Semiautomated Production of Cell-Free Biosensors

Cell-free synthetic biology biosensors have potential as effective in vitro diagnostic technologies for the detection of chemical compounds, such as toxins and human health biomarkers. They have several advantages over conventional laboratory-based diagnostic approaches, including the ability to be assembled, freeze-dried, distributed, and then used at the point of need. This makes them an attractive platform for cheap and rapid chemical detection across the globe. Though promising, a major challenge is scaling up biosensor manufacturing to meet the needs of their multiple uses. Currently, cell-free biosensor assembly during lab-scale development is mostly performed manually by the operator, leading to quality control and performance variability issues. Here we explore the use of liquid-handling robotics to manufacture cell-free biosensor reactions. We compare both manual and semiautomated reaction assembly approaches using the Opentrons OT-2 liquid handling platform on two different cell-free gene expression assay systems that constitutively produce colorimetric (LacZ) or fluorescent (GFP) signals. We test the designed protocol by constructing an entire 384-well plate of fluoride-sensing cell-free biosensors and demonstrate that they perform close to expected detection outcomes.

Fast and bioluminescent detection of antibiotic contaminants by on-demand transcription of RNA scaffold arrays

Cell-free biosensors have inspired low-cost and field-applicable methods to detect antibiotic contaminants. However, the satisfactory sensitivity of current cell-free biosensors is mostly achieved by sacrificing the rapidity, which prolongs turnaround time by hours. Additionally, the software-based result interpretation provides an obstacle for delivering these biosensors to untrained individuals. Here, we present a bioluminescence-based cell-free biosensor, termed enhanced Bioluminescence sensing of Ligand-Unleashed RNA Expression (eBLUE). The eBLUE leveraged antibiotic-responsive transcription factors to regulate the transcription of RNA arrays that can serve as scaffolds for reassembling and activating multiple luciferase fragments. This process converted target recognition into an amplified bioluminescence response, enabling smartphone-based quantification of tetracycline and erythromycin directly in milk within 15 min. Moreover, the detection threshold of eBLUE can be easily tuned according to the maximum residue limits (MRLs) established by government agencies. Owing to this tunable nature, the eBLUE was further repurposed as an on-demand semi-quantification platform, allowing for fast (∼20 min) and software-free identification of safe and MRL-exceeding milk samples only by glancing over the smartphone photographs. Overall, the sensitivity, rapidity and user-friendliness of eBLUE demonstrate its potentials for practical applications, especially in resource-limited and household settings.

A cell-free fluorescence biosensor based on allosteric transcription factor NalC for detection of pentachlorophenol

Pentachlorophenol (PCP) was once used as a pesticide, germicide, and preservative due to its stable properties and resistance to degradation. This study aimed to design a biosensor for the quantitative and prompt detection of capable of PCP. A cell-free fluorescence biosensor was developed while employing NalC, an allosteric Transcription Factor responsive to PCP and In Vitro Transcription. By adding a DNA template and PCP and employing Electrophoretic Mobility Shift Assay while monitoring the dynamic fluorescence changes in RNA, this study offers evidence of NalC's potential applicability in sensor systems developed for the specific detection of PCP. The biosensor showed the capability for the quantitative detection of PCP, with a Limit of Detection (LOD) of 0.21 μM. Following the addition of Nucleic Acid Sequence-Based Amplification, the fluorescence intensity of RNA revealed an excellent linear relationship with the concentration of PCP, showing a correlation coefficient (R2) of 0.9595. The final LOD was determined to be 0.002 μM. This study has successfully translated the determination of PCP into a fluorescent RNA output, thereby presenting a novel approach for detecting PCP within environmental settings.

Cell-free arsenic biosensors with applied nanomaterials: critical analysis

Arsenic is a ubiquitously found metalloid in our ecosystem because of natural and anthropogenic activities. People exposed to a higher level of arsenic become susceptible to several disorders, including cancer. According to current statistics, the population chronically exposed to arsenic has surpassed 200 million. Therefore, its detection in our environment is of great importance. There are many analytical techniques for the assessment of arsenic in different kinds of environmental samples. Among these techniques, the biosensor is considered a convenient platform and a widely applied analytical device for rapid qualitative and quantitative analysis in the field of environmental monitoring, food safety, and disease diagnosis. Today, there is a trend of including nanomaterials in sensors and biosensors because it empowers researchers to explore new arsenic detection methods and to enhance their analytical capabilities. In this review article, we summarized the latest developments in arsenic biosensors in particular with emphasis on the works based on cell-free approaches that are protein/enzyme-based, DNA-based, and aptamer-based utilizing various transduction platforms. In the meantime, we compared the capabilities that were related to these cell-free arsenic biosensors. This review article also highlights the development and application of novel nanomaterials for arsenic detection.