Parallelized Wireless Sensing System for Continuous Monitoring of Microtissue Spheroids

Thermal segment microwell plate control for automated liquid handling setups

Automated high-throughput liquid handling operations in biolabs necessitate miniaturised and automatised equipment for effective space utilisation and system integration. This paper presents a thermal segment microwell plate control unit designed for enhanced microwell-based experimentation in liquid handling setups. The development of this device stems from the need to move towards geometry standardization and system integration of automated lab equipment. It incorporates features based on Smart Sensor and Sensor 4.0 concepts. An enzymatic activity assay is implemented with the developed device on a liquid handling station, allowing fast characterisation via a high-throughput approach. The device outperforms other comparable devices in certain metrics based on automated liquid handling requirements and addresses the needs of future biolabs in automation, especially in high-throughput screening.

Highly Sensitive Near-Field Electrochemical Sensor for In Vivo Monitoring of Respiratory Patterns

Real-time tracking of respiratory patterns provides noninvasive and quick access for evaluating pathophysiological conditions yet remains challenging due to limited temporal resolution and poor sensitivity to dig out fingerprints of respiratory waveforms. Here, we report an electrochemical sensor for accurately tracing respiratory patterns of small animal models based on the electrochemical impedance mechanism for wireless coupling of a graphdiyne oxide (GYDO)-modified sensing coil chip and a reader coil chip via near-field magnetic induction. In the electrochemical impedance measurement mode, an alternating current is applied through the reader coil chip to perturb proton transport at the GYDO interface of the sensing coil chip. As demonstrated, a high-frequency perturbing condition significantly reduces the interfacial resistance for proton transport by 5 orders of magnitude under 95% relative humidity (RH) and improves the low-humidity responses with a limit of detection down to 0.2% RH, enabling in vivo accurate profiling of respiratory patterns on epileptic rats. The electrochemical impedance coupling system holds great potential for new wireless bioelectronics.

GO/CNT-OH/Nafion Nanocomposite Humidity Sensor Based on the LC Wireless Method

In recent years, LC resonant sensors have gained widespread attention for their extensive applications in industries such as pharmaceutical storage and food transportation. A wireless passive sensor with a good sensing performance is proposed based on a GO/CNT-OH/Nafion nanocomposite. The sensor was fabricated via inkjet printing technology, and the surface morphology of the GO/CNT-OH/Nafion nanocomposite was characterized by SEM measurement. It is found that the MWCNTs support the GO layer and the hydrophobic chains of Nafion interact with the hydrophobic layer of GO, resulting in a larger cavity and hydrophilic surface of the entire material. This structure well reflects the fact that the mixing of MWCNTs and Nafion provides the entire material with a stronger water absorption. The experimental study shows that the proposed humidity sensor has a frequency variation of 103 kHz/%RH at low humidity (30-60% RH) and a sensitivity of 931 kHz/%RH at high humidity (60-95% RH), while the sensitivity value from 30-95% RH is 547 kHz/% RH. The response time and recovery time are 110 s and 115 s, respectively. In addition, the tests showed that the GO/CNT-OH/Nafion nanocomposite applied to the humidity sensor had a maximum humidity hysteresis of about 3% RH at 30-95% RH, the resonant frequency remained basically unchanged after 50 h of testing, and the whole sensor possessed a good stability. After conducting several repeated experiments, it was found that the resonant frequency error of the whole sensor was low and did not affect the overall sensing test, which proved the reproducible preparation of the sensor. Finally, the humidity-sensing mechanism of the proposed sensor was analyzed in this paper, and it was found that GO enhanced the hygroscopic properties of GO/CNT-OH/Nafion nanocomposite when it was supported by MWCNT-OH and included uniformly dispersed Nafion. Therefore, our proposed humidity sensor is suitable for humidity detection above 30% RH in both sealed and open environments.

Wireless dielectrophoresis trapping and remote impedance sensing via resonant wireless power transfer

Nearly all biosensing platforms can be described using two fundamental steps-collection and detection. Target analytes must be delivered to a sensing element, which can then relay the transduced signal. For point-of-care technologies, where operation is to be kept simple, typically the collection step is passive diffusion driven-which can be slow or limiting under low concentrations. This work demonstrates an integration of both active collection and detection by using resonant wireless power transfer coupled to a nanogap capacitor. Nanoparticles suspended in deionized water are actively trapped using wireless dielectrophoresis and positioned within the most sensitive fringe field regions for wireless impedance-based detection. Trapping of 40 nm particles and larger is demonstrated using a 3.5 V_RMS, 1 MHz radiofrequency signal delivered over a distance greater than 8 cm from the nanogap capacitor. Wireless trapping and release of 1 µm polystyrene beads is simultaneously detected in real-time over a distance of 2.5 cm from the nanogap capacitor. Herein, geometric scaling strategies coupled with optimal circuit design is presented to motivate combined collection and detection biosensing platforms amenable to wireless and/or smartphone operation.

