Study of cell and drug interactions based on dual-mode detection using SPR and fluorescence imaging.

The investigation of the interactions between cells and drugs forms a crucial aspect of biological and clinical medical studies. Generally, single-cell or local-cellular studies require a microscopic imaging system with high magnifications, which suffers from low detection throughputs and poor time responses. The study presented in this paper combined SPR and fluorescence to achieve cell localization, real-time monitoring of cell images and quantitative analysis of drugs. In order to obtain more comprehensive, accurate and real-time data, a dual-mode system based on surface plasmon resonance (SPR) and fluorescence was constructed based on a 4× magnification lens. This enables simultaneous studies of an entire cell and a specific region of the cell membrane. An adaptive adjustment algorithm was established for distorted SPR images, achieving temporal and spatial matching of the dual-mode detection. The combination of SPR and fluorescence not only achieved micro-detection but also complemented the qualitative or quantitative limitations of SPR or fluorescence method alone. In system characterization, the response signal of SPR was noticed to increase with the increasing concentration of EGF in stimulated cells. It indicated that this platform could be employed for quantitative detection of the cell membrane region. Upon addition of EGF, a peak in the SPR curve was observed, and the cells in the corresponding SPR image turned whiter. This indicated that the platform can simultaneously monitor the SPR response signal and image changes. The response time of fluorescence in EGF testing was several seconds earlier than SPR, revealing that signal transduction first occurred in the whole cell and then propagated to the cell membrane region. The inhibitory ability of Gefitinib on cells was verified in a fast and real-time manner within 20 min. The results indicated that the detection limit of this method was 20 IU/mL for EGF and 10 µg/mL for Gefitinib. In conclusion, this study demonstrates the advantages of SPR and fluorescence dual-mode techniques in the analysis of cell-drug interactions, as well as their strong potential in drug screening.

Single-cell impedance cytometry of anticancer drug-treated tumor cells exhibiting mitotic arrest state to apoptosis using low-cost silver-PDMS microelectrodes.

Chemotherapeutic drugs such as paclitaxel and vinblastine interact with microtubules and thus induce complex cell states of mitosis arrest at the G2/M phase followed by apoptosis dependent on drug exposure time and concentration. Microfluidic impedance cytometry (MIC), as a label-free and high-throughput technology for single-cell analysis, has been applied for viability assay of cancer cells post drug exposure at fixed time and dosage, yet verification of this technique for varied tumor cell states after anticancer drug treatment remains a challenge. Here we present a novel MIC device and for the first time perform impedance cytometry on carcinoma cells exhibiting progressive states of G2/M arrest followed by apoptosis related to drug concentration and exposure time, after treatments with paclitaxel and vinblastine, respectively. Our results from impedance cytometry reveal increased amplitude and negative phase shift at low frequency as well as higher opacity for HeLa cells under G2/M mitotic arrest compared to untreated cells. The cells under apoptosis, on the other hand, exhibit opposite changes in these electrical parameters. Therefore, the impedance features differentiate the HeLa cells under progressive states post anticancer drug treatment. We also demonstrate that vinblastine poses a more potent drug effect than paclitaxel especially at low concentrations. Our device is fabricated using a unique sacrificial layer-free soft lithography process as compared to the existing MIC device, which gives rise to readily aligned parallel microelectrodes made of silver-PDMS embedded in PDMS channel sidewalls with one molding step. Our results uncover the potential of the MIC device, with a fairly simple and low-cost fabrication process, for cellular state screening in anticancer drug therapy.

Multi-parameter surface plasmon resonance instrument for multiple nucleic acid quantitative detection.

