Au/TiO2-based molecularly imprinted photoelectrochemical sensor for dibutyl phthalate detection.

A photoelectrochemical molecular imprinting sensor based on Au/TiO2 nanocomposite was constructed for the detection of dibutyl phthalate. Firstly, TiO2 nanorods were grown on fluorine-doped tin oxide substrate by hydrothermal method. Then, gold nanoparticles were electrodeposited on TiO2 to fabricate Au/TiO2. Finally, molecular imprinted polymer was electropolymerized on the Au/TiO2 surface to construct MIP/Au/TiO2 PEC sensor for DBP. The conjugation effect of MIP accelerates the electron transfer between TiO2 and MIP, which can greatly improve the photoelectric conversion efficiency and sensitivity of the sensor. In addition, MIP can also provide sites for highly selective recognition of dibutyl phthalate molecules. Under optimal experimental conditions, the prepared photoelectrochemical sensor was used for the quantitative determination of DBP and the results showed a wide linear range (50 to 500 nM), a low limit of detection (0.698 nM), and good selectivity. The sensor was used in a study of real water samples to show that it has promising applications in environmental analysis.

Photoelectrochemical aptasensor based on nanocomposite of CdSe@SnS2 for ultrasensitive and selective detection of sulfamethazine.

A photoelectrochemical (PEC) aptasensor based on CdSe@SnS2 nanocomposite has been developed to detect sulfamethazine (SMZ). The introduction of CdSe into SnS2 displayed an amplified PEC signal, which was higher than that of pure CdSe and SnS2, attributable to its enhanced light harvesting capacity and promoted PEC energy conversion efficiency. Due to the formation of specific non-covalent bonds, the SMZ-binding aptamer (SBA) has significant specificity and sensitivity. When SMZ was incubated on a CdSe@SnS2 modified electrode fixed with aminated SBA, the formation of the SMZ/SBA complex increased the space resistance of electron transfer and hindered the electronic migration between the electrodes, resulting in a decrease in photocurrent. The greater the adsorbed amount on the SBA, the lower the photocurrent produced.  Under optimized conditions the photocurrent response of MCH/SBA/CdSe@SnS2/FTO was inversely proportional to the SMZ concentration in the range 0.1 to 100 pM, with a detection limit (3 S/N) of 0.025 pM (at 0 V vs. Hg/HgCl). The recoveries ranged from 95.8 to 104% with relative standard deviations (RSDs) < 6.3% (n = 3) in actual water sample. This PEC aptasensor which shows considerable potential in SMZ detection applications has high selectivity, reproducibility, and good stability.

A dual-signal self-checking photoelectrochemical immunosensor based on the sole composite of MIL-101(Cr) and CdSe quantum dots for the detection of α-fetoprotein.

Designing a photoelectrochemical (PEC) immunosensor that can produce dual photocurrent signals which can refer to each other is a great importance but a big challenge. In this manuscript, a novel dual photocurrent signals immunosensor was constructed for the detection of α-fetoprotein (AFP). Unlike the usual method of using two composite materials to provide cathode and anode photocurrent respectively, this work applies only one compound of MIL-101 (Cr) and CdSe quantum dots (QDs). Thereinto, we found that the photocurrent polarity of MIL-101(Cr) would switch by adjusting applied voltage. And then CdSe QDs was introduced by simple ultrasound mixing to boost the dual photocurrent signals. Furthermore, in the composite of M&C, the electron transfer path between MIL-101(Cr) and CdSe QDs may switch between "Z-type" and "Ⅱ-type" by adjusting voltage. Benefiting by the dual signals, the proposed sensor can not only perform sensitively quantitative detection of α-fetoprotein (AFP), but also can intuitively estimate the accuracy and reliability of the test result by determining whether the corresponding relationship of "cathode photocurrent-analyte concentration-anode photocurrent" is established. The linear ranges of the sensing electrodes as cathode and anode are the same, both from 0.1 to 300 ng mL-1. The limit of detection (LOD) is 0.082 ng mL-1 (S/N = 3) when it used as an anode, and the LOD is 0.054 ng mL-1 (S/N = 3) when it served as cathode. Furthermore, this sensor showed acceptable stability, reproducibility, specificity, and feasibility of detecting AFP in human serum, which has broad development prospects in the early clinical diagnosis.

On-surface synthesis of size- and shape-controlled two-dimensional Aun nanoclusters using a flexible fullerene molecular template.

Synthesizing nano-clusters with a well-defined size, shape, and composition is an important and challenging goal in nanotechnology. Here we report the application of a single layer C60 molecule as an effective molecular template for the synthesis of size- and shape-selected two-dimensional gold clusters (Aun) on a graphite substrate. This molecular template facilitates the preferential formation of Au19 clusters with a selectivity as high as 90%. Density-functional-theory (DFT) calculations found an energy minimum associated with C60-stabilized two-dimensional Au19 clusters.

