Reversible Thermoelectric Regulation of Electromagnetic and Chemical Enhancement for Rapid SERS Detection.

Actively controlling surface-enhanced Raman scattering (SERS) performance plays a vital role in highly sensitive detection or in situ monitoring. Nevertheless, it is still challenging to achieve further modulation of electromagnetic enhancement and chemical enhancement simultaneously in SERS detection. In this study, a silver nanocavity structure with graphene as a spacer layer is coupled with thermoelectric semiconductor P-type gallium nitride (GaN) to form an electric-field-induced SERS (E-SERS) for dual enhancement. After applying the electric field, the intensity of SERS signals is further enhanced by over 10 times. The thermoelectric field enables fast and reproducible doping of graphene, thereby modulating its Fermi level over a wide range. The thermoelectric field also regulates the position of the plasmon resonance peak of the silver nanocavity structure, rendering synchronous dual electromagnetic and chemical regulation. Additionally, the method enables the trace detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). A detailed theoretical analysis is performed based on the experimental results and finite-element calculations, paving the way for the fabrication of high-efficient E-SERS substrates.

Thermoelectrically Driven Dual-Mechanism Regulation on SERS and Application Potential for Rapid Detection of SARS-CoV-2 Viruses and Microplastics.

Electric-induced surface-enhanced Raman scattering (E-SERS) has been widely studied for its flexible regulation of SERS after the substrate is prepared. However, the enhancement effect is not sufficiently high in the E-SERS technology reported thus far, and no suitable field of application exists. In this study, a highly sensitive thermoelectrically induced SERS substrate, Ag/graphene/ZnO (AGZ), was fabricated using ZnO nanoarrays (NRs), graphene, and Ag nanoparticles (NPs). Applying a temperature gradient to the ZnO NRs enhanced the SERS signals of the probe molecules by a factor of approximately 20. Theoretical and experimental results showed that the thermoelectric potential enables the simultaneous modulation of the Fermi energy level of graphene and the plasma resonance peak of Ag NPs, resulting in a double enhancement in terms of physical and chemical mechanisms. The AGZ substrate was then combined with a mask to create a wearable thermoelectrically enhanced SERS mask for collecting SARS-CoV-2 viruses and microplastics. Its SERS signal can be enhanced by the temperature gradient created between a body heat source (∼37 °C) and a cold environment. The suitability of this method for virus detection was also examined using a reverse transcription-polymerase chain reaction and SARS-CoV-2 virus antigen detection. This work offers new horizons for research of E-SERS, and its application potential for rapid detection of the SARS-CoV-2 virus and microplastics was also studied.

SSA-VMD for UWB Radar Sensor Vital Sign Extraction.

The combination of advanced radar sensor technology and smart grid has broad prospects. It is meaningful to monitor the respiration and heartbeat of grid employees under resting state through radar sensors to ensure that they are in a healthy working state. Ultra-wideband (UWB) radar sensor is suitable for this application because of its strong penetration ability, high range resolution and low average power consumption. However, due to weak heartbeat amplitude and measurement noise, the accurate measurement of the target heart rate is a challenge. In this paper, singular spectrum analysis (SSA) is proposed to reconstruct the eigenvalues of noisy vital signs to eliminate noise peaks around the heartbeat rate; combined with the variational modal decomposition (VMD), the target vital signs can be extracted with high accuracy. The experiment confirmed that the target vital sign information can be extracted with high accuracy from ten subjects at different distances, which can play an important role in short distance human detection and vital sign monitoring.

High-precision synchronization detection method for bistatic radar.

To improve the accuracy of radar ranging and positioning under complex backgrounds, a high-precision synchronization detection method for bistatic radar is proposed based on different-frequency phase processing. First, the transmit signal and receive signal are converted to radio frequency pulses by frequency conversion. Then, the transmit signal is roughly measured with a field-programmable gate array. The obtained rough signal is used as the reference signal under the control of the direct digital synthesizer frequency synthesizer. Second, the transmit signal and receive signal are each synchronized with the reference signal in a different-frequency phase detection. These detection results are used as the starting signal and stopping signal of the counter gate. Finally, all the signals are counted, and the time synchronization between the transmit signal and the receive signal is implemented by processing the counting value. The experimental results show that a time synchronization precision of 1.5 ps and a frequency stability of 6.2 × 10-13/s can be reached. This method has the advantages of a fast time response, good noise suppression, and high measurement precision and strong system reliability.

Precise frequency synchronization detection method based on the group quantization stepping law.