Multiplex nucleic acid assays can simultaneously detect the characteristics of different target nucleic acids in complex mixtures and are used in disease diagnosis, environmental monitoring, and food safety. However, traditional nucleic acid amplification assays have limitations such as complicated operation, long detection time, unstable fluorescent labeling, and mutual interference of multiplex nucleic acids. We developed a real-time, rapid, and label-free surface plasmon resonance (SPR) instrument for multiplex nucleic acid detection. The multiparametric optical system based on total internal reflection solves the multiplex detection problem by cooperating with linear light source, prism, photodetector, and mechanical transmission system. An adaptive threshold consistency correction algorithm is proposed to solve the problem of inconsistent responsiveness of different detection channels and the inability of quantitative comparison. The instrument achieves label-free and amplification-free rapid detection of these biomarkers for miRNA-21 and miRNA-141, which are widely expressed in breast cancer and prostate cancer. The multiplex nucleic acid detection takes 30 min and the biosensor has good repeatability and specificity. The instrument has a limit of detection (LODs) of 50 nM for target oligonucleotides, and the smallest absolute amount of sample that can be detected is about 4 pmol. It provides a simple and efficient point-of-care testing (POCT) detection platform for small molecules such as DNA and miRNA.

A Micro-Hotplate-Based Oven-Controlled System Used to Improve the Frequency Stability of MEMS Resonators.

This paper introduces a chip-level oven-controlled system for improving the temperature stability of MEMS resonators wherein we designed the resonator and the micro-hotplate using MEMS technology, then bounding them in a package shell at the chip level. The resonator is transduced by AlN film, and its temperature is monitored by temperature-sensing resistors on both sides. The designed micro-hotplate is placed at the bottom of the resonator chip as a heater and insulated by airgel. The PID pulse width modulation (PWM) circuit controls the heater according to the temperature detection result to provide a constant temperature for the resonator. The proposed oven-controlled MEMS resonator (OCMR) exhibits a frequency drift of 3.5 ppm. Compared with the previously reported similar methods, first, the OCMR structure using airgel combined with a micro-hotplate is proposed for the first time, and the working temperature is extended from 85 °C to 125 °C. Second, our work does not require redesign or additional constraints on the MEMS resonator, so the proposed structure is more general and can be practically applied to other MEMS devices that require temperature control.

Concepts and Key Technologies of Microelectromechanical Systems Resonators.

In this paper, the basic concepts of the equivalent model, vibration modes, and conduction mechanisms of MEMS resonators are described. By reviewing the existing representative results, the performance parameters and key technologies, such as quality factor, frequency accuracy, and temperature stability of MEMS resonators, are summarized. Finally, the development status, existing challenges and future trend of MEMS resonators are summarized. As a typical research field of vibration engineering, MEMS resonators have shown great potential to replace quartz resonators in timing, frequency, and resonant sensor applications. However, because of the limitations of practical applications, there are still many aspects of the MEMS resonators that could be improved. This paper aims to provide scientific and technical support for the improvement of MEMS resonators in timing, frequency, and resonant sensor applications.

An Ultrahigh Linear Sensitive Temperature Sensor Based on PANI:Graphene and PDMS Hybrid with Negative Temperature Compensation.

The detection of human body temperature is one of the important indicators to reflect the physical condition. In order to accurately judge the state of the human body, a high-performance temperature sensor with fast response, high sensitivity, and good linearity characteristics is urgently needed. In this paper, the positive temperature characteristics of graphene-polydimethylsiloxane (PDMS) composite with high sensitivity were studied. Besides, doping polyaniline (PANI) with special negative temperature characteristics as the temperature compensation of the composite finally creatively solved the problem of sensor nonlinearity from the material level. Thus, the PANI:graphene and PDMS hybrid temperature sensor with extraordinary linearity and high sensitivity is realized by establishing the space-gap model and mathematical theoretical analysis. The prepared sensor exhibits high sensitivity (1.60%/°C), linearity (R2 = 0.99), accuracy (0.3 °C), and time response (0.7 s) in the temperature sensing range of 25-40 °C. Based on this, the fabricated temperature sensor can combine with the read-out circuit and filter circuit with a high-precision analog digital converter (ADC) to monitor real-time skin temperature, ambient temperature, and respiratory rate, et al. This high-performance temperature sensor reveals its great potential in electronic skin, disease diagnosis, medical monitoring, and other fields.

Light-Controlled Reconfigurable Optical Synapse Based on Carbon Nanotubes/2D Perovskite Heterostructure for Image Recognition.

