Songjun Li

Electrochemical immunosensor with N-doped graphene-modified electrode for label-free detection of the breast cancer biomarker CA 15-3.

Highly sensitive and label-free detection of the biomarker carbohydrate antigen 15-3 (CA 15-3) remains a challenge in the diagnosis of breast cancer. Here, a novel electrochemical immunosensor capable of sensitive and label-free detection of CA 15-3 is reported. This unique immunosensor, equipped with a highly conductive graphene (i.e., N-doped graphene sheets)-modified electrode, exhibited significantly increased electron transfer and high sensitivity toward CA 15-3. This novel immunosensor, with a low detection limit of 0.012 U/mL, worked well over a broad linear range of 0.1-20 U/mL. Unlike conventional immunosensors, which usually involve complicated label processing and time-consuming separations, the use of highly conductive graphene avoids the need for labels and is simple in nature. The strategy developed for this immunosensor provides a promising approach for clinical research and diagnostic applications.

Enzyme-free electrochemical immunosensor configured with Au-Pd nanocrystals and N-doped graphene sheets for sensitive detection of AFP.

A novel electrochemical immunosensor capable of enzyme-free detection of alpha fetoprotein (AFP) is reported. This immunosensor was fabricated in a sandwich-like format where catalytic Au-Pd nanocrystals and highly conductive N-doped graphene sheets were incorporated. The significant catalysis by Au-Pd nanocrystals toward hydrogen peroxide, along with the increased electron transfer by graphene sheets, caused signal generation and increased sensitivity, which enables the enzyme-free detection of AFP. With a low detection limit at 0.005 ng mL(-1), this novel immunosensor worked well over the broad linear range of 0.05-30 ng mL(-1). Unlike previously reported enzyme-based electrochemical immunosensors, which often involve the complicated steps for enzyme loading and necessary treatments to keep the activity of enzyme, this novel immunosensor is simple in nature and employed catalytic Au-Pd nanoparticles and highly conductive graphene, which thus enables reliable and sensitive detection for clinic usage.

Facile solvothermal synthesis of porous ZnFe2O4 microspheres for capacitive pseudocapacitors

A facile and cost-effective solvothermal approach to the fabrication of ZnFe2O4 microspheres composed of nanocrystals has been developed. The morphology and structure of the products were characterized by X-ray powder diffraction, transmission electron microscopy, and field-emission scanning electronic microscopy, and N2-adsorption–desorption. Meanwhile, the magnetic properties of the product were investigated via vibrating sample magnetism. Finally, the electrochemical performance of the obtained ZnFe2O4 microspheres was measured by cyclic voltammetry and galvanostatic charge–discharge techniques. The results show that such structured ZnFe2O4 has a specific capacitance of 131 F g−1 and stable cycling performance with 92% capacitance retention after 1000 cycles, which make it have a potential application as a supercapacitor electrode material.

A temperature-responsive nanoreactor.

An originally designed temperature-responsive nanoreactor is reported. The nanoreactor is made of Ag nanoparticles and a functional polymer composite of poly(acrylamide) (PAAm) and poly(2-acrylamide-2-methylpropanesulfonic acid) (PAMPS). At a relatively low temperature (e.g., 20 °C), this nanoreactor displayed weak reactivity because of the interpolymer complexation between PAAm and PAMPS, which largely restricted the access of reactants to the encapsulated Ag nanoparticles. On the contrary, at a relatively high temperatures (e.g., 40 °C), the nanoreactor demonstrated significant catalytic activity resulting from the dissociation of the interpolymer complexation between PAAm and PAMPS, which allowed reactants to get access to the encapsulated Ag nanoparticles. By taking account of previously reported PNIPAm-based nanoreactors, which show inverse temperature response, i.e., reactivity decreases whilst temperature increases, this temperature-responsive nanoreactor would greatly facilitate and enrich the increasing studies on smart nanomaterials, generating numerous applications in a wide range of areas, such as catalysis and sensing.

Unique double-shelled hollow silica microspheres: template-guided self-assembly, tunable pore size, high thermal stability, and their application in removal of neutral red

A novel type of monodisperse and double-shelled hollow silica microspheres was reported. This unique double-shelled structure was fabricated using a consecutive template-guided self-assembly. Cationic poly(styrene) (CPS) particles prepared by emulsifier-free polymerization were first used as the template to coat with tetraethylorthosilicate (TEOS) in the presence of coupling agent methacryloxypropyltrimethoxysilane (MPS), forming the core/shell type of CPS/SiO2 particles. The resulting CPS/SiO2 particles were further used as the template and in situ polymerized with styrene, a cationic co-monomer 2-(methacryloyl)ethyltrimethyl ammonium chloride (DMC), followed by electro-statically guided self-assembly and polymerization of TEOS on the surface, generating the sandwich-like CPS/SiO2/CPS/SiO2 particles. Finally, the unique double-shelled hollow silica spheres were produced by one-step removal of the CPS core and CPS layer from the sandwich-like particles. The structure of the monodisperse and intact double-shelled hollow silica microspheres was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET), Elemental Analysis (EA), and 29Si Nuclear Magnetic Resonance (29Si-NMR). Unlike previously reported hollow silica microspheres which have one single shell, the novel silica microspheres have two shells, enabling improved thermal stability and larger BET surface area. Notably, the interior cavity and shell-to-shell distance can be effectively tuned simply by controlling the interior CPS core diameter and the outer CPS template layer. The absorption and separation of the neutral red (NR) in synthesized hollow silica spheres showed favorable adsorption behavior, such as higher absorbent amount of dye and lower rate of dye desorbed for NR in comparison to single-shelled hollow silica, which thereby makes it potentially more applicable in environmental separation and adsorption.

