Lianqun Zhou

Investigation of Halide-Induced Aggregation of Au Nanoparticles into Spongelike Gold

We present a facile method for fabricating spongelike Au structures by halide-induced aggregation and fusion of gold nanoparticles (AuNPs). Halide ions (F(-), Cl(-), Br(-), and I(-)) showed distinctly different effects on the synthesized AuNPs, which were characterized by localized surface plasmon resonance (LSPR) and dynamic light scattering measurements. A noticeable red-shift in the LSPR peak was found after Br(-) and I(-) ion treatment, which indicates the adsorption of halide atoms or ions on the AuNPs. The surface potential of AuNPs varied by treatment with different types of halides; this finding indicates that different halide ions have different effects on the AuNPs. Br(-) and I(-) ions showed strong affinity toward the AuNPs. The different affinities of halide ions toward the AuNPs play an important role in controlling the formation process of spongelike gold. Citrate ions adsorbed on AuNPs were displaced by halide ions to different extents. Such displacement determined the aggregation and fusion behaviors of the AuNPs and eventually the formation of different spongelike structures.

Color-switchable, emission-enhanced fluorescence realized by engineering C-dot@C-dot nanoparticles

This paper reports the preparation and properties of color-switchable fluorescent carbon nanodots (C-dots). C-dots that emit dark turquoise and green-yellow fluorescence under 365 nm UV illumination were obtained from the hydrothermal decomposition of citric acid. Dark green fluorescent C-dots were obtained by conjugating prepared C-dots to form C-dot@C-dot nanoparticles. After successful conjugation of the C-dots, the fluorescence emission undergoes a blue-shift of nearly 20 nm (∼0.15 eV) under UV excitation at 370 nm. The C-dots emit goldenrod, green-yellow, and gold light under excitation at 455 nm, which shows that the prepared C-dots are color-switchable. Furthermore, conjugation of the C-dots results in enhanced, red-shifted absorption of the π-π* transition of the aromatic sp(2) domains due to the conjugated π-electron system. N incorporation in the carbon structure leads to a degree of dipoles for all the aromatic sp(2) bonds. The enhanced absorption in a wide range from 226 to 601 nm indicates extended conjugation in the C-dot@C-dot structure. The time-resolved average lifetimes for the three different types of C-dots prepared in this study are 7.10, 7.65, and 4.07 ns. The radiative rate (reduced decay lifetime) increases when the C-dots are conjugated in the C-dot@C-dot nanoparticles, leading to the enhanced fluorescence emission. The fluorescence emission of the C-dot@C-dot nanoparticles can be used in applications such as flow cytometry and cell imaging.

Large‐Scale Horizontally Aligned ZnO Microrod Arrays with Controlled Orientation, Periodic Distribution as Building Blocks for Chip‐in Piezo‐Phototronic LEDs

A novel method of fabricating large-scale horizontally aligned ZnO microrod arrays with controlled orientation and periodic distribution via combing technology is introduced. Horizontally aligned ZnO microrod arrays with uniform orientation and periodic distribution can be realized based on the conventional bottom-up method prepared vertically aligned ZnO microrod matrix via the combing method. When the combing parameters are changed, the orientation of horizontally aligned ZnO microrod arrays can be adjusted (θ = 90° or 45°) in a plane and a misalignment angle of the microrods (0.3° to 2.3°) with low-growth density can be obtained. To explore the potential applications based on the vertically and horizontally aligned ZnO microrods on p-GaN layer, piezo-phototronic devices such as heterojunction LEDs are built. Electroluminescence (EL) emission patterns can be adjusted for the vertically and horizontally aligned ZnO microrods/p-GaN heterojunction LEDs by applying forward bias. Moreover, the emission color from UV-blue to yellow-green can be tuned by investigating the piezoelectric properties of the materials. The EL emission mechanisms of the LEDs are discussed in terms of band diagrams of the heterojunctions and carrier recombination processes.

Detection of trace microcystin-LR on a 20 MHz QCM sensor coated with in situ self-assembled MIPs

A 20 MHz quartz crystal microbalance (QCM) sensor coated with in situ self-assembled molecularly imprinted polymers (MIPs) was presented for the detection of trace microcystin-LR (MC-LR) in drinking water. The sensor performance obtained using the in situ self-assembled MIPs was compared with traditionally synthesized MIPs on 20 MHz and normal 10 MHz QCM chip. The results show that the response increases by more than 60% when using the in situ self-assembly method compared using the traditionally method while the 20 MHz QCM chip provides four-fold higher response than the 10 MHz one. Therefore, the in situ self-assembled MIPs coated on a high frequency QCM chip was used in the sensor performance test to detect MC-LR in tap water. It showed a limit of detection (LOD) of 0.04 nM which is lower than the safety guideline level (1 nM MC-LR) of drinking water in China. The low sensor response to other analogs indicated the high specificity of the sensor to MC-LR. The sensor showed high stability and low signal variation less than 2.58% after regeneration. The lake water sample analysis shows the sensor is possible for practical use. The combination of the higher frequency QCM with the in situ self-assembled MIPs provides a good candidate for the detection of other small molecules.