Two-dimensional (2D) halide perovskite material is characterized by a mixed conducting behavior that possesses both electronic and ionic conductivity. The study on the influence of the light on ion migration in the 2D perovskite is helpful to improve the performance of perovskite-based optoelectronic devices. Here, we constructed an exfoliated 2D perovskite/carbon nanotubes (CNTs) heterostructure optical synapse, in which CNTs can be used as nanoprobes to qualitatively observe the ion aggregation or dissipation process in 2D perovskite, and found that light significantly changes the memory curve of the reconfigurable optical synapses. Through the molecular dynamic simulation, the dynamic process of ion migration in the heterostructure was simulated and the electrostatic interaction effect of nonequilibrium charge distribution of CNTs on iodide ion was demonstrated. Finally, an effective light-controlled process was realized through the synapses, which in situ regulated the performance of the weight-value discretized BP (WD-BP) neural network. This work lays a foundation for the future development of intelligent nano-optoelectronic devices.

Integration of a multichannel surface plasmon resonance sensor chip and refractive index matching film array for protein detection in human urine.

Most prism-based surface plasmon resonance (SPR) experiments use matching fluid with a similar refractive index to mount the chip on the optical prism. The fluidity of the matching fluid easily affects the transmission of the optical signal. In this paper, an integrated SPR sensor chip comprises a three-layer structure of flow layer, metal layer and refractive index matching layer is demonstrated to address the problems related to consistency and uniformity. The Young's modulus, array spacing, shape and other parameters of the matching film were calculated and optimized. The chip can self-adhere to the optical prism, and effectively avoids the generation of air bubbles. The refractive index detection sensitivity of the integrated SPR sensor chip was 3.4359 × 10-6 RIU (refractive index unit), and the chip stabilization time has been effectively shortened. The integrated SPR sensor chip was also used to detect kappa light chain protein and human serum albumin (HSA) in urine samples. The detection limit of kappa light chain protein was 0.06 µg/mL compared with 18.5 µg/mL by conventional immunoturbidimetry. The integrated SPR sensor chip based on refractive index matching film array has great potential in biomedical detection and other fields, including point-of-care testing (POCT).

Real-Time Detection of LAMP Products of African Swine Fever Virus Using Fluorescence and Surface Plasmon Resonance Method.

African swine fever (ASF) is a swine disease with a very high fatality rate caused by a complex double-stranded DNA virus. The fluorescence PCR detection method is widely used for virus nucleic acid detection. Surface plasmon resonance (SPR) is a label-free and real-time detection method, unlike the fluorescence PCR detection method. In this research, we detected the loop-mediated isothermal amplification (LAMP) products of the African swine fever virus by using the SPR and fluorescence methods separately and simultaneously. By comparing the positive and negative control results, we found that the SPR response unit is completely different before and after the LAMP process. In addition, the fluorescence results on a chip showed that with an increase in the concentration of the sample, the cycle threshold (CT) value decreased, which is consistent with commercial instruments. Both the decline rate of the SPR response unit and the CT value of the fluorescence realized were used to distinguish the positive control from the negative control and water, which indicates that the SPR method can be combined with fluorescence to detect LAMP products. This research provides a label-free and simple method for detecting LAMP products.

Methods and platforms for analysis of nucleic acids from single-cell based on microfluidics.

Single-cell nucleic acid analysis aims at discovering the genetic differences between individual cells which is well known as the cellular heterogeneity. This technology facilitates cancer diagnosis, stem cell research, immune system analysis, and other life science applications. The conventional platforms for single-cell nucleic acid analysis more rely on manual operation or bulky devices. Recently, the emerging microfluidic technology has provided a perfect platform for single-cell nucleic acid analysis with the characteristic of accurate and automatic single-cell manipulation. In this review, we briefly summarized the procedure of single-cell nucleic acid analysis including single-cell isolation, single-cell lysis, nucleic acid amplification, and genetic analysis. And then, three representative microfluidic platforms for single-cell nucleic acid analysis are concluded as valve-, microwell-, and droplet-based platforms. Furthermore, we described the state-of-the-art integrated single-cell nucleic acid analysis systems based on the three platforms. Finally, the future development and challenges of microfluidics-based single-cell nucleic acid analysis are discussed as well.

