomer. The occupation of assembled tetracycline templates on the surface of Fe3O4@POSS-COOH directed the selective occurrence of imprinting polymerization through copolymerization of vinyl end groups of Fe3O4@POSS, leading to the formation of tetracycline imprinted nanocomposite with a high density of effective recognition sites. The obtained MI-material exhibited high capacity and favorable selectivity towards tetracycline antibiotics. By applying the proposed MI-material as magnetic solid phase extraction adsorbents, four tetracyclines were prominently enriched from milk samples. The MI-material based analytical platform was sensitive for the determination of TCs in milk samples with LOD values in the range of 2.23-26.84 ng mL-1 and recoveries ranged from 86.2% to 105.7%. This work proposed an improved strategy for preparing efficient MI-materials based on Fe3O4@POSS, which provides a new insight into the chemical properties of Fe3O4@POSS.

Cu(â ¡) triggering redox-regulated anti-aggregation of gold nanoparticles for ultrasensitive visual sensing of iodide.

In this study, we proposed a novel anti-aggregation of gold nanoparticles (AuNPs) strategy for colorimetric sensing of iodide ions (I-) regulated by the redox reaction between the target ions and the ion cross-linking agent. Cu2+ as interlinking ion can induce aggregation of arginine capped AuNPs (Arg-AuNPs) due to the formation of Arg-Cu2+-Arg analogous structure resulting from the chelation between Cu2+ and arginine, with a clear color change of solution from red to blue. In the presence of I-, however, Cu2+ would be readily reduced owing to the formation of CuI, AuNPs underwent a transformation from an aggregation to a dispersion state depending on the concentration of I-, leading color changes from blue to red. The corresponding color variation in the process of anti-aggregation of AuNPs can be monitored through UV-vis spectrophotometer or by the naked-eye, making quantitative analysis of I- feasible in a convenient colorimetric or visual way. The assay only took 5 min, showing high sensitivity with a lowest detectable concentration of 10 nM and excellent selectivity for I- over other anions tested, which was successfully applied for the detection of I- in drinking water and table salt samples.

Facile synthesis of a boronate affinity sorbent from mesoporous nanomagnetic polyhedral oligomeric silsesquioxanes composite and its application for enrichment of catecholamines in human urine.

A boronate-decorated nanomagnetic organic-inorganic hybrid material was facilely synthesized by utilizing the nanomagnetic polyhedral oligomeric silsesquioxanes (POSS) composite (Fe3O4@POSS) as the base platform. A simple copolymerization occurred between 3-acrylamidophenylboronic acid (AAPBA) and the residual end vinyl groups supplied by the substrate. Here the special emphasis was placed on the octavinyl POSS, which not only acted as the building blocks for a hybrid architecture but also facilitated the process of grafting boronate groups onto the surface of POSS based nanomagnetic composite (Fe3O4@POSS). The successful immobilization of affinity ligand-AAPBA on the Fe3O4@POSS was confirmed by Fourier transform infrared (FT-IR), elemental analysis, inductively coupled plasma atomic emission spectrometer (ICP-AES), field emission scanning electron microscope. A magnetic solid-phase extraction (MSPE) for cis-diols enrichment was developed using the as-prepared Fe3O4@POSS-AAPBA material as an affinity sorbent and three catecholamines (CAs), namely noradrenaline, epinephrine and isoprenaline, as model analytes. Under the optimal extraction conditions, sensitive and simultaneous analysis of three CAs from the urine sample was achieved by high-performance liquid chromatography with UV detection (HPLC-UV). The limits of detection (LOD, S/N = 3) and the limits of quantitation (LOQ, S/N = 10) for the target analytes were 0.81-1.32 ng mL-1 and 2.70-4.40 ng mL-1, respectively. Also good recoveries (85.5-101.7%) and repeatability (RSD≤10.1%) were obtained by this method. This work not only showed a facility for the utilization of Fe3O4@POSS as a substrate for constructing a boronate functionalized nanomagnetic sorbent, but also demonstrated the capability of the derived material for recognition of trace amount of cis-diols biomolecules presented in complicated biological matrices.

Mesostructured nanomagnetic polyhedral oligomeric silsesquioxanes (POSS) incorporated with dithiol organic anchors for multiple pollutants capturing in wastewater.

A functionalizable organosiliceous hybrid magnetic material was facilely constructed by surface polymerization of octavinyl polyhedral oligomeric silsesquioxane (POSS) on the Fe3O4 nanoparticles. The resultant Fe3O4@POSS was identified as a mesoporous architecture with an average particle diameter of 20 nm and high specific surface area up to 653.59 m(2) g(-1). After it was tethered with an organic chain containing dithiol via thiol-ene addition reaction, the ultimate material (Fe3O4@POSS-SH) still have moderate specific area (224.20 m(2) g(-1)) with almost identical porous morphology. It turns out to be a convenient, efficient single adsorbent for simultaneous elimination of inorganic heavy metal ions and organic dyes in simulate multicomponent wastewater at ambient temperature. The Fe3O4@POSS-SH nanoparticles can be readily withdrawn from aqueous solutions within a few seconds under moderate magnetic field and exhibit good stability in strong acid and alkaline aqueous matrices. Contaminants-loaded Fe3O4@POSS-SH can be easily regenerated with either methanol-acetic acid (for organic dyes) or hydrochloric acid (for heavy metal ions) under ultrasonication. The renewed one keeps appreciable adsorption capability toward both heavy metal ions and organic dyes, the removal rate for any of the pollutants exceeds 92% to simulate wastewater with multiple pollutants after repeated use for 5 cycles. Beyond the environmental remediation function, thanks to the pendant vinyl groups, the Fe3O4@POSS derived materials rationally integrating distinct or versatile functions could be envisaged and consequently a wide variety of applications may emerge.