Label-free independent quantitation of viable and non-viable cells using a multivariable multi-resonant sensor

Electrochemical assay of mammalian cell viability

We present the first use of amperometric detection to assess the viability of mammalian cells in continuous mode, directly in the cell culture medium. Vero or HeLa cells were injected into electrochemical sensors equipped with a 3-electrode system and containing DCIP 50 µM used as the redox mediator. DCIP was reduced by the viable cells and the reduced form was detected amperometrically at 300 mV vs silver pseudo-reference. The continuous regeneration of the oxidized form of the mediator ensured a stable redox state of the cell environment, allowing the cells to survive during the measurement time. The electrochemical response was related to cell metabolism (no response with dead cells or lysed cells) and depended on both mediator concentration and cell density. The protocol was applied to both cells in suspension and adhered cells. It was also adapted to detect trans-plasma membrane electron transfer (tPMET) by replacing DCIP by ferricyanide 500 µM and using linear scan voltammetry (2 mV/s). The pioneering results described here pave the way to the development of routine electrochemical assays for cell viability and for designing a cell-based analytical platform.

Contact-Free, Passive, Electromagnetic Resonant Sensors for Enclosed Biomedical Applications: A Perspective on Opportunities and Challenges

Inexpensive and accurate tools for monitoring conditions in enclosed environments (through garments, bandages, tissue, etc.) have been a long-standing goal of medicine. Passive resonant sensors are a promising solution for such wearable health sensors as well as off-body diagnostics. They are simple circuits with inherent inductance and capacitance (LC tank) that have a measurable resonant frequency. Changes in local parameters, e.g., permittivity or geometry, effect inductance and capacitance which cause a resonant frequency shift response. This signal transduction has been applied to several biomedical applications such as intracranial pressure, hemodynamics, epidermal hydration, etc. Despite these many promising applications presented in the literature, resonant sensors still do not see widespread adoption in biomedical applications, especially as wearable or embedded sensing devices. This perspective highlights some of the current challenges facing LC resonant sensors in biomedical applications, such as positional sensitivity, and potential strategies that have been developed to overcome them. An outlook on adoption in medicine and health monitoring is presented, and a perspective is given on next steps for research in this field.

Digital electrical impedance analysis for single bacterium sensing and antimicrobial susceptibility testing

Single-molecule and single-cell analysis techniques have opened new opportunities for characterizing and analyzing heterogeneity within biological samples. These detection methods are often referred to as digital assays because the biological sample is partitioned into many small compartments and each compartment contains a discrete number of targets (e.g. cells). Using digital assays, researchers can precisely detect and quantify individual targets, and this capability has made digital techniques the basis for many modern bioanalytical tools (including digital PCR, single cell RNA sequencing, and digital ELISA). However, digital assays are dominated by optical analysis systems that typically utilize microscopy to analyze partitioned samples. The utility of digital assays may be dramatically enhanced by implementing cost-efficient and portable electrical detection capabilities. Herein, we describe a digital electrical impedance sensing platform that enables direct multiplexed measurement of single cell bacterial cells. We outline our solutions to the challenge of multiplexing impedance sensing across many culture compartments and demonstrate the potential for rapidly differentiating antimicrobial resistant versus susceptible strains of bacteria.