The toxicity of artificial nanoparticles is a major concern in industrial applications. Cellular uptake of hard nanoparticles could follow either endocytic or nonendocytic pathways, leading to different stimuli to the cells. Yet the cellular responses to nanoparticles following different pathways have not been compared due to the lack of an independent nonendocytic delivery method. We applied a unique delivery method, nanochannel electroporation (NEP), to produce predominantly nonendocytic uptakes of quantum dots (Q-dots) and multiwalled carbon nanotubes (MWCNTs) with different chemical modifications. NEP delivery bypassed endocytosis by electrophoretic injection of nanoparticles into human bronchial epithelial (BEAS-2B) cells at different dosages. Conventional exposure by direct nanoparticle suspending in cell culture medium was also performed as control. The dosage-dependent responses to nanoparticles under different uptake pathways were compared. Fluorescence colocalization demonstrated that nanoparticles followed both endocytic and nonendocytic pathways for cell entry in contact exposure, whereas NEP delivery of nanoparticles bypassed endocytosis. Nonendocytic entry resulted in much higher oxidation stress and, for MWCNTs, more cell death in BEAS-2B cells. Despite the observation that most nanoparticles were taken up by cells through endocytosis, the minor nonendocytic entry of nanoparticles seemed to dominate the overall cellular response in conventional contact exposure. Our finding suggests that prevention against nonendocytic uptake could help reduce the toxicity of hard nanoparticles.

Investigation of single molecule DNA dynamics in confined environments has led to important applications in DNA analysis, separation, and sequencing. Here, we studied the electrophoretic transport of DNA molecules through nanochannels shorter than the DNA contour length and calculated the associated translocation time curves. We found that the longer T4 DNA molecules required a longer time to traverse a fixed length nanochannel than shorter λ DNA molecules and that the translocation time decreased with increasing electric field which agreed with theoretical predictions. We applied this knowledge to design an asymmetric electric pulse and demonstrate the different responses of λ and T4 DNA to the pulses. We used Brownian dynamics simulations to corroborate our experimental results on DNA translocation behaviour. This work contributes to the fundamental understanding of polymer transport through nanochannels and may help in designing better separation techniques in the future.

We present our work on DNA dynamics in short polymeric nanochannels under pulsed electric fields and simulate their behavior using Brownian Dynamics. Our results show that the time taken by a DNA molecule to traverse a short nanochannel varies non-linearly with the applied voltage and depends on the length of the translocating DNA. We exploit this to separate two DNA of different lengths by applying an asymmetric electrical pulse.

In this paper, we describe a robust low temperature fabrication method for centimeter-long surface-micromachined nanofluidic channels. Unlike conventional approaches, in this method we dry etch sacrificial layers to form the cavities of the channels from the side, thereby eliminating the length restriction intrinsic to a channel etch and release process. To characterize the process, we examine the deformation of the cross section of different width nanochannels due to stress gradient of the wall material. We calculate the maximum edge deformation of a 5 mu m wide channel due to stress to be similar to 18 nm. In addition, we modified the model describing the channel release process to account for the stress-induced deformation and compared the results with the experiment. Finally, to demonstrate the efficacy of the completed process, the nanochannels were successfully filled with ethanol and water, surface hydrophobicity was characterized by meniscus measurements of the filled fluid, and electroosmotic experiments were performed to determine the surface charge and other channel characteristics.

Microlens characterization is a prerequisite for improving fabrication process, and for satisfying the end user needs. In this paper we explore techniques to characterize geometrical properties of microlens made by thermal reflow: viz. microlens profile; radius of curvature; microlens height; contact angle and focal length. The geometrical characterization is done using techniques such as contact profilometry, scanning electron microscopy (SEM), optical microscopy, white light confocal microscopy and fluorescence confocal microscopy. All the above techniques are studied and compared, keeping in mind the characterization requirements of polymer microlens made by thermal reflow technique.