Shashanka Doddamani

About the project 

                  While working in the Research and Development of Bhat Biotech's PCR Machine - DNAmp, I got an opportunity to work with Dr. Arun Chandra Shekar, President of R&D, Bhat Biotech India Pvt Ltd. From the past 2 years under his guidance researchers were working on the use of measurement of electrical properties of sample during the PCR process. I was inspired by this idea and conveyed my interests in developing it in to a product. That's how the work on iAmp began, it was very challenging to make it a reality because long before they tried using Operational Amplifiers base circuit and failed in getting results. After going through many papers, patents, and pefroming meauremtns using LCR meter i found out that the real use comes only if we could measure the Impedance, Phase, and Capacitance of the biological sample under test. This led me to design a new circuit.     

 

Challenge I: Design and Development of a measurement Circuit

                            I studied more about the design and implementation of LCR bridge, Frequency Generators, and Analog to Digital Converters to measure the impedance, but for our application going for an LCR bridge was not a feasible solution. Hence I started to search for ready on chip solution for the impedance measurement which combines on board Frequency Generator with Analog to Digital Converter (ADC); Analog Devices Impedance Converter & Analyser was a perfect fit. I ordered an evaluation board and spent days experimenting on different samples.

                     Finally I selected proper calibration resistor, voltage, frequency, and settling time for the impedance measurement and programmed the microcontroller to control 16 of those ICs, thereby successfully tested 16 different samples simultaneously during a single PCR run. To get perfect measurement values I calibrate individual channels against a calibration resistor.  

                     

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                   

                   Only impedance was not enough in characterising the DNA sample. Hence I used measured Phase and Impedance to calculate the Capacitance, which gave wonderful results. I confirmed the result by comparing it with a LCR meter Capacitance reading.    

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                                 

 

                 

 

                     This is the plot of change in capacitance from initial capacitance v/s number of PCR cycles. According to theory, for every cycle number of copies of DNA doubles. Hence right from the cycle 2 we are able to differentiate between Sample, Negative, and Blank. Capacitance of the sample increases because the number of copies of DNA increases, in negative and blank since there is no increase in number of copies of DNA the capacitance drops slightly. You may ask why negative is above the blank? Simple reason is negative has a copy of non target DNA but blank does not contain any copies of DNA.

 

Challenge II: Development of an algorithm for the computer software to control the machine and generate reports  

                          Next challenge was to develop an algorithm for

the computer software to analyse the data measured and give

the final report about the sample under test. I successfully

completed it and now it is being used by the Java based computer

application to control the machine and generate reports.