Expression of water-soluble nucleocapsid protein of SARS-CoV-2 and analysis of its immunogenicity

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to be a major public health concern. Nucleocapsid (N) protein is the most abundant structural protein on SARS-CoV-2 virions and induces the production of antibodies at the early stage of infection. Large-scale preparation of N protein is essential for the development of immunoassays to detect antibodies to SARS-CoV-2 and the control of virus transmission. In this study, expression of water-soluble N protein was achieved through inducing protein expression at 25°C with 0.5 mM IPTG for 12 h. Western blot and ELISA showed that recombinant N protein could be recognized by sera collected from subjects immunized with Sinovac inactivated SARS-CoV-2 vaccine. Four monoclonal antibodies namely 2B1B1, 4D3A3, 5G1F8, and 7C6F5 were produced using hybridoma technology. Titers of all four monoclonal antibodies in ELISA reached more than 1.28×10 6.0. Moreover, all monoclonal antibodies could react specifically with N protein expressed by transfection of pcDNA3.1-N into BHK-21 cells in IPMA and IFA. These results indicated that water-soluble N protein retained high immunogenicity and possessed the same epitopes as that of native N protein on virions. In addition, the preparation of water-soluble N protein and its monoclonal antibodies laid the basis for the development of immunoassays for COVID-19 detection.

A compact radio-frequency ion source for high brightness and low energy spread negative oxygen ion beam production

A high brightness and low energy spread (∆E) ion source is essential to the production of a high-quality primary ion beam applied in secondary ion mass spectrometry (SIMS). A compact 13.56 MHz radio-frequency (RF) ion source with an external planar spiral antenna has been developed as a candidate ion source for the production of negative oxygen ion beams for SIMS application. This ion source is designed with a three-and-a-half-turn water-cooled planar antenna for RF power coupling, a multi-cusp magnetic field for effective plasma confinement, and a three-electrode extraction system. The experimental results show that more than 50 µA negative oxygen ion beams have been extracted, which consist of 56% O-, 25% O2-, and 19% O3-. The ion energy distribution of the negative oxygen ion beam exhibits a Gaussian distribution with a minimum ∆E of 6.3 eV. The brightness of the O- beam is estimated to be 82.4 A m-2 Sr-1 V-1. The simulation, design, and experimental study results of this RF ion source will be presented in this paper.

Rapid screening of monoclonal antibodies against porcine circovirus type 2 using colloidal gold-based paper test

A proof of concept for using paper test as a suitable method in the production of monoclonal antibodies (MAbs) is reported. The paper test which detects antibodies against porcine circovirus type 2 (PCV2) using colloidal gold-labelled capsid protein as the antigen probe was applied exclusively in the screening of anti-PCV2 MAbs. It allowed the detection of 118 single cell clones within 30 min using naked eyes. MAbs with specific binding to authentic epitopes on the virus were selected using a blocking strategy in which the antibody was pre-incubated with PCV2 viral sample before applying to the test paper. Five hybridomas secreting MAbs against the capsid protein were obtained, with only three of them capable of binding to PCV2. The results were validated and confirmed using enzyme-linked immunosorbent assay and immunofluorescence assay. The paper test is simple, rapid, and independent on professional technicians and proves to be an excellent approach for the screening of MAbs against specific targets.

Controllable magnetization precession dynamics and damping anisotropy in Co2FeAl Heusler-alloy films

Magnetization dynamics of the epitaxially-grown Co₂FeAl (CFA) thin films have been systematically investigated by the time-resolved magneto-optical Kerr effect (TR-MOKE). The dependences of precession frequency f, relaxation time τ and magnetic damping factor α upon the orientation of applied magnetic field are found to have a strong four-fold symmetry. Two series of samples with various substrate temperatures (T_s) and thickness (t_CFA) were prepared and a large Gilbert damping difference between the hard and easy axes is extracted to be 3.3 × 10^-3 after subtracting the extrinsic contributions of spin pumping, two-magnon scattering and magnetic inhomogeneities. The four-fold variation of Gilbert damping relates closely to the in-plane magnetocrystalline anisotropy and can be attributed to the anisotropic distribution of spin-orbit coupling. Our findings provide new insights into the anisotropic properties of magnetization and damping, which is very helpful for designing and optimizing advanced spintronic devices on different demands.