Photoelectrochemical immunosensor based on CdSe@BiVO4 Co-sensitized TiO2 for carcinoembryonic antigen.

The fast and accurate detection of Carcinoembryonic Antigen (CEA) plays an important role in clinical cancer treatment and therapy. An ultrasensitive photoelectrochemical (PEC) immunosensor for the detection of CEA was constructed using CdSe@BiVO4 co-sensitized TiO2 nanorods as photoactive materials. TiO2 nanorods were assembled on the FTO modified electrode to immobilize capture antibodies. With a sandwich immunoassay format, CEA and signal antibodies labelled CdSe@BiVO4 were introduced in sequence via specific immunoreaction, and the ultrahigh sensitivity of this immunoassay results from the following three aspects. Firstly, the co-sensitization of BiVO4 and CdSe extends the absorption range of TiO2 from ultraviolet region to visible light region, which can adequately utilize the light energy; Secondly, the effective matching of energy levels among TiO2, CdSe and BiVO4 accelerates the separation and transfer of photogenerated electron-hole pairs and significantly improves the PEC performance; Finally, the introduced Au evidently expedites the interfacial electron transfer from TiO2 to FTO electrode, further resulting in noticeably increased photocurrent. Based on multiple signal amplification strategy, a largely linear detection range from 0.01 ng mL-1 to 50 ng mL-1 with a low detection limit (0.5 pg mL-1) were obtained. In addition, the prepared immunosensor with attractive properties provides a promising platform for PEC detection.

Orientational Epitaxy of van der Waals Molecular Heterostructures.

The shape of individual building blocks is an important parameter in bottom-up self-assembly of nanostructured materials. A simple shape change from sphere to spheroid can significantly affect the assembly process due to the modification to the orientational degrees of freedom. When a layer of spheres is placed upon a layer of spheroids, the strain at the interface can be minimized by the spheroid taking a special orientation. C70 fullerenes represent the smallest spheroids, and their interaction with a sphere-like C60 is investigated. We find that the orientation of the C70 within a close-packed C70 layer can be steered by contacting a layer of C60. This orientational steering phenomenon is potentially useful for epitaxial growth of multilayer van der Waals molecular heterostructures.

The stabilization mechanism and size effect of nonpolar-to-polar crystallography facet tailored ZnO nano/micro rods via a top-down strategy.

A simple and efficient top-down strategy, the chemical vapor etching method, is reported for synthesizing corrugated ZnO nano/micro rods (NRs). The stabilization mechanism of this unique nanostructure has been determined through a combination of aberration-corrected field emission scanning electron microscopy, high-resolution transmission electron microscopy, and first-principles calculations. The experimental data are in good agreement with the theoretical calculations, and a remarkable nonpolar-to-polar surface faceting transition is demonstrated. The corrugated-shaped structure results from the remarkable stability of the defect-induced reconstructions (O vacancy, Zn-Zn dimer), which makes the high-index polar {303[combining macron]1} and {101[combining macron]1[combining macron]} planes lower in energy compared to the nonpolar {101[combining macron]0} plane. Based on the results of first-principles surface calculations, a general formula is established to provide an accurate description of the unusual size effect of the length of the corrugated unit vs. the NR diameter, and it also offers direct explanations for certain experimental observations. The present study deepens our atomic-level understanding of the detailed structure and stability of polar surface decorated corrugated ZnO NRs, and points to a viable path towards designing polar-stable wurtzite structures.

Tailoring the surface of ZnO nanorods into corrugated nanorods via a selective chemical etch method.

Using the chemical vapour deposition method, we successfully converted smooth ZnO nanorods (NRs) into corrugated NRs by simply increasing the reaction time. The surface morphology and crystallographic structure of the corrugated NRs were investigated. The corrugated NRs were decorated by alternant [Formula: see text] and [Formula: see text] planes at the exposed side surfaces while the conventional [Formula: see text] planes disappeared. No twinning boundaries were found in the periodically corrugated structures, indicating that they were type II corrugated NRs. Further investigation told us that they were selectively etched. We introduced a hydrothermal method to synthesize the smooth ZnO NRs and then etched them in a tube furnace at 950 °C with a flow of carbon monoxide. By separating the growth stage and the selective etching stage, we explicitly demonstrated a successfully selective etching effect on ZnO NRs with a carbon monoxide reducing atmosphere for the first time. An etching mechanism based on the selective reaction between carbon monoxide and the different exposed surfaces was proposed. Our results will improve the understanding of the growth mechanism on coarse or corrugated NRs and provide a new strategy for the application of surface controlled nanostructured materials.