BioMachines That Can Sense the Environment
Biosensors
Biosensors are like electronic sensors used in devices but majorly consist of biological parts. They can be distinguished by specific components depending on the substance they are used to detect. A biosensor works like a smoke alarm which goes off in the presence of biologically significant ‘analytes’.
Leland C. Clark, the ‘Father of Biosensors’, developed the first biosensor to detect oxygen. Nowadays, they are used to detect methane, nitrogen or even the amount of stress (reactive oxygen species) in your body.
A typical biosensor has the following parts:
- Analyte: The substance we want to detect — for example, methane.
- Bioreceptor: This molecule is like a sniffer dog that recognises our analyte of interest
- Transducer: It helps create a recognition signal upon the detection of the analyte. This process is called ‘signalisation’.
- Analyte Electronics: This processes the transduced signal and prepares it for display. The processed signal is then computed for display.
- Display: This part of the sensor consists of hardware and software. It works like a computer display that shows us the processed data.
Fig1: A diagram showing components of a typical biosensor and the direction in which the process proceeds.
Whole-cell biosensors
Whole-cell biosensors use living cells as the sensor and can recognise a broader range of “analytes” with higher sensitivity.
They are used to obtain useful information on the effect of a stimulus on a living body and help us observe variations easily. These changes in the organism, once discovered, can be used in future experiments, offering better sensitivity. So if you contract a gastric infection, the cell biosensors can tell precisely what is wrong in the gut and how we can fix that.
The most commercially successful whole-cell biosensors till date are toxicity sensors based on bacteria that are naturally luminescent in the dark such as Vibrio harveyi, Vibrio (Photobacterium) fischeri, and Photobacterium phosphoreum. In these cases, light is produced continuously by the action of a luminescence gene (LuxAB), so any toxic substance that interferes with the bacteria’s metabolism will reduce this light emission. This attenuation can be detected using a luminometer (a device to detect light intensity). However, these sensors are not very specific and are only useful for preliminary screening of toxins in the environment.
Whole-cell biosensors have a very high potential, and it becomes more promising when genetically modified cells are used for recognising anomalies in the environment.
Fig2: Aschematic showing a typical whole-cell biosensor
The fascinating aspect of synthetic biology is the modifications made in the genes of a microorganism. It includes applying engineering principles to biology to get the desired biological changes.
Since whole-cell biosensors consist of a biorecognition element along with a chosen reporter, synthetic biology is perfectly suited for advancement of these sensors. To validate the potential of this approach to synthetic biology, iGEM(International genetically engineered machine) competition was established in 2005. The first project based on biosensors submitted to iGEM 2006 by the team from the University of Edinburgh was an arsenic biosensor which could be used to detect arsenic in developing countries, a toxin that can lead to shock, cancer or even death. Another example of an iGEM project is the methane biosensor, “MethNote’, developed by the team from IISER Bhopal in 2018 to improve the environmental monitoring of methane.
Synthetic biology has helped other biosensors to develop as well. For example, nanotube biosensors developed by researchers, using synthetic biology has improved their sensing capabilities in the complex biofluids. This system is made up of nanotubes wrapped by Xeno nucleic acids (XNA) or the synthetic DNA that can tolerate changes in salt concentration in our bodies, to relay stable signals.
Biosensors are widely used in disease diagnosis and various other fields, including research. These devices require the interaction of different disciplines of science and technology. The biosensors used today have evolved with enhanced selectivity, reproducibility, stability, sensitivity and linearity, resulting in better experimental outcomes for research purposes. Whole-cell biosensors are the biosensors that offer a versatile and widely applicable method for detecting the presence of the analytes. These devices have great potential and researchers are trying to enhance them using synthetic biology which offers numerous possible improvements in terms of response tuning, signal processing, and direct interface with electronic devices for further signal processing and output.
-Anurag Yadav, IISER Bhopal
REFERENCES
https://www.ncbi.nlm.nih.gov/books/NBK84465/#nap13239.app1.s59
https://www.europeanpharmaceuticalreview.com/news/77636/biosensor-synthetic-biology/
https://www.sciencedirect.com/science/article/abs/pii/S0925400596019065?via%3Dihub
