Nanofluidic Single Molecule Detection

Nanofluidic single-molecule detection Nanofluidic single-molecule sensors... 

To date, nanofluidic single-molecule detection has been done in two ways. One takes the advantage of the comparable size of nanochannels and macromolecules and detects the modulation of ion current through a nanochannel or a nanopore when an individual macromolecule enters the nanochannel/nanopore. This method is well known as resistive-pulse sensing or the Coulter principle. The other uses a nanochannel as a confined region to limit the number of molecules inside the nanochannel and uses other methods such as optical microscopy to sense a single molecule inside the nanochannel. Both approaches have demonstrated successful detection of single molecules inside nanofluidic channels. However, to date, only a few examples for each approach have been reported since nanofluidic systems have been developed only within the last decade. 

Nanofluidic Single-Molecule Detection Based on the Comparable Size of the Nanochannel and the Molecule... 

S. Bhat, J. Herrmann, P. Armishaw, P. Corbisier, and K. R. Emslie, Single molecule detection in nanofluidic digital array enables accmate measurement of DNA copy number, Analytical and Bioanalytical Chemistry, vol. 394, no. 2, pp. 457-467, May 2009. 

Fluorescence measurements are very important in studies on microfluidics and nanofluidics, with main applications on flow visualization and single-molecule detection. To achieve measurements with higher spatial resolution, which becomes more significant with the rapid development of nanofiuidics, research efforts should be focused on developing more advanced fluorescence microscopy setups. The particularly useful setups will be the ones that can break the classic optical diffraction limit. 

These nanopores were not fabricated in batches but made individually in expensive tools, and the fluid cells at each side of the nanopore are bulk fluid cells, which may consume a significant amount of sample. Efforts of making on-chip nanofluidic systems for single-molecule detection based oti the same principle started with a 3 pm long, 200 nm in diameter PDMS nanochannel on a glass substrate [3]. The channel size (200 nm) is much larger than a typical nanopore (<10 nm) due to the limitation of... 

Nanofluidic systems constructed for fluorescent single-molecule detection are relatively simple with nanochannels connected to... 

Nanofluidic systems are also ideally suitable for certain single-molecule detection techniques such as total internal reflection fluorescence (TIRF) microscopy. TIRF utilizes evanescent waves, which are generated by total internal reflection of a laser beam, to excite the fluorescence signal, and since evanescent waves decay exponentially, the molecule of interest must locate to the close proximity of the interface of the glass and liquid. Nanofluidic systems confine molecules of interest in nanochannels, which is well in the evanescent field of TIRF microscopy. 

For both detection approaches, it is of great interest to study the complex interactiOTis between the molecules of interest and the nanoenvironment. The high surface area to volume ratio in nanochannels can change the behavior of molecules significantly from that in bulk solutions. The complex interactions between the molecules of interest and the ions and surface charges are still not fully understood yet. These effects must be clarified before extensive applications of nanofluidic systems for single-molecule detection. 

Photometer is important for identifying the materials in micro- and nanoscale flow, especially when the channel size is small and the flow speed is high. Although photometer itself does not have spatial resolution, the development of nanofluidics for single-molecule detection should be desirable to develop new experimental methods and applications for single-molecule-based applications. 

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