Multi-Responsive Sensor Based on Porous Hydrogen-Bonded Organic Frameworks for Selective Sensing of Ions and Dopamine Molecules.

Hydrogen-bonded organic frameworks (HOFs), as an emerging porous material, have attracted increasing research interest in fluorescence sensing due to their inherent fluorescence emission units with unique physicochemical properties. Herein, based on the organic building block 3,3',5,5'-tetrakis-(4-carboxyphenyl)-1,1'-biphenyl (H4TCBP), the porous material HOF-TCBP was successfully synthesized using hydrogen bond self-assembly in a DMF solution. The fluorescence properties of the HOF-TCBP solution showed that when the concentration was high, excimers were easily formed, the PL emission was red-shifted, and the fluorescence intensity became weaker. HOF-TCBP showed good sensitivity and selectivity to metal ions Fe3+, Cr3+, and anion Cr2O72-. In addition, HOF-TCBP can serve as a label-free fluorescent sensor material for the sensitive and selective detection of dopamine (DA). HOF-based DA sensing is actually easy, low-cost, simple to operate, and highly selective for many potential interfering substances, and it has been successfully applied to the detection of DA in biological samples with satisfactory recoveries (101.1-104.9%). To our knowledge, this is the first report of HOF materials for efficient detection of the neurotransmitter dopamine in biological fluids. In short, this work widely broadens the application of HOF materials as fluorescent sensors for the sensing of ions and biological disease markers.

Fabrication of large size individual octahedral tungsten oxide hydrate and Au NPs as SERS platforms for sensitive detection of cytochrome C.

Surface-enhanced Raman scattering (SERS) has attracted much attention with its powerful trace detection and analysis capabilities, especially biological and environmental molecules. However, building a protein SERS detection platform based on semiconductor devices is a huge challenge. Herein, through the synergy of NH3 and nickel foam, a large-sized semiconductor tungsten oxide hydrate platform (WOHP) was synthesized. The crystal plane of a single WOHP particle is larger than the excitation spot. As a SERS substrate, WOHP can make full use of the excitation light without destroying the structure during the protein molecules detection process. Through the synergy of WOHP and Au NPs, the enhancement factor is 1.5 × 104. Raman peaks of WOHP can be used as references for the detection of typical protein cytochrome C (Cyt C). As the Cyt C concentration decreases, the ICyt C/IWOHP ratio decreases, and the signal can still be obtained when the concentration is as low as 5 × 10-9 mol L-1. More importantly, the method does not affect the catalytic activity of Cyt C and can be applied to the detection of Cyt C concentration in serum.

Yb/Ho Codoped Layered Perovskite Bismuth Titanate Microcrystals with Upconversion Luminescence: Fabrication, Characterization, and Application in Optical Fiber Ratiometric Thermometry.

Optical thermometry has attracted great interest owing to its noncontact and fast responsive properties in practical applications. However, some sensing errors may occur in many optical ratiometric thermometers due to the overlap of emission peaks, suggesting the necessity of developing excellent luminescent materials. Here, we report the fabrication and characterization of Bi4Ti3O12:Yb/Ho for ratiometric thermometry. Bismuth titanate was selected as the matrix due to its low phonon energy, high machinability, and satisfactory thermal stability. The temperature sensing was constructed on the intensity ratio of the two upconversion emission bands with wide separation in Bi4Ti3O12:Yb/Ho under 980 nm excitation. The wide separation endows the materials with high signal discrimination for temperature detection. The developed materials were characterized in terms of crystal structure, reflectance, and emission spectra for thermometry application. The maximum relative sensitivity was shown to be as high as 2.11% K-1. More importantly, an optical fiber thermometry was developed based on the fabricated microcrystals, which can find its potential applications in harsh environments.

Constructing Asymmetrical Ni-Centered {NiN2O4} Octahedra in Layered Metal-Organic Structures for Near-Room-Temperature Single-Phase Magnetoelectricity.

Layered metal-organic structures (LMOSs) as magnetoelectric (ME) multiferroics have been of great importance for realizing new functional devices in nanoelectronics. Until now, however, achieving such room-temperature and single-phase ME multiferroics in LMOSs have proven challenging due to low transition temperature, poor spontaneous polarization, and weak ME coupling effect. Here, we demonstrate the construction of a LMOS in which four Ni-centered {NiN2O4} octahedra form in layer with asymmetric distortions using the coordination bonds between diphenylalanine molecules and transition metal Ni(II). Near room-temperature (283 K) ferroelectricity and ferromagnetism are observed to be both spontaneous and hysteretic. Particularly, the multiferroic LMOS exhibits strong magnetic-field-dependent ME polarization with low-magnetic-field control. The change in ME polarization with increasing applied magnetic field µ0H from 0 to 2 T decreases linearly from 0.041 to 0.011 µC/cm2 at the strongest ME coupling temperature of 251 K. The magnetic domains can be manipulated directly by applied electric field at 283 K. The asymmetrical distortion of Ni-centered octahedron in layer spurs electric polarization and ME effect and reduces spin frustration in the octahedral geometry due to spin-charge-orbital coupling. Our results represent an important step toward the production of room-temperature single-phase organic ME multiferroics.

