Droplet-based separation tools for multidimensional biological separations

Proteins have been extensively studied over the last decade as comprehensive understanding of the proteome can definitely lead to the discovery of novel biomarkers, early-stage disease diagnoses and the development of diagnostic tools and novel drug therapies. One of the crucial and fundamental processes in protein analysis is protein separation, which is usually performed as multidimensional separations to achieve high resolution and high peak capacity. However, high performance analyses are difficult to achieve due to the challenges involved in efficiently integrating different dimensions. In this work, we present the development of a microfluidic device for the effective transfer of protein droplets into the second separation dimension. Consequently, the device provides a stable, reproducible, easy to operate, portable and flexible system to connect a first dimension separation to the downstream second dimension analysis via droplets. The droplets act to preserve the resolution during transfer between separation techniques. In summary, a fluorescently labeled protein ladder serving as a representative of proteins separated from the first dimension is compartmentalized into droplets using the robotic droplet generator. These protein droplets are then transferred via the interfacing microdevice into the second dimension where the released proteins are further separated using capillary gel electrophoresis. Herein, several designs of interfacing microdevices were evaluated for the successful transfer of droplet contents (droplet injection) into the second dimension. The buffer for capillary gel electrophoresis was developed to achieve high-speed and high-resolution separations of proteins in droplet-based injection format. Several fluorescent dyes were also examined for protein labeling to achieve high fluorescent intensities necessary when using this droplet format. Successful droplet-based separation of proteins necessitates the seamless integration of all the developed components. This has been demonstrated here. This interface automates the oil depletion process, minimizes dead volume, prevents dispersion of analyte bands and reduces sample loss at the interface between separation dimensions. Furthermore, optimization of the entire system used in conjunction with the interfacing microdevice provided for ease of operation and more efficient droplet injections. Moreover, droplet injection into parallel separation channels was achieved, highlighting the interfaces capacity for high-throughput analyses.Open Acces

Fully CMOS-compatible top-down fabrication of sub-50 nm silicon nanowire sensing devices

This article reports the fabrication of sub-50 nm field effect transistor (FET)-type silicon (Si) nanowire (Si NW) chemical and biological sensing devices with a junctionless architecture, as well as on the initial characterisation of their electrical and sensing performance. The devices were fabricated using a fully complementary metal-oxide-semiconductor (CMOS)-compatible top-down process on silicon-on-insulator (SOI) wafers. The fabrication process was mainly based on high-resolution electron beam lithography (EBL) and reactive ion etching (RIE) but also included photolithography (mix-and-match lithography), thin film deposition by electron beam evaporation, lift-off, thermal annealing and wet etching. The sensing performance of a matrix of nanowire devices, i.e. containing 1, 3 and 20 NWs with lengths of 0.5, 1 and 10 μm was examined. Each element of the matrix also contained five devices with different NW widths: 10, 20, 30, and 50 nm and 5 μm (a Si belt reference device). Electrical characterisation of the devices showed excellent performance as backgated junctionless nanowire transistors (JNTs): high on-currents in the range of 1-10 μA and high ratios between the on-state and off-state currents (I on/Ioff) of 6-7 orders of magnitude. In addition, the results of ionic strength sensing experiments demonstrate the very good sensing capabilities of these devices. To the best of our knowledge, these nanowire sensors are among the smallest top-down fabricated Si NW devices reported to date