Real-time and continuous monitoring of lactate levels in sweat has been used as an indicator of physiological information to evaluate exercise outcomes and sports performance. We developed an optimal enzyme-based biosensor to detect the concentrations of lactate in different fluids (i.e., a buffer solution and human sweat). The surface of the screen-printed carbon electrode (SPCE) was first treated with oxygen plasma and then surface-modified by lactate dehydrogenase (LDH). The optimal sensing surface of the LDH-modified SPCE was identified by Fourier transform infrared spectroscopy and electron spectroscopy for chemical analysis. After connecting the LDH-modified SPCE to a benchtop E4980A precision LCR meter, our results showed that the recorded response was a function of the lactate concentration with a wide dynamic range of 0.1–100 mM (R2 = 0.95) and a limit of detection of 0.1 mM which was unachievable without using redox species A state-of-the-art electrochemical impedance spectroscopy (EIS) chip was developed to integrate the LDH-modified SPCE for a portable bioelectronic platform in the detection of lactate in human sweat. We believe the optimal sensing surface can improve the sensitivity of lactate sensing in a portable bioelectronic EIS platform for early diagnosis or real-time monitoring during different physical activities.
This article presents a multimodal electrochemical sensing system-on-chip (SoC), including the functions of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and temperature sensing. CV readout circuitry achieves an adaptive readout current range of 145.5 dB through an automatic range adjustment and resolution scaling technique. EIS has an impedance resolution of 9.2 m Ω/√ Hz at a sweep frequency of 10 kHz and an output current of up to 120 μA. With an impedance boost mechanism, the maximum detectable load impedance is extended to 22.95 k Ω, while the total harmonic distortion is less than 1%. A resistor-based temperature sensor using a swing-boosted relaxation oscillator can achieve a resolution of 31 mK in 0-85 °C. The design is implemented in a 0.18 μm CMOS process. The total power consumption is 1 mW.
Aggregating a lot of subcarriers will generate high peak‐to‐average power ratio (PAPR) which makes the overall system performance degradation. Among the existing PAPR reduction methods for orthogonal frequency‐division multiplexing (OFDM)‐based systems, iterative clipping and filtering (ICF) may be easy to implement, but ICF may cause signal distortion, so that the system cannot approximate the processed signals to the original signals which degrades error rates at receivers. Here, the authors proposed a new method based on ICF with smoothed clipping signals, and find the optimised filter to achieve the minimum error vector magnitude and efficiently reduce PAPR. Owing to the lack of a wide range of continuous bandwidth, the Third Generation Partnership Project proposed carrier aggregation (CA) technology in LTE‐advanced systems. CA can aggregate many contiguous or non‐contiguous fragment spectrums for supporting larger bandwidth and higher peak data rate. Here, the authors also evaluate the developed PAPR reduction scheme for the use in CA scenarios. The efficacy of the proposed scheme is demonstrated in the simulation results.
Neuromorphic devices utilizing atomically thin 2D materials show promise for large-scale computing by emulating biological neural networks. Floating gate transistors (FGTs) typically fall into two categories based on the selection of the semiconductor channel layer material. One category involves unipolar semiconductors that transmit only one type of majority carrier, while the second category consists of ambipolar semiconductors, tunable to switch the type of majority carrier. This flexibility enables devices to switch modes and respond to specific stimulation, such as molybdenum ditelluride (MoTe 2 ), proven to be valid as a channel material [1]. Here, MoTe 2 , hexagonal boron nitride (h-BN), and graphene (Gr) were applied to construct the ambipolar FGT (AFGT). Additionally, access regions (ARs) were introduced in the AFGT to fabricate AR-based AFGT (AR-AFGT), altering the transmission mechanism of carriers in the channel layer compared with the AFGT device [2].2D van der Waal materials were stacked in the order of Gr/h-BN/MoTe 2 to fabricate AFGTs with source/drain electrodes overlapping the Gr, serving as the floating gate (FG), with a channel length of about 2 µm . Gr/h-BN/MoTe 2 AR-AFGTs were fabricated by placing ARs, which do not overlap with FG, in proximity to source/drain electrodes with a channel length of 10 µm. We measured and compared the transfer characteristic of AFGT and AR-AFGT devices. The AFGT exhibited obvious ambipolar behavior with dominant n-branch and p-branch. However, in the case of AR-AFGT, a significant n-branch portion was observed. These phenomena may arise from the AR increasing the distance from the electrode to the storage layer, indicating that MoTe 2 acts as a unipolar material. Our study compared AFGT and AR-AFGT devices, highlighting their unique traits. While AFGT exhibited significant ambipolar behavior, AR-AFGT, influenced by the increased distance, displayed a distinct unipolar profile with an emphasis on the n-branch. The integration of AR stands out as a key factor for creating adaptable neuromorphic devices. References Wu, E., et al., Tunable and nonvolatile multibit data storage memory based on MoTe2/boron nitride/graphene heterostructures through contact engineering. Nanotechnology, 2020. 31 (48): p. 485205. Sasaki, T., et al., Material and Device Structure Designs for 2D Memory Devices Based on the Floating Gate Voltage Trajectory. ACS Nano, 2021. 15 (4): p. 6658-6668. Figure 1
Incorporating sensor nodes with data aggregation capability to transmit less data flow in wireless sensor networks could reduce the total energy consumption. However, the penalty from data retransmissions due to collision could jeopardize the advantages from data aggregation. In this paper, for the first time, we consider the energy consumption tradeoffs between the data aggregation and retransmission in wireless sensor network. By using the CSMA-CA MAC protocol, the retransmission energy consumption function is well formulated. We propose a rigorous non-linear mathematical formulation, where the objective function is to minimize the total energy consumption of data transmission subject to data aggregation tree and data retransmission. The solution approach is based on Lagrangean relaxation in conjunction with the optimization-based heuristics. From the computational experiments, it is shown that the proposed algorithms could construct more energy efficient data aggregation tree with MAC layer retransmission mechanism than existing data centric algorithms up to 93%.
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