Whispering-gallery mode resonators for highly unidirectional laser action.

Optical microcavities can be designed to take advantage of total internal reflection, which results in resonators supporting whispering-gallery modes (WGMs) with a high-quality factor (Q factor). One of the crucial problems of these devices for practical applications such as designing microcavity lasers, however, is that their emission is nondirectional due to their radial symmetry, in addition to their inefficient power output coupling. Here we report the design of elliptical resonators with a wavelength-size notch at the boundary, which support in-plane highly unidirectional laser emission from WGMs. The notch acts as a small scatterer such that the Q factor of the WGMs is still very high. Using midinfrared (λ ∼ 10 µm) injection quantum cascade lasers as a model system, an in-plane beam divergence as small as 6 deg with a peak optical power of ∼5 mW at room temperature has been demonstrated. The beam divergence is insensitive to the pumping current and to the notch geometry, demonstrating the robustness of this resonator design. The latter is scalable to the visible and the near infrared, thus opening the door to very low-threshold, highly unidirectional microcavity diode lasers.

Fluorescence off-on nanosensor based on MoS2 nanosheets and oligonucleotides for the alternative detection of mercury(II) ions or silver(I) ions.

As traditional methods for detection of heavy metal pollution in water involve complex procedures and require expensive equipment, there is a great deal of interest in the development of rapid and simple methods for determining heavy metal ions in water. Here, a nanobiosensor based on molybdenum disulphide (MoS2) nanosheets and fluorophore (FAM) labeled oligonucleotides was proposed, and fluorescence spectroscopy was adopted for detection of Hg2+ or Ag+ ions in aqueous solution. The principle underlying detection by the sensor involves the formation of T-Hg2+-T or C-Ag+-C mismatches by single-stranded DNA (ssDNA) rich in thymine (T) or cytosine (C), thereby forming stable double-stranded DNA (dsDNA) structures. By exploiting the different adsorption capacity of MoS2 nanosheets for ssDNA and dsDNA, when oligonucleotides were in a single chain state, MoS2 nanosheets possessed a strong adsorption capacity for ssDNA, resulting in fluorescence quenching of FAM. After the addition of Hg2+ or Ag+, ssDNA formed double chains structure, the fluorescence recovered due to the weak adsorption capacity of MoS2 nanosheets for dsDNA. Along this line, an "off-on" mode fluorescence nanobiosensor was designed to alternatively detect these two heavy metal ions in water. The sensor showed high sensitivity and excellent selectivity for both Hg2+ and Ag+ ions, with minimum detection limits of 6.8 nM and 8.9 nM, respectively.

The Morphology Dependent Interaction between Silver Nanoparticles and Bovine Serum Albumin.

Biological applications of silver nanoparticles (AgNPs) depend on the covalently attached or adsorbed proteins. A series of biological effects of AgNPs within cells are determined by the size, shape, aspect ratio, surface charge, and modifiers. Herein, the morphology dependent interaction between AgNPs and protein was investigated. AgNPs with three different morphologies, such as silver nanospheres, silver nanorods, and silver nanotriangles, were employed to investigate the morphological effect on the interaction with a model protein: bovine serum albumin (BSA). The adsorptive interactions between BSA and the AgNPs were probed by UV-Vis spectroscopy, fluorescence spectroscopy, dynamic light scattering (DLS), Fourier transform infrared spectrometry (FTIR), transmission electron microscopy (TEM), and circular dichroism (CD) techniques. The results revealed that the particle size, shape, and dispersion of the three types of AgNPs markedly influence the interaction with BSA. Silver nanospheres and nanorods were capsulated by protein coronas, which led to slightly enlarged outer size. The silver nanotriangles evolved gradually into nanodisks in the presence of BSA. Fluorescence spectroscopy confirmed the static quenching the fluorescence emission of BSA by the three AgNPs. The FTIR and CD results suggested that the AgNPs with different morphologies had different effects on the secondary structure of BSA. The silver nanospheres and silver nanorods induced more pronounced structural changes than silver nanotriangles. These results suggest that the formation of a protein corona and the aggregation behaviors of AgNPs are markedly determined by their inherent morphologies.