MGRNN: Structure Generation of Molecules Based on Graph Recurrent Neural Networks.

Molecular structure generation is a critical problem for materials science and has attracted growing attention. The problem is challenging since it requires to generate chemically valid molecular structures. Inspired by the recent work in deep generative models, we propose a graph recurrent neural network model for drug molecular structure generation, briefly called MGRNN (Molecular Graph Recurrent Neural Networks). MGRNN combines the advantages of both iterative molecular generation algorithm and the efficiency of the training strategies. Moreover, MGRNN shows: (i) efficient computation for training; (ii) high model robustness for data; and (iii) an iterative sampling process, which allows to use chemical domain expertise for valency checking. Experimental results show that MGRNN is able to generate 69 % chemically valid molecules even without chemical knowledge and 100 % valid molecules with chemical rules.

Accelerating the Selection of Covalent Organic Frameworks with Automated Machine Learning.

Covalent organic frameworks (COFs) have the advantages of high thermal stability and large specific surface and have great application prospects in the fields of gas storage and catalysis. This article mainly focuses on COFs' working capacity of methane (CH4). Due to the vast number of possible COF structures, it is time-consuming to use traditional calculation methods to find suitable materials, so it is important to apply appropriate machine learning (ML) algorithms to build accurate prediction models. A major obstacle for the use of ML algorithms is that the performance of an algorithm may be affected by many design decisions. Finding appropriate algorithm and model parameters is quite a challenge for nonprofessionals. In this work, we use automated machine learning (AutoML) to analyze the working capacity of CH4 based on 403,959 COFs. We explore the relationship between 23 features such as the structure, chemical characteristics, atom types of COFs, and the working capacity. Then, the tree-based pipeline optimization tool (TPOT) in AutoML and the traditional ML methods including multiple linear regression, support vector machine, decision tree, and random forest that manually set model parameters are compared. It is found that the TPOT can not only save complex data preprocessing and model parameter tuning but also show higher performance than traditional ML models. Compared with traditional grand canonical Monte Carlo simulations, it can save a lot of time. AutoML has broken through the limitations of professionals so that researchers in nonprofessional fields can realize automatic parameter configuration for experiments to obtain highly accurate and easy-to-understand results, which is of great significance for material screening.

Rapid PCR powered by microfluidics: A quick review under the background of COVID-19 pandemic.

PCR has been widely used in different fields including molecular biology, pathogen detection, medical diagnosis, food detection and etc. However, the difficulty of promoting PCR in on-site point-of-care testing reflects on challenges relative to its speed, convenience, complexity, and even cost. With the emerging state-of-art of microfluidics, rapid PCR can be achieved with more flexible ways in micro-reactors. PCR plays a critical role in the detection of SARS-CoV-2. Under this special background of COVID-19 pandemic, this review focuses on the latest rapid microfluidic PCR. Rapid PCR is concluded in two main features, including the reactor (type, size, material) and the implementation of thermal cycling. Especially, the compromise between speed and sensitivity with microfluidic PCR is explored based on the system ratio of (thermal cycling time)/(reactor size). Representative applications about the detection of pathogens and SARS-CoV-2 viruses based on rapid PCR or other isothermal amplification are discussed as well.

Automatic medium exchange for micro-volume cell samples based on dielectrophoresis.

Cell medium exchange is a crucial step for life science and medicine. However, conventional cell medium exchange methods, including centrifuging and filtering, show limited ability for micro-volume cell samples such as circulating tumor cell (CTC) and circulating fetal cell (CFC). In this paper, we proposed an automatic medium exchange method for micro-volume cell samples based on dielectrophoresis (DEP) in microfluidic chip. Fresh medium and cell suspension were introduced into the microfluidic channel as the laminar flow. Plane stair-shaped interdigital electrodes were employed to drive the cells from the cell suspension to fresh media directly by DEP force. Additionally, we characterized and optimized the cell medium exchange according to both the theory and experiments. In the end, we achieved a 96.9% harvest rate of medium exchange for 0.3 µL samples containing micro-volume cells. For implementing an automatic continuous cell medium exchange, the proposed method can be integrated into the automatic cell processing system conveniently. Furthermore, the proposed method is a great candidate in micro-volume cell analysis and processing, cell electroporation, single cell sequencing, and other scenarios.

