A Sensitive Magnetic Arsenite-Specific Biosensor Hosted in Magnetotactic Bacteria

ABSTRACT According to the World Health Organization, arsenic is the water contaminant that affects the largest number of people worldwide. To limit its impact on the population, inexpensive, quick, and easy-to-use systems of detection are required. One promising solution could be the use of whole-cell biosensors, which have been extensively studied and could meet all these criteria even though they often lack sensitivity. Here, we investigated the benefit of using magnetotactic bacteria as cellular chassis to design and build sensitive magnetic bacterial biosensors. Promoters potentially inducible by arsenic were first identified in silico within the genomes of two magnetotactic bacteria strains, Magnetospirillum magneticum AMB-1 and Magnetospirillum gryphiswaldense MSR-1. The ArsR-dependent regulation was confirmed by reverse transcription-PCR experiments. Biosensors built by transcriptional fusion between the arsenic-inducible promoters and the bacterial luciferase luxCDABE operon gave an element-specific response in 30 min with an arsenite detection limit of 0.5 μM. After magnetic concentration, we improved the sensitivity of the biosensor by a factor of 50 to reach 10 nM, more than 1 order of magnitude below the recommended guidelines for arsenic in drinking water (0.13 μM). Finally, we demonstrated the successful preservation of the magnetic bacterium biosensors by freeze-drying. IMPORTANCE Whole-cell biosensors based on reporter genes can be designed for heavy metal detection but often require the optimization of their sensitivity and specific adaptations for practical use in the field. Magnetotactic bacteria as cellular hosts for biosensors are interesting models, as their intrinsic magnetism permits them to be easily concentrated and entrapped to increase the arsenic-response signal. This paves the way for the development of sensitive and immobilized whole-cell biosensors tailored for use in the field.

Graphene oxide-gated mesoporous silica nanocontainers using aptamers for arsenite detection with glucometer readout

A newly portable detection sensing platform based on a graphene oxide (GO)-gated mesoporous silica nanocontainer (MSN) was designed for arsenite detection through the target-responsive release of glucose from the MSN with a glucometer readout.

PRELIMINARY INVESTIGATIONS ON AN ENZYME IMMOBILIZED OPTICAL BIOSENSOR FOR ARSENITE DETECTION

Arsenite is an inorganic form of arsenic that poses hazardous effect to human. It is a common environmental heavy metal contaminant ubiquitously found in water and groundwater. In this study, an optical biosensor for arsenite determination was developed by immobilization of crude arsenite oxidase (Aio) extracted from recombinant E. coli, in chitosan solution coated on triacetyl-cellulose membrane employing DCPIP as colour indicator. The arsenite oxidase (Aio) was successfully expressed and extracted from recombinant E. coli strain BL21 (DE3). The protein concentration and specific activity of the crude arsenite oxidase were determined. Expression of Aio was confirmed by SDS-PAGE. The crude Aio was also successfully immobilized in chitosan and coated on triacetyl cellulose membrane. The response time and dynamic range of the optical biosensor were optimized. The response time of the developed biosensor was 15 minutes. The amount of DCPIP reduced (DA) was inversely proportional to the arsenite concentration. Standard calibration curve for arsenite detection was achieved within the range of arsenite concentration from 25 µM to 200 µM. The maximum detection limit was determined to be 250 µM arsenite.