Self-switchable catalysis by a nature-inspired polymer nanoreactor containing Pt nanoparticles

A nature-inspired polymer nanoreactor with self-switchable catalytic ability is reported. This nanoreactor was made of platinum nanoparticles and a unique polymer composite of poly(1-vinylimidazole) (PVI) and poly(2-(trifluoromethyl)acrylic acid) (PTFMA) that exhibited “self-healing” properties. This nanoreactor revealed weak reactivity at relatively low temperatures due to the complementary interaction between PVI and PTFMA, which inhibited access to the catalytic sites of platinum. In contrast, the nanoreactor demonstrated significant reactivity at relatively high temperatures, resulting from the dissociation of the interpolymer interaction. Unlike reported nanoreactors which usually involve the thermal phase transition of PNIPAm, this novel nanoreactor has adopted the “self-healing” properties of supramolecular building blocks. The proposed design suggests new opportunities for developing smart nanoreactors capable of self-switchable catalysis.

A successive-reaction nanoreactor made of active molecularly imprinted polymer containing Ag nanoparticles

A successive-reaction nanoreactor made of a unique molecularly imprinted polymer containing Ag nanoparticles is reported. This molecularly imprinted polymer was fabricated using two well-coupled templates, i.e., 4-nitrophenyl acetate and 4-nitrophenol. The catalytic hydrolysis of the former by this nanoreactor led to the formation of the latter, which was further reduced by the nanoreactor to 4-aminophenol. Unlike reported nanoreactors, which usually promote one single reaction, this novel nanoreactor can run cascade reactions. The proposed integration of active molecularly imprinted polymers with metal nanoparticles opens a new opportunity for creating functional catalysts for complicated chemical processes.

A Cascade‐Reaction Nanoreactor Composed of a Bifunctional Molecularly Imprinted Polymer that Contains Pt Nanoparticles

This study was aimed at addressing the present challenge of cascade reactions, namely, how to furnish the catalysts with desired and hierarchical catalytic ability. This issue was addressed by constructing a cascade-reaction nanoreactor made of a bifunctional molecularly imprinted polymer containing acidic catalytic sites and Pt nanoparticles. The acidic catalytic sites within the imprinted polymer allowed one specified reaction, whereas the encapsulated Pt nanoparticles were responsible for another coupled reaction. To that end, the unique imprinted polymer was fabricated by using two well-coupled templates, that is, 4-nitrophenyl acetate and 4-nitrophenol. The catalytic hydrolysis of the former compound at the acidic catalytic sites led to the formation of the latter compound, which was further reduced by the encapsulated Pt nanoparticles to 4-aminophenol. Therefore, this nanoreactor demonstrated a catalytic-cascade ability. This protocol opens up the opportunity to develop functional catalysts for complicated chemical processes.

A positively temperature-responsive, substrate-selective Ag nanoreactor.

An original Ag nanoreactor capable of positively temperature-responsive and substrate-selective catalysis was prepared in this study. This nanoreactor was made of Ag nanoparticles encapsulated in a 4-nitrophenol (NP)-imprinted polymer matrix that exhibited a temperature-sensitive interpolymer interaction between poly(acrylamide) (PAAm) and (2-acrylamide-2-methylpropanesulfonic acid) (PAMPS). At relatively low temperatures (such as 20 degrees C), this nanoreactor did not demonstrate significant NP-selective catalysis due to the interpolymer complexation between PAAm and PAMPS, which caused shrinking in the imprinted networks. Conversely, at relatively high temperatures (such as 40 degrees C), this nanoreactor provided significant NP-selective catalysis resulting from the dissociation of the interpolymer complexes between PAAm and PAMPS. Unlike traditional Ag nanoreactors, which lack positively temperature-responsive catalysis or substrate-selective ability, this unique nanoreactor employed both the imprinting of the substrate molecule (i.e., NP) and a temperature-sensitive PAAm/PAMPS network, thereby making positively temperature-responsive, substrate-selective catalysis feasible.

High photocatalytic activity of hierarchical SiO2@C-doped TiO2 hollow spheres in UV and visible light towards degradation of rhodamine B

Ongoing research activities are targeted to explore high photocatalytic activity of TiO2-based photocatalysts for the degradation of environmental contaminants under UV and visible light irradiation. In this work, we devise a facile, cost-effective technique to in situ synthesize hierarchical SiO2@C-doped TiO2 (SCT) hollow spheres for the first time. This strategy mainly contains the preparation of monodisperse cationic polystyrene spheres (CPS), sequential deposition of inner SiO2, the preparation of the sandwich-like CPS@SiO2@CPS particles, and formation of outer TiO2. After the one-step removal of CPS templates by calcination at 450°C, hierarchical SiO2@C-doped TiO2 hollow spheres are in situ prepared. The morphology, hierarchical structure, and properties of SCT photocatalyst were characterized by TEM. SEM, STEM Mapping, BET, XRD, UV-vis spectroscopy, and XPS. Results strongly confirm the carbon doping in the outer TiO2 lattice of SCT hollow spheres. When the as-synthesized SCT hollow spheres were employed as a photocatalyst for the degradation of Rhodamine B under visible-light and ultraviolet irradiation, the SCT photocatalyst exhibits a higher photocatalytic activity than commercial P25, effectively overcoming the limitations of poorer UV activity for many previous reported TiO2-based photocatalysts due to doping.