Dual-Engine Powered Paper Photoelectrochemical Platform Based on 3D DNA Nanomachine-Mediated CRISPR/Cas12a for Detection of Multiple miRNAs.

This work proposed a novel double-engine powered paper photoelectrochemical (PEC) biosensor based on an anode-cathode cooperative amplification strategy and various signal enhancement mechanisms, which realized the monitoring of multiple miRNAs (such as miRNA-141 and miRNA-21). Specifically, C3N4 quantum dots (QDs) sensitized ZnO nanostars and BiOI nanospheres simultaneously to construct a composite photoelectric layer that amplified the original photocurrent of the photoanode and photocathode, respectively. Through the independent design and partition of a flexible paper chip to functionalize injection holes and electrode areas, the bipolar combination completed the secondary upgrade of signals, which also provided biological reaction sites for multitarget detection. With the synergistic participation of a three-dimensional (3D) DNA nanomachine and programmable CRISPR/Cas12a shearing tool, C3N4 QDs lost their attachment away from the electrode surface to quench the signal. Moreover, electrode zoning significantly reduced the spatial cross talk of related substances for multitarget detection, while the universal trans-cleavage capability of CRISPR/Cas12a simplified the operation. The designed PEC biosensor revealed excellent linear ranges for detection of miRNA-141 and miRNA-21, for which the detection limits were 5.5 and 3.4 fM, respectively. With prominent selectivity and sensitivity, the platform established an effective approach for trace multitarget monitoring in clinical applications, and its numerous pioneering attempts owned favorable reference values.

Interface Nanoarchitectonics of TiO2/g-C3N4 2D/2D Heterostructures for Enhanced Antibiotic Degradation and Cr(VI) Reduction.

Mixed-phase TiO2 nanosheets were loaded on superior thin g-C3N4 nanosheets by a one-step solvothermal synthesis to form unique two-dimensional (2D)/2D heterostructures, which increased the interface area between TiO2 and g-C3N4, resulting in the easy migration of photogenerated carriers between two components. The rate of photocatalytic reactions increased significantly. Ciprofloxacin, tetracycline hydrochloride, and oxytetracycline hydrochloride were selected as target substances to test the photocatalytic degradation properties of the sample. The photoreduction performance of Cr(VI) was also tested. The results indicate that the photocatalytic degradation rate of antibiotics using TiO2/g-C3N4 heterostructures under visible light irradiation was twice that of g-C3N4. It took only 30 min to remove Cr(VI) (20 mg/L) under full solar spectrum irradiation; the photoreduction rate of Cr(VI) is also nearly twice that of pure TiO2. The improved performance was attributed to the rich active sites brought by mixed-phase TiO2 nanosheets. The extensive interface made the rapid migration of photogenerated carriers possible. The heterostructures revealed a band gap of 2.81 eV, which is less than that of TiO2 (3.2 eV), resulting in the increased absorption of visible light. Meanwhile, the mixed phase of TiO2 was beneficial for the separation of photogenerated carriers.

Construction of Highly Efficient Fe3O4@AlOOH Lamellar Adsorbent for Removal of Congo Red.

Fe3O4@AlOOH adsorbent with high efficient adsorption capacity was successfully synthesized by controlling the hydrolysis rate for aluminum isopropoxide (AIP) and introducing inductive agent thioglycolic acid (TGA). Al(OH)3-TGA clusters played a key role in the formation of Fe3O4@AlOOH adsorbent with lamellar structure. Morphology characterization revealed that magnetic Fe3O4 nanoparticles were uniformly deposited on the surface of AlOOH. The lamellar structure of AlOOH and the strong magnetic intensity of Fe3O4 were helpful for its rapid separation from solution under external magnetic field. Hence, the sample could be regenerated easily and reused in the later adsorption-desorption cycles. The as-prepared sample exhibited ultrafast adsorption rate and high adsorption capacity in the removal of Congo Red (CR) from aqueous solution. The maximum adsorption capacity of Fe3O4@AlOOH towards CR was 280.90 mg/g and CR was completely removed from the aqueous solution within 60 seconds. The adsorption process was well described by the Langmuir isotherm model. Electrostatic adsorption was considered as the main adsorption mechanism. Moreover, Fe3O4@AlOOH sample tended to adsorb CR more effectively in the neutral and acidic solution.