A biomimetic bioelectronic tongue: A switch for On- and Off- response of acid sensations

The perception of sour taste in mammals is important for its basic modality properties and avoiding toxic substances. We explore a biomimetic bioelectronic tongue, which integrate MEA (microelectrode array) and taste receptor cell for acid detection as a switch. However, the acid-sensing mechanism and coding of the taste receptor cells in the periphery is not well understood, with long-standing debate. Therefore, we firstly construct a Hodgkin-Huxley type mathematical model of whole-cell acid-sensing taste receptor cells based on the electrophysiologic patch clamp recordings with different acid sensitive receptor expressing and different acidic stimulations. ASICs and PKDL channels are two most promising candidates for acidic sensation. ASICs channels contribute to the On response, and PKDL channels coding the Offset stimulations respectively, which function as a pair for switch. Therefore, with the advantage of effective and noninvasive detection for MEA, a sour taste biosensor based on MEA and taste receptor cells was designed and established to detect sour response from the elementary acid sensitive taste receptor cells during and after stimulus. From simulation and extracelluar potential recordings, we found the biomimetic bioelectronic tongue was acid-sensitive, as acid stimulation pH decrease, the firing frequency significantly increase. Furthermore, this reliable and effective MEA based bioelectronic tongue functioned as a switch for stimulation On and Off. This study provided a powerful platform to recognize sour stimulation and help elucidate the sour taste sensation and coding mechanism.

Stability enhanced, repeatability improved Parylene-C passivated on QCM sensor for aPTT measurement

Determination of blood clotting time is essential in monitoring therapeutic anticoagulants. In this work, Parylene-C passivated on quartz crystal microbalance (P-QCM) was developed for the activated partial thromboplastin time (aPTT) measurement. Compared with typical QCM, P-QCM possessed a hydrophobic surface and sensitive frequency response to viscoelastic variations on electrode surface. Fibrin could be adsorbed effectively, due to the hydrophobicity of the P-QCM surface. Comparing with typical QCM, the peak-to-peak value (PPV) of P-QCM was increased by 1.94% ± 0.63%, which indicated enhancement of signal-to-noise ratio. For P-QCM, the coefficient of variation (CV) of frequency decrease and aPTT were 2.58% and 1.24% separately, which demonstrated improvement of stability and reproducibility. Moreover, compared with SYSMEX CS 2000i haematology analyzer, clinical coefficient index (R2) was 0.983. In conclusion, P-QCM exhibited potential for improving stability, reproducibility and linearity of piezoelectric sensors, and might be more promising for point of care testing (POCT) applications.

A quartz crystal microbalance sensor for endotoxin assay by monitoring limulus amebocyte lysate protease reaction

Endotoxin is able to trigger strong innate immune responses by interacting with specific receptors on immune cells. Therefore, accurate and rapid detection of endotoxin is of primary importance. In this study, endotoxin induced viscosity variation of limulus amebocyte lysate (LAL) reagent is monitored by a quartz crystal microbalance (QCM) sensor with enhanced signal. Based on the analysis of the relationship between endotoxin concentration and QCM frequency shift with time, an effective sensing strategy is developed for endotoxin assay, which shows excellent sensitivity and specificity in the linear detection range from 0.005 to 10 EU mL-1. Moreover, this QCM sensor could be reused after a simple regeneration procedure. Therefore, it has potential practical utility for endotoxin determination in various applications.

A Multi-Parameter Decoupling Method with a Lamb Wave Sensor for Improving the Selectivity of Label-Free Liquid Detection

The anti-symmetric modes (A01 mode for low frequency, A03 mode for high frequency) and symmetric modes (S0 mode) produced by Lamb wave sensor are used to detect multi-parameters of a liquid, such as its density, sound velocity and viscosity. These modes are found to be very different to the parameters. For example, the A01 mode is very sensitive to the liquids density but the A03 mode is sensitive to its sound velocity. The measurements of the attenuation with S0 mode can give out liquids viscosity after its density been determined by A01 mode. That could be a way to distinguish an unknown liquid with high sensitivity or to solve the problem of the selectivity of label free detection on biosensors.

Influence of gases on Lamb waves propagations in resonator

We investigate gases effects on the Lamb wave resonant modes. Various frequency ranges are studied for the antisymmetric mode considering wave velocities either higher or lower than the gas sound velocity. We observe that the relative frequency shifts in the low frequency range of the antisymmetric mode is rather important; in the high frequency range of this mode, the quality factor decreases quickly when the Lamb wave phase velocity approaches the gas sound velocity. We find a good agreement between calculations and experiments in air and helium. The results suggest the possibility to get aerodynamics parameters of gas flow.

Surface/Interface Carrier-Transport Modulation for Constructing Photon-Alternative Ultraviolet Detectors Based on Self-Bending-Assembled ZnO Nanowires

Surface/interface charge-carrier generation, diffusion, and recombination/transport modulation are especially important in the construction of photodetectors with high efficiency in the field of nanoscience. In the paper, a kind of ultraviolet (UV) detector is designed based on ZnO nanostructures considering photon-trapping, surface plasmonic resonance (SPR), piezophototronic effects, interface carrier-trapping/transport control, and collection. Through carefully optimized surface/interface carrier-transport modulation, a designed device with detectivity as high as 1.69 × 1016/1.71 × 1016 cm·Hz1/2/W irradiating with 380 nm photons under ultralow bias of 0.2 V is realized by alternating nanoparticle/nanowire active layers, respectively, and the designed UV photodetectors show fast and slow recovery processes of 0.27 and 4.52 ms, respectively, which well-satisfy practical needs. Further, it is observed that UV photodetection could be performed within an alternative response by varying correlated key parameters, through efficient surface/interface carrier-transport modulation, spectrally resolved photoresponse of the detector revealing controlled detection in the UV region based on the ZnO nanomaterial, photodetection allowed or limited by varying the active layers, irradiation distance from one of the electrodes, standing states, or electric field. The detailed carrier generation, diffusion, and recombination/transport processes are well illustrated to explain charge-carrier dynamics contributing to the photoresponse behavior.