Cell-based electrochemical biosensors for water quality assessment

Incorporating yeast biosensors into paper-based analytical tools for pharmaceutical analysis

Paper-based devices serve to address many analytical questions both inside and outside of the laboratory setting. For the first time, yeast is used to construct a whole-cell, paper-based biosensor device. This biologically based paper analytical device (BioPAD) is sensitive to antibiotics in the tetracycline family, and it could potentially address questions of pharmaceutical quality as well as antibiotic contamination in liquids. Our BioPAD can qualitatively discriminate the presence/absence of doxycycline over a range of 30-10,000 μg/mL. In an analysis of a doxycycline dosage form (tablet) commonly used for malaria prophylaxis, BioPADs identified the presence of antibiotic with 92 and 95 % sensitivity, evaluated by eye and computer-assisted image analysis, respectively, with no false positives by either method. BioPADs were found to remain viable for at least 415 days when stored at 4 °C. This research demonstrates the utility of whole yeast cells in paper-based pharmaceutical testing, and it highlights the potential for the development of yeast-based BioPADs to address a range of qualitative analytical questions, especially in low resource settings.

Biotoxin detection using cell-based sensors

Cell-based biosensors (CBBs) utilize the principles of cell-based assays (CBAs) by employing living cells for detection of different analytes from environment, food, clinical, or other sources. For toxin detection, CBBs are emerging as unique alternatives to other analytical methods. The main advantage of using CBBs for probing biotoxins and toxic agents is that CBBs respond to the toxic exposures in the manner related to actual physiologic responses of the vulnerable subjects. The results obtained from CBBs are based on the toxin-cell interactions, and therefore, reveal functional information (such as mode of action, toxic potency, bioavailability, target tissue or organ, etc.) about the toxin. CBBs incorporate both prokaryotic (bacteria) and eukaryotic (yeast, invertebrate and vertebrate) cells. To create CBB devices, living cells are directly integrated onto the biosensor platform. The sensors report the cellular responses upon exposures to toxins and the resulting cellular signals are transduced by secondary transducers generating optical or electrical signals outputs followed by appropriate read-outs. Examples of the layout and operation of cellular biosensors for detection of selected biotoxins are summarized.

Development of Fieldable Lab-on-a-Chip Systems for Detection of a Broad Array of Targets From Toxicants to Biowarfare Agents

In today's world, there is an ever growing need for lightweight, portable sensor systems to detect chemical toxicants and biological toxins. The challenges encountered with such detection systems are numerous, as there are a myriad of potential targets in various sample matrices that are often present at trace-level concentrations. At ERDC-CERL, the Lab-on-a-Chip (LoaC) group is working with a number of academic and small business collaborators to develop solutions to meet these challenges. This report will focus on recent advances in three distinct areas: (1) the development of a flexible platform to allow fieldable LoaC analyses of water samples, (2) cell-, organelle-, and synthetic biology-based toxicity sensors, and (3) nanofluidic/microfluidic interface (NMI) sample enrichment devices. To transition LoaC-based sensors from the laboratory bench to the field, a portable hardware system capable of operating a wide variety of microfluidic chip-based assays has been developed. As a demonstration of the versatility of this approach assays for the separation and quantitation of anionic contaminants (i.e., perchlorate), quantitation of heavy metals (Pb and Cd), and cell-based toxicity sensors have been developed and demonstrated. Sensors harboring living cells provide a rapid means of assessing water toxicity. Cell-based sensors exploit the sensitivity of a living cell to discrete changes in its environment to report the presence of toxicants. However, this sensitivity of cells to environmental changes also hinders their usability in nonlaboratory settings. Therefore, isolating intact organelles (i.e., mitochondria) offers a nonliving alternative that preserves the sensitivity of the living cells and allows the electrochemical reporting of the presence of a contaminant. Pursuing a synthetic biology approach has also allowed the development of nonliving reporting mechanisms that utilize engineered biological pathways for novel sensing and remediation applications. To help overcome the challenges associated with the detection of target species at trace-level concentrations, NMIs are being developed for the enrichment of charged species in solution. NMI concentrators can be classified as either electroosmotic flow or electrophoresis-dominant devices. Further advances in electrophoresis-dominant concentrators will aid in the analysis of samples that contain proteins and other substances prone to surface adsorption. These recent advances illustrate how LoaC systems provide a suitable platform for development of fieldable sensors to detect a broad range of chemical/biological pollutants and threats.

A potentiometric flow biosensor based on ammonia-oxidizing bacteria for the detection of toxicity in water

A flow biosensor for the detection of toxicity in water using the ammonia-oxidizing bacterium (AOB) Nitrosomonas europaea as a bioreceptor and a polymeric membrane ammonium-selective electrode as a transducer is described. The system is based on the inhibition effects of toxicants on the activity of AOB, which can be evaluated by measuring the ammonium consumption rates with the ammonium-selective membrane electrode. The AOB cells are immobilized on polyethersulfone membranes packed in a holder, while the membrane electrode is placed downstream in the flow cell. Two specific inhibitors of the ammonia oxidation—allylthiourea and thioacetamide—have been tested. The IC₅₀ values defined as the concentration of an inhibitor causing a 50% reduction in the ammonia oxidation activity have been measured as 0.17 μM and 0.46 μM for allylthiourea and thioacetamide, respectively. The proposed sensor offers advantages of simplicity, speed and high sensitivity for measuring toxicity in water.

