Xiangheng Niu

Recent advances in non-enzymatic electrochemical glucose sensors based on non-precious transition metal materials: opportunities and challenges

With the booming requirements for diabetes management, food quality control, and bioprocess inspection, monitoring of glucose in various matrices has drawn unprecedented interest of both academic and industrial researchers recently. As a relatively new class of glucose sensors, enzyme-free detection of the target is capable of providing several fascinating characters such as ultra-high sensitivity, excellent stability, and simple fabrication. Considering the rapid expansion of the glucose determination field without using any biological enzymes, here we focus our attention on updating the latest advances in non-enzymatic electrochemical glucose sensors based on non-noble transition metal materials achieved in the past few years. In this minireview, both the superiorities and the intrinsic drawbacks of detecting glucose by employing non-precious materials including Ni, Cu, Co, Mn, and Fe are intensively highlighted, followed by a systematic discussion on the important progress harvested for enzymeless glucose sensing. Finally, the potential opportunities of non-noble transition metal materials in fabricating high-performance enzyme-free glucose sensors are given, and the current challenges for their practical applications are also summarized.

One-Pot Anchoring of Pd Nanoparticles on Nitrogen-Doped Carbon through Dopamine Self-Polymerization and Activity in the Electrocatalytic Methanol Oxidation Reaction

Exploration of advanced electrocatalysts to promote the sluggish methanol oxidation reaction (MOR) is of vital importance for developing high efficiency and low-cost direct methanol fuel cells. Highly dispersed palladium nanoparticles (Pd NPs) anchored on a nitrogen-doped carbon support were fabricated using a facile one-pot dopamine self-polymerization mediated redox strategy, in which dopamine not only acted as a moderate reductant to induce the formation of Pd NPs during self-polymerization but was also the precursor of the nitrogen-doped carbon support for Pd. The synthesized hybrid features the following characteristics: 1) High dispersity of Pd NPs, which exposed a high abundance of active surfaces and sites for heterogeneous electrocatalysis; 2) metal-support interactions, which may affect the surface chemistry and electron distribution of active Pd NPs; 3) the Pd NPs were partially imbedded or encapsulated into the support, thus reducing the possible agglomeration of Pd NPs during cyclic measurements. The electrocatalyst with such favorable features provided higher mass activity (2.2 times that of commercial Pd/C) and better durability (reduced loss of activity during simulated frequent startup-shutdown operations) for the MOR in alkaline media.

Anneal-shrinked Cu2O dendrites grown on porous Cu foam as a robust interface for high-performance nonenzymatic glucose sensing

Enzyme-free electrochemical detection of glucose in alkaline media with favorable properties has been acquired by fabricating a robust and large-surface sensing platform, which is composed of anneal-shrinked Cu2O dendrites grown on porous Cu foam. On the one hand, the good compatibility of electrodeposited Cu2O architectures and Cu foam substrate, together with a post-deposition anneal at 200°C, offers a mechanically stable interface for glucose determination. On the other hand, the macropores of Cu foam that is decorated with unique Cu2O dendrites provide large active surface for electrocatalytic reaction and mass transport. As a result, selective sensing of glucose in the linear concentration range of 0.001-1.4mM was achieved on the fabricated sensor, with a sensitivity of as high as 5.04mAcm-2mM-1 and a detection limit of 0.13μM. Desired long-term performance stability was obtained, partially due to the strong adhesion of Cu2O microstructures to the Cu foam support after annealing. Practical monitoring of glucose in serum samples was also demonstrated on the proposed sensor.

