In the research of bio-molecular chips and sensors,extra electric biases are most often employed to control and manipulate the DNA and protein molecules moving through micro/nano-fluidic channels.In order to accurately and flexibly control the bio-molecules as they move within the channels,a clear understanding of how the current changes within the buffer solution caused by an applied bias is fundamental.In this report,the current changed value of different buffer solutions,e.g.,KCl,TE,and TBE was systematically studied with real-time monitoring and quantitative analysis in the situation of the buffers moving through a fluidic channel with a 5 m inner diameter,driven by biases of 50 or 100 mV.The results revealed that the relationship between the current changed value and the pause interval of the applied electric field is highly consistent with the Hill Equation,which is helpful for accurately detecting and manipulating single biomolecules in microfluidic sensors and biochips.
As one of the most important realizations of stimulated emission depletion(STED) microscopy, the continuouswave(CW) STED system, constructed by using CW lasers as the excitation and STED beams, has been investigated and developed for nearly a decade. However, a theoretical model of the suppression factors in CW STED has not been well established. In this investigation, the factors that affect the spatial resolution of a CW STED system are theoretically and numerically studied. The full-width-at-half-maximum(FWHM) of a CW STED with a doughnut-shaped STED beam is also reanalyzed. It is found that the suppression function is dominated by the ratio of the local STED and excitation beam intensities. In addition, the FWHM is highly sensitive to both the fluorescence rate(inverse of fluoresce lifetime) and the quenching rate, but insensitive to the rate of vibrational relaxation. For comparison, the suppression function in picosecond STED is only determined by the distribution of the STED beam intensity scaled with the saturation intensity. Our model is highly consistent with published experimental data for evaluating the spatial resolution. This investigation is important in guiding the development of new CW STED systems.
