Integrated Microdevice for Long-Term Automated Perfusion Culture without Shear Stress and Real-Time Electrochemical Monitoring of Cells

Microfluidic Gradient Culture Arrays for Cell Pro-oxidation Analysis Using Bipolar Electrochemiluminescence

A microfluidic gradient array is a widely used screening and analysis device, which has characteristics of high efficiency, high automation, and low consumption. Bipolar electrode electrochemiluminescence (BPE-ECL) has special value in microfluidic array chips. The combination of the microfluidic gradient and BPE arrays has potential for high-throughput screening. In this article, a microfluidic BPE array chip for gradient culture and conditional screening of cancer cells was designed. The generation of concentration gradients, continuous culture of cancer cells with high throughput, and drug screening through BPE-ECL of the Ru(bpy)₃²⁺/TPrA system can be performed in one chip. We tested gradient pro-oxidation of MCF-7 by ascorbic acid and the synergistic effect of pro-oxidation on doxorubicin. The method achieves high analysis efficiency through a BPE array while simplifying the tedious procedures required by cell culture methods.

On-chip MIC by Combining Concentration Gradient Generator and Flanged Chamber Arrays

Minimum inhibition concentration (MIC) of antibiotic is an effective value to ascertain the agent and minimum dosage of inhibiting bacterial growth. However, current techniques to determine MIC are labor intensive and time-consuming, and require skilled operator and high initial concentration of bacteria. To simplify the operation and reduce the time of inhibition test, we developed a microfluidic system, containing a concentration generator and sub-micro-liter chambers, for rapid bacterial growth and inhibition test. To improve the mixing effect, a micropillar array in honeycomb-structure channels is designed, so the steady concentration gradient of amoxicillin can be generated. The flanged chambers are used to culture bacteria under the condition of continuous flow and the medium of chambers is refreshed constantly, which could supply the sufficient nutrient for bacteria growth and take away the metabolite. Based on the microfluidic platform, the bacterial growth with antibiotic inhibition on chip can be quantitatively measured and MIC can be obtained within six hours using low initial concentration of bacteria. Overall, this microfluidic platform has the potential to provide rapidness and effectiveness to screen bacteria and determine MIC of corresponding antibiotics in clinical therapies.

Electrochemical measurement of quantal exocytosis using microchips

Carbon-fiber electrodes (CFEs) are the gold standard for quantifying the release of oxidizable neurotransmitters from single vesicles and single cells. Over the last 15 years, microfabricated devices have emerged as alternatives to CFEs that offer the possibility of higher throughput, subcellular spatial resolution of exocytosis, and integration with other techniques for probing exocytosis including microfluidic cell handling and solution exchange, optical imaging and stimulation, and electrophysiological recording and stimulation. Here we review progress in developing electrochemical electrode devices capable of resolving quantal exocytosis that are fabricated using photolithography.

Photochemical Synthesis of Shape-Controlled Nanostructured Gold on Zinc Oxide Nanorods as Photocatalytically Renewable Sensors

Biosensors always suffer from passivation that prevents their reutilization. To address this issue, photocatalytically renewable sensors composed of semiconductor photocatalysts and sensing materials have emerged recently. In this work, we developed a robust and versatile method to construct different kinds of renewable biosensors consisting of ZnO nanorods and nanostructured Au. Via a facile and efficient photochemical reduction, various nanostructured Au was obtained successfully on ZnO nanorods. As-prepared sensors concurrently possess excellent sensing capability and desirable photocatalytic cleaning performance. Experimental results demonstrate that dendritic Au/ZnO composite has the strongest surface-enhanced Raman scattering (SERS) enhancement, and dense Au nanoparticles (NPs)/ZnO composite has the highest electrochemical activity, which was successfully used for electrochemical detection of NO release from cells. Furthermore, both of the SERS and electrochemical sensors can be regenerated efficiently for renewable applications via photodegrading adsorbed probe molecules and biomolecules. Our strategy provides an efficient and versatile method to construct various kinds of highly sensitive renewable sensors and might expand the application of the photocatalytically renewable sensor in the biosensing area.

Vesicular exocytosis and microdevices - microelectrode arrays

Among all the analytical techniques capable of monitoring exocytosis in real time at the single cell level, electrochemistry (particularly amperometry at a constant potential) using ultramicroelectrodes has been demonstrated to be an important and convenient tool for more than two decades. Indeed, because the electrochemical sensor is located in the close vicinity of the emitting cell ("artificial synapse" configuration), much data can be gathered from the whole cell activity (secretion frequency) to the individual vesicular release (duration, fluxes or amount of molecules released) with an excellent sensitivity. However, such a single cell analysis and its intrinsic benefits are at the expense of the spatial resolution and/or the number of experiments. The quite recent development of microdevices/microsystems (and mainly the microelectrode arrays (MEAs)) offers in some way a complementary approach either by combining spectroscopy-microscopy or by implementing a multianalysis. Such developments are described and discussed in the present review over the 2005-2014 period.

