In this work, surface renewable pH electrodes comprising RuO2–graphite–epoxy composites were developed. Three electrode types with different composite ratios were fabricated and their performance was investigated in detail by the potentiometric method. The experimental results show that the RuO2 based pH sensors exhibit sub-Nernstian responses of 40–50 mV pH−1 in the pH range 2–12 and the one with the highest amount of RuO2 shows the best performance. It is found that the properties of electrodes would change as they are aged in pH 7 buffer, and 10 days seem to be enough to get a stable result. The pH sensing mechanism is discussed on the basis of electrochemical impedance measurements. Finally, renewability of the pH electrodes is discussed and it is found that the electrodes exhibit stable pH sensitivity.

Here, we introduce an integrated biochip which offers accurate thermal control and sensitive electrochemical detection of DNA amplification in real-time. The biochip includes a 10-μl microchamber, a temperature sensor, a heater, and a contactless impedance biosensor. A pair of interdigitated electrodes is employed as the impedance biosensor and the products of the amplification are determined directly through tracing the impedance change, without using any labels, redox indicators, or probes. Real-time monitoring of strand-displacement amplification and rolling circle amplification was successfully performed on the biochip and a detection limit of 1 nM was achieved. Amplification starting at an initial concentration of 10 nM could be discriminated from that starting at 1 nM started concentration as well as from the negative control. Since an insulation layer covers the electrodes, the electrodes are spared from erosion, hydrolysis and bubble formation on the surface, thus, ensuring a long lifetime and a high reusability of the sensor. In comparison to bench-top apparatus, our chip shows good efficiency, sensitivity, accuracy, and versatility. Our system requires only simple equipments and simple skills, and can easily be miniaturized into a micro-scale system. The system will then be suitable for a handheld portable device, which can be applied in remote areas. It covers merits such as low cost, low-power consumption, rapid response, real-time monitoring, label-free detection, and high-throughput detection.Highlights► Integrated biochip for impedance detection of DNA amplification in real-time is reported. ► The chip includes temperature controlling electrodes and interdigitated EC electrodes. ► The biochip exhibits rapid detection efficiency and high sensitivity for SDA. ► The biochip is developed first to monitor RCA in real-time.

This paper reports the design and implementation of a contactless conductivity detection system which combines a thermal control cell, a data processing system and an electrochemical (EC) cell for label-free isothermal nucleic acid amplification and real-time monitoring. The EC cell consists of a microchamber and interdigitated electrodes as the contactless conductivity biosensor with a cover slip as insulation. In our work, contactless EC measurements, the effects of trehalose on amplification, and chip surface treatment are investigated. With the superior performance of the biosensor, the device can detect the amount of pure DNA at concentrations less than 0.1 pg μl−1. The EC cell, integrated with a heater and a temperature sensor, has successfully implemented nicking-based strand-displacement amplification at an initial concentration of 2.5 μM and the yields are monitored directly (dismissing the use of probes or labels) on-line. This contactless detector carries important advantages: high anti-interference capability, long detector life, high reusability and low cost. In addition, the small size, low power consumption and portability of the detection cell give the system the potential to be highly integrated for use in field service and point of care applications.

A highly sensitive protein detection method based on a novel enzyme-labeled gold nanoparticle (AuNP) probe has been developed. In this method, we firstly prepared the enzyme-labeled AuNP probe by coating AuNP with antibody, single-stranded DNA (ssDNA), and horseradish peroxidase (HRP). Magnetic microparticle (MMP) functionalized with another antibody was used as capture probe. Then, target protein was sandwiched by the enzyme-labeled AuNP probe and the capture probe through immunoreaction. The target immunoreaction event could be sensitively transduced via the enzymatically amplified optical signal. By using this strategy, carcinoembryonic antigen (CEA), as a model protein, was detected with high sensitivity and good specificity. The detection limit for this approach was 12 ng L−1, which was approximately 130-fold more sensitive than the conventional enzyme-linked immunosorbent assay (ELISA). The practical application of the proposed immunoassay was carried out for determination of CEA in serum samples. The demonstrated capability of the proposed method shows potentially applications for early diagnoses of diseases.