Impedance Imaging of Cells and Tissues: Design and Applications

Due to their label-free and noninvasive nature, impedance measurements have attracted increasing interest in biological research. Advances in microfabrication and integrated-circuit technology have opened a route to using large-scale microelectrode arrays for real-time, high-spatiotemporal-resolution impedance measurements of biological samples. In this review, we discuss different methods and applications of measuring impedance for cell and tissue analysis with a focus on impedance imaging with microelectrode arrays in in vitro applications. We first introduce how electrode configurations and the frequency range of the impedance analysis determine the information that can be extracted. We then delve into relevant circuit topologies that can be used to implement impedance measurements and their characteristic features, such as resolution and data-acquisition time. Afterwards, we detail design considerations for the implementation of new impedance-imaging devices. We conclude by discussing future fields of application of impedance imaging in biomedical research, in particular applications where optical imaging is not possible, such as monitoring of ex vivo tissue slices or microelectrode-based brain implants.

Recent Advances in Multicellular Tumor Spheroid Generation for Drug Screening

Multicellular tumor spheroids (MCTs) have been employed in biomedical fields owing to their advantage in designing a three-dimensional (3D) solid tumor model. For controlling multicellular cancer spheroids, mimicking the tumor extracellular matrix (ECM) microenvironment is important to understand cell-cell and cell-matrix interactions. In drug cytotoxicity assessments, MCTs provide better mimicry of conventional solid tumors that can precisely represent anticancer drug candidates' effects. To generate incubate multicellular spheroids, researchers have developed several 3D multicellular spheroid culture technologies to establish a research background and a platform using tumor modelingvia advanced materials science, and biosensing techniques for drug-screening. In application, drug screening was performed in both invasive and non-invasive manners, according to their impact on the spheroids. Here, we review the trend of 3D spheroid culture technology and culture platforms, and their combination with various biosensing techniques for drug screening in the biomedical field.

Wireless Microfluidic Sensor for Metal Ion Detection in Water

In the present work, a wireless microfluidic sensor based on low-temperature cofired ceramic (LTCC) technology for real-time detection of metal ions in water is proposed. The wireless sensor is composed of a planar spiral inductor and parallel plate capacitor (LC) resonant antenna, which integrates with the microchannel in the LTCC substrate between the capacitor plates. Aqueous solutions of Pb(NO₃)₂, Cd(NO₃)₂, Mg(NO₃)₂, Ca(NO₃)₂, NaNO₃, and KNO₃ with concentrations of 0-100 mM were tested with the sensors. The metal ion and its concentration in water can be tested by the amplitude of the reflection coefficient (S ₁₁) and the resonance frequency (f _r) of the wireless microfluidic sensor. The metal ion species can be distinguished from the wireless response behavior of the sensor. The detection limit of the sensor for the selected metal ionic solutions could reach as low as 5 μM. The normalized sensitivity of the sensor is 0.47%, which is higher than that of the reported liquid microfluidic sensors based on microwave resonators. The wireless microfluidic sensor of this study is promising for rapid and convenient detection of heavy metal ion pollutants in the industrial wastewater.

Automated 3D Microphysiometry Facilitates High-Content and Highly Reproducible Oxygen Measurements within 3D Cell Culture Models

Microphysiometry is a powerful technique to study metabolic parameters and detect changes to external stimuli. However, applying this technique for automated label-free and real-time measurements within cell-laden three-dimensional (3D) cell culture constructs remains a challenge. Herein, we present an entirely automated microphysiometry setup that combines needle-type microsensors with motorized sample and sensor positioning systems inside a standard tissue-culture incubator. The setup records dissolved oxygen as a metabolic parameter along the z-direction within cell-laden 3D constructs in a minimally invasive manner. The microphysiometry setup was applied to characterize the spatial oxygen distribution within thick cell-laden 3D constructs, study the time-dependent changes on the oxygen tension within 3D breast cancer models following a chemotherapeutic treatment, and identify kinetics and recovery effects after drug exposure over 5 weeks. Our data suggest that the microphysiometry setup enables highly reproducible measurements without human intervention, due to the high degree of automation and positional accuracy. The results demonstrate the applicability of the setup to provide valuable long-term insights into oxygenation within 3D models using minimally invasive, label-free, and entirely automated analysis methods.