Fangying Wu

Sensitive detection of carcinoembryonic antigen using surface plasmon resonance biosensor with gold nanoparticles signal amplification.

A new method for real-time detection of carcinoembryonic antigen (CEA) in human serum with high sensitivity and selectivity using surface plasmon resonance (SPR) biosensor was developed. Two kinds of antibodies were used to recognize CEA at different epitopes with high affinity and specificity. Gold nanoparticles (GNPs) modified with streptavidin (SA) were used to further enhance signal specifically via biotin-streptavidin interaction. The binding capacity of the streptavidin-modified gold nanoparticles (SA-GNPs) for ligand biotin was quantified by titration with biotin (5-fluorescein) conjugate to be 10.54 biotin binding sites per 100 nm(2). The developed GNPs enhanced sandwich SPR biosensor successfully fulfilled the sensitive detection of CEA in the range of 1-60 ng/mL with a detection limit of 1.0 ng/mL. Compared to the direct assay format, sandwich format without GNPs and SA-GNPs enhanced sandwich format led to 4.2-fold and 13.8-fold in the sensitivity, respectively. This sensor also showed good selectivity for CEA in the interference study. The results demonstrated that the proposed method could provide a high sensitivity and selectivity in the detection of CEA and offer a promising alternative for cancer biomarker than traditional clinical examinations.

Ultrasensitive turn-on fluorescent detection of trace thiocyanate based on fluorescence resonance energy transfer.

Thiocyanate (SCN(-)) is a small anion byproduct of cyanide metabolism. Several methods have been reported to measure SCN(-) above the micromolar level. However, SCN(-) is derived from many sources such as cigarettes, waste water, food and even car exhaust and its effect is cumulative, which makes it necessary to develop methods for the detection of trace SCN(-). In this paper, a simple and ultrasensitive turn-on fluorescence assay of trace SCN(-) is established based on the fluorescence resonance energy transfer (FRET) between gold nanoparticles (AuNPs) and fluorescein. The detection limit is 0.09 nM, to the best of our knowledge, which has been the lowest detection LOD ever without the aid of costly instrumentation. The fluorescence of fluorescein is significantly quenched when it is attached to the surface of AuNPs. Upon the addition of SCN(-), the fluorescence is turned on due to the competition action between SCN(-) and fluorescein towards the surface of AuNPs. Under an optimum pH, AuNPs size and concentration, incubation time, the fluorescence enhancement efficiency [(IF-I0)/I0] displays a linear relationship with the concentration of SCN(-) in the range of 1.0 nM to 40.0 nM. The fluorescein-AuNP sensor shows absolutely high selectivity toward SCN(-) than other 16 anions. The common metal ions, amino acids and sugars have no obvious interference effects. The accuracy and precision were evaluated based on the recovery experiments. The cost effective sensing system is successfully applied for the determination of SCN(-) in milk products and saliva samples.

The use of tungsten disulfide dots as highly selective, fluorescent probes for analysis of nitrofurazone.

Tungsten disulfide (WS2) is a two-dimensional transition metal dichalcogenide, which is of particular interest because it has highly anisotropic bonding, which leads to strongly anisotropic electrical and mechanical properties. Thus, in this work, a simple hydrothermal process was developed to produce photoluminescence from WS2 dots. This was achieved in the presence of sodium tungstate and reduced L-glutathione; the emitted fluorescence produced a quantum yield as high as 0.066. The WS2 dots and the associated fluorescence were investigated with the use of transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared and UV-vis spectroscopies. The WS2 dots were used as a fluorescent probe to analyze nitrofurazone (NFZ). The associated fluorescence resonance energy transfer (FRET) mechanism was also investigated and the emitted fluorescence was found to be linear in the range of 0.17-166 μmol L(-1) with a detection limit of 0.055 μmol L(-1). The proposed method was successfully applied for analysis of NFZ in nasal drops and water samples.