[The clinical efficacy of laparoscopic cornuotomy on interstitial tubal pregnancy which diameter was shorter than 3 cm]

Objective: To investigate the clinical efficacy of Laparoscopic cornuotomy on Interstitial Tubal Pregnancy (IP) which diameter was shorter than 3 cm. Methods: The women who had IP under 3 cm diameter were selected from January, 2016 to December, 2018 at the Department of Gynecology, JiaXing Maternity and Child Health care Hospital. A total of 32 IP patients were divided into two groups. They were all treated with laparoscopic surgery. 17 patients were in study group, conducted by a cornuotomy and suturing the cornual.15 patients were in control group, conducted by a cornual resection and suturing the cornual. Patients' genenral conditions were not significantly different(all P values>0.05). The peri-surgical data and the related clinical data were compared in the two groups. Results: All the 32 patients were successfully treated by laparoscopic surgery. The mean operating time was significantly shorter for cornuotomy than for cornual resection[ (33±6) min vs (53±9) min, P<0.05].Changes in blood loss[(45±5) ml vs (50±7) ml]、the total hospital stays[ (4.4±1.4) d vs (4.6±1.4) d] and the recovery time of HCG[(16±5) d vs (15±5) d] were not significantly different between the two groups (all P values>0.05) . There were no persistent ectopic pregnancy and uterine rupture happened in two groups. Compared with the control group,the interval time to pregnancy was shorter[ (8±3) m vs (16±4) m, P<0.05] and the number of full-term pregnancy cases were more (9 vs 3, P<0.05). Conclusion: The Laparoscopic cornuotomy was feasible and safe on interstitial tubal pregnancy which diameter was shorter than 3cm. It deserved popularization in the clinical work and regarded as one of selection operative treatment on interstitial heterotopic pregnancy.

Laser ablation plasma with solenoid field confinement

A Laser Ion Source (LIS) can produce high charge state and high intensity ion beams (∼emA), especially, refractory metallic ion beams, which makes it a promising candidate as an ion source for heavy ion cancer therapy facilities and future accelerator complexes, where pulsed high intensity and high charged heavy ion beams are required. However, it is difficult for the LIS to obtain a long pulse width while ensuring high current intensity, thus limiting the application of the LIS. To solve the conflict, magnetic fields are proposed to confine the expansion of the laser produced plasma. With a solenoid along the normal direction to the target surface, the lateral adiabatic expansion of the laser ablation plasma is suppressed which extends the pulse width of the ion beam effectively. The characteristics of laser ablation plasma with solenoid field confinement will be presented and discussed in this paper.

Production of O- and O2 - beams with the negative ion source at Institute of Modern Physics

A negative oxygen ion source is under development to produce O^- and O₂ ^- beams used for a secondary ion mass spectrometer at Institute of Modern Physics (IMP), and both filament and radio frequency (RF) schemes are tested. The filament driven ion source, which was initially designed for H^- production, has a 10-pole multicusp plasma chamber, two sets of virtual magnetic filters, and a 3-electrode extraction system. The RF scheme, which is improved by changing a RF back plate from the filament ion source, has an external planar spiral RF antenna behind an AlN window. The RF power system consists of a continuous wave (CW) 13.56 MHz/2 kW power supply, a capacitive automatching network and a water-cooled flat RF antenna made from a 6-mm copper tube. Oxygen and carbon dioxide gases are used to produce O^- and O₂ ^- ion beams, and ion composition is analyzed by using a Wien filter. However, the lifetime of filaments sustains from several minutes to hours before fracture occurred while the RF one can work stably with no maintenance, and the experiment results will be given on O^- ion production with two different technologies using our ion source test facility.

Magnetic precession modes with enhanced frequency and intensity in hard/NM/soft perpendicular magnetic films