Endothelial cell monolayer (EM), acting as a barrier between blood and tissue, plays an important role in pathophysiological processes. Here we describe a novel microfluidic chip that is applied for convenient and high throughput in vitro permeability assays of EM. The chip included a gradient generator and an array of cell culture chambers. A microporous membrane as a scaffold component was built between a polydimethylsiloxane (PDMS) layer and a glass substrate to grow EM. Cell culture chambers were separated by microchannels and microvalves. The concentration gradient of compound solutions could be generated automatically and affected EM in different chambers. The permeability of EM at different time with histamine stimulation was in situ measured by the fluorescence detection of the leaked tracer. The existence of continuous flow in the channels allowed EM in a dynamic microenvironment and increased the amount of tracer through the EM, comparing to transwell assays. According to the prototype chip, the chip with a bigger array of cell culture chambers could be achieved easily and applied in the high throughput screening for drugs.

For a comprehensive understanding of cells or tissues, it is important to enable multiple studies under the controllable microenvironment of a chip. In this report, we present an integrated microfluidic cell culture platform in which endothelial cells (ECs) are under static conditions or exposed to a pulsatile and oscillatory shear stress. Through the integration of a microgap, self-contained flow loop, pneumatic pumps, and valves, the novel microfluidic chip achieved multiple functions: pulsatile and oscillatory fluid circulation, cell trapping, cell culture, the formation of ECs barrier, and adding shear stress on cells. After being introduced into the chip by gravity, the ECs arranged along the microgap with the help of hydrodynamic forces and grew in the microchannel for more than 7 days. The cells proliferated and migrated to form a barrier at the microgap to mimic the vessel wall, which separated the microenvironment into two compartments, microchannel and microchamber. An optimized pneumatic micropump was embedded to actuate flow circulation in a self-contained loop that induced a pulsatile and oscillatory shear stress at physiological levels on the ECs in the microchannel. All the analyses were performed under either static or dynamic conditions. The performance of the barrier was evaluated by the diffusion and distribution behaviors of fluorescently labeled albumin. The permeability of the barrier was comparable to that in traditional in vitro assays. The concentration gradients of the tracer formed in the microchamber can potentially be used to study cell polarization, migration and communications in the future. Additionally, the morphology and cytoskeleton of the ECs response to the pulsatile and oscillatory shear stress were analyzed. The microfluidic chip provided a multifunctional platform to enable comprehensive studies of blood vessels at the cell or tissue level.

The present paper described a rapid and ultrasensitive detection method using a microfluidic chip for analyzing 7-aminoclonazepam (7-ACZP) residues in human urine. A microfluidic chip-based immunoassay with laser-induced fluorescence (LIF) detection based on the water-soluble denatured bovine serum albumin (dBSA)-coated CdTe quantum dots (QDs) was prepared for the ultrasensitive detection of 7-ACZP. The whole procedure including the chip and the control software was designed and constructed in our own laboratory. The detection of 7-ACZP could be completed within 5 min. The results demonstrated that under the optima conditions, 7-ACZP residues could be detected with a precision of 5% relative standard deviation (RSD), and the linear range and the limit of detection (LOD) for 7-ACZP were 1.1–60.1 and 0.021 ng mL−1, respectively. This method was compared with ELISA and showed a good correlation. This microfluidic chip with LIF detection was applied to the determination of 7-ACZP residues in positive human urine samples, and the results were confirmed by high-performance liquid chromatography and tandem mass spectrometry (LC/MS/MS). This ultrasensitive detection technique was proved to be practical for clinical use.