Morphology Controlling of ZnO Sub-Micron- and Micro-Structures from Sub-Micron Zinc Citrate Precursor.

A wet-chemical route has been demonstrated to investigate the morphology evolution of high crystalline ZnO sub-micron- and micro-structures created from a zinc citrate precursor consisted of zinc citrate nanoparticles. The concentrations of precursor zinc citrate and the addition of trisodium citrate were key factors in the controlling of ZnO micro-morphology. Assembled growth resulted in the formation of ZnO sub-micron- and micro-structure with twin-cone and flower-like morphologies. The ZnO flower was consisted of cone petals. The shape of ZnO microstructures was further adjusted using trisodium citrate to created thin and thick hexagonal-plates. In the case of a high Zn concentration, thick hexagonal-plates were split into a flower-like morphology. The investigation of morphological evolution indicated that trisodium citrate is critical to control the growth rate of polar (0001) plane. The formation of a flower-like structure is ascribed to the assembly of crystal units with a high zinc citrate concentration.

Synthesis and Photoluminescence of Red to Near-Infrared-Emitting CdTe( x) Se(1−x) /CdZnS Core/Shell Quantum Dots.

Red to near-infrared (NIR)-emitting ternary-alloyed CdTe (x) Se(1−x) (x = 0­0.3) quantum dots (QDs) with tetrapod and dot morphologies have been synthesized by a facile method using oleic acid (OA) as single capping agent. The controlled dot-shaped and tetrapod-shaped CdTe( x) Se(1−x) QDs can be successfully obtained by adjusting the content of Te element. It is clear that CdTe (x) Se(1−x) QDs display the tunable emission peaks from the visible light (613.4 nm) to the NIR range (791.6 nm). With an inorganic CdZnS shell coated on the surface of CdTe(0.1)Se(0.9) cores, the stability and PL efficiency of the resulting core/shell QDs can be improved dramatically, accompanied with the red-shift of emission peaks to longer wavelength (795.6 nm). Peculiarly, a large blue shift of emission spectrum of CdTe(0.3)Se(0.7)/CdZnS core/shell QDs is observed, which is mainly ascribed to the shrink of the size of QDs by the fracture of tetrapod arms.

Controllable Synthesis of Polyhedral Fe3O4 Hollow Spheres Using Hexamethylenetetramine as Structure-Directing Agent.

Polyhedral Fe3O4 hollow spheres were synthesized using hexamethylenetetramine as structure-directing agent and the effect of hexamethylenetetramine on the morphology was investigated in detailed. The comparison for samples prepared with and without hexamethylenetetramine indicated that hexamethylenetetramine played a vital role in the formation process of the hollow polyhedral structure. The formation process and growth mechanism of Fe3O4 spheres with hollow polyhedral morphology were preliminarily explored according to a detailed time-dependent morphology and structure evolution. It was deduced that the hollow polyhedral structure can be ascribed to the cooperation of oriented aggregation and Ostwald ripening mechanisms. The as-prepared Fe3O4 hollow spheres with polyhedral structures which possess high magnetization saturation value (73 emu/g) at room temperature, large cavity and huge specific surface area (57.12 m2·g­1) are expected to have wide potential applications, for example in the drug delivery process, magnetic separation and waste treatment in the future.

Photoluminescence Quenching of CdTe Quantum Dots Generated via Glutathione-Capped Au Nanocrystals.

The photoluminescence (PL) quenching of thioglycolic acid (TGA)-capped CdTe quantum dots (QDs) by glutathione (GSH)-capped Au nanocrystals (NCs) were investigated via PL degradated measurement. It was found that the PL of the QDs with several sizes can be effectively quenched by GSH-Au NCs. The size and PL peak wavelengths of QDs have no significant impact on the quenching processing. Through the characterizations of UV-visble absorption spectrum, Zeta potential and steady-state, and time-resolved fluorescence spectroscopy, it was proved that the PL quenching of the QDs by GSH-Au NCs was attributed to static quenching caused by the formation of a QDs-Au complex. The binding parameters calculated from modified Stern-Volmer equation showed that the binding affinities between the GSH-Au NCs and CdTe QDs was in the order of 10(5) L x mol(-1), which indicated that the binding force was larger and the effective quenching occurred. The thermodynamic parameters studies revealed that the binding was characterized by positive enthalpy and positive entropy changes and hydrophobic force played a major role for QDs-Au association. In addition, all the quenching experiments were conducted in the phosphate-buffered saline (PBS) buffer solution at pH 7.4 and the investigation is expected to be applied in the biology.

