We present a high-speed electrical detection scheme based on a custom-designed CMOS amplifier which allows the analysis of DNA translocation in glass nanopipettes on a microsecond timescale. Translocation of different DNA lengths in KCl electrolyte provides a scaling factor of the DNA translocation time equal to p = 1.22, which is different from values observed previously with nanopipettes in LiCl electrolyte or with nanopores. Based on a theoretical model involving electrophoresis, hydrodynamics and surface friction, we show that the experimentally observed range of p-values may be the result of, or at least be affected by DNA adsorption and friction between the DNA and the substrate surface.

Glass or quartz nanopipettes have found increasing use as tools for studying the biophysical properties of DNA and proteins, and as sensor devices. The ease of fabrication, favourable wetting properties and low capacitance are some of the inherent advantages, for example compared to more conventional, silicon-based nanopore chips. Recently, we have demonstrated high-bandwidth detection of double-stranded (ds) DNA with microsecond time resolution in nanopipettes, using custom-designed electronics. The electronics design has now been refined to include more sophisticated control features, such as integrated bias reversal and other features. Here, we exploit these capabilities and probe the translocation of short dsDNA in the 100 bp range, in different electrolytes. Single-stranded (ss) DNA of similar length are in use as capture probes, so label-free detection of their ds counterparts could therefore be of relevance in disease diagnostics.

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the evanescent field, and can be interpreted as a density or a refractive index of the cellular material. The quantitative nature of SPR images and the direct relationship to refractive index changes at the surface sensor allow for visualization new insights into mechanisms of cell biology at an interface. When applied to mammalian cells, such as rat aortic smooth muscle cells, cellular components near the sensor surface such as the cell membrane, focal adhesions, and cell nucleus are visualized in the SPRI image. Focal adhesion sizes measured by SPRI are similar with those highlighted with fluorescent antibody stained vinculin. In addition, a positive correlation between focal adhesion size and protein density is observed by SPR imaging. When SPRI is applied to pathogenic biofilms of Streptococcus mutans, distinct components of the bacterial biofilm at the surface including individual bacteria, bacterial microcolonies, and extracellular polymeric substance (EPS) are observed. SPRI shows that the refractive index of bacteria in a biofilm increases over time compared to that of bacteria not in a biofilm, which remains constant. SPRI also indicates that the EPS material generated in the biofilm at early time points is thicker near the bacterial microcolony periphery. This suggests that the EPS matrix is generated at the colony edge and that SPRI can be used to monitor the dynamics of EPS production in biofilms.

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