Fabrication of fluorescent carbon dots-linked isophorone diisocyanate and β-cyclodextrin for detection of chromium ions

A water-soluble fluorescent carbon dots (FCDs) from cellulose was prepared using one-pot simple hydrothermal method. In this work, a novel fluorescent probe material, fluorescent carbon dots-linked isophorone diisocyanate and β-cyclodextrin (FCDs-IPDI-CD), was prepared with FCDs, isophorone diisocyanate (IPDI) and β-cyclodextrin (β-CD) as raw materials. The structure and morphology of FCDs-IPDI-CD were characterized using the Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). The as-prepared FCDs-IPDI-CD exhibits excellent emission property and high stability. The fluorescence of the FCDs-IPDI-CD could be quenched by Cr(VI) ions, and the results indicate that FCDs-IPDI-CD can be used as an effective fluorescent probe for the detection of Cr(VI) ions with good selectivity and sensitivity in an aqueous solution. The influences of environment factors (such as pH, reaction time) on relative fluorescence intensity were studied. According to the optimum conditions, a new sensitive method detecting Cr(VI) ions was established. The method has been successfully applied to detect Cr(VI) ions in water and soil samples with satisfactory results.

Fe3O4@PVIM@Zn(ii) magnetic microspheres for luteolin recognition via combined reflux-precipitation polymerization and metal-ion affinity strategy

Magnetic microspheres (Fe3O4@PVIM@Zn(II)) composed of a high magnetic-response Fe3O4 core and a Zn(II)-immobilized cross-linked polyvinyl imidazole (PVIM) shell via reflux-precipitation polymerization and metal-ion affinity strategy were fabricated. Integrating the advantages of specific uptake and fast separation, Fe3O4@PVIM@Zn(II) was adopted as an ideal pathway for luteolin (LTL) recognition. As-prepared Fe3O4@PVIM@Zn(II) possessed core–shell structure, uniform size (200 nm), high magnetic responsiveness (32.6 emu g−1), and a very easy synthesis process. X-ray photoelectron spectroscopy (XPS) suggested a strong interaction between the nitrogen heterocyclic ring of PVIM and Zn(II), which produced abundant binding sites for LTL. The batch mode experiments can be well described by pseudo-first-order kinetic models and a Langmuir isotherm. A rapid binding equilibrium (within 45 min) and large monolayer adsorption capacity (23.92 mg g−1) at 298 K were also observed. In addition, Fe3O4@PVIM@Zn(II) displayed remarkable selectivity to LTL; the purification process using Fe3O4@PVIM@Zn(II) can make purified LTL from approximately 85% to 94.26%. The antibacterial activity of purified LTL was outstanding by means of a Staphylococcus aureus (ATCC29213) resistance experiment. Considering its multiple merits, Fe3O4@PVIM@Zn(II) exhibited great potential for specific binding with natural products, such as flavonoids.

Fabrication of hydrophobic polymer foams with double acid sites on surface of macropore for conversion of carbohydrate.

Herein we reported a simple and novel synthetic strategy for the fabrication of two kinds of hydrophobic polymer foam catalysts (i.e. Cr(3+)-HPFs-1-H(+) and HPFs-1-H(+)) with hierarchical porous structure, inhomogeneous acidic composition and Lewis-Brønsted double acid sites distributed on the surface, which was used to one-pot conversion of carbohydrate (such as cellulose, glucose and fructose) to a key chemical platform (i.e. 5-hydroxymethylfurfural, HMF). The water-in-oil (W/O) high internal phase emulsions (HIPEs), stabilized by both Span 80 and acidic prepolymers as analogous particles offered the acidic actives, were used as the template for simultaneous polymerization of oil phase in the presence of divinylbenzene (DVB) and styrene (St). After subsequent ion-exchange process, Lewis and Brønsted acid sites derived from exchanged Cr(3+) and H(+) ion were both fixed on the surface of cell of the catalysts. The HPFs-1-H(+) and Cr(3+)-HPFs-1-H(+) had similar hierarchical porous, hydrophobic surface and acid sites (HPFs-1-H(+) with macropores ranging from 0.1 μm to 20 μm, uniform mesopores in 14.4 nm, water contact angle of 122° and 0.614 mmolg(-1) of Brønsted acid sites, as well as Cr(3+)-HPFs-1-H(+) with macropores ranging from 0.1 μm to 20 μm, uniform mesopores in 13.3 nm, water contact angle of 136° and 0.638 mmolg(-1) of Lewis-Brønsted acid sites). It was confirmed that Lewis acid sites of catalyst had a slight influence on the HMF yield of fructose came from the function of Brønsted acid sites, and Lewis acid sites were in favor of improving the HMF yield from cellulose and glucose. This work opens up a simple and novel route to synthesize multifunctional polymeric catalysts for efficient one-pot conversion of carbohydrate to HMF.