A local redox cycling-based electrochemical chip device with nanocavities for multi-electrochemical evaluation of embryoid bodies

An electrochemical device, which consists of electrode arrays, nanocavities, and microwells, was developed for multi-electrochemical detection with high sensitivity. A local redox cycling-based electrochemical (LRC-EC) system was used for multi-electrochemical detection and signal amplification. The LRC-EC system consists of n(2) sensors with only 2n bonding pads for external connection. The nanocavities fabricated in the sensor microwells enable significant improvement of the signal amplification compared with the previous devices we have developed. The present device was successfully applied for evaluation of embryoid bodies (EBs) from embryonic stem (ES) cells via electrochemical measurements of alkaline phosphatase (ALP) activity in the EBs. In addition, the EBs were successfully trapped in the sensor microwells of the device using dielectrophoresis (DEP) manipulation, which led to high-throughput cell analysis. This device is considered to be useful for multi-electrochemical detection and imaging for bioassays including cell analysis.

Functionalized graphene-based biomimetic microsensor interfacing with living cells to sensitively monitor nitric oxide release

We present a biomimetic and reusable microsensor with sub-nanomolar sensitivity by elaboratly functionalizing graphene for monitoring NO release in real-time.

It is a great challenge to develop electrochemical sensors with superior sensitivity that concurrently possess high biocompatibility for monitoring at the single cell level. Herein we report a novel and reusable biomimetic micro-electrochemical sensor array with nitric oxide (NO) sensing-interface based on metalloporphyrin and 3-aminophenylboronic acid (APBA) co-functionalized reduced graphene oxide (rGO). The assembling of high specificity catalytic but semi-conductive metalloporphyrin with high electric conductive rGO confers the sensor with sub-nanomolar sensitivity. Further coupling with the small cell-adhesive molecule APBA obviously enhances the cytocompatibility of the microsensor without diminishing the sensitivity, while the reversible reactivity between APBA and cell membrane carbohydrates allows practical reusability. The microsensor was successfully used to sensitively monitor, in real-time, the release of NO molecules from human endothelial cells being cultured directly on the sensor. This demonstrates its potential application in the detection of NO with very low bioactive concentrations for the better understanding of its physiological function and for medical tracking of patient states.

Continuous flow micro-bioreactors for the production of biopharmaceuticals: the effect of geometry, surface texture, and flow rate

We used continuous flow micro-devices as bioreactors for the production of a glycosylated pharmaceutical product (a monoclonal antibody). We cultured CHO cells on the surface of PMMA/PDMS micro-channels that had been textured by micromachining and coated with fibronectin. Three different micro-channel geometries (a wavy channel, a zigzag channel, and a series of donut-shape reservoirs) were tested in a continuous flow regime in the range of 3 to 6 μL min(-1). Both the geometry of the micro-device and the flow rate had a significant effect on cell adhesion, cell proliferation, and monoclonal antibody production. The most efficient configuration was a series of donut-shaped reservoirs, which yielded mAb concentrations of 7.2 mg L(-1) at residence times lower than one minute and steady-state productivities above 9 mg mL(-1) min(-1). These rates are at about 3 orders of magnitude higher than those observed in suspended-cell stirred tank fed-batch bioreactors.

Optimal periodic perfusion strategy for robust long-term microfluidic cell culture

Long-term cell culture in microfluidic devices is an essential prerequisite for "on a chip" biological and physiological based studies. We investigated how medium delivery, from continuous to periodic perfusion, affects long-term cell cultures in a microfluidic platform. Computational simulations suggested that different delivery strategies result in different temporal profiles of accumulation and washing out of endogenous (EnF) and exogenous (ExF) factors, respectively. Thus, cultures exposed to the same overall amount of medium with different temporal profiles were analysed in terms of homogeneity, cell morphology and phenotype. Murine and human cell lines (C2C12 and HFF) and mouse embryonic stem cells (mESC) were cultured in microfluidic channels. An ad hoc experimental setup was developed to perform continuous and periodic medium delivery into the chip, tuning the flow rate, the perfusion time, and the interval of perfusion while using the same amount of medium volume. Periodic medium delivery with a short perfusion pulse ensured cell homogeneity compared to standard cell culture. Conversely, a continuous flow resulted in cell heterogeneity, with abnormal morphology and vesiculation. Only dramatic and unfeasible increasing of perfused medium volume in the continuous configuration could rescue normal cell behaviour. Consistent results were obtained for C2C12 and HFF. In order to extend these results to highly sensitive cells, mESC were cultured for 6 days in the microfluidic channels. Our analysis demonstrates that a periodic medium delivery with fast pulses (with a frequency of 4 times per day) resulted in a homogeneous cell culture in terms of cell viability, colony morphology and maintenance of pluripotency markers. According to experimental observations, the computational model provided a rational description of the perfusion strategies and of how they deeply shape the cell microenvironment in microfluidic cell cultures. These results provide new insight to define optimal strategies for homogeneous and robust long-term cell culture in microfluidic systems, an essential prerequisite for lab on chip cell-based applications.

