In the past two decades, Micro Fluidic Systems (MFS) have emerged as a powerful tool for biosensing, particularly in enriching and purifying molecules and cells in biological samples. Compared with conventional sensing techniques, distinctive advantages of using MFS for biomedicine include ultra-high sensitivity, higher throughput, in-situ monitoring and lower cost. This review aims to summarize the recent advancements in two major types of micro fluidic systems, continuous and discrete MFS, as well as their biomedical applications. The state-of-the-art of active and passive mechanisms of fluid manipulation for mixing, separation, purification and concentration will also be elaborated. Future trends of using MFS in detection at molecular or cellular level, especially in stem cell therapy, tissue engineering and regenerative medicine, are also prospected.

Although the stability of the nanobubble remains a controversial issue that is subject to the classical predictions of high Laplace pressure, we demonstrate that a hydrogen nanobubble can be generated and stabilized in an aqueous solution of Keyhole limpet hemocyanin (KLH) protein via an electron radiolysis process. The hydrogen gas inside the nanobubble is in a “dense gas” phase that is characterized by a Knudsen number and number density of hydrogen molecules. The dynamics of nanobubbles are analyzed using time-series electron microscopy images. The growth of small nanobubbles will be affected by the largest neighboring nanobubble; however, a diffusive shielding effect for small nanobubbles is observed. Locally, anti-Ostwald ripening of nanobubbles can be observed; however, the global growth behavior among the nanobubbles is randomly correlated because the characteristic diffusion length of the hydrogen molecules is considerably greater than the average spacing among the nanobubbles.

Scanning electron microscopy has been developed for topographic analysis at the nanometer scale. Herein, we present a silicon p-n diode with multi-annular configuration to detect backscattering electrons (BSE) in a homemade desktop scanning electron microscope (SEM). The multi-annular configuration enables the enhancement of the topography contrast of 82.11 nA/μm as compared with the commercial multi-fan-shaped BSE detector of 40.08 nA/μm. Additionally, we integrated it with lateral p-n junction processing and aluminum grid structure to increase the sensitivity and efficiency of the multi-annular BSE detector that gives higher sensitivity of atomic number contrast and better surface topography contrast of BSE images for low-energy detection. The responsivity data also shows that MA-AL and MA p-n detectors have higher gain value than the MA detector does. The standard deviation of measurements is no higher than 1%. These results verify that MA p-n and MA-AL detectors are stable and can function well in SEM for low-energy applications. It is demonstrated that the multi-annular (MA) detectors are well suited for imaging in SEM systems.

We present the development of conductive nanoporous CNT/chitosan membrane for charge‐selective transport of charged molecules, carboxylfluorescein (CF), substance P, and tumor necrosis factor‐alpha (TNF‐α). The membrane was made porous and conductive via gelatin nanoparticle leaching technique and addition of carbon nanotubes, respectively. These nanoporous membranes discriminate the diffusion of positive‐charged molecules while inhibiting the passage of negative‐charged molecules as positive potential was applied. The permeation selectivity of these membranes is reversed by converting the polarity of applied potential into negative. Based on this principle, charged molecules (carboxylfluorescein, substance P, and TNF‐α) are successfully filtered through these membranes. This system shows 30 times more selective for CF than substance P as positive potential was applied, while 2.5 times more selective for substance P than CF as negative potential was applied.