Correction: An azobenzene-modified redox-active ionic liquid electrolyte for supercapacitors.

Correction for 'An azobenzene-modified redox-active ionic liquid electrolyte for supercapacitors' by Yuhua Zhao et al., Chem. Commun., 2022, https://doi.org/10.1039/d2cc04081f.

An azobenzene-modified redox-active ionic liquid electrolyte for supercapacitors.

A new redox-active ionic liquid (2-(4-(phenyldiazenyl)phenoxy)ethyl)-1-methyl-imidazolium tetrafluoroborate ([ABEMIM][BF4]) is demonstrated. It is incorporated into another ionic liquid ([EMIM][BF4]) to form a mixed IL electrolyte, which can markedly improve the capacitance performance of carbon-based supercapacitors via extra pseudocapacitance contribution. It opens up a new path to develop high-energy supercapacitors through introducing a redox-active ionic liquid to electrolytes.

Large aperture vertical cavity surface emitting laser with distributed-ring contact.

To overcome the serious current crowding effect in top-emitting vertical cavity surface emitting lasers (VCSELs) with large aperture, a distributed-ring-contact (DRC) VCSEL is proposed and demonstrated. A maximal cw light output power of more than 0.3 W and a wall-plug efficiency of 17.4% are achieved for a 300 µm-diameter VCSEL. The DRC VCSEL exhibits a more homogeneous emission profile, and the laser emits at 803.3 nm with a narrow spectrum (less than 0.2 nm FWHM).

Emission properties of electrically pumped triangular shaped microlasers.

We study the emission properties of electrically pumped triangular-shaped microlasers with rounded corners. We find no signs of directional emission for the relatively large cavities (dimension approximately 100 microm) used in our experiments, in full agreement with ray simulation results. The broad emission characteristics that we observe can be fine-tuned by adjusting the resonator geometry as is verified through simulations which might prove useful for applications in optical devices.

Surface chemistry of gold nanoparticles determines interactions with bovine serum albumin.

Protein coronas provide a novel technique for the bio identification of nanoparticles in physiological environments, to further elucidate the biological effects of nanoparticles in biomedical applications. Herein, we investigated the adsorption of bovine serum albumin (BSA) on gold nanoparticles (AuNPs) with different surface modifications (citrate, cysteine, polyethylene glycol (PEG), and cetyltrimethylammonium bromide (CTAB)) using UV-vis absorption spectroscopy, fluorescence spectroscopy, circular dichroism (CD), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and transmission electron microscopy (TEM) techniques. It was revealed that the binding of AuNPs modified with citrate, cysteine, PEG (2k), and CTAB to BSA, appeared to be of the static quenching type, with binding constants in the range of from 108 to 1010 M-1. We also found that the conformation of BSA underwent various changes upon association with the different AuNP surface modifications. In addition, the preliminary results indicated that the thicknesses of protein coronas and the aggregation behaviors of AuNPs were closely related to their surface properties. These findings offered important insights into the essence of the interactions between nanoparticles and proteins toward the development of safe and effective nanomaterials in biological systems.

DNA-functionalized gold nanoparticle-based fluorescence polarization for the sensitive detection of silver ions.

Despite their practical applications, Ag+ ions are environmental pollutants and affect human health. So the effective detection methods of Ag+ ions are imperative. Herein, we developed a simple, sensitive, selective, and cost-effective fluorescence polarization sensor for Ag+ detection in aqueous solution using thiol-DNA-functionalized gold nanoparticles (AuNPs). In this sensing strategy, Ag+ ions can specifically interact with a cytosine-cytosine (CC) mismatch in DNA duplexes and form stable metal-mediated cytosine-Ag+-cytosine (C-Ag+-C) base pairs. The formation of the C-Ag+-C complex results in evident changes in the molecular volume and fluorescence polarization signal. To achieve our aims, we prepared two complementary DNA strands containing C-base mismatches (probe A: 5'-SH-A10-TACCACTCCTCAC-3' and probe B: 5'-TCCTCACCAGTCCTA-FAM-3'). The stable hybridization between probe A and probe B occurs with the formation of the C-Ag+-C complex in the presence of Ag+ ions, leading to obvious fluorescence quenching in comparison to the system without AuNP enhancement. The assay can be used to identify nanomolar levels of Ag+ within 6 min at room temperature, and has extremely high specificity for Ag+, even in the presence of higher concentrations of interfering metal ions. Furthermore, the sensor was successfully applied to the detection of Ag+ ions in environmental water samples and showed excellent selectivity and high sensitivity, implying its promising application in the future.

