Biosensor can be defined as a device which is used to detect an analyte. Microfluidic bio sensor comes mainly in two categories. They are Florescent based devices and electrochemistry based devices. This categorisation of the microfluidic biosensor is based on its detection capability. One important characteristic of both these devices is that both of them utilises functional liposomes for target recognition and binding. A number of biorecognition elements are used to functionalise liposomes.
They include receptors, antigens, antibodies and nucleic acid probes. For the purpose of immobilisation another biorecognition element is used. It is used for the immobilisation of target-liposome-magnetic bead complex within the microfluidic device. This type of biorecognition element will be bounded to paramagnetic beads. After the completion of immobilisation signal amplification will be done. This is done with the help of signal generating molecules, which will be in the encapsulated form. It is the lysis of the lipisome which allow the signal amplification. It is applicable to both florescent based devices and electrochemistry based devices.
Inside the microfluidic biosensor device there will be a serpentine channel. This is the channel which is used for the formation of two other channels. The first channel is formed by liposome-target-magnetic bead complex. The second channel delivers the surfactant which is utilised to lyse the liposome. The liposome will be captured at the capture zone. Capture zone is the meeting point of these two channels. It is located at the downstream in the junction of the two channels. The target detection by the microfluid biosensor depends on the type of biorecognition element used.
In order to evaluate the magnetic capture zone the device must be mounted on to a florescence scope. Then only the capture zone can be evaluated. The background signal will be negligible if there is no target present. If any target is present then a group of lipisome target can be seen at the output side. But there won’t be much amplification in the signal received. Further amplification is brought about by the surfactant, which is delivered from the second channel. Then the output will look like a beam of florescent particles.
In the case of a microfluid biosensor which is based on electrochemistry, electroactive compound will be used rather than florescent molecules. Florescent molecules are used by florescent based microfluidic biosensor devices. The electroactive microfluidic biosensor utilise Inter Digitated Ultramicroelectrode Array (IDUA). IDUA contains a number of anode and cathode pads arranged in a systematic manner. They are nanofabricated. The anode pad as well as the cathode pad consists of fingers which are held opposite to each other in an over lapping pattern. Working of the IDUA is based on the Red-ox (Reduction-oxidation) reaction. When any electroactive red-ox couple comes in contact with this IDUA, reduction of the oxidised form takes place on the cathode part.
Also, a small voltage must be given to the IDUA device. Since the anode and cathode pads are held opposite to each other, the reduced form gets converted back to the oxidised form in the anode placed adjacent to the cathode. Again it will be transferred into the cathode and turned into the reduced form. Thus this cyclic process goes on as a result of which an electron flow will be created. This electron flow results in a current which is proportional to the concentrate of analyte given.
The result can be displayed on any devices by properly connecting the output to the display. Thus the concentration of the analyte can be found out using the IUDA. The output current developed can be detected with the help of a potentiostat.
