Effect of surface charge of polyethyleneimine-modified multiwalled carbon nanotubes on the improvement of polymerase chain reaction

In molecular biology, polymerase chain reaction (PCR) has played an important role but suffers a general problem with low efficiency and specificity. Development of suitable additives to improve the PCR specificity and efficiency and the understanding of the PCR enhancing mechanism still remain a great challenge. Here we report the use of polyethyleneimine (PEI)-modified multiwalled carbon nanotubes (MWCNTs) with different surface charge polarities as a novel class of enhancers to improve the specificity and efficiency of PCR. The materials used included the positively charged PEI-modified MWCNTs (CNT/PEI), the neutral CNT/PEI modified with acetic anhydride (CNT/PEI.Ac), and the negatively charged CNT/PEI modified with succinic anhydride (CNT/PEI.SAH). We show that the specificity and efficiency of an error-prone two-round PCR are greatly impacted by the surface charge polarity of the PEI-modified MWCNTs. Positively charged CNT/PEI could significantly enhance the specificity and efficiency of PCR with an optimum concentration as low as 0.39 mg L−1, whereas neutral CNT/PEI.Ac had no such effect. Although negatively charged CNT/PEI.SAH could enhance the PCR, the optimum concentration required (630 mg L−1) was more than 3 orders of magnitude higher than that of positively charged CNT/PEI. The present study suggests that the PCR enhancing effect may be primarily based on the electrostatic interaction between the positively charged CNT/PEI and the negatively charged PCR components, rather than only on the thermal conductivity of MWCNTs.