High frequency magnetic precessions with strong intensity are strongly desired in material systems for high performance magnetic memory or nano-oscillator applications with ultrafast manipulation speed. Here, we demonstrate an exchange-coupled asymmetric composite film structure of Ta/Pd/[Pd/Co]₅/Cu(t_Cu)/[Co/Ni]₅/Ta with adjustable strong perpendicular magnetic anisotropy and interlayer coupling strength, in which the dynamic magnetic properties are systematically studied by using time-resolved magneto-optical Kerr effect spectroscopy. It is demonstrated that the in-phase precession frequency is between those of the single hard magnetic [Pd/Co]₅ and soft [Co/Ni]₅ multilayers, which can be significantly enhanced for the strongly coupled case at t_Cu < 1 nm. Moreover, in the weakly coupled samples with t_Cu = 1.0-3.0 nm, besides the common in-phase acoustic mode, an out-of-phase optical mode occurs simultaneously with a frequency even higher than that of the hard magnetic [Pd/Co]₅ layer. The optical mode precession frequency and amplitude show an unusual non-monotonic variation trend with the increase of t_Cu, which has been theoretically analyzed and attributed to the co-effect of decreased coupling strength and increased magnetic anisotropy field difference between the two multilayer stacks. Moreover, by adjusting t_Cu and the [Co/Ni] repetition number N, an optical mode of strong intensity can be actively achieved, even reaching 80% as compared to the acoustic mode. These results provide effective control and better understanding of magnetic dynamics in perpendicular composite films, which are of key importance for developing ultrafast spintronics-based devices.

Controllable Interfacial Coupling Effects on the Magnetic Dynamic Properties of Perpendicular [Co/Ni]5/Cu/TbCo Composite Thin Films

Dynamic magnetic properties in perpendicularly exchange-coupled [Co/Ni]₅/Cu (t_Cu = 0-2 nm)/TbCo structures show strong dependences on the interfacial antiferromagnetic strength J_ex, which is controlled by the Cu interlayer thickness. The precession frequency f and effective damping constant α_eff of a [Co/Ni]₅ multilayer differ distinctly for parallel (P) and antiparallel (AP) magnetization orientation states. For samples with a thin t_Cu, f of the AP state is apparently higher, whereas α_eff is lower than that in the P state, owing to the unidirectional exchange bias effect (H_EB) from the TbCo layer. The differences in f and α_eff between the two states gradually decrease with increasing t_Cu. By using a uniform precession model including an additional H_EB term, the field-dependent frequency curves can be well-fitted, and the fitted H_EB value is in good agreement with the experimental data. Moreover, the saturation damping constant α₀ displays a nearly linear correlation with J_ex. It decreases significantly with J_ex and eventually approaches a constant value of 0.027 at t_Cu = 2 nm where J_ex vanishes. These results provide a better understanding and effective control of magnetization dynamics in exchange-coupled composite structures for spintronic applications.

Magnetic damping and perpendicular magnetic anisotropy in Pd-buffered [Co/Ni]5 and [Ni/Co]5 multilayers

The magnetic damping α₀ increases continuously with underlayer thickness, showing no correlation with PMA strength but a similar variation behavior to 1/M_s. Such α₀ increase is ascribed to the formation of more disordered spins at NM/FM interface.

New development of laser ion source for highly charged ion beam production at Institute of Modern Physics (invited)

A laser ion source based on Nd:YAG laser has been being studied at the Institute of Modern Physics for the production of high intensity high charge state heavy ion beams in the past ten years, for possible applications both in a future accelerator complex and in heavy ion cancer therapy facilities. Based on the previous results for the production of multiple-charged ions from a wide range of heavy elements with a 3 J/8 ns Nd:YAG laser [Zhao et al., Rev. Sci. Instrum. 85, 02B910 (2014)], higher laser energy and intensity in the focal spot are necessary for the production of highly charged ions from the elements heavier than aluminum. Therefore, the laser ion source was upgraded with a new Nd:YAG laser, the maximum energy of which is 8 J and the pulse duration can be adjusted from 8 to 18 ns. Since then, the charge state distributions of ions from various elements generated by the 8 J Nd:YAG laser were investigated for different experimental conditions, such as laser energy, pulse duration, power density in the focal spot, and incidence angle. It was shown that the incidence angle is one of the most important parameters for the production of highly charged ions. The capability of producing highly charged ions from the elements lighter than silver was demonstrated with the incidence angle of 10° and laser power density of 8 × 10(13) W cm(-2) in the focal spot, which makes a laser ion source complementary to the superconducting electron cyclotron resonance ion source for the future accelerator complex especially in terms of the ion beam production from some refractory elements. Nevertheless, great efforts with regard to the extraction of intense ion beams, modification of the ion beam pulse duration, and reliability of the ion source still need to be made for practical applications.