Microbial biosensors: engineered microorganisms as the sensing machinery

Whole-cell biosensors are a good alternative to enzyme-based biosensors since they offer the benefits of low cost and improved stability. In recent years, live cells have been employed as biosensors for a wide range of targets. In this review, we will focus on the use of microorganisms that are genetically modified with the desirable outputs in order to improve the biosensor performance. Different methodologies based on genetic/protein engineering and synthetic biology to construct microorganisms with the required signal outputs, sensitivity, and selectivity will be discussed.

Impedimetric microbial sensor for real-time monitoring of phage infection of Escherichia coli

We describe an impedimetric microbial sensor for real-time monitoring of the non-lytic M13 bacteriophage infection of Escherichia coli cells using a gold electrode covalently grafted with a monolayer of lipopolysaccharide specific antibody. After infection, damage to the lipopolysaccharide layer on the outer membrane of E. coli causes changes to its surface charge and morphology, resulting in the aggregation of redox probe, Fe(CN)6(3-/4-) at the electrode surface and thereby increases its electron-transfer rate. This consequent decrease of electron-transfer resistance in the presence of bacteriophage can be easily monitored using Faradaic impedance spectroscopy. Non-lytic bacterium-phage interaction which is hardly observable using conventional microscopic methods is detected within 3h using this impedimetric microbial sensor which demonstrates its excellent performance in terms of analysis time, ease and reduced reliance on labeling steps during in-situ monitoring of the phage infection process.

An integrative method for the evaluation, monitoring, and comparison of seagrass habitat structure

Assessing environmental condition is essential for the management of coasts and their resources, but better management decisions occur when large databases are simplified into more manageable units of information. Here we present the habitat structure index (HSI), which enables rapid assessment and direct comparison of seagrass habitat structure using scores of 0 (poor) to 100 (excellent) based on integrating five habitat variables: area, continuity, proximity, percentage cover, and species identity. Acquiring data to calculate the HSI can be done in situ or from video recordings, and requires relatively simple methodology of belt transects, estimating percentage cover, and basic taxonomy. Spatiotemporal comparisons can usefully identify locations and periods of seagrass habitat change, potentially providing an early warning indicator of habitat damage and decline in environmental quality. Overall, the integrative approach of the HSI represents a step toward simplifying the exchange of environmental information among researchers, coastal managers, and governing bodies.

Orthogonal cell-based biosensing: fluorescent, electrochemical, and colorimetric detection with silica-immobilized cellular communities integrated with an ITO-glass/plastic laminate cartridge

This is the first report of a living cell-based environmental sensing device capable of generating orthogonal fluorescent, electrochemical, and colorimetric signals in response to a single target analyte in complex media. Orthogonality is enabled by use of cellular communities that are engineered to provide distinct signals in response to the model analyte. Coupling these three signal transduction methods provides additional and/or complementary data regarding the sample which may reduce the impact of interferants and increase confidence in the sensor's output. Long-term stability of the cells was addressed via 3D entrapment within a nanostructured matrix derived from glycerated silicate, which allows the device to be sealed and stored under dry, ambient conditions for months with significant retention in cellular activity and viability (40% viability after 60 days). Furthermore, the first co-entrapment of eukaryotic and bacterial cells in a silica matrix is reported, demonstrating multianalyte biodetection by mixing disparate cell lines at intimate proximities which remain viable and responsive. These advances in cell-based biosensing open intriguing opportunities for integrating living cells with nanomaterials and macroscale systems.

Cell-based sensor system using L6 cells for broad band continuous pollutant monitoring in aquatic environments

Pollution of drinking water sources represents a continuously emerging problem in global environmental protection. Novel techniques for real-time monitoring of water quality, capable of the detection of unanticipated toxic and bioactive substances, are urgently needed. In this study, the applicability of a cell-based sensor system using selected eukaryotic cell lines for the detection of aquatic pollutants is shown. Readout parameters of the cells were the acidification (metabolism), oxygen consumption (respiration) and impedance (morphology) of the cells. A variety of potential cytotoxic classes of substances (heavy metals, pharmaceuticals, neurotoxins, waste water) was tested with monolayers of L6 cells (rat myoblasts). The cytotoxicity or cellular effects induced by inorganic ions (Ni²⁺ and Cu²⁺) can be detected with the metabolic parameters acidification and respiration down to 0.5 mg/L, whereas the detection limit for other substances like nicotine and acetaminophen are rather high, in the range of 0.1 mg/L and 100 mg/L. In a close to application model a real waste water sample shows detectable signals, indicating the existence of cytotoxic substances. The results support the paradigm change from single substance detection to the monitoring of overall toxicity.