Synthesis and Optical Properties of CdTe(x)Se(1-x)-Based Red to Near-Infrared Emitting Quantum Dots.

A series of red to near-infrared (NIR) emitting quantum dots (QDs) with spherical morphologies and tunable photoluminescence (PL) properties have been synthesized by a facile organic route using octadecene (ODE) as solvent and oleic acid (OA) as single capping agent. CdSe cores with the average size of 4.5 nm display the typical optical behaviors with the PL emission peak around 610 nm. The coating CdZnS shells are introduced on the surface of CdSe cores for improving the photostability and PL efficiency of the initial QDs. As the thickness of CdZnS shells increasing, the gradual red-shift of emission wavelength varying from 617 to 634 nm of the resulting QDs can be observed, along with the remarkable increase of PL quantum yield (QY). The composition-dependent CdTe(x)Se(1-x) (CdTeSe) cores with the emission in NIR region are easily carried out by adjusting the molar ratio of Se/Te. The abnormal variation of optical bowling effect is mainly ascribed to the composition effect of alloyed QDs. Compared with CdTe0.1Se0.9/CdZnS core/shell QDs, the introducing of CdZnS shells on CdTe0.05Se0.95 cores can exhibit better passivation effect on surface status, consequently leading to the red-shifted emission peaks in the range of 739-752 nm with the maximum PL QY reaching up to 45.09%. The unique PL properties of CdTeSe-based QDs in the red to NIR range make these core/shell QDs attractive for future biological sensing and labeling applications.

Aqueous synthesis of MPA-capped CdTe nanocrystals emitted in near infrared with high quantum yield.

The high luminescent near infrared (NIR)--emitting CdTe nanocrystals (NCs) with 3-mercaptopropionic acid (MPA) as the stabilized molecules had been sucessfully fabricated by a facile and simple water-reflux method. By virtue of the characterizations for the as-prepared MPA-capped CdTe NCs, such as UV-Vis absorption, steady-state photoluminescence (PL), time-resolved PL spectra and PL image, the optical properties, diameters and morphologies of the CdTe NCs were investigated detailedly. With the increase of reflux time, the PL peak wavelength of NCs gradually shifted from red light to NIR spectra range within 7 h, and the PL quantum yield (QY) was increased firstly and then decreased slightly. It was worth noted that the NCs still showed a relative high PL QY of 47% as well as a narrow full width at half maximum (FWHM) of PL spectra even when the NCs emitted at the NIR wavelength of 754 nm. In addition, the average PL lifetime also exhibited an obvious increase as the growth of CdTe NCs due to the formation of thin CdS shell on the surface of CdTe. The PL stabilities for these NIR-emitting NCs (754 nm) in phosphate-buffered saline (PBS) buffer solution with various concentrations ranged from 0.005 to 0.1 M were also checked accordingly, and the results indicated that the as-prepared NIR-emitting CdTe NCs had a satisfied PL stability, implying a potential application in the biological field. Hopefully, all the superiority of these NIR-emitting CdTe NCs, such as high PL QY and PL lifetime, narrow FWHM of PL spectra, high PL stability in PBS solution, would make them to be a good candidate for biological applications in future.

A visible light photoelectrochemical sensor for tumor marker detection using tin dioxide quantum dot-graphene as labels.

