1 Biosensors Based Diagnosis

Transcript

Hello, everybody welcome to the fourth week of the course detection, diagnosis and management of plant diseases. In this particular week we’ll be dealing with topics that is ‘Advancements in Diagnostic Technologies’ and we’ll be starting the first talk with ‘Biosensors based techniques’.

So, the variety of biosensors have been developed recently and it is been commercialized for various applications and they are helping the diagnosticians to detect plant pathogens in a very efficient and precise. So, depending on the operating principle of the sensor the analytes could be detected that using a sensor based on Electrical, Chemical, Electrochemical, Optical, magnetic or even vibrational signals. So based on this methodologies of biosensing this biosensors are developed for detection of plant pathogens. The limit of detection could be enhanced by the use of nanomaterial matrices as transducers and the specificity could be enhanced by the use of bio recognition elements such as DNA, antibody, enzymes and so on. So biological probes can be of various origins like antibodies, nucleic acids and many other factors like bacteriophages and so on. This all probes can identify the pathogen target and their signal is then transduce through a plug transduction platform and then the signal is amplified for detection signal in the output devices can help us to actually detect the pathogen that is associated with a plant disease.

So Biosensor platforms based on nanomaterials, nanomaterials display electronic and optical properties and can be synthesized using different types of materials for electronics and sensing applications. The popularity of nanomaterials for sensor development could be attributed to high surface area, high electronic conductivity and plasmonics properties of nanomaterials that enhance the limit of detection. So that is why nanomaterials is gaining popularity for being used as biosensors fordetection of plant pathology. The immobilization of the bio recognition elements such as DNA, antibody in enzyme can be achieved using various approaches including biomolecule adsorption, covalent attachment and capsulation or a sophisticated combination of these methods.

The nanomaterials used for wire sensors construction include metal andmetal oxide nanoparticles, quantum dots, carbon nanomaterials as well as carbon nanotubes and graphene as well as polymeric nanomaterials. so all this includes by development of construction of nanomaterial Biosensors. Nanoparticles have been utilized with other biological materials such as antibody for detecting pathogens like Xanthomonas axonopodis that causes the bacterial spot disease in several plants. Gold nanoparticles based optical immuno sensors have been developed for detection of pathogens like karnal bunt in wheat using Surface Plasmon Resonance in short we call it as (SPR). In addition to single probe sensors nano chips had also been made of micro arrays which contained fluorescent oligo probes that were also developed for detecting single nucleotide change in bacteria and viruses with high sensitivity and specificity based on DNA hybridization. So, varieties of used with of nanoparticles whether it has been used alone or in combination with other enzymes and biomolecules, its application is being white in plant pathology for detection of plant pathogens.

Second group is Affinity Biosensors so compared to the nonspecific nanoparticle based biosensors inclusion of a bio recognition element can greatly increase the specificity of the sensor. Consequently, the other types of bio sensors have been developed and among them affinity biosensors are very popular. The affinity biosensors the sensing is achieved based on reaction on the bio recognition element and the target analyte. So it’s not the basically the particle but it is a particle associated with the bio sensor its affinity for detecting the target analyte, it is important and this bio-recognization basically help the biosensors to detect and then transduce the signal and followed by amplification of the signal. So affinity biosensors can be developed using antibody and DNA as recognition elements.

So antibody based biosensor – the antibody based biosensors provide several advantages such as fast detection, improved sensitivity, real-time analysis and potential for quantification. The biosensors enables the pathogen detection in air, water and seeds with different platforms for greenhouses on-field even post harvest storages of processors and distributors of crops and fruits. The principle of establishing antibody-based immuno sensors lies in the coupling of specific antibody with a transducer which convert the binding element to a signal that can be analyzed such as polyacetylene, polypyrrole or polyaniline. So antibody combined with a nanoparticle that actually recognized the analyte and it is being used very widely nowadays, for detection of certain plant pathogens. So, technically the biosensor is signal distant transfused and then it went for data analysis and finally we get the outcome of the result. Whether the bio- sensor may be antibody based or it may be based on DNA. The other process remains the same and the final output is analyzed based on the data it generates from the biosensor. So antibody based biosensors could detect plant pathogens such as Cowpee mosaic viru, Tobacco mosaic virus, Lettuce mosaic virus Fusarium culmorum, Puccinia striiformis, Phytophthora infestans, orchid viruses and Aspergillus niger and so on. So it has been widely used to detect 0various fungal and viral pathogens from different plant species. Antibody based biosensors technology has made tremendous progress upon implementation on nanotechnology. Gold nanorods (AuNRs) functionalized by antibodies have been used to detect Cymbidium mosaic virus (CymMV), Odontoglossum ringspot virus (ORSV) for rapiddiagnosis of viral infections. So nanoparticle cube based biosensors has been further enhanced when it is tagged with an antibody. The strength of then anoparticles has even gone beyond itsoriginal limit with the use of this biosensor and this combined biosensor of nanoparticles and antibody gives very high specific recognition of the pathogen analyte and it gives a proper identification of the pathogen that is associated with the plant disease.

Next, is DNA/ RNA based affinity biosensor. Due to possibility of detention at a molecular level the DNA based biosensors enables early detection of diseases before any visual symptoms appear. So this is a very important method of analyzing plant pathogen. There is RNA based affinity biosensor and because it is able to detect pathogens before the pathogen multiplies to a great extent and produce a definite symptom on the host plants. The application of specific DNA sequences have been widely used for detection of bacteria, fungi and genetically modified organisms. Based on specific nucleic acid hybridization of the immobilized DNA probe on the sensor and the underlying DNA sequence, DNA 08:49 based biosensors allows rapid, simple and economical testing of genetic and infectious diseases. The most commonly adopted DNA probe is 08:59 single-stranded DNA on electrodes with electroactive indicators to measure hybridization between the probe DNA and the complimentary DNA analyte. So, once the probe DNA and the complimentary DNA analyte they interacts or hybridized, an electrical signal is generated and based on this signal generation the presence of the bacteria can be called Or the pathogen can be detected on the Device. Bacterial pathogens are detectable by DNA based biosensors due to their unique nucleic acid sequence which can be specifically hybridized with complementary DNA probe. The recognition of analyte DNA is dependent upon the formation of stable hydrogen bond between the DNA probe and the analyte DNA sequence. This is different from the antibody based biosensors where hydrophobic ionic and hydrogen bonds play a role in stabilization of the 0 antigen-antibody complex. But in case of the DNA based biosensors it is the stable hydrogen bond that plays into a Role. In addition to DNA- DNA hybridization for bacterial detection the specific habitation of DNA and complementary RNA was also exploited for detection of plant viruses such as cymbidium mosaic virus as well as Odontoglossum ringspot virus.

So it is not only DNA and DNA hybridization, it is DNA and complementary RNA based hybridization. That is technology is also being used for detection of certain plant viruses. So, here we have we have seen that how biosensors are being used for detection of plant pathogens. In the beginning we have talked about the nano particles which are used as a biosensors for detection of plant pathogens, then we have also talked about the nano particles which was then located with a antibody with enhanced its efficacy to detect a certain plant pathogens, then we have also talked about DNA- DNA hybridization and DNA/ RNA complementary hybridization methods for detection of certain plant pathogens. And these particular molecules has been used as biosensors for detection of specific plant pathogens. Sometimes even it produces its definite symptom on the host plants the pathogen can be detected on the basis of DNA- DNA hybridization method.

So with this we have come to an end of the first talk of this week and in the next talk we will be discussing about Volatile organic compounds as biosensors for pathogen diagnosis.

Thank you very much.