Continuous differential impedance spectroscopy of single cells

Antimicrobial susceptibility testing in 90 min by bacterial cell count monitoring

The rise in antimicrobial resistance has become a serious global health problem. Restrictive use of antibiotics seems the only option to temper this accession since research in new antibiotics has halted. Antimicrobial stewardship programmes rely on quick access to susceptibility data. This study evaluated the concept of bacterial cell count monitoring as a fast method to determine susceptibility. Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus strains were tested for amoxicillin/piperacillin and gentamicin by three conventional methods (VITEK2®, Etest® and broth-macrodilution). Bacterial cell count monitoring reliably predicted susceptibility after 90 min for Escherichia coli and after 120 min for Pseudomonas aeruginosa and Staphylococcus aureus without any minor, major or very major discrepancies. Time-to-result was reduced by 74%, 83% and 76%, respectively. Bacterial cell count monitoring shows great potential for rapid susceptibility testing.

Integration of a pump and an electrical sensor into a membrane-based PDMS microbioreactor for cell culture and drug testing

To the extent possible, artificial organs should have characteristics that match those of the in vivo system. To this end, microfabrication techniques allow us to create microenvironments that can help maintain cell organization and functionality in in vitro cultures. We present three new microbioreactors, each of which allows cells to be cultured in a perfused microenvironment similar to that found in vivo. Our microbioreactors use new technology that permits integration onto the chip (35 mm × 20 mm) of an electrical sensor, in addition to one or more pumping systems and associated perfusion circuitry. The monitoring of Caco-2 cell cultures using electrical impedance spectroscopy (EIS) has allowed us to measure the effects of cell growth, cellular barrier formation and the presence of chemical compounds and/or toxins. Specifically, we have investigated the ability of the electrical sensor to maintain appropriate sensitivity and precision. Our results show that the sensor was very sensitive not only to the presence or the absence of the cells, but also to changes in cell state. Our perfused microbioreactors are highly efficient miniaturized tools that are easy to operate. We anticipate that they will offer promising new opportunities in many types of cell culture research, including drug screening and tissue engineering.

Towards the realization of label-free biosensors through impedance spectroscopy integrated with IDES technology

Impedance spectroscopy (IS) is a powerful technique for analysis of the complex electrical impedance of a large variety of biological systems, because it is sensitive both to surface phenomena and to changes of bulk properties. A simple and convenient method of analysis of cell properties by IS is described. An interdigitated electrodes configuration was used for the measurements; human epithelial cells were grown on the device to investigate the complex dielectric response as a function of frequency, in order to test the suitability of the device for use as a label-free biosensor. To test the ability of the device to detect channels in the cell membrane, the effect of drugs known to affect membrane integrity was also investigated. The frequency response of the admittance (i.e. the reciprocal of the impedance) can be well fitted by a model based on very simple assumptions about the cells coating the device surface and the current flow; from the calculations, membrane-specific capacitance and information about cell adhesion can be inferred. These preliminary efforts have shown that our configuration could lead to a label-free non-invasive technique for biosensing and cellular behavior monitoring which might prove useful in investigation of the basic properties of cells and the effect of drugs by estimation of some fundamental properties and modification of the electrical characteristics of the device.

System-level biochip for impedance sensing and programmable manipulation of bladder cancer cells

This paper develops a dielectrophoretic (DEP) chip with multi-layer electrodes and a micro-cavity array for programmable manipulations of cells and impedance measurement. The DEP chip consists of an ITO top electrode, flow chamber, middle electrode on an SU-8 surface, micro-cavity arrays of SU-8 and distributed electrodes at the bottom of the micro-cavity. Impedance sensing of single cells could be performed as follows: firstly, cells were trapped in a micro-cavity array by negative DEP force provided by top and middle electrodes; then, the impedance measurement for discrimination of different stage of bladder cancer cells was accomplished by the middle and bottom electrodes. After impedance sensing, the individual releasing of trapped cells was achieved by negative DEP force using the top and bottom electrodes in order to collect the identified cells once more. Both cell manipulations and impedance measurement had been integrated within a system controlled by a PC-based LabVIEW program. In the experiments, two different stages of bladder cancer cell lines (grade III: T24 and grade II: TSGH8301) were utilized for the demonstration of programmable manipulation and impedance sensing; as the results show, the lower-grade bladder cancer cells (TSGH8301) possess higher impedance than the higher-grade ones (T24). In general, the multi-step manipulations of cells can be easily programmed by controlling the electrical signal in our design, which provides an excellent platform technology for lab-on-a-chip (LOC) or a micro-total-analysis-system (Micro TAS).

