Development and validation of an automated microfluidic perfusion platform for parallelized screening of compounds in vitro

Monoamine transporters are of great interest for their role in the physiological activity of the body and their link to mental and behavioural disorders. Currently, static well-plate assays or manual perfusion systems are used to characterize the interaction of psychostimulants, antidepressants and drugs of abuse with the transporters but still suffer from significant drawbacks caused by lack of automation, for example, low reproducibility, non-comparability of results. An automated microfluidic platform was developed to address the need for more standardized procedures for cell-based assays. An automated system was used to control and drive the simultaneous perfusion of 12 channels on a microfluidic chip, establishing a more standardized protocol to perform release assays to study monoamine transporter-mediated substrate efflux. D-Amphetamine, GBR12909 (norepinephrine transporter) and p-chloroamphetamine, paroxetine (serotonin transporter) were used as control compounds to validate the system. The platform was able to produce the expected releasing (D-Amphetamine, p-chloroamphetamine) or inhibiting (GBR12909, paroxetine) profiles for the two transporters. The reduction of manual operation and introduction of automated flow control enabled the implementation of stronger standardized protocols and the possibility of obtaining higher throughput by increasing parallelization.

APELLA: Open-Source, miniaturized All-in-One powered Lab-on-a-Disc platform

We present an unconventional approach to a common Lab-on-a-Disc (LoD) that combines a quadcopter propulsion system, a miniaturized 2.4 GHz Wi-Fi spy camera, 9.74 Watt Qi wireless power, and an Arduino into an open-source, miniaturized All-in-one powered lab-on-disc platform (APELLA). The quadcopter propulsion generates thrust to rotate (from 0.1 to 24.5 Hz) or shake the LoD device, while the spy camera enables a real-time (30 frames per second) and high definition (1280 × 720 pixels) visualization of microfluidic channels without requiring a bulky and heavy stroboscopic imaging setup. A mobile device can communicate with an Arduino microcontroller inside the APELLA through a Bluetooth interface for closed loop and sequential frequency control. In a proof-of-concept study, the APELLA achieved comparable mixing efficiency to a traditional spin stand and can capture rapid microfluidic events at low rotational frequencies (<5Hz). The APELLA is low-cost (c.a. 100 Euro), compact (15.6 × 15.6 × 10 cm³), lightweight (0.59 kg), portable (powered by a 5 V USB power bank), and energy efficient (uses < 6% power of the conventional system), making it ideal for field deployment, education, resource-limited labs.

Moving perfusion culture and live-cell imaging from lab to disc: proof of concept toxicity assay with AI-based image analysis

In vitro, cell-based assays are essential in diagnostics and drug development. There are ongoing efforts to establish new technologies that enable real-time detection of cell-drug interaction during culture under flow conditions. Our compact (10 × 10 × 8.5 cm) cell culture and microscope on disc (CMoD) platform aims to decrease the application barriers of existing lab-on-a-chip (LoC) approaches. For the first time in a centrifugal device, (i) cells were cultured for up to six days while a spindle motor facilitated culture medium perfusion, and (ii) an onboard microscope enabled live bright-field imaging of cells while the data wirelessly transmitted to a computer. The quantification of cells from the acquired images was done using artificial intelligence (AI) software. After optimization, the obtained cell viability data from the AI-based image analysis proved to correlate well with data collected from commonly used image analysis software. The CMoD was also suitable for conducting a proof-of-concept toxicity assay with HeLa cells under continuous flow. The half-maximal inhibitory time (IT50) for various concentrations of doxorubicin (DOX) in the case of HeLa cells in flow, was shown to be lower than the IT50 obtained from a static cytotoxicity assay, indicating a faster onset of cell death in flow. The CMoD proved to be easy to handle, enabled cell culture and monitoring without assistance, and is a promising tool for examining the dynamic processes of cells in real-time assays.

Monitoring cell endocytosis of liposomes by real-time electrical impedance spectroscopy

Evaluation and understanding the effect of drug delivery in in vitro systems is fundamental in drug discovery. We present an assay based on real-time electrical impedance spectroscopy (EIS) measurements that can be used to follow the internalisation and cytotoxic effect of a matrix metalloproteinase (MMP)-sensitive liposome formulation loaded with oxaliplatin (OxPt) on colorectal cancer cells. The EIS response identified two different cellular processes: (i) a negative peak in the cell index (CI) within the first 5 h, due to onset of liposome endocytosis, followed by (ii) a subsequent CI increase, due to the reattachment of cells until the onset of cytotoxicity with a decrease in CI. Free OxPt or OxPt-loaded Stealth liposomes did not show this two-stage EIS response; the latter can be due to the fact that Stealth cannot be cleaved by MMPs and thus is not taken up by the cells. Real-time bright-field imaging supported the EIS data, showing variations in cell adherence and cell morphology after exposure to the different liposome formulations. A drastic decrease in cell coverage as well as rounding up of cells during the first 5 h of exposure to OxPt-loaded (MMP)-sensitive liposome formulation is reflected by the first negative EIS response, which indicates the onset of liposome endocytosis. Graphical abstract.