Highly selective and sensitive detection of heparin based on competition-modulated assembly and disassembly of fluorescent gold nanoclusters

We report a facile yet effective strategy for the fluorescence assay of heparin based on assembly and disassembly of the glutathione-protected gold nanoclusters (GSH-Au NCs) modulated via the competitive interaction of cetyltrimethyl ammonium bromide (CTAB) with heparin and GSH. Firstly, CTAB can increase the fluorescence of Au NCs by forming a nanocomposite via electrostatic and hydrophobic self-assembly. By adding heparin to the assay, CTAB is removed from the nanocomposites because of its higher affinity for heparin, quenching the fluorescence signal. Such a fluorescence feature induced via assembly and disassembly of the NCs enables our assay to possess high selectivity and sensitivity. The linear response toward heparin was obtained over the range 0.1–1.6 μg mL−1 with a low detection limit of 0.075 μg mL−1. Furthermore, satisfactory sensing perfomance for heparin in human serum makes this method hold great promise in heparin-related biomedical applications.

Self-assembled diblock conjugated polyelectrolytes as electron transport layers for organic photovoltaics

Interfacial morphology is not only paramount for charge extraction and transport but also dramatically affects the morphology of the upper active layer, thereby influencing the ultimate power conversion efficiency. However, detailed investigation of the instinctive self-assembly of conjugated polyelectrolytes (CPEs) as the electron transport layers (ETLs) in polymer solar cells (PSCs) has rarely been investigated. Meanwhile, the correlations between the structural assembly of CPEs ETLs on the crystalline ordering, morphology of the upper active layer and the final photovoltaic performance are mystical stories. Herein, two water/alcohol-soluble diblock CPEs with different backbone PFEO-b-PCNBr and PFEO-b-PTNBr are synthesized via Kumada catalyst transfer coupling reactions as ETLs for inverted bulk-heterojunction PSCs. Both PFEO-b-PCNBr and PFEO-b-PTNBr offer an ohmic contact between the ITO electrode and the active layer by substantially reducing the work function of the ITO via modulating the interfacial dipoles. More intriguingly, the spontaneous self-assembly of the diblock polymers can act as a template to induce the upper active layer to form ordered wide nanowire and nanofiber morphology. The more ordered morphology is beneficial for charge extraction and transportation. Consequently, the devices based on poly(3-hexylthiophene) (P3HT):(6,6)-phenyl-C61 butyric acid methyl ester (PC61BM) with ZnO/PFEO-b-PCNBr and ZnO/PFEO-b-PTNBr as ETLs deliver notable power conversion efficiencies (PCEs) of 3.6% and 3.8%, respectively, which is distinctly enhanced compared to 3.0% for the device with pure ZnO as an ETL. These findings indicate that the self-assembled diblock CPEs ETLs provide a novel strategy for optimization of the morphology of the upper active layer and performance of the PSCs.

Specific pH effect for selective colorimetric assay of glutathione using anti-aggregation of label-free gold nanoparticles

An operationally simple colorimetric method for measuring glutathione (GSH) concentration was developed using anti-aggregation of gold nanoparticles (AuNPs) in this work. At a pH of 5.8, cysteine (Cys) could rapidly induce the aggregation of AuNPs, thereby resulting in color change and AuNPs absorbance ratio (A650 nm/A520 nm) change. However, the added glutathione (GSH) can cause the anti-aggregation process to occur. This method was based on the regulation of pH, which on one hand can selectively detect GSH over Cys by the process of anti-aggregation of AuNPs and on the other hand can distinguish GSH from homocysteine (Hcys), and cystine (Cye) through specific selectivity. Under optical conditions, the detection of GSH can be finished within 5 min. The concentration range of the probe is 0.1–1.0 μM and the limit of detection (LOD) can be reached to 20.3 nM.

Cu2+-Mediated turn-on fluorescence assay for sulfide ions using glutathione-protected gold nanoclusters: enhanced sensitivity, good reusability, and cell imaging

We develop a simple assay for highly selective and sensitive fluorescence detection of sulfide ions (S2−) using glutathione-protected gold nanoclusters (GSH-Au NCs). This approach was based on the much higher affinity of CuS than that of the Cu–GSH complex, which makes the fluorescence of the NCs quenched by Cu2+ recover upon addition of S2−. Importantly, the assistance of Cu2+ enables S2− detection in the “turn-on” mode, eventually enhancing detection sensitivity toward S2− about 15 times more compared to that in the “turn-off” mode. Under the optimal conditions, the linear fluorescence response toward S2− was given within the concentration range of 2 to 24 μM with a low detection limit of 0.7 μM. Also, the GSH-Au NCs show good reusability for S2− detection due to effective removal of the bridging reagent Cu2+ by S2−. This phenomenon is further exploited as an integrated logic gate and successfully employed for imaging S2− in living cells.