Exploring the interaction of silver nanoparticles with lysozyme: Binding behaviors and kinetics.

The role of nanoparticle interaction with biomolecules to form a biocorona is the key to nanoparticle behavior and its consequences in the physiological environment. Since the adsorbed biocorona decides the fate of a nanomaterials in vivo, and thus a comprehensive understanding of the dynamic interactions of the proteins with the nanoparticle is imperative. Herein we investigate the interaction of a model protein, lysozyme with silver nanoparticles (AgNPs) using fluorescence, synchronous fluorescence, UV-vis absorption spectrum and circular dichroism (CD) techniques under the physiological conditions. The results indicated that the binding of AgNPs to lysozyme may be a static quenching mechanism. With the analysis of the fluorescence spectral data, the binding constants and the thermodynamic parameters were determined, which suggests that the binding of AgNPs to lysozyme is a spontaneous process. Moreover, it was demonstrated that the main acting forces between AgNPs and lysozyme may be hydrophobic interactions. At the same time, the conformational change of lysozyme induced by AgNPs was investigated with synchronous fluorescence spectroscopy and CD techniques. The results of kinetic studies reveal that the adsorption of lysozyme on AgNPs surface tends to follow pseudo-second-order kinetic characteristic with obvious hysteresis effect.

Probing the binding of trypsin to glutathione-stabilized gold nanoparticles in aqueous solution.

We investigate the interaction of trypsin with glutathione-stabilized Au nanoparticles (NPs) using fluorescence, synchronous fluorescence and ultraviolet (UV) absorption spectroscopy. We find that trypsin binds strongly to the Au NPs with a static quenching mechanism, and that the interaction is characteristic of positive cooperative binding. Furthermore, we determine the binding constants and the thermodynamic parameters, which suggest that the main binding forces between the glutathione-stabilized Au NPs and trypsin are electrostatic interactions and hydrogen bonding. Analysis of UV-vis absorption spectra suggests that aggregation of the Au NPs occurs in the trypsin/Au NPs system, which significantly alters the conformation of the protein.

Exploring DNA binding properties and biological activities of dihydropyrimidinones derivatives.

The effects of substituent modifications for three dihydropyrimidinones derivatives on DNA binding properties were investigated using viscometry in combination with spectroscopy and isothermal titration calorimetry (ITC). The results indicated that substitution in 4 rd position of benzene ring has significant effects on DNA binding mode, affinity and energetics. Electron-donating substitution was favorable for intercalating into DNA bases and had higher DNA binding affinity. However, electron-withdrawing substitution was preferable to bind to DNA in partial intercalation mode with relatively weak DNA binding affinity. Simultaneously, electron-donating substitution could result in more favorable binding enthalpy relative to electron-donating substitution and the parent compound. Antitumor activities of these analogs over BEL-7402 and PC-12 cells were studied to explore the structure activity relationships (SARs), which suggested that electron-donating substitution in 4 rd position of benzene ring could greatly enhance the antitumor activities. However, electron-withdrawing substitution has little effect on the antitumor activity. The present results favor the development of potential drugs related with dihydropyrimidinones derivatives in the treatment of some diseases.

Exploring the binding mechanism of phosphoramidate derivative with DNA: spectroscopy, calorimetry and modeling.