A one-step molded microfluidic chip featuring a two-layer silver-PDMS microelectrode for dielectrophoretic cell separation.

Dielectrophoresis (DEP) is a powerful technique for label-free cell separation in microfluidics. Easily-fabricated DEP separators with low cost and short turnaround time are in extremely high demand in practical applications, especially clinical usage where disposable devices are needed. DEP separators exploiting microelectrodes made of conducting polydimethylsiloxane (PDMS) composites enable the construction of advantageous 3D volumetric electrodes with a simple soft-lithography process. Yet, existing devices incorporating microelectrodes in conducting PDMS generally have their fluidic sidewalls constructed using a different material, and consequently require extra lithography of a sacrificial layer on the semi-finished master for molding the electrode and fluidic sidewalls in separate steps. Here we demonstrate a novel microfluidic DEP separator with a 3D electrode and fluidic structure entirely integrated within silver-PDMS composites. We develop a further simplified one-step molding process with lower cost using a readily-available and reusable SU8 master, eliminating the need for the additional lithography step in existing techniques. The uniquely designed two-layer electrode exhibits a spatially non-uniform electric field that enables cell migration in the vertical direction. The electrode upper layer then offers a harbor-like region for the trapping of the target cells that have drifted upwards, which shelters them from being dragged away by the main flow streams in the lower layer, and thus allows higher operation flow rate. We also optimize the upper layer thickness as a critical dimension for protecting the trapped cells from high drag and show easy widening of our device by elongation of the digits. We demonstrate that the elongated digits involving more parallel flow paths maintain a high capture efficiency of 95.4% for live cells with 85.6% purity in the separation of live/dead HeLa cells. We also investigate the device feasibility in a viability assay for cells post anti-cancer drug treatment.

Flexible Electrocorticography Electrode Array for Epileptiform Electrical Activity Recording under Glutamate and GABA Modulation on the Primary Somatosensory Cortex of Rats.

Epilepsy is a common neurological disorder. There is still a lack of methods to accurately detect cortical activity and locate lesions. In this work, a flexible electrocorticography (ECoG) electrode array based on polydimethylsiloxane (PDMS)-parylene was fabricated to detect epileptiform activity under glutamate (Glu) and gamma-aminobutyric acid (GABA) modulation on primary somatosensory cortex of rats. The electrode with a thickness of 20 µm has good flexibility to establish reliable contact with the cortex. Fourteen recording sites with a diameter of 60 µm are modified by electroplating platinum black nanoparticles, which effectively improve the performance with lower impedance, obtaining a sensitive sensing interface. The electrode enables real-time capturing changes in neural activity under drug modulation. Under Glu modulation, neuronal populations showed abnormal excitability, manifested as hypsarrhythmia rhythm and continuous or periodic spike wave epileptiform activity, with power increasing significantly. Under GABA modulation, the excitement was inhibited, with amplitude and power reduced to normal. The flexible ECoG electrode array could monitor cortical activity, providing us with an effective tool for further studying epilepsy and locating lesions.

An immunoassay cassette with a handheld reader for HIV urine testing in point-of-care diagnostics.

