**4. Conclusions**

We describe here an electrical percolation-based label free biosensor capable of quantifying a standard protein. With the goal of meeting the need for a rapid, simplified and affordable analytical device, the biosensors were developed using carbon nanotubes, a specific antibody and cellulose filtration paper. Based on the electrical-percolation principle, the biosensors were hypothesized to sense analytes on the basis of antibody-antigen complex formation, leading to a disruption of the SWCNT-antibody network's continuity and an increase in the network's resistance. The developed biosensors comprised an antibody specific to a standard protein, BSA, and were tested with various concentrations of this protein in order to evaluate our hypothesis. Our results show a positive correlation between BSA concentration and biosensor response. The detection limit of the newly developed biosensors was found to be comparable with ELISA. Additionally, the time necessary for detection was found to transcend that of ELISA, and the cost-e ffectiveness, ease of use and simplicity surpasses those of recent label-free biosensor developments. Further research needs to be carried out in order to conclusively compare the range of detection of the presented method with that of ELISA or other traditional methods. Importantly, the ability to substitute the specific antibody incorporated in the biosensor makes this method incredibly versatile. Due to the high sensitivity, specificity, a ffordability and rapidity of this device, we believe that it will find wide applications in both biological research and clinical diagnostics.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2079-6374/9/4/144/s1, Table S1: Source code for programmed Arduino Uno ohmmeter unit.

**Author Contributions:** Conceptualization, J.J.; methodology, J.J., M.L., P.W. and A.B.; Software, P.W.; validation, J.J.; formal analysis, J.J.; investigation, J.J.; resources, J.J., M.L. and A.B.; data curation, J.J.; writing-original draft preparation, J.J.; writing-review and editing, J.J. and A.B.; visualization, J.J.; supervision, A.B.; project administration, J.J.; funding acquisition, J.J.

**Funding:** This research received no external funding.

**Acknowledgments:** This work was performed at the Bioengineering for Biofuels and Bioproducts Lab and the Biomedical Instrumentation and Signal Analysis Lab at the University of Manitoba. Thank you to Moussavi, Lithgow and Levin for your help and guidance. Thank you to the graduate students and high school students working in both of these labs who o ffered support and assistance.

**Conflicts of Interest:** The authors declare no conflict of interest.
