arXiv subjects

Jun-Chau Chien

Publications and source records attributed to Jun-Chau Chien.

3 recordsLinked to original sources

arXiv2025

Theoretical Studies of Sub-THz Active Split-Ring Resonators for Near-Field Imaging

This paper develops a theoretical framework for the design of Active Split-Ring Resonators (ASRRs). An ASRR is a Split-Ring Resonator (SRR) equipped with a tunable negative resistor, enabling both switchability and quality factor boosting and tuning. These properties make ASRRs well-suited for integration into dense arrays on silicon chips, where pixelated near-fields are generated and leveraged for high-resolution 2D imaging of samples. Such imagers pave the way for real-time, non-invasive, and low-cost imaging of human body tissue. The paper investigates ASRR coupling to host transmission lines, nonlinear effects, signal flow, and the influence of various noise sources on detection performance. Verified through simulations, these studies provide design guidelines for optimizing the Signal-to-Noise Ratio (SNR) and power consumption of a single pixel, while adhering to the constraints of a scalable array.

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arXiv2022

Dual-aptamer Drift Cancelling Techniques to Improve Long-term Stability of Real-Time Structure-Switching Aptasensors

This paper presents a dual-aptamer scheme to cancel the signal drifts from structure-switching aptamers during long-term monitoring. Electrochemical aptamer-based (E-AB) biosensors recently demonstrated their great potential for in vivo continuous monitoring. Nevertheless, the detection accuracy is often limited by the signaling drifts. Conventionally, these drifts are removed by the kinetic differential measurements (KDM) when coupled with square-wave voltammetry. Yet we discover that KDM does not apply to every aptamer as the responses at different SWV frequencies heavily depend on its structure-switching characteristics and the redox reporters' electron transfer (ET) kinetics. To this end, we present a "dual-aptamer" scheme that uses two aptamers responding differentially to the same molecular target for drift cancellation. We identify these paired aptamers through (1) screening from the existing aptamers pool and (2) engineering the signaling behavior of the redox reporters. We demonstrate their differential signaling to ampicillin and ATP molecules and show that the aptamer pair bears common drifts in undilute goat serum. Through cancellation, sensor drift is reduced by 370-fold. Benefiting from the "differential" signaling, the recording throughput is also doubled using differential readout electronics. The authors believe the proposed technique is beneficial for long-term in vivo monitoring.

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arXiv2020

Design and Analysis of a Sample-and-Hold CMOS Electrochemical Sensor for Aptamer-based Therapeutic Drug Monitoring

In this paper, we present the design and the analysis of an electrochemical circuit for measuring the concentrations of therapeutic drugs using structure-switching aptamers. Aptamers are single-stranded nucleic acids, whose sequence is selected to exhibit high affinity and specificity toward a molecular target, and change its conformation upon binding. This property, when coupled with a redox reporter and electrochemical detection, enables reagent-free biosensing with a sub-minute temporal resolution for in vivo therapeutic drug monitoring. Specifically, we design a chronoamperometry-based electrochemical circuit that measures the direct changes in the electron transfer (ET) kinetics of a methylene blue reporter conjugated at the distal-end of the aptamer. To overcome the high-frequency noise amplification issue when interfacing with a large-size (> 0.25 mm2) implantable electrode, we present a sample-and-hold (S/H) circuit technique in which the desired electrode potentials are held onto noiseless capacitors during the recording of the redox currents. This allows disconnecting the feedback amplifiers to avoid its noise injection while reducing the total power consumption. A prototype circuit implemented in 65-nm CMOS demonstrates a cell-capacitance-insensitive input-referred noise (IRN) current of 15.2 pArms at a 2.5-kHz filtering bandwidth. Tested in human whole blood samples, changes in the ET kinetics from the redox-labeled aminoglycoside aptamers at different kanamycin concentrations are measured from the recorded current waveforms. By employing principal component analysis (PCA) to compensate for the sampling errors, a detection limit (SNR = 1) of 3.1 uM under 1-sec acquisition is achieved at 0.22-mW power consumption.

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