The future of diseases treatments substantially depends on deep understanding of the working mechanisms of single enzymes which are responsible for many vital operations in the body. Over the past two decades, extreme progress has been made developing techniques such as single-molecule fluorescence, magnetic and optical tweezers and scanning probes that can address the challenge of characterizing the activity of single biomolecules. Though optical and mechanical techniques have been well represented, electronic transduction has generally been taking a backseat presumably due to the big challenge in fabrication of such an electronic device as a candidate.
Carbon Nanotube Transistors for Single Molecule Bioelectronics
Over the past decade, abundant research has demonstrated the biosensing capabilities of carbon nanotubes, and recently this sensitivity has been extended to single-molecule electronics. The electronic nature of the FET technique has immediate benefits such as microsecond time resolution and long-duration capabilities, which are both advantages over fluorescence for studying the conformational dynamics and processivity of a single molecule. We have attached single enzymes to single-walled carbon nanotube field-effect transistors (SWNT-FETs) and demonstrated the versatile ability of tracking an enzyme’s conformational states and revealing distributive and processed enzyme movements.
What We Have Achieved So Far
Dr. Gul has reviewed the operation of single-enzyme transistors made using single-walled carbon nanotubes while he was pursuing his PhD in Prof. Collins' Group. These novel hybrid devices transduce the motions and catalytic activity of a single protein into an electronic signal for real-time monitoring of the protein’s activity. Analysis of these electronic signals reveals new insights into enzyme function and proves the electronic technique to be complementary to other single-molecule methods based on fluorescence. As one example of the nanocircuit technique, we have studied the Klenow Fragment (KF) of DNA polymerase I as it catalytically processes single-stranded DNA templates. The fidelity of DNA polymerases makes them a key component in many DNA sequencing techniques, and we demonstrate that KF nanocircuits readily resolve DNA polymerization with single-base sensitivity. Consequently, template lengths can be directly counted from electronic recordings of KF’s base-by-base activity. After measuring as few as 20 copies, the template length can be determined with <1 base pair resolution, and different template lengths can be identified and enumerated in solutions containing template mixtures.