I am trying to measure the change in resistance with varying protein concentration to detect the protein-protein binding with a carbon nanotube based chemiresistor. I am getting erratic responses when I am washing probe-functionalized CNT with PB in between 2 consecutive sample incubation. Should I dry the transducing nanoparticle completely before taking the electrical measurement or is it okay if there are some moisture left on the cnt when I measure the resistance? Does moisture play a vital role on the p-doped CNT during the resistance measurement? Any reference article also would be very helpful. Thanks.
Relaxation frequencies[1] from different origin (and mechanisms) result in a very strong dependence of your (total) electronic and ionic "(EIS[2]-complex) resistance[3]" measurements by moisture[4,5].
1. Relaxation frequencies are vigorously depending by moisture[3-5], due to different thermal and transport mechanisms[4].
2. The principles of electrochemical impedance spectroscopy http://lacey.se/science/eis/eis-principles/
3. An Introduction to Electrochemical Impedance Spectroscopy (EIS) https://www.jlab.org/conferences/tfsrf/Thursday/Th2_1-EIS%20intro%20Reece.pdf
4. Boost in the thermal stability, ionic conductivity and director relaxation frequency in the composite of liquid crystal and functionalised multi-walled carbon nanotubes https://www.tandfonline.com/doi/abs/10.1080/02678292.2020.1783588
5. Carbon nanotubes: Sensor properties. A review https://www.sciencedirect.com/science/article/pii/S2452177917300178
This kind of erratic response might be minimized by maintaining the same physical condition during measurement. Not only moisture, but light and even temperature have also significant effect on measurement of resistance of such doped CNT.
Thank you Dr Ioannis Samaras and Dr Sukhendu Jana . I conducted several experiments with the CNT FET with antibody, but I am not getting consistent result. After the first wash with PB before starting to measure the electrical response from the sample incubation, I am getting a very high resistance, then when I start incubating sample, I am getting comparatively lower resistance, which should be opposite as the protein binding should increase the resistance in p-doped CNT. Can you explain why this happens? Thanks.
Dear Touhid Bin Anwar ,
when you start incubating sample you are getting a very high resistance , due to high (bad interfacial) electrical contact resistance (impedance) between CNT and (metal) electrode(s) of the (CNT-)FET.
So, try to improve the (interfacial) electrical contacts' resistance[1], before incubation.
1. Low-Resistance Electrical Contact to Carbon Nanotubes With Graphitic Interfacial Layer
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.419.6007&rep=rep1&type=pdf
You are saying that you have observed
some anomalous results. Can you provide a schematic diagram for measurement. It will help to understand better.
Dear Dr. Sukhendu Jana
I deposit CNT on specific place on paper substrate (I use paper based biosensors), functionalize them with biomolecules and then use a Keithley source meter to measure the change of current for a voltage swipe between -0.1V to 0.1V. The inverse of the I-V plot slope gives me the resistance, which I don't get consistence, like I get the same downward slope both for sample and control. Also, if I take multiple measurement of the same sample consecutively, then I get increased/ decreased resistance. Hope this helps you understand my situation. Thanks.
Dear Touhid Bin Anwar ,
could you, please, show:
1) a photo of the (CNT on paper) substrate with the electrodes, and/or
2) some (high and low rate) I-V plots ?
thanks for sharing. I have understood the situation. Suggesting you for an annealing with some suitable temperature of the film after deposition. It may improve the consistency.