In this study, one of the amino phosphine ester derivatives α-(3-hydroxy-4-methoxyphenyl)-N-phenyl-α-aminophosphonate (HMPAP) was synthesized, and the molecular interaction of HMPAP with ct-DNA has been investigated by UV-Vis absorption spectra, fluorescence spectra, isothermal titration calorimetry (ITC) and molecular modeling. The binding constant (K(b)) of HMPAP to ct-DNA at different temperatures were calculated from fluorescence spectra. According to the UV-Vis absorption spectra, ethidium bromide displacement studies and ITC experimental results, we can conclude that HMPAP is an intercalator. The molecular modeling results indicated that HMPAP can slide into the G-C rich region of ct-DNA. ITC data showed that ct-DNA/HMPAP binding is enthalpy controlled. Furthermore, the results obtained from molecular modeling corroborated the experimental results obtanied from spectroscopic and ITC investigations.

DNA binding properties and biological evaluation of dihydropyrimidinones derivatives as potential antitumor agents.

The binding properties of two medicinally important dihydropyrimidinones derivatives 5-(Ethoxycarbonyl)-6-methyl-4-phenyl-3,4-dihydropyrimidin-2(1H)-one (EMPD) and 5-(Ethoxycarbonyl)-6-methyl-4-(4-chlorophenyl)-3,4-dihydropyrimidin-2(1H)-one (EMCD) with calf-thymus DNA (ctDNA) were investigated by spectroscopy, viscosity, isothermal titration calorimetry (ITC) and molecular modeling techniques. Simultaneously, their biological activities were evaluated with MTT assay method. The binding constants determined with spectroscopic titration and ITC were found to be in the same order of 10(4)M(-1). According to the results of viscosity studies, fluorescence competitive binding experiment and ITC investigations, intercalative binding was evaluated as the dominant binding modes between the two compounds and ctDNA. Furthermore, the results of molecular modeling corroborated those obtained from spectroscopic, viscosimetric and ITC investigations. Evaluation of the antitumor activities of the two derivatives against different tumor cell lines proved that they exhibited significant tumor cell inhibition rate, accordingly blocking DNA transcription and replication. The present results favor the development of potential drugs related with dihydropyrimidinones derivatives in the treatment of some diseases.

Exploring the mechanism of interaction between 5-(ethoxycarbonyl)-6-methyl-4-(4-methoxyphenyl)-3,4-dihydropyrimidin-2(1H)-one and human serum albumin: Spectroscopic, calorimetric and molecular modeling studies.

In this paper, binding interaction of 5-(ethoxycarbonyl)-6-methyl-4-(4-methoxyphenyl)-3,4-dihydropyrimidin-2(1H)-one (EMMD) with human serum albumin (HSA) under physiological conditions was investigated by using spectroscopy, isothermal titration calorimetry (ITC) and molecular modeling techniques. The results of spectroscopic studies suggested that EMMD have a strong ability to quench the intrinsic fluorescence of HSA through static quenching procedure. ITC investigations indicated that drug-protein complex was stabilized by hydrophobic forces and hydrogen bonds, which was consistent with the results of molecular modeling studies. Competitive experiments indicated the displacement of warfarin by EMMD, which revealed that the binding site of EMMD to HSA was located at subdomain IIA.

Study on the binding of fluoride, bromide and iodide to ovalbumin by using ion-selective electrodes.

The interactions of F(-), Br(-) and I(-) with ovalbumin (OVA) were studied in acetate buffers of pH 5.68, at 288.15 K, 298.15 K and 308.15 K, using ion-selective electrodes. The data for the ion-protein systems were treated according to the Klotz equation, and the number of binding sites and the binding constants were determined. It is shown that the binding sites of F(-) on OVA molecule are more than those of Br(-) and I(-), and that the binding sites of F(-), Br(-) and I(-) on OVA molecule decreases with increasing temperature. At the same time, our studies indicate that the binding constants for the interactions of F(-), Br(-) and I(-) with OVA show a same trend: They decrease as temperature increases. These were reasonably interpreted with the structural and thermodynamic factors. The thermodynamic functions (DeltaG(), DeltaH(), DeltaS()) at different temperatures were calculated with thermodynamic equations, and the enthalpy change for the interactions were also determined by isothermal titration calorimetry (ITC) at 298.15 K, which indicate that the interactions of F(-), Br(-) and I(-) with OVA are mainly electrostatic interaction. Simultaneously, there are also partial desolvation of solutes and solvent reorganization effect.