Components in lab-on-chip systems

The need for improved sensor performance has led to the emergence of micro and nanofluidics. These fields seek to develop miniaturized analysis systems that combine the desired attributes in a compact and cost-effective setting. These platforms are commonly labeled as labs-on-chip or micro total analysis systems (pTAS)2, often using optical methods to realize a desired functionality. The preeminent role that optics play has recently led to the notion of optofluidics as an independent field that deals with devices and methods in which optics and fluidics enable each other3. Most of the initial lab-on-chip advances, however, occurred in the area of fluidics, while the optical components continued to consist largely of bulk components such as polarizers, filters, lenses, and objectives. 

In recent years, laser-based biosensors have become important tools in many fields such as analytical biochemistry, pharmaceutical research and development, and food/environ-mental monitoring. However, the volumes of the optic components in these biosensors limit their application in portable microdevices. In order to obtain more powerful, miniaturized, and cheaper biosensors using lasers, novel biological sensing principles, detection means, and fabrication methods need to be sought. The integration of biosensors and microfluidic chips will be an important direction for developments in laser-based biosensors. Biosensors can be used as microscale detection tools in lab-on-a-chip for the research and development of miniaturized detection devices, i.e., micro-total analysis systems. 

The dominance of electrophoresis over chromatography has been a trend in separations with Lab-on-a-Chip devices. The reason is that from an engineering point of view, it is easier to apply a voltage across the terminals of microchannels than the application of a pressure difference. In CE, electrokinetic control of fluid transport eliminates the need for external components such as pumps and valves. Furthermore, miniaturization of chromatography systems involves technical challenges that are usually not necessary in CE. However, LC is the most used separation technique in conventional systems. Therefore, investigation for implementing this technique in Lab-on-a-Chip devices is an active trend. 

Labs-on-chips are planar capillary systems in which the capillaries are typically 10-50 pm deep and 10—400 pm wide. The channels are several centimeters long to allow mixing of components, the performance of (bio)chemical reactions, or the separation of compounds. A typical layout is shown... 

Another limitation of existing Lab-on-Chip devices is the inability to encorperate active optical components directly into the same inexpensive structure that contains the microfluidic components. As a result of the widespread adoption of PDMS as a material of choice for microfluidic systems, there has been a large thrust towards creating structures which can be easily cast into the soft elastomer fluidics and provide this more advanced functionality. One such example was presented by Li et al. [10] who demonstrated an optofluidic dye laser. In their implementation, a solution of Rhodamine 6G lasing dye in... 

Significant advances have occurred during the past decade to miniaturize the size of the measurement system in order to make online analysis economically feasible and to reduce the time delays that often are present in analyzers. Recently, chemical sensors have been placed on microchips, even those requiring multiple physical, chemical, and biochemical steps (such as electrophoresis) in the analysis. This device has been called lab-on-a-chip. The measurements of chemical composition can be direct or indirect, the latter case referring to applications where some property of the process stream is measured (such as refractive index) and then related to composition of a particular component. 

To date, several SPR biosensor systems with integrated automated fluidic system have been reported [2,19,20]. However, these devices rely on bulky components (e.g., external pumps and valves), which limits their further miniaturization. In future, we expect that development of more compact fluidic units will benefit from current advances in the micropumps and microvalves [21] and microfluidic technologies pursued for Micro Total Analysis Systems (/xTAS) and Lab-on-a-Chip devices [22-24]. 

An ideal on-site detection system would be inexpensive, sensitive, