Youju Huang

Nanomaterials for electrochemical non-enzymatic glucose biosensors

This review overviews the recent development of nanomaterials for the application of electrochemical non-enzymatic glucose biosensors. The electrocatalytic mechanism and glucose sensing performance of a variety of nanostructured materials including metallic nanoparticles, metal oxides, metal complexes, alloys and carbon nanomaterials are discussed. The merits and shortfalls of each nanomaterial as electrocatalyst for non-enzymatic biosensing are evaluated and the prospects of non-enzymatic glucose biosensors are presented.

Janus Polymer/Carbon Nanotube Hybrid Membranes for Oil/Water Separation

A robust and simple method is provided to fabricate Janus polymer/carbon nanotube (CNT) hybrid membranes for oil/water separation. Starting from CNT membranes formed by dispensing, hydrophobic poly(styrene) (PS) and hydrophilic poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) were grated from different sides of the photoactive CNT membranes via self-initiated photografting and photopolymerization (SIPGP) to achieve Janus polymer/CNTs hybrid membranes. The obtained membranes have excellent oil/water selectivity in the removal of oil from water. Moreover, they can effectively separate both surfactant-stabilized oil-in-water and water-in-oil emulsions because of the anisotropic wettability of the membranes.

Robust preparation of superhydrophobic polymer/carbon nanotube hybrid membranes for highly effective removal of oils and separation of water-in-oil emulsions

A facile and robust strategy for fabricating superhydrophobic polymer/carbon nanotube hybrid membranes via covalent attachment of hydrophobic polymer, such as polystyrene onto carbon nanotube membrane is proposed. The as-prepared hybrid membranes can selectively remove a wide range of organic solvents from water with high absorption capacity and good recyclability. Moreover, the obtained membrane shows excellent separation properties for surfactant-stabilized water in oil emulsions with separation efficiency as high as 99.94% and high flux (5000 L m−2 h−1 bar−1). Therefore, the superhydrophobic hybrid membranes enable an efficient separation for various oil/water emulsions, showing attractive potential for practical oil/water separation.

Fluorescent pH sensor based on Ag@SiO2 core-shell nanoparticle.

We have demonstrated a novel method for the preparation of a fluorescence-based pH sensor by combining the plasmon resonance band of Ag core and pH sensitive dye (HPTS). A thickness-variable silica shell is placed between Ag core and HPTS dye to achieve the maximum fluorescence enhancement. At the shell thickness of 8 nm, the fluorescence intensity increases 4 and 9 times when the sensor is excited at 405 and 455 nm, respectively. At the same time, the fluorescence intensity shows a good sensitivity toward pH value in the range of 5-9, and the ratio of emission intensity at 513 nm excited at 455 nm to that excited at 405 nm versus the pH value in the range of 5-9 is determined. It is believed that the present pH sensor has the potential for determining pH real time in the biological sample.

Dark-field microscopy studies of polarization-dependent plasmonic resonance of single gold nanorods: rainbow nanoparticles.

Orientation sensors require the monitoring of polarization-dependent surface plasmons of single nanoparticles. Herein, we present both the longitudinal and transverse surface plasmonic resonance from a single gold nanorod (AuNR) using conventional dark-field microscopy. The relative peak intensities of the transverse and longitudinal surface plasmons of a single AuNR can be successfully tuned by polarized excitation, which is an important step towards the use of transverse plasmon resonance of single AuNRs without photo-induced reshaping of nanoparticles. More interestingly, compared with AuNRs with small diameters, unique optical properties from AuNRs with diameters greater than 30 nm are revealed. As a result, optical images with different colors, rainbow nanoparticles (sea green, brown, red, yellow and green), depending on the polarization angle, can be revealed by a single AuNR. This result holds great promise for polarization-controlled colorimetric nanomaterials and single particle tracers in living cells and microfluidic flows.