A precise frequency synchronization detection method is proposed based on the group quantization steeping law. Based on the different-frequency group quantization phase processing, high-precision frequency synchronization can be achieved by measuring phase comparison result quantization. If any repeated phase differences in the quantized phase comparison results are used as the starting and stopping signal of the counter gate, the time interval between identical phase differences is a group period as gate time. By measuring and analyzing the quantized phase comparison results, the ±1-word counting error is overcome in the traditional frequency synchronization detection method, and the system response time is significantly shortened. The experimental results show that the proposed frequency synchronization detection method is advanced and scientific. The measurement resolution is notably stable and the frequency stability better than the E-12/s level can be obtained. The method is superior to the traditional frequency synchronization detection method in many aspects, such as system reliability and stability, detection speed, development cost, power consumption and volume.

High-Resolution Group Quantization Phase Processing Method in Radio Frequency Measurement Range.

Aiming at the more complex frequency translation, the longer response time and the limited measurement precision in the traditional phase processing, a high-resolution phase processing method by group quantization higher than 100 fs level is proposed in radio frequency measurement range. First, the phase quantization is used as a step value to quantize every phase difference in a group by using the fixed phase relationships between different frequencies signals. The group quantization is formed by the results of the quantized phase difference. In the light of frequency drift mainly caused by phase noise of measurement device, a regular phase shift of the group quantization is produced, which results in the phase coincidence of two comparing signals which obtain high-resolution measurement. Second, in order to achieve the best coincidences pulse, a subtle delay is initiatively used to reduce the width of the coincidences fuzzy area according to the transmission characteristics of the coincidences in the specific medium. Third, a series of feature coincidences pulses of fuzzy area can be captured by logic gate to achieve the best phase coincidences information for the improvement of the measurement precision. The method provides a novel way to precise time and frequency measurement.

Co-expression of tonoplast Cation/H(+) antiporter and H(+)-pyrophosphatase from xerophyte Zygophyllum xanthoxylum improves alfalfa plant growth under salinity, drought and field conditions.

Salinity and drought are major environmental factors limiting the growth and productivity of alfalfa worldwide as this economically important legume forage is sensitive to these kinds of abiotic stress. In this study, transgenic alfalfa lines expressing both tonoplast NXH and H(+)-PPase genes, ZxNHX and ZxVP1-1 from the xerophyte Zygophyllum xanthoxylum L., were produced via Agrobacterium tumefaciens-mediated transformation. Compared with wild-type (WT) plants, transgenic alfalfa plants co-expressing ZxNHX and ZxVP1-1 grew better with greater plant height and dry mass under normal or stress conditions (NaCl or water-deficit) in the greenhouse. The growth performance of transgenic alfalfa plants was associated with more Na(+), K(+) and Ca(2+) accumulation in leaves and roots, as a result of co-expression of ZxNHX and ZxVP1-1. Cation accumulation contributed to maintaining intracellular ions homoeostasis and osmoregulation of plants and thus conferred higher leaf relative water content and greater photosynthesis capacity in transgenic plants compared to WT when subjected to NaCl or water-deficit stress. Furthermore, the transgenic alfalfa co-expressing ZxNHX and ZxVP1-1 also grew faster than WT plants under field conditions, and most importantly, exhibited enhanced photosynthesis capacity by maintaining higher net photosynthetic rate, stomatal conductance, and water-use efficiency than WT plants. Our results indicate that co-expression of tonoplast NHX and H(+)-PPase genes from a xerophyte significantly improved the growth of alfalfa, and enhanced its tolerance to high salinity and drought. This study laid a solid basis for reclaiming and restoring saline and arid marginal lands as well as improving forage yield in northern China.

High-resolution frequency measurement method with a wide-frequency range based on a quantized phase step law.

A wide-frequency and high-resolution frequency measurement method based on the quantized phase step law is presented in this paper. Utilizing a variation law of the phase differences, the direct different frequency phase processing, and the phase group synchronization phenomenon, combining an A/D converter and the adaptive phase shifting principle, a counter gate is established in the phase coincidences at one-group intervals, which eliminates the ±1 counter error in the traditional frequency measurement method. More importantly, the direct phase comparison, the measurement, and the control between any periodic signals have been realized without frequency normalization in this method. Experimental results show that sub-picosecond resolution can be easily obtained in the frequency measurement, the frequency standard comparison, and the phase-locked control based on the phase quantization processing technique. The method may be widely used in navigation positioning, space techniques, communication, radar, astronomy, atomic frequency standards, and other high-tech fields.