Development of a paper-based microanalysis device doped with multi-walled carbon nanotubes for in vitro evaluation of fluorene cytotoxicity

Developing a cost-effective and simple micro-analysis tool has long been an important objective in the toxicological detection of fluorene. In this study, a disposable paper-based micro-analysis device (μ-PAD) was designed using graphite doped with multi-walled carbon nanotubes (MWCNTs) to hand draw the electrode (MWCNTs/μ-PAD). We investigated the feasibility of the designed MWCNTs/μ-PAD as a cell-sensing platform using voltammetry measurements. Its application for evaluating the cytotoxicity of fluorene was studied based on the electrochemical determination of human breast cancer cells induced by fluorene. The results showed a dose-dependent toxicity effect of fluorene on cellular activity. The measurements were comparable with those obtained using a methyl-thiazolyl-tetrazolium assay. The detection limit of the MWCNTs/μ-PAD for human breast cancer cells was as low as 4.00 × 10³ cells·mL^-1 owing to the enhanced catalytic activity of the MWCNTs. Notably, the MWCNTs/μ-PAD-which had a diameter of 7.00 mm-allowed a sampling volume of 10.0 μL, which is 50.0 times less than the sampling volume required with a conventional electrode (500 μL). Advantages such as the simplicity of manufacture, low consumption, low cost, rapid detection, and disposability, suggest that the MWCNTs/μ-PAD could provide new opportunities and directions for in vitro microanalysis.

Label-Free Bioelectrochemical Methods for Evaluation of Anticancer Drug Effects at a Molecular Level

Cancer is a multifactorial family of diseases that is still a leading cause of death worldwide. More than 100 different types of cancer affecting over 60 human organs are known. Chemotherapy plays a central role for treating cancer. The development of new anticancer drugs or new uses for existing drugs is an exciting and increasing research area. This is particularly important since drug resistance and side effects can limit the efficacy of the chemotherapy. Thus, there is a need for multiplexed, cost-effective, rapid, and novel screening methods that can help to elucidate the mechanism of the action of anticancer drugs and the identification of novel drug candidates. This review focuses on different label-free bioelectrochemical approaches, in particular, impedance-based methods, the solid supported membranes technique, and the DNA-based electrochemical sensor, that can be used to evaluate the effects of anticancer drugs on nucleic acids, membrane transporters, and living cells. Some relevant examples of anticancer drug interactions are presented which demonstrate the usefulness of such methods for the characterization of the mechanism of action of anticancer drugs that are targeted against various biomolecules.

Leaky Optoelectrical Fiber for Optogenetic Stimulation and Electrochemical Detection of Dopamine Exocytosis from Human Dopaminergic Neurons

In Parkinson's disease, the degeneration of dopaminergic neurons in substantia nigra leads to a decrease in the physiological levels of dopamine in striatum. The existing dopaminergic therapies effectively alleviate the symptoms, albeit they do not revert the disease progression and result in significant adverse effects. Transplanting dopaminergic neurons derived from stem cells could restore dopamine levels without additional motor complications. However, the transplanted cells disperse in vivo and it is not possible to stimulate them on demand to modulate dopamine release to prevent dyskinesia. In order to address these issues, this paper presents a multifunctional leaky optoelectrical fiber for potential neuromodulation and as a cell substrate for application in combined optogenetic stem cell therapy. Pyrolytic carbon coated optical fibers are laser ablated to pattern micro-optical windows to permit light leakage over a large area. The pyrolytic carbon acts as an excellent electrode for the electrochemical detection of dopamine. Human neural stem cells are genetically modified to express the light sensitive opsin channelrhodopsin-2 and are differentiated into dopaminergic neurons on the leaky optoelectrical fiber. Finally, light leaking from the micro-optical windows is used to stimulate the dopaminergic neurons resulting in the release of dopamine that is detected in real-time using chronoamperometry.

Extraction, Enrichment, and in situ Electrochemical Detection on Lab-on-a-Disc: Monitoring the Production of a Bacterial Secondary Metabolite

Development of microsystems, which enable "sample-to-answer" detection from real samples, is often challenging. We present the first integration of supported liquid membrane extraction combined with electrochemical detection on a centrifugal fluidic platform. The developed lab-on-a-disc (LoD) system enabled the separation, enrichment, and subsequent electrochemical detection of the target analyte from a complex sample mixture. As a case study, we quantified the amount of a dietary supplement and pharmaceutical precursor, p-coumaric acid, from bacterial growth media at different time points during production. The assay, extraction, and detection, performed on the LoD device, proved to be a low cost and environmentally friendly approach, requiring only a few tens of microliters of organic solvent and enabled detection in a 3 μL volume. In addition, the data obtained from the centrifugal platform showed a good correlation with data obtained from the high performance liquid chromatography analysis.