Currently, most HIV tests are performed with blood samples, or alternatively saliva samples are used for HIV testing. Simple HIV tests need to be performed in hospitals or other medical agencies instead of more invasive HIV blood tests. To enable point-of-care (POC) HIV diagnostics, based on a recently developed lateral flow strip for HIV urine testing, a microfluidic immunoassay cassette with a handheld optical reader is developed. Based on lateral flow strip with gold colloid reporter, the integrated immunoassay cassette can perform sample introduction, metering, discharging, applying and detection which simplifies HIV testing. An indicator is incorporated into the cassette to guide sample introduction based on color change, and further, the excess test sample is stored inside the sealed cassette to avoid any contamination. The low-cost handheld optical reader can provide a test result within a few seconds, which is useful for simple, sensitive and affordable HIV onsite detection. Instead of using normal white LEDs, a customized back light module embedded with green LEDs is adopted to illuminate the lateral flow strip with an appropriate working current to achieve optimal performance. Compared to the standard lateral flow strips using a benchtop reader, with the disposable immunoassay cassette assisted by the handheld optical reader, more convenient, easier-to-operate, and more affordable HIV urine testing can be achieved in POC diagnostics.

Development of a Portable SPR Sensor for Nucleic Acid Detection.

Nucleic acid detection is of great significance in clinical diagnosis, environmental monitoring and food safety. Compared with the traditional nucleic acid amplification detection method, surface plasmon resonance (SPR) sensing technology has the advantages of being label-free, having simple operation, and providing real-time detection. However, the angle scanning system in many SPR angle modulation detection applications usually requires a high-resolution stepper motor and complex mechanical structure to adjust the angle. In this paper, a portable multi-angle scanning SPR sensor was designed. The sensor only uses one stepping motor to rotate a belt, and the belt pulls the mechanical linkages of incident light and reflected light to move in opposite directions for achieving the SPR angle scanning mode that keeps the incident angle and reflected angle equal. The sensor has an angle scanning accuracy of 0.002°, response sensitivity of 3.72 × 10-6 RIU (refractive index unit), and an angle scanning range of 30°-74°. The overall size of the system is only 480 mm × 150 mm × 180 mm. The portable SPR sensor was used to detect nucleic acid hybridization on a gold film chip modified with bovine serum albumin (BSA). The result revealed that the sensor had high sensitivity and fast response, and could successfully accomplish the hybridization detection of target DNA solution of 0.01 µmol/mL.

Free convective PCR: From principle study to commercial applications-A critical review.

Polymerase chain reaction (PCR) is an extremely important tool for molecular diagnosis, as it can specifically amplify nucleic acid templates for sensitive detection. As another division of PCR, free convective PCR was invented in 2001, which can be performed in a capillary tube pseudo-isothermally within a significantly short time. Convective PCR thermal cycling is implemented by inducing thermal convection inside the capillary tube, which stratifies the reaction into spatially separate and stable melting, annealing, and extension zones created by the temperature gradient. Convective PCR is a promising tool that can be used for nucleic acid diagnosis as a point-of-care test (POCT) due to the significantly simplified heating strategy, reduced cost, and shortened detection time without sacrificing sensitivity and accuracy. Here, we review the history of free convective PCR from its invention to development and its commercial applications.

Flexible capacitive pressure sensor with sensitivity and linear measuring range enhanced based on porous composite of carbon conductive paste and polydimethylsiloxane.

In recent years, the development of electronic skin and smart wearable body sensors has put forward high requirements for flexible pressure sensors with high sensitivity and large linear measuring range. However, it turns out to be difficult to increase both of them simultaneously. In this paper, a flexible capacitive pressure sensor based on a porous carbon conductive paste-polydimethylsiloxane composite is reported, the sensitivity and the linear measuring range of which were developed using multiple methods including adjusting the stiffness of the dielectric layer material, fabricating a microstructure and increasing the dielectric permittivity of the dielectric layer. The capacitive pressure sensor reported here has a relatively high sensitivity of 1.1 kPa-1 and a large linear measuring range of 10 kPa, making the product of the sensitivity and linear measuring range 11, which is higher than that of the most reported capacitive pressure sensors to our best knowledge. The sensor has a detection of limit of 4 Pa, response time of 60 ms and great stability. Some potential applications of the sensor were demonstrated, such as arterial pulse wave measuring and breath measuring, which shows it as a promising candidate for wearable biomedical devices. In addition, a pressure sensor array based on the material was also fabricated and it could identify objects in the shape of different letters clearly, which shows promising application in future electronic skins.