Monolithically integrated biophotonic lab-on-a-chip for cell culture and simultaneous pH monitoring

A poly(dimethylsiloxane) biophotonic lab-on-a-chip (bioPhLoC) containing two chambers, an incubation chamber and a monitoring chamber for cell retention/proliferation and pH monitoring, respectively, is presented. The bioPhLoC monolithically integrates a filter with 3 μm high size-exclusion microchannels, capable of efficiently trapping cells in the incubation chamber, as well as optical elements for real-time interrogation of both chambers. The integrated optical elements made possible both absorption and dispersion measurements, which were comparable to those made in a commercially available cuvette. The size-exclusion filter also showed good and stable trapping capacity when using yeast cells of variable size (between 5 and 8 μm diameter). For cell culture applications, vascular smooth muscle cells (VSMC), with sizes between 8 and 10 μm diameter, were used as a mammalian cell model. These cells were efficiently trapped in the incubation chamber, where they proliferated with a classical spindle-shaped morphology and a traditional hill-and-valley phenotype. During cell proliferation, pH changes in the culture medium due to cell metabolism were monitored in real time and with high precision in the monitoring chamber without interference of the measurement by cells and other (cell) debris.

On-chip selective capture of cancer cells and ultrasensitive fluorescence detection of survivin mRNA in a single living cell

The rapid recognition of cancer cells and detection of tumor biomarker survivin mRNA plays a critical role in the early diagnosis of many cancers. Based on the integration of specific cancer cell capture and intracellular survivin mRNA detection, this work presents a novel and sensitive on-chip approach for the bioanalysis of survivin mRNA in a single living cell. The microchannel surface was firstly modified with a prostate stem cell antigen (PSCA) monoclonal antibody as the recognition element for prostate cancer cells (PC-3). As a result of the antigen-antibody specific affinity interactions, PC-3 cells could be selectively captured on the microchannel surface. After cell capture, nano-sized graphene oxide-poly(ethylene glycol) bis(amine) (NGO-PEG) was employed as a quencher and carrier of a signal tag, fluorescein isothiocyanate (FITC)-labeled antisense oligonucleotide (F-S1), which is complementary to part of survivin mRNA (target survivin mRNA), to transfect into the captured PC-3 cells. Upon the selective binding of S1 to intracellular survivin mRNA, F-S1 will be released from the NGO-PEG, inducing the fluorescence recovery of FITC. This antibody-based microfluidic device enables simple and inexpensive monitoring of the amount of survivin mRNA in single captured cell without the need for sample pretreatment. The survivin mRNA content in each PC-3 cell was estimated to be (4.8 ± 1.8) × 10(6) copies. This strategy opens a different perspective for ultrasensitive survivin mRNA detection, which may facilitate the early screening for malignancy.

A novel microfluidic platform with stable concentration gradient for on chip cell culture and screening assays

In this work a novel microfluidic platform for cell culture and assay is developed. On the chip a static cell culture region is coupled with dynamic fluidic nutrition supply structures. The cell culture unit has a sandwich structure with liquid channels on the top, the cell culture reservoir in the middle and gas channels on the bottom. Samples can be easily loaded into the reservoir and exchange constantly with the external liquid environment by diffusion. Since the flow direction is perpendicular to the liquid channel on the top of the reservoir, the cells in the reservoir are shielded from shear-force. By assembling the basic units into an array, a steady concentration gradient can be generated. Cell culture models both for continuous perfusion and one-off perfusion were established on the chip. Both adherent and suspended cells were successfully cultured on the chip in 2D and 3D culture modes. After culturing, the trapped cells were recovered for use in a later assay. As a competitive candidate for a standard cell culture and assay platform, this chip is also adaptable for cytotoxicity and cell growth assays.

A biopharmaceutical plant on a chip: continuous micro-devices for the production of monoclonal antibodies

We report a proof-of-principle for the use of micro-devices as continuous bioreactors for the production of monoclonal antibodies. We culture CHO cells on the surface of PMMA "zigzag" channels textured with semi-spherical cavities coated with fibronectin, observing steady-state productivities 100 times higher than those observed in full scale systems.

Vascular lumen simulation and highly-sensitive nitric oxide detection using three-dimensional gelatin chip coupled to TiC/C nanowire arrays microelectrode

Reproducing the physiological environment of blood vessels for the in vitro investigation of endothelial cell functions is very challenging. Here, we describe a vascular-like structure based on a three-dimensional (3D) gelatin chip with good compatibility and permeability which is also cost-effective and easy to produce. The controllable lumen diameter and wall thickness enable close mimicking of blood vessels in vitro. The 3D gelatin matrix between adjacent lumens is capable of generating soluble-factor gradients inside, and diffusion of molecules with different molecular weights through the matrix is studied. The cultured human umbilical vein endothelial cells proliferate on the gelatin lumen linings to form a vascular lumen. The hemodynamic behavior including adhesion, alignment of endothelial cells (ECs) under shear stress and pulsatile stretch is studied. Furthermore, a microelectrode comprising TiC/C nanowire arrays is fabricated to detect nitric oxide with sub-nM detection limits and NO generation from the cultured ECs is monitored in real time. This vascular model reproduces the surrounding parenchyma of endothelial cells and mimics the hemodynamics inside blood vessels very well, thereby enabling potential direct investigation of hemodynamics, angiogenesis, and tumor metastasis in vitro.