Highly sensitive protein detection method based on nanoparticles and enzyme-linked immunosorbent assays (ELISAs), named Nano-ELISA, was introduced. In this method, the micro-magnetic beads were modified with monoclonal antibody of the target protein p53. Gold nanoparticles (AuNPs) were modified with another monoclonal detector antibody and Horseradish peroxidase (HRP, for signal amplification). The presence of target protein p53 causes the formation of the sandwich structures (magnetic beads–target protein–AuNP probes) through the interaction between the antibodies and the antigen p53. The HRP at the surface of AuNPs catalytically oxidize the substrate and generate optical signals that reflected the quantity of the target protein. Down to 5 pg mL−1 of protein was detected in less than 2 h with this method. The detection sensitivity of p53 classic ELISA kit is 0.125 ng mL−1. This method is as simple as ELISA and has higher sensitivity than ELISA, which can potentially be exploited in clinic. This method can be used to detect protein markers of tumors, nervous system or other diseases for early diagnostics.

In this work, a new laser-induced fluorescence (LIF) detection system based on a line laser beam for microfluidic chip electrophoresis analysis was developed. This detection system had the advantages of simple optical structure, compactness, and ease in constructing. Highly sensitive detection was realized by detecting the fluorescence light emitted in the micro-channel through the vertical intersection between the line laser source and micro-channel. The filtered line source was established by a bevel laser beam and a micro-gap which could facilitate the alignment of line laser beam with the microfluidic channel. Both the theoretical analysis and experimental study demonstrated that the detection system with a 0.07 mm-width micro-gap had enough sensitivity and adequate separation efficiency. By this system, a detection limit (S/N > 12) of 1.284 × 10−10 M fluorescein isothiocyanate was obtained, and the plate number could reach to 6100, which were comparable to those of optimized confocal or orthogonal LIF systems for microchip based capillary electrophoresis. The reproductibility of the detection system was evaluated by Sybr Green labeled DNA markers contained five fragments. Finally, the multi-PCR products including 165 bp, 266 bp, 378 bp and 881 bp fragments could be successfully achieved for baseline separation by this system within 4 min. The work undertaken can gear toward a semi-automated handheld system with substantial time and cost saving.

This paper reports on a microdispensing system for fast, stably and uniformly printing microarrays of DNA or protein on the nylon membrane for biological assay. This pneumatic actuation system is different from other common printing methods and adopts contact spotting technique instead of droplet injection. As a key component in the system, a microdispensing chip is successfully designed and fabricated by employing multilayer SU-8 spin-coating and photolithograph technologies, and the chip can simultaneously produce up to 25 individual fluid spots with the average diameters of 384 μm. A pressure of 10 kPa is optimal to dispense a 9:1 mixture of DMSO and percolated ink with the coefficient of variation (CV) of diameters as low as 2.6%, high stability and good reproducibility. A 3:7 mixture of DNA probe and DMSO can be perfectly printed on a 5 × 5 array by our microdispensing system as well as by a conventional computerized robotic system. Comparative study of two hybridized results has proved that our microdispenser is suitable and practical to produce moderate or low density microarray for biological assay.

The ability to culture individual neurons and direct their connections on functional interfaces provides a platform for investigating information processing in neuronal networks. Numerous methods have been used to design ordered neuronal networks on microelectrode arrays (MEAs) for neuronal electrical activities recording. However, so far, no method has been implemented, which simultaneously provides high-resolution neuronal patterns and low-impedance microelectrode. To achieve this goal, we employed a chemical vapor-deposited, non-fouling poly (ethylene) glycol (PEG) self-assembled monolayer to provide a cell repellant background on the MEAs. Photolithography, together with plasma etching of the PEG monolayer, was used to fabricate different patterns on MEAs. No electrode performance degradation was observed after the whole process. Dissociated cortical neurons were cultured on the modified MEAs, and the patterns were maintained for more than 3 weeks. Spontaneous and evoked neuronal activities were recorded. All of the results demonstrate this surface engineering strategy allows successful patterning of neurons on MEAs, and is useful for future studies of information processing in defined neuronal networks on a chip.Highlights► Biomolecule patterning was realized by photolithgraphing chemical vapor deposited 2-[methoxy(polyethylenoxy)propyl] trichlorosilane. ► A patterned neuronal network was maintained for more than 3 weeks. ► Recorded neuronal networks activities showed high signal to noise ratio.