Tianxiang Zhang

A sensitive photoelectrochemical biosensor for AFP detection based on ZnO inverse opal electrodes with signal amplification of CdS-QDs.

In this work, ZnO inverse opals structure (IOs) based photoelectrochemical (PEC) electrode was fabricated for alpha-fetoprotein (AFP) detection. Then, the uniform CdS quantum dots (QDs) were hydrothermally synthesized, which allowed the binding of AFP and glucose oxidase (GOD) on CdS QDs, forming the AFP-CdS-GOD composite. The competitive immunosensor of AFP and the AFP-CdS-GOD composite with anti-AFP antibodies (Ab) immobilized on FTO (fluorine-doped tin oxide) /ZnO IOs electrode was successfully applied to the detection of AFP. GOD could catalyze glucose to produce hydrogen peroxide (H2O2) acting as an electron donor to scavenge photogenerated holes in the valence band of CdS QDs, reducing the recombination of electrons and holes of CdS QDs. Also the effective energy level matching between the conduction bands of CdS QDs and ZnO widened the range of light absorption, allowing for electron injection from excited CdS QDs to ZnO upon visible light irradiation, which enhanced the photocurrent. The results show that the immunosensor of AFP possesses a large linear detection range of 0.1-500 ng/ml with a detection limit of 0.01 ng/ml. It also exhibits excellent anti-interference property and acceptable stability. This work provides a promising method for achieving excellent photoelectrochemical biosensor detection of other proteins.

Facilely prepared carbon dots and rare earth ion doped hybrid composites for ratio-metric pH sensing and white-light emission

A facile method was developed to synthesize fluorescent carbon-dot–Eu3+ hybrid composites (CD–Eu–HCs) by one-pot hydrothermal methods. The prepared composites demonstrate unique dual fluorescence which originates from the blue emission of the CDs and intrinsic photoluminescence of the Eu3+ ions, respectively. Moreover, such dual fluorescent characteristics show quite different responses for different pH value environments and have been developed in a ratiometric pH sensor. Lastly, they can realize white light emission by co-doping of Tb3+ and the color temperature becomes tunable by adjusting the relative proportion of Eu3+.

Silane modified upconversion nanoparticles with multifunctions: imaging, therapy and hypoxia detection

Herein, we report a facile route to synthesize silane coated upconversion nanoparticles (UCNPs@silane) with an ultrathin layer (the thickness: 1–2 nm), which not only provides good biocompatibility, but also affords hydrophobic interspace to load organic molecules to realize multifunctions. Besides the function of upconversion imaging of UCNPs, cancer therapy and oxygen level detection can also be realized by the addition of chemotherapy drug, PTX, and oxygen sensitive molecules, Platinum (II) octaethylporphine (PtOEP). In bio-experiments, besides the MTT assays, therapy efficacy of UCNPs@PTX@silane can also be detected with the confocal laser scanning microscopy (CLSM) by staining methods. UCNPs@PtOEP@silane can afford minimally invasive analysis of dissolved oxygen and then respond sensitively to the variance of intracellular oxygen concentration affected by therapeutic UCNPs@PTX@silane.

Remarkable Enhancement of Upconversion Luminescence on Cap-Ag/PMMA Ordered Platform and Trademark Anticounterfeiting

High brightness of upconversion luminescence (UCL) for a thinner layer of UC nanoparticles is significant for routine applications of effective trademark anticounterfeiting technology. In this work, efficient UCL of NaYF4:Yb3+,Er3+/Tm3+ was realized by combining a Ta2O5 dielectric layer on the cyclical island silver films supported by poly(methyl methacrylate) opal photonic crystals (PCs). The synergistic modulation of localized surface plasmon resonance and PC effect results in a significant improvement of the local electromagnetic field and an optimum UC enhancement of 145 folds. Furthermore, colorful pattern nanoprinting has been applied to this composite and used for trademark anticounterfeiting. The combination of angle-dependent PC effect and infrared-to-visible UCL represents a more advanced anticounterfeiting technique.

Photoelectrochemical detection of alpha-fetoprotein based on ZnO inverse opals structure electrodes modified by Ag 2 S nanoparticles

In this work, a new photoelectrochemical biosensor based on Ag2S nanoparticles (NPs) modified macroporous ZnO inverse opals structure (IOs) was developed for sensitive and rapid detection of alpha fetal protein (AFP). Small size and uniformly dispersed Ag2S NPs were prepared using the Successive Ionic Layer Adsorption And Reaction (SILAR) method, which were adsorbed on ZnO IOs surface and frame work as matrix for immobilization of AFP. The composite structure of ZnO/Ag2S expanded the scope of light absorption to long wavelength, which can make full use of the light energy. Meanwhile, an effective matching of energy levels between the conduction bands of Ag2S and ZnO are beneficial to the photo-generated electrons transfer. The biosensors based on FTO (fluorine-doped tinoxide) ZnO/Ag2S electrode showed enough sensitivity and a wide linear range from 0.05 ng/mL to 200 ng/mL with a low detection limit of 8 pg/mL for the detection of AFP. It also exhibited high reproducibility, specificity and stability. The proposed method was potentially attractive for achieving excellent photoelectrochemical biosensor for detection of other proteins.