Hierarchical Flowerlike Gold Nanoparticles Labeled Immunochromatography Test Strip for Highly Sensitive Detection of Escherichia coli O157:H7

Gold nanoparticles (AuNPs) labeled lateral-flow test strip immunoassay (LFTS) has been widely used in biomedical, feed/food, and environmental analysis fields. Conventional ILFS assay usually uses spherical AuNPs as labeled probes and shows low detection sensitivity, which further limits its widespread practical application. Unlike spherical AuNP used as labeled probe in conventional ILFS, in our present study, a hierarchical flowerlike AuNP specific probe was designed for LFTS and further used to detect Escherichia coli O157:H7 (E. coli O157:H7). Three types of hierarchical flowerlike AuNPs, such as tipped flowerlike, popcornlike, and large-sized flowerlike AuNPs were synthesized in a one-step method. Compared with other two kinds of Au particles, tipped flowerlike AuNPs probes for LFTS particularly exhibited highly sensitive detection of E. coli O157:H7. The remarkable improvement of detection sensitivity of tipped flowerlike AuNPs probes can be achieved even as low as 10(3) colony-forming units (CFU)/mL by taking advantages of its appropriate size and hierarchical structures, which is superior over the detection performance of conventional LFTS. Using this novel tipped flower AuNPs probes, quantitative detection of E. coli O157:H7 can be obtained partially in a wide concentration range with good repeatability. This hierarchical tipped flower-shaped AuNPs probe for LFTS is promising for the practical applications in widespread analysis fields.

Synthesis and Self-Assembly of Highly Monodispersed Quasispherical Gold Nanoparticles

We report the synthesis of cetyltrimethylammonium bromide (CTAB) assisted seed mediated growth of highly pure and monodispersed quasispherical gold nanoparticles (QAuNPs) and their self-assembly on the silica/glass substrates. The seed-mediated growth approach was modified to prepare size-tunable monodispersed QAuNPs with sizes ranging from 20 to 150 nm. The larger, more uniform seeds and lower CTAB concentration resulted in the formation of relatively large QAuNPs with improved monodispersity (relative standard deviation (RSD) of ∼5-8%) and high purity in their shapes. In addition, CATB-capped QAuNPs can be spontaneously assembled into closely packed and highly aligned superstructures with well-defined mutillayers (two to six layers) on silica substrates. Furthermore, CATB-capped QAuNPs can easily construct density-controllable QAuNP chips by electrostatic self-assembly, showing their promising applications for single-nanoparticle plasmonic sensors.

Light-triggered reversible self-assembly of gold nanoparticle oligomers for tunable SERS.

A photoresponsive amphiphilic gold nanoparticle (AuNP) is achieved through the decoration of AuNP with hydrophilic poly(ethylene glycol) (PEG) and hydrophobic photoresponsive polymethacrylate containing spiropyran units (PSPMA). Owing to the photoresponsive property of spiropyran units, the amphiphilic AuNPs can easily achieve the controllable assembly/disassembly behaviors under the trigger by light. Under visible light, spiropyran units provide weak intermolecular interactions between neighbored AuNPs, leading to isolated AuNPs in the solution. While under UV light irradiation, spiropyran units in the polymer brushes transform into merocyanine isomer with conjugated structure and zwitterionic state, promoting the integration of adjacent AuNPs through π-π stacking and electrostatic attractions, further leading to the formation of Au oligomers. The smart reversible AuNP oligomers exhibited switchable plasmonic coupling for tuning surface-enhanced Raman scattering (SERS) activity, which is promising for the application of SERS based sensors and optical imaging.

Controlled functionalization of carbon nanotubes as superhydrophobic material for adjustable oil/water separation

A robust strategy for fabricating superhydrophobic carbon nanotube (CNT)-based hybrid materials as a separation membrane through the covalent attachment of the fluorine-bearing organosilane 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDTS) onto –OH functionalized CNTs is proposed. This method resulted in PFDTS/CNT superhydrophobic materials with controlled functionalization that could be used to effectively separate various surfactant-stabilized water-in-oil emulsions with high separation efficiency and high flux. It maintains stable superhydrophobicity and high separation efficiency under extreme conditions, including high or low temperature and strongly acidic or alkaline solutions, and shows fire-retardant properties.

Functionalization of Biodegradable PLA Nonwoven Fabric as Superoleophilic and Superhydrophobic Material for Efficient Oil Absorption and Oil/Water Separation

Although the construction of superwettability materials for oil/water separation has been developed rapidly, the postprocess of the used separation materials themselves is still a thorny problem due to their nondegradation in the natural environment. In this work, we reported the functionalization of polylactic acid (PLA) nonwoven fabric as superoleophilic and superhydrophobic material for efficient treatment of oily wastewater with eco-friendly post-treatment due to the well-known biodegradable nature of PLA matrix.