Engineered approaches to the stem cell microenvironment for cardiac tissue regeneration

Micro- and nanoscale engineering approaches in medicine have the potential to recreate physiologically relevant stem cell microenvironments to enhance our understanding of stem cell behaviour and bring stem cell therapy closer to fruition. The realization of such advancements will impact a number of therapeutic applications, the most immediate of which may be the repair of heart tissue. Despite profound advances in creating physiologically relevant in vivo stem cell niches through the control of biochemical regulatory factors, further synergism of innovative techniques promise to elucidate the impact of a number of physical cues such as stem cell differentiation into cardiac cells, the electromechanical coupling among these cells, and the formation of bioengineered cardiac tissue grafts. This review examines the recent physiologically relevant micro- and nanoengineering efforts that have been made to address these factors. In Sections II and III, we introduce the traditional focuses of stem cell derived cardiac tissue: differentiation directed by transcription factors and structural cues within the stem cell niche. However, the majority of this review, Sections IV-VII, endeavours to highlight innovative and unconventional microscale engineering techniques that have employed topographic, biomaterial, microfluidic, mechanical, electrical, and optical stimulation for stem cell based cardiac tissue engineering.

Classification of cell types using a microfluidic device for mechanical and electrical measurement on single cells

This paper presents a microfluidic system for cell type classification using mechanical and electrical measurements on single cells. Cells are aspirated continuously through a constriction channel with cell elongations and impedance profiles measured simultaneously. The cell transit time through the constriction channel and the impedance amplitude ratio are quantified as cell's mechanical and electrical property indicators. The microfluidic device and measurement system were used to characterize osteoblasts (n=206) and osteocytes (n=217), revealing that osteoblasts, compared with osteocytes, have a larger cell elongation length (64.51 ± 14.98 μm vs. 39.78 ± 7.16 μm), a longer transit time (1.84 ± 1.48 s vs. 0.94 ± 1.07 s), and a higher impedance amplitude ratio (1.198 ± 0.071 vs. 1.099 ± 0.038). Pattern recognition using the neural network was applied to cell type classification, resulting in classification success rates of 69.8% (transit time alone), 85.3% (impedance amplitude ratio alone), and 93.7% (both transit time and impedance amplitude ratio as input to neural network) for osteoblasts and osteocytes. The system was also applied to test EMT6 (n=747) and EMT6/AR1.0 cells (n=770, EMT6 treated by doxorubicin) that have a comparable size distribution (cell elongation length: 51.47 ± 11.33 μm vs. 50.09 ± 9.70 μm). The effects of cell size on transit time and impedance amplitude ratio were investigated. Cell classification success rates were 51.3% (cell elongation alone), 57.5% (transit time alone), 59.6% (impedance amplitude ratio alone), and 70.2% (both transit time and impedance amplitude ratio). These preliminary results suggest that biomechanical and bioelectrical parameters, when used in combination, could provide a higher cell classification success rate than using electrical or mechanical parameter alone.

A new floating electrode structure for generating homogeneous electrical fields in microfluidic channels

In this article a new parallel electrode structure in a microfluidic channel is described that makes use of a floating electrode to get a homogeneous electrical field. Compared to existing parallel electrode structures, the new structure has an easier production process and there is no need for an electrical connection to both sides of the microfluidic chip. With the new chip design, polystyrene beads suspended in background electrolyte have been detected using electrical impedance measurements. The results of electrical impedance changes caused by beads passing the electrodes are compared with results in a similar planar electrode configuration. It is shown that in the new configuration the coefficient of variation of the impedance changes is lower compared to the planar configuration (0.39 versus 0.56) and less dependent on the position of the beads passage in the channel as a result of the homogeneous electrical field. To our knowledge this is the first time that a floating electrode is used for the realization of a parallel electrode structure. The proposed production method for parallel electrodes in microfluidic channels can easily be applied to other applications.

A microfluidic device for simultaneous electrical and mechanical measurements on single cells

This paper presents a microfluidic device for simultaneous mechanical and electrical characterization of single cells. The device performs two types of cellular characterization (impedance spectroscopy and micropipette aspiration) on a single chip to enable cell electrical and mechanical characterization. To investigate the performance of the device design, electrical and mechanical properties of MC-3T3 osteoblast cells were measured. Based on electrical models, membrane capacitance of MC-3T3 cells was determined to be 3.39±1.23 and 2.99±0.82 pF at the aspiration pressure of 50 and 100 Pa, respectively. Cytoplasm resistance values were 110.1±37.7 kΩ (50 Pa) and 145.2±44.3 kΩ (100 Pa). Aspiration length of cells was found to be 0.813±0.351 μm at 50 Pa and 1.771±0.623 μm at 100 Pa. Quantified Young's modulus values were 377±189 Pa at 50 Pa and 344±156 Pa at 100 Pa. Experimental results demonstrate the device's capability for characterizing both electrical and mechanical properties of single cells.