Enhanced upconversion luminescence on the plasmonic architecture of Au–Ag nanocages

Au–Ag nanocages with tunable surface plasmon resonance peaks were synthesized via the galvanic replacement reaction. These tunable nanocubes with strong plasmonic effect were further fabricated into thin films composed of a random assembly of Au–Ag nanocages, which show great broadening of surface plasmon resonance absorption. After optimizing, through coupling with the excitation light, the overall upconversion luminescence intensity of NaYF4:Yb3+, Er3+ on the surface of the Au–Ag nanocage film under 980 nm excitation was improved more than 15 fold.

Carbon dot/polyvinylpyrrolidone hybrid nanofibers with efficient solid-state photoluminescence constructed using an electrospinning technique

Carbon dots (CDs) are the promising candidates for application in optoelectronic and biological areas due to their excellent photostability, unique photoluminescence, good biocompatibility, low toxicity and chemical inertness. However, the self-quenching of photoluminescence as they are dried into the solid state dramatically limits their further application. Therefore, realizing efficient photoluminescence and large-scale production of CDs in the solid state is an urgent challenge. Herein, solid-state hybrid nanofibers based on CDs and polyvinylpyrrolidone (PVP) are constructed through an electrospinning process. The resulting solid-state hybrid PVP/CD nanofibers present much enhanced photoluminescence performance compared to the corresponding pristine colloidal CDs due to the decrease in non-radiative recombination of electron-holes. Owing to the suppressed self-quenching of CDs, the photoluminescence quantum yield is considerably improved from 42.9% of pristine CDs to 83.5% of nanofibers under the excitation wavelength of 360 nm. This has great application potential in optical or optoelectronic devices.

Photoluminescence enhancement of carbon dots induced by hybrids of photonic crystals and gold–silver alloy nanoparticles

Carbon dots are attracting worldwide interest owing to their unique optical properties and great potential for application. However, orange/red emission carbon dots are still rare and exhibit relatively low efficiency. In this work, we present a novel strategy to enhance the fluorescence intensity of orange carbon dots, by synergistically manipulating an electromagnetic field through opal photonic crystals and the localized surface plasmon resonance of a metal structure. An optimum intensity enhancement of 25-fold was obtained for a modulated sample of PMMA opal photonic crystals and 53-fold for PMMA opal photonic crystals/Au–Ag alloy plasmon hybrids. The local electromagnetic field distribution for the PMMA opal photonic crystals/Au–Ag hybrid is calculated by the finite difference time domain method. Furthermore, a fingerprint identification system based on synergistic modulation is realized in the composite system, which provides novel insights into the potential applications of carbon dot films.

Green fluorescent organic nanoparticles based on carbon dots and self-polymerized dopamine for cell imaging

Fluorescent organic nanoparticles (FONs) based on polydopamine (PDA) have recently emerged as a novel fluorescent probe due to its facile synthesis procedure, good water solubility, and excellent biocompatibility. However, previously reported PDA-FONs show low monodispersity and efficiency, which largely limit their application. In this study, we report a new type of FONs that has been prepared using carbon dots (CDs) as seeds and assembled via the self-polymerization of dopamine molecules. The prepared FONs showed high efficiency and monodispersity; moreover, via controlling the time of the polymerization reaction, different FONs could be obtained, which demonstrated similar structures but with tunable emission properties, and the emission gradually evolved from blue to green with the increasing reaction time. The mechanism of the prepared FONs was confirmed to be via the Forster resonance energy transfer (FRET) effect occuring between CDs and polymerized dopamine, leading to high efficiency and tunable emission. The FONs were also explored for cell imaging and cytotoxicity experiments, and they showed excellent biocompatibility and good prospects in biotechnological applications.

DNA stabilized Ag–Au alloy nanoclusters and their application as sensing probes for mercury ions

Metal nanoclusters (NCs) have attracted plenty of attention because of their unique properties and great application potentials. In this work, DNA scaffold Ag–Au alloy nanoclusters (Ag–Au ANCs) were fabricated by a one pot wet-chemical strategy and characterized by various techniques, including TEM, XPS and mass spectrometery (MS). The results indicate that owing to the strong interaction between DNA and Ag+, the silver NCs were formed first, then bundled with Au shells. In the Ag–Au ANCs, some of the Au is in an oxidized state as Au(I), which can largely modify the optical properties of the silver NCs. The Ag–Au ANCs demonstrate tunable emissions from green to red with highly improved stability. The fluorescence of Ag–Au ANCs was explored to detect Hg2+ in contrast to Ag NCs. The detection using Ag–Au ANCs demonstrated highly improved and excellent linearity and selectivity, which could effectively avoid the disturbance of Cu2+ and was promising for applications.