All-inorganic halide perovskite CsPbBr3: a DFT study of a self-powered formaldehyde sensor.

The high surface activity and large specific surface area of metal halide perovskite materials create favorable conditions for improving the sensitivity and selectivity of gas sensors. Meanwhile, the high photoelectric conversion efficiency makes perovskite materials the best candidates for new self-powered gas sensing systems. Therefore, the adsorption mechanism of several volatile organic compounds (VOCs) on CsPbX3 (X = Cl, Br, and I) surfaces was investigated based on first-principles calculations and the non-equilibrium Green's function, including C2H6, CH4, CH3OH, and CH2O. The results show that CsPbBr3 (CPB) has excellent gas-sensing properties for CH2O molecules. The current-voltage (I-V) curves indicate that the transport properties of CH2O after adsorption on the CPB surface had a clear response. Moreover, the good mechanical response makes the adsorption process reversible and provides the possibility for flexible devices. Finally, the good absorption spectrum lays the foundation for the application of CPB in photovoltaic (PV) self-powered sensors. Therefore, we predict that CPB is expected to be a candidate for a CH2O gas sensor with high sensitivity and selectivity.

Gas-Sensing Properties of Cu2S-MoSe2 Nanosheets to NO2 and NH3 Gases.

Cu2S-MoSe2 was selected as a gas-sensing material to detect NO2 and NH3. Based on density functional theory calculations, the adsorption structures, density of states, molecular orbit, and recovery time were studied to analyze the gas-sensing mechanism of Cu2S-MoSe2 to gases. Calculation results show that Cu2S clusters receive a stable doping structure on the MoSe2 surface. Compared with intrinsic MoSe2, Cu2S-MoSe2 shows more excellent adsorption performance to NO2 and NH3 due to the active feature of the Cu2S dopant. After NO2 and NH3 adsorption, the energy gap decreases, indicating an improvement of the conductivity, which is greatly significant for gas sensing. For double NH3 adsorption, the conductivity of the entire system increases more than that of a double NO2 adsorption system, signifying the sensitivity of Cu2S-MoSe2 is greater for NH3 than NO2. The results of theoretical recovery time show that Cu2S-MoSe2 is sensitive for NH3 detection at room temperature (298 K) and NO2 detection at high temperature (400 K).

Monolayer Janus Te2Se-based gas sensor to detect SO2 and NOx: a first-principles study.

In this study, the adsorption of gas molecules, such as O2, NH3, CO, CO2, H2O, NOx (x = 1, 2) and SO2, on Janus Te2Se monolayer has been investigated by means of density functional theory (DFT) calculations. We show that Janus Te2Se monolayer is preferable for SO2 and NOx molecules with suitable adsorption strength and apparent charge transfers. We further calculated the current-voltage (I-V) curves using the nonequilibrium Green's function (NEGF) method. The transport feature exhibits distinct responses with a dramatic change of I-V curves before and after NOx (SO2) adsorption on Janus Te2Se. Thus, we predict that Janus Te2Se could be a promising candidate for SO2 and NOx sensors with high selectivity and sensitivity. Moreover, the effect of strain on the gas/substrate adsorption systems was also studied, implying that the strained Janus Te2Se monolayer could enhance the sensitivity and selectivity to SO2 and NO2. The adsorbed SO2 and NO2 on Janus Te2Se could escape by releasing the applied strain, which indicates that the capture process is reversible. Our study widens the application of Janus Te2Se not only as piezoelectric materials, but also as a potential gas sensor or capturer of SO2 and NOx with high sensitivity and selectivity.

Reduced graphene-oxide transducers for biosensing applications beyond the Debye-screening limit.

In the field of label-free biosensing, various transducer materials and strategies are under investigation to overcome the Debye-screening limitation of charged biomolecules. We demonstrate an in-line, impedimetric aptasensor with reduced graphene-oxide (rGO) thin films as transducers to detect prostate specific antigens (PSA) in a physiological buffer solution. Unlike classical electrochemical impedance spectroscopy (EIS), this direct, label-free and fully-electronic biosensor approach does not need any redox markers. As specific capture molecules, short anti-PSA aptamers ensured a close binding of the target molecules to the transducer surfaces. Results showed a limit of detection smaller than 33 pM of PSA and a wide detection range from 0.033 to 330 nM fully covering the clinically relevant range of PSA (0.115-0.290 nM). This promising performance can be attributed to the bipolar electronic transport characteristics of the ultra-thin rGO layers similar to pristine graphene. The attachment of target biomolecules to the films changes the resistance of the rGO thin films. Such an in-line EIS configuration with rGO thin films opens promising prospects for biosensing beyond the Debye-screening limitation, which is a major challenge for conventional semiconductor field-effect devices towards clinical applications.

High-yield production of canine parvovirus virus-like particles in a baculovirus expression system.

An optimized VP2 gene from the current prevalent CPV strain (new CPV-2a) in China was expressed in a baculovirus expression system. It was found that the VP2 proteins assembled into virus-like particles (VLPs) with antigenic properties similar to those of natural CPV and with an especially high hemagglutination (HA) titer (1:2(20)). Dogs intramuscularly or orally immunized with VLPs produced antibodies against CPV with >1:80 hemagglutination inhibition (HI) units for at least 3 months. The CPV VLPs could be considered for use as a vaccine against CPV or as a platform for research on chimeric VLP vaccines against other diseases.

[Facial nerve monitoring in parotid gland surgery].

OBJECTIVE: To investigate the use and effect of facial nerve monitoring in parotid gland surgery. METHOD: Twenty-two patients with benign parotid tumor who received parotidectomy with continuous monitoring of the facial nerve were selected to analyse. RESULT: Each patient had a total resection of tumor without facial nerve paresis or sialocele formation. No recurrence was found during follow-up. CONCLUSION: Facial nerve monitoring is a useful tool in parotid gland surgery.