Two Are Better than One: Halloysite Nanotubes-Supported Surface Imprinted Nanoparticles Using Synergy of Metal Chelating and Low pKa Boronic Acid Monomers for Highly Specific Luteolin Binding under Neutral Condition

Surface-imprinted nanoparticles with double recognition (DM-MIPs) are fabricated onto halloysite nanotubes (HNTs) for highly specific separation of natural flavone luteolin (LTL) under neutral condition. Specifically, a two-step strategy via consecutive surface-initiated atom transfer radical polymerization (SI-ATRP) is employed to introduce inherent recognition of molecular imprinting and reversible covalent affinity of boronic acid ligands and immobilized Zn2+ into DM-MIPs. First, Zn2+-immobilized poly(vinyl imidazole) (PVLD) shell based on the HNTs via the first SI-ATRP is prepared to capture LTL by metal chelating. Then HNTs-supported surface imprinted nanoparticles are prepared using low pKa boronic acid monomer 4-(2-acrylamidoethylcarbamoyl)-3-fluorophenylboronic acid (AMC-FPBA) via the second SI-ATRP. Taking advantage of low apparent pKa of AMC-FPBA and large high-affinity binding site density, DM-MIPs possess a promising binding with cis-diol-containing LTL under neutral condition. In static adsorption, DM-MIPs show large LTL loading amount (83.42 mg g-1), fast capture kinetics, remarkable selectivity, and excellent recyclability at pH = 7.0. More importantly, by reducing the pH to 4.0, the loaded TLL can be simply released. As a proof of this concept, a commercially available LTL with 85% purity can be easily enriched and further purified, and the product exhibits the similar antibacterial performance with standard substance.

A novel water-soluble chitosan linked fluorescent carbon dots and isophorone diisocyanate fluorescent material toward detection of chromium(VI)

In this work, a NCO-capped intermediate was first prepared from fluorescent carbon dots (FCDs) and isophorone diisocyanate (IPDI) via an in situ method in the presence of dibutyltin dilaurate as the catalyst. Based on the fact that –NCO groups can react with the hydroxyl and amino groups in chitosan polymeric chains, a novel water-soluble chitosan linked fluorescent carbon dots and isophorone diisocyanate (FCDs–IPDI–CTS) fluorescent material was obtained from the NCO-capped intermediate and chitosan. The prepared FCDs–IPDI–CTS material shows blue fluorescence under UV exposure. The structure and morphology of the as-prepared FCDs–IPDI–CTS material were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The as-prepared FCDs–IPDI–CTS material exhibits excellent fluorescence properties and good stability. It could be quenched by chromium(VI) and has been further used as a novel fluorescent probe for selective detection of chromium(VI). The optimum conditions for sensing Cr(VI) were investigated. Based on the optimum conditions, a new sensitive method for sensing Cr(VI) was established. This method has been successfully applied to detect Cr(VI) in water and soil samples with satisfactory results.

Three hidden talents in one framework: a terephthalic acid-coordinated cupric metal–organic framework with cascade cysteine oxidase- and peroxidase-mimicking activities and stimulus-responsive fluorescence for cysteine sensing

A metal-organic framework (CuBDC) that possesses cascade cysteine oxidase- and peroxidase-mimicking activities and stimulus-responsive fluorescence was designed by coordinating cupric ions with terephthalic acid. The three-in-one CuBDC provided a new and extremely convenient turn-on fluorescence platform for selective and reliable detection of cysteine.