Selective and high-sensitive label-free detection of ascorbic acid by carbon nitride quantum dots with intense fluorescence from lone pair states.

Label-free detection of ascorbic acid (AA) with high sensitivity and specificity based on the effects of AA on fluorescence quenching of carbon nitride quantum dots (CNQDs) is described. The CNQDs with a high fluorescence quantum yield of 21% and good dispersibility in water are prepared by reacting g-C3N4 sheets with ethylenediamine (EN). Fluorescence at 510 nm from the CNQDs is quenched gradually by addition of AA. As the AA concentration increases, the activity of the lone pair (LP) state of the CNQDs diminishes resulting in reduced fluorescence from the CNQDs and the mechanism of the static quenching effect is discussed. Since the CNQDs have a large specific surface area and abundant amino groups and AA exists in the anionic form at the physiological pH, the electrostatic interaction between CNQDs and AA inhibits excitation and emission of the LP states in the CNQDs. Owing to steric effects and hydrogen bonding, the CNQDs constitute a sensitive and selective detection platform for AA in a wide range from 0.5 to 200 µM with a detection limit of 150 nM (signal-to-noise ratio of 3). More importantly, the strategy can successfully be applied to the detection of AA concentrations in serum samples. This simple method which provides quantitative AA determination has large potential in clinical and health-related applications and the mechanism provides insights into intracellular AA monitoring.

Facile synthesis of highly monodisperse EuSe nanocubes with size-dependent optical/magnetic properties and their electrochemiluminescence performance.

We reported a facile and robust method for the synthesis of highly monodisperse EuSe nanocubes (EuSe NCs) with controllable edge lengths in the range of 8-70 nm. The EuSe NCs were formed through the aggregation of EuSe small particles (cores) and then their surface reconstruction under the influence of 1-dodecanethiol (DDT) that acted as a capping surfactant. DDT was not only found to be critical to the nucleation temperature of preparing EuSe NCs, but also played a decisive role in the formation of structurally well-defined nanocubes. The results indicated that the remarkable monodispersity and high shape consistency of EuSe NCs were highly controlled by the change in the DDT concentration. Furthermore, the size-dependent optical/magnetic properties based on the quantum size effect and the influence of edge lengths of EuSe NCs were also investigated and discussed. More importantly, the electrochemiluminescence (ECL) performance of EuSe NCs was first reported. This will make possible more biomedical applications in future.

Amperometric Glucose Biosensor Based on Effective Self-Assembly Technology for Preparation of Poly(allylamine hydrochloride)/Au Nanoparticles Multilayers.

Novel nanomaterials and nanotechnology for use in bioassay applications represent a rapidly advancing field. This study developed a novel method to fabricate the glucose biosensor with good gold nanoparticles (AuNPs) fixed efficiency based on effective self-assembly technology for preparation of multilayers composed of poly(allylamine hydrochloride) (PAH) and AuNPs. The electrochemical properties of the biosensor based on (AuNPs/PAH)n/AuNPs/glucose oxide (GOD) with different multilayers were systematically investigated. Among the resulting glucose biosensors, electrochemical properties of the biosensor with three times self-assembly processes ((AuNPs/PAH)3/AuNPs/GOD) is best. The GOD biosensor exhibited a fast amperometric response (5 s) to glucose, a good linear current-time relation over a wide range of glucose concentrations from 0.05 to 162 mM, and a low detection limit of 0.029 mM. The GOD biosensor modified with (AuNPs/PAH)n layers will have essential significance and practical application in future owing to the simple method of fabrication and good performance.

Au-F127 strawberry-like nanospheres as an electrochemical interface for sensitive detection of carcinoembryonic antigen in real sample.

Nanomaterial-based signal-amplification strategies hold a great promise in realizing sensitive biological detection. A simple label-free electrochemical immunosensor for sensitive detection of carcinoembryonic antigen (CEA) was developed by immobilizing anti-CEA antibodies onto the Au-F127 strawberry-like nanospheres modified glassy carbon electrode (Au-F127/GCE). The Au-F127 strawberry-like nanospheres offered a large surface and multifunctional substrate for the effective immobilization of anti-CEA and the existence of Au could accelerate electron transfer and make the electrochemical signal amplified. The Au-F127 nanocomposites and anti-CEA were characterized by transmission electron microscopy (TEM), polycrystalline electron diffraction ring pattern, ultra-violet visible (UV-vis) spectra and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectra. Electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV) were employed to verify the stepwise assembly of the immunosensor and evaluated the analytical performance of the fabricated immunosensor, respectively. The immunosensor showed a wide liner response range between 0.01 and 80 ng mL(-1) with a low detection limit of 0.24 pg mL(-1) at a signal-to-noise (S/N) ratio of 3. Additionally, the proposed method was successfully applied to determine CEA in human serum samples with satisfactory results.