(Nanowerk Spotlight) Chemical detection outside laboratory settings poses persistent technical challenges. Environmental monitoring, industrial quality control, and medical diagnostics require identifying specific molecules in complex mixtures. Current portable detection methods, such as test strips or electronic sensors, often lack sensitivity or struggle to detect multiple chemicals simultaneously. Traditional laboratory analysis provides precise results but requires expensive equipment, trained personnel, and days or weeks to process samples.
Living cells naturally detect and respond to chemicals with remarkable sensitivity. Their molecular detection systems, refined by evolution, can identify specific compounds at extremely low concentrations and process multiple signals simultaneously. Biologists have learned to harness these capabilities by engineering bacteria and yeast cells to produce visible signals when they encounter target molecules. These cellular sensors can detect compounds at concentrations far lower than conventional methods. However, using engineered cells outside the laboratory remains impractical because they require careful maintenance and protection from environmental stresses.
Materials scientists have recently developed new methods to protect living cells while preserving their functionality. Parallel advances in microfluidic technology enable precise control of tiny liquid volumes in miniature channels on portable chips. These developments create an opportunity to transform cellular sensors from laboratory curiosities into practical field devices.
Overview of the ELMlab-on-chip biosensing platform. This illustration depicts the step-by-step development of an on-site multiplexed detection system using a bottom-up approach. The construction of artificial chimeric receptor modules and precise modulation of receptor density enables the development of engineered living biosensors with fine-tuned sensitivity and response. Ionic and covalent cross-linking strategies are employed to fabricate the ELMs with substance permeability and commendable mechanical robustness, ensuring enhanced signal output and prolonged storage stability. Finally, by encoding the spatial locations of orthogonal stimuli-responsive ELMs into a microfluidic chip, a portable ELMlab-on-chip biosensing platform is developed for the multiplexed detection of chemicals in the field. (Image: Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)
The researchers first modified yeast and bacteria cells by adding genes that produce fluorescent proteins in response to specific chemicals. They precisely engineered these genetic circuits by controlling the number of receptor proteins on each cell’s surface. More receptors increase sensitivity but can also lead to false positives, while fewer receptors provide more selective detection. By optimizing this balance, they achieved detection of some compounds at concentrations as low as two nanomoles per liter – equivalent to finding a grain of salt dissolved in an Olympic swimming pool.
To protect these engineered cells, the team developed a two-layer encapsulation system. They embedded the cells in soft beads made from alginate, a natural polymer derived from seaweed. These beads provide a supportive environment while allowing chemicals to pass through. A tougher outer shell, combining alginate with polyacrylamide, adds physical protection. The resulting capsules, each about two millimeters wide, withstand significant compression without breaking and keep the cells alive and functional for over a month.
The researchers integrated these sensor capsules into a microfluidic chip with separate chambers for different sensors. This design enables simultaneous detection of multiple chemicals from a single sample. A compact detection system uses LED lights to excite the fluorescent proteins and a smartphone camera to measure their brightness. The high density of cells within each capsule – over 100 times greater than in liquid cultures – produces strong signals that the smartphone can easily detect.
Field testing with water samples from China’s Xiangjiang River demonstrated the system’s capabilities. The sensors reliably detected several compounds, including hormones and steroids, at very low concentrations. Each sensor type responded only to its target chemical without interference from other substances in the river water. The entire detection process took about four hours, compared to days or weeks for laboratory analysis.
The sensor capsules maintained their capabilities after a month of storage at room temperature, suggesting practical viability for field applications. The system successfully detected multiple chemicals simultaneously in real environmental samples, demonstrating its potential for immediate practical use.
This technology transforms living cells into practical sensors for field use. By combining synthetic biology, materials science, and microfluidic engineering, the researchers have created a system that preserves the sensitivity of cellular sensors while making them robust enough for real-world applications. The approach enables rapid on-site testing that currently requires laboratory facilities. Future development could expand the range of detectable chemicals and adapt the technology for medical diagnostics and food safety testing.
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