Monitoring intra- and extracellular redox capacity of intact barley aleurone layers responding to phytohormones

Redox regulation is important for numerous processes in plant cells including abiotic stress, pathogen defence, tissue development, seed germination and programmed cell death. However, there are few methods allowing redox homeostasis to be addressed in whole plant cells, providing insight into the intact in vivo environment. An electrochemical redox assay that applies the menadione-ferricyanide double mediator is used to assess changes in the intracellular and extracellular redox environment in living aleurone layers of barley (Hordeum vulgare cv. Himalaya) grains, which respond to the phytohormones gibberellic acid and abscisic acid. Gibberellic acid is shown to elicit a mobilisation of electrons as detected by an increase in the reducing capacity of the aleurone layers. By taking advantage of the membrane-permeable menadione/menadiol redox pair to probe the membrane-impermeable ferricyanide/ferrocyanide redox pair, the mobilisation of electrons was dissected into an intracellular and an extracellular, plasma membrane-associated component. The intracellular and extracellular increases in reducing capacity were both suppressed when the aleurone layers were incubated with abscisic acid. By probing redox levels in intact plant tissue, the method provides a complementary approach to assays of reactive oxygen species and redox-related enzyme activities in tissue extracts.

The role of micro-scale current sensing in biomedicine: A unifying view and design guidelines

The electrical activity of cells is regulated by ion fluxes and chemical signaling between them is sustained by redox-reactive molecules. Consequently, current sensing represents a straightforward way to interface electronics with biology and a common detection tool in several applications spanning from patch-clamp and nanopores to micro-scale impedance tracking. Reaching pA resolution at the ms timescale represents a challenge for the readout circuit and here all the criticalities involved in the optimal design of the sensing electrode are reviewed. Advantages vs. drawbacks and risks of the use of silicon as active vs. passive substrate respectively are illustrated by means of experimental examples.

Interdependence of initial cell density, drug concentration and exposure time revealed by real-time impedance spectroscopic cytotoxicity assay

We investigated the combined effect of the initial cell density (12,500, 35,000, 75,000, and 100,000 cells cm(-2)) and concentration of the anti-cancer drug doxorubicin on HeLa cells by performing time-dependent cytotoxicity assays using real-time electrochemical impedance spectroscopy. A correlation between the rate of cell death and the initial cell seeding density was found at 2.5 μM doxorubicin concentration, whereas this was not observed at 5 or 100 μM. By sensing the changes in the cell-substrate interaction using impedance spectroscopy under static conditions, the onset of cytotoxicity was observed 5 h earlier than when using a standard colorimetric end-point assay (MTS) which measures changes in the mitochondrial metabolism. Furthermore, with the MTS assay no cytotoxicity was observed after 15 h of incubation with 2.5 μM doxorubicin, whereas the impedance showed at this time point cell viability that was below 25%. These results indicate that impedance detection reveals cytotoxic events undetectable when using the MTS assay, highlighting the importance of combining impedance detection with traditional drug toxicity assays towards a more in depth understanding of the effect of anti-cancer drugs on in vitro assays. Moreover, the detection of doxorubicin induced toxicity determined with impedance under static conditions proved to be 6 times faster than in perfusion culture.

Impedimetric toxicity assay in microfluidics using free and liposome-encapsulated anticancer drugs

In this work, we have developed a microfluidic cytotoxicity assay for a cell culture and detection platform, which enables both fluid handling and electrochemical/optical detection. The cytotoxic effect of anticancer drugs doxorubicin (DOX), oxaliplatin (OX) as well as OX-loaded liposomes, developed for targeted drug delivery, was evaluated using real-time impedance monitoring. The time-dependent effect of DOX on HeLa cells was monitored and found to have a delayed onset of cytotoxicity in microfluidics compared with static culture conditions based on data obtained in our previous study. The result of a fluorescent microscopic annexin V/propidium iodide assay, performed in microfluidics, confirmed the outcome of the real-time impedance assay. In addition, the response of HeLa cells to OX-induced cytotoxicity proved to be slower than toxicity induced by DOX. A difference in the time-dependent cytotoxic response of fibrosarcoma cells (HT1080) to free OX and OX-loaded liposomes was observed and attributed to incomplete degradation of the liposomes, which results in lower drug availability. The matrix metalloproteinase (MMP)-dependent release of OX from OX-loaded liposomes was also confirmed using laryngopharynx carcinoma cells (FaDu). The comparison and the observed differences between the cytotoxic effects under microfluidic and static conditions highlight the importance of comparative studies as basis for implementation of microfluidic cytotoxic assays.

Integrating electrochemical detection with centrifugal microfluidics for real-time and fully automated sample testing

Here we present a robust, stable and low-noise experimental set-up for performing electrochemical detection on a centrifugal microfluidic platform.