Magnetization switching by combining electric field and spin-transfer torque effects in a perpendicular magnetic tunnel junction

Effective manipulation of magnetization orientation driven by electric field in a perpendicularly magnetized tunnel junction introduces technologically relevant possibility for developing low power magnetic memories. However, the bipolar orientation characteristic of toggle-like magnetization switching possesses intrinsic difficulties for practical applications. By including both the in-plane (T_//) and field-like (T_⊥) spin-transfer torque terms in the Landau-Lifshitz-Gilbert simulation, reliable and deterministic magnetization reversal can be achieved at a significantly reduced current density of 5×10⁹ A/m² under the co-action of electric field and spin-polarized current, provided that the electric-field pulse duration exceeds a certain critical value τ_c. The required critical τ_c decreases with the increase of T_⊥ strength because stronger T_⊥ can make the finally stabilized out-of-plane component of magnetization stay in a larger negative value. The power consumption for such kind of deterministic magnetization switching is found to be two orders of magnitude lower than that of the switching driven by current only.

Perpendicular magnetic anisotropy and magnetization dynamics in oxidized CoFeAl films

Half-metallic Co-based full-Heusler alloys with perpendicular magnetic anisotropy (PMA), such as Co₂FeAl in contact with MgO, are receiving increased attention recently due to its full spin polarization for high density memory applications. However, the PMA induced by MgO interface can only be realized for very thin magnetic layers (usually below 1.3 nm), which would have strong adverse effects on the material properties of spin polarization, Gilbert damping parameter, and magnetic stability. In order to solve this issue, we fabricated oxidized Co₅₀Fe₂₅Al₂₅ (CFAO) films with proper thicknesses without employing the MgO layer. The samples show controllable PMA by tuning the oxygen pressure (P_O2) and CFAO thickness (t_CFAO), large perpendicular anisotropy field of ~8.0 kOe can be achieved at P_O2 = 12% for the sample of t_CFAO= 2.1 nm or at P_O2= 7% for t_CFAO= 2.8 nm. The loss of PMA at thick t_CFAO or high P_O2 results mainly from the formation of large amount of CoFe oxides, which are superparamagnetic at room temperature but become hard magnetic at low temperatures. The magnetic CFAO films, with strong PMA in a relatively wide thickness range and small intrinsic damping parameter below 0.028, would find great applications in developing advanced spintronic devices.

Simulation of direct plasma injection for laser ion beam acceleration with a radio frequency quadrupole

The direct plasma injection scheme (DPIS) has been being studied at Institute of Modern Physics since several years ago. A C(6+) beam with peak current of 13 mA, energy of 593 keV/u has been successfully achieved after acceleration with DPIS method. To understand the process of DPIS, some simulations have been done as follows. First, with the total current intensity and the relative yields of different charge states for carbon ions measured at the different distance from the target, the absolute current intensities and time-dependences for different charge states are scaled to the exit of the laser ion source in the DPIS. Then with these derived values as the input parameters, the extraction of carbon beam from the laser ion source to the radio frequency quadrupole with DPIS is simulated, which is well agreed with the experiment results.

Study on space charge effect in an electrostatic ion analyzer applied to measure laser produced ions

The abundance of different ions produced by laser ion sources is usually analyzed by an electrostatic ion analyzer (EIA). Ion current intensities in the range of several mA/cm(2) at the position of the EIA have been achieved from the laser ion source developed by the Institute of Modern Physics; this indicates that a noticeable influence of space charge effect during the ion transmission will occur. Hence, while the parameters of the EIA or the beams are changed, such as ion species, current intensity, the ions' transmission efficiency through the EIA is different, which will result in an uncertainty in the estimation of the ions' yields. Special attention is focused on this issue in this paper. Ion's transmissions through the EIA under different circumstances are studied with simulations and experiments, the results of which are consistent with each other.

The study towards high intensity high charge state laser ion sources

As one of the candidate ion sources for a planned project, the High Intensity heavy-ion Accelerator Facility, a laser ion source has been being intensively studied at the Institute of Modern Physics in the past two years. The charge state distributions of ions produced by irradiating a pulsed 3 J/8 ns Nd:YAG laser on solid targets of a wide range of elements (C, Al, Ti, Ni, Ag, Ta, and Pb) were measured with an electrostatic ion analyzer spectrometer, which indicates that highly charged ions could be generated from low-to-medium mass elements with the present laser system, while the charge state distributions for high mass elements were relatively low. The shot-to-shot stability of ion pulses was monitored with a Faraday cup for carbon target. The fluctuations within ±2.5% for the peak current and total charge and ±6% for pulse duration were demonstrated with the present setup of the laser ion source, the suppression of which is still possible.