In this paper, a simple and sensitive sandwich-type photoelectrochemical (PEC) immunosensor for measurement of biomarkers on a gold nanoparticle-modified indium tin oxide (ITO) electrode through electrodeposition for point-of-care testing was developed by using a tin dioxide quantum dot-graphene nanocomposite (G-SnO2) as an excellent label with amplification techniques. The capture antibody (Ab1) was firstly immobilized on the gold nanoparticle-modified ITO electrode due to the covalent conjugation, then the antigen and the AuNP/PDDA-G-SnO2 nanocomposite nanoparticle labeled signal antibody (Ab2) were conjugated successively to form a sandwich-type immunocomplex through a specific interaction. Under irradiation with a common ultraviolet lamp (∼365 nm, price $50), the SnO2 NPs were excited and underwent charge-separation to yield electrons (e(-)) and holes (h(+)). As the holes were scavenged by ascorbic acid (AA), the electrons were transferred to the ITO electrode through RGO to generate a photocurrent. The photocurrents were proportional to the CEA concentrations, and the linear range of the developed immunosensor was from 0.005 to 10 ng mL(-1) with a detection limit of 0.036 pg mL(-1). The proposed sensor shows high sensitivity, stability, reproducibility, and can become a promising platform for other biomolecular detection.

Effect of mercaptocarboxylic acids on luminescent properties of CdTe quantum dots.

CdTe quantum dots (QDs) were prepared in an aqueous solution using various mercaptocarboxylic acids, such as 3-mercaptopropionic acid (MPA) and thioglycolic acid (TGA), as stabilizing agents. The experimental result indicated that these stabilizing agents played an important role for the properties of the QDs. Although both TGA and MPA-capped CdTe QDs exhibited the tunable photoluminescence (PL) from green to red color, the TGA-capped QDs revealed a higher PL quantum yield (QY) up to 60% than that of MPA-capped QDs (up to 50%) by using the optimum preparation conditions, such as a pH value of ~11.2 and a TGA/Cd molar ratio of 1.5. PL lifetime measurements indicate that the TGA-capped QDs exhibited a short average lifetime while the MPA-capped QDs revealed a long one. Furthermore, the average lifetime of the TGA-capped QDs increased with the increase of the QDs size, while a decreased lifetime for the MPA-capped QDs was obtained. This means that the PL lifetime depended strongly on the surface state of the CdTe QDs. These results should be utilized for the preparation and applications of QDs.

CdSe/Cd(x)Zn1-xS core/shell nanocrystals: core morphology and luminescent property.

CdSe cores with rod (an aspect ratio of 1.8, d-5 nm) and spherical (an aspect ratio of 1, d-5 nm) morphologies were fabricated by two kinds of organic approaches through adjusting growth processes. Because of large difference of size and morphology, two kinds of cores revealed different absorption spectra. However, these cores exhibited almost same photoluminescence (PL) spectra with a red-emitting PL peak of around 625 nm. This is ascribed that they have a similar size in diameter. A graded Cd(x)Zn1-xS shell of larger band gap was grown around CdSe rods and spheres using oleic acid as a capping agent. Based on the growth kinetics of CdS and ZnS, interfacial segregation was created to preferentially deposit CdS near the core, providing relaxation of the strain at the core/shell interface. For spherical CdSe cores, the homogeneous deposition of the Cd(x)Zn1-xS shell created spherical core/shell nanocrystals (NCs) with a size of 7.1 nm in diameter. In the case of using CdSe cores with rod morphology, the anisotropic aggregation behaviors of CdS monomers on CdSe rods led to the size (approximately 10 nm in diameter) of spherical CdSe/Cd(x)Zn1-xS core/shell NCs with a small difference to the length of the CdSe rod (approximately 8.9 nm). The resulting spherical core/shell NCs created by the rod and spherical cores exhibited almost same PL peak wavelength (652 and 653 nm for using rod and spherical cores, respectively), high PL efficiency up to 50%, and narrow PL spectra (36 and 28 nm of full with at half maximum of PL spectra for the core/shell NCs with CdSe spheres and rods, respectively). These core/shell NCs provide an opportunity for the study of the evolution of PL properties as the shape of semiconductor NCs.

Reprogramming thermodynamic-limiting oxidation cycle in NiFe-based oxygen evolution electrocatalyst through Mo doping induced surface reconstruction.

Engineering of robust nonprecious electrocatalysts toward anodic oxygen evolution reaction (OER) is of great significance for lowering the cost and energy consumption for renewable fuel production. Herein, we report NiFeMoOx nanosheets as high-performance OER electrocatalyst through promoting the thermodynamic-limiting oxidation cycle process in NiFe oxyhydroxide via high-valence Mo doping. The NiFeMoOx nanosheets are prepared by an elaborate in-situ solvothermal etching-depositing process with NiFe alloy framework as substrate and metal precursors. The resultant nanosheets exhibit outstanding alkaline OER activity, requires only 235/282/327 mV overpotentials to achieve current density of 10/100/300 mA cm-2, respectively, with a good long-term stability at 20 mA cm-2 for 72 h. Besides, the Tafel slope low to 28.1 mV dec-1 indicates a favorable OER kinetics. The superior catalytic activity of NiFeMoOx nanosheets should be attributed to the lower oxidation states of Ni and Fe induced by high-valence dopant, leading to easier surface reconstruction at low charge oxidation cycling during OER, thereby effectively reducing the overpotential. The synergy between the electronic effect among multimetallic sites and the unique morphology is expected to inspire the development of robust OER electrocatalyst for industrial application.

Ultrahigh Charge Separation Achieved by Selective Growth of Bi4O5I2 Nanoplates on Electron-Accumulating Facets of Bi5O7I Nanobelts.

Ultrahigh charge separation was observed in Bi4O5I2/Bi5O7I two-dimensional (2D)/one-dimensional (1D) hierarchical structures (HSs) constructed by selective growth of 2D monocrystalline Bi4O5I2 nanoplates on the electron-accumulating (100) facet of 1D monocrystalline Bi5O7I nanobelts. In addition to the presence of type-II heterojunction between Bi4O5I2 and Bi5O7I elementary entities in 2D/1D HSs, the type-II (100)/(001) surface heterojunction in Bi5O7I nanobelt substrates was also confirmed by means of density functional theory (DFT) calculations and selective photoreduction/oxidation deposition experiments. The synergistic effect of two kinds of heterojunctions in Bi4O5I2/Bi5O7I 2D/1D HSs endowed them with ultrahigh charge carrier separation and transfer characteristics. In contrast with the control sample (BB40-C) constructed by growing Bi4O5I2 nanoplates on whole four sides of Bi5O7I nanobelts, Bi4O5I2/Bi5O7I 2D/1D HSs demonstrated significantly enhanced charge transfer between Bi5O7I nanobelt substrates and Bi4O5I2 nanoplates, owing to respective electron and hole accumulations on (100) and (001) facets of Bi5O7I substrates caused by (100)/(001) surface heterojunction. The enhanced separation behavior was successfully verified by steady/transient-state photoluminescence, electrochemical techniques, and photocatalytic degradation experiments. Based on the above effective charge separation of Bi4O5I2/Bi5O7I 2D/1D HSs as well as the routine advantages for 2D/1D HSs, such as the excellent charge transport in monocrystalline elementary entities, much higher specific surface area, and enhanced light absorption by multiple reflections, the optimal BB40 HSs demonstrated ultrahigh photocatalytic performance than the control samples, whose apparent rates for Rhodamine B [or tetracycline hydrochloride (TC)] degradation were 7.1 (2.9 for TC), 10.3 (4.7 for TC), and 2.2 (1.7 for TC) times those of pristine Bi5O7I nanobelts, Bi4O5I2 nanoplates, and BB40-C, respectively. It is hoped that this crystal facet selection during the heterostructure construction in this work could provide a new strategy or some enlightenment for the exploration of highly active 2D/1D HSs or other-dimensional heterostructure nanomaterials applied in the fields of photocatalysts, solar cells, sensors, and others.

BSA activated CdTe quantum dot nanosensor for antimony ion detection.

A novel fluorescent nanosensor for Sb(3+) determination was reported based on thioglycolic acid (TGA)-capped CdTe quantum dot (QD) nanoparticles. It was the first antimony ion sensor using QD nanoparticles in a receptor-fluorophore system. The water-soluable TGA-capped CdTe QDs were prepared through a hydrothermal route, NaHTe was used as the Te precursor for CdTe QDs synthesis. Bovine serum albumin (BSA) conjugated to TGA-capped CdTe via an amide link interacting with carboxyl of the TGA-capped CdTe. When antimony ion enters the BSA, the lone pair electrons of the nitrogen and oxygen atom become involved in the coordination, switching off the QD emission and a dramatic quenching of the fluorescence intensity results, allowing the detection of low concentrations of antimony ions. Using the operating principle, the antimony ion sensor based on QD nanoparticles showed a very good linearity in the range 0.10-22.0 microg L(-1), with the detection limit lower than 2.94 x 10(-8) g L(-1) and the relative standard deviation (RSD) 2.54% (n = 6). In a study of interferences, the antimony-sensitive TGA-QD-BSA sensor showed good selectivity. Therefore, a simple, fast, sensitive, and highly selective assay for antimony has been built. The presented method has been applied successfully to the determination of antimony in real water samples (n = 6) with satisfactory results.

Coordination environment evolution of Co(ii) during dehydration and re-crystallization processes of KCoPO4·H2O towards enhanced electrocatalytic oxygen evolution reaction.

Development of efficient and stable electrodes for electrocatalytic oxygen evolution reaction (OER) is essential for energy storage and conversion applications, such as hydrogen generation from water splitting, rechargeable metal-air batteries and renewable fuel cells. Alkali metal cobalt phosphates show great potential as OER electrocatalysts. Herein, an original electrode design strategy is reported to realize an efficient OER electrocatalyst through engineering the coordination geometry of Co(ii) in KCoPO4·H2O by a facile dehydration process. Experimental result indicated that the dehydration treatment is accompanied by a structural transformation from orthorhombic KCoPO4·H2O to hexagonal KCoPO4, involving a concomitant coordination geometry evolution of Co(ii) from octahedral to tetrahedral configuration. More significantly, the local structural evolution leads to an advantageous electronic effect, i.e. increased Co-O covalency, resulting in an enhanced intrinsic OER activity. To be specific, the as-produced KCoPO4 can deliver a current density of 10 mA cm-2 at a low overpotential of 319 mV with a small Tafel slope of 61.8 mV dec-1 in alkaline electrolyte. Thus, this present research provides a new way of developing alkali metal transition-metal phosphates for efficient and stable electrocatalytic oxygen evolution reaction.

Catalytic dynamic spectrofluorimetry determination of trace antimony using new type arsenoxylphenylazo rhodanine.

A precise, simple, new spectrofluorimetry method is proposed for determination of trace antimony which is based on the reaction between potassium periodate and the new type fluorescent reagent 3-o-chlorophenyl-5-(2'- arsenoxylphenylazo) rhodanine (2ClRAAP). The possible mechanism is proposed. The fluorescence intensity is investigated to be sharply enhanced by the oxidation of 3-o-chlorophenyl-5-(2'-arsenoxylphenylazo) rhodanine by potassium periodate with antimony as catalyst in the buffer medium of potassium hydrogen phthalate-sodium hydroxide (pH 5.2). Under the optimum conditions the great increase of fluorescence intensity has a linear relationship against the concentration of antimony in the range of 0.2-10 microg L(-1) with a detection limit of 1.65 x 10(-10) g mL(-1). This proposed method led to the satisfied determination of antimony in environment water.

Preparation and Phase Transfer of Hydrophobic CdSe-Based Quantum Dots.

Monodispersed CdTe(x)Se1-x and CdSe cores were synthesized via organic methods. The as-prepared cores were coated with a Cd(y)Zn1-yS shell by an epitaxial growth. Compared with the cores, an obvious red shift was observed in both the absorption and photoluminescence (PL) spectra of core-shell quantum dots (QDs) and the PL efficiency was improved. The CdSe-based core-shell QDs were transferred from oil to water phase by the encapsulation of amphiphilic polymers. The ligands of QDs, namely hexadecylamine (HDA) and oleic acid (OA), dramatically influenced the process of phase transfer. The process of phase transfer of HDA-coated CdTe(x)Se1-x/CdyZn1-yS core-shell QDs was failed, however, the OA-coated CdSe/CdyZn1-yS core-shell QDs can be successfully transferred from oil to water phase. This is ascribed that the surface ligand HDA falls from CdTe(x)Se1-x/Cd(y)Zn1-yS core-shell QDs during the process of phase transfer, leading to non-interaction between QDs and amphiphilic polymers. The effect of molecular weight of the poly(styrene-co-maleic anhydride) (PSMA) on the phase transfer was also investigated. For the QDs with the same size, the PSMA with high molecular weight exhibit a shorter time in the process of phase transfer compared with light molecular weight. Furthermore, the size of the QDs also affects the process of the phase transfer from oil to water phase. The smaller of the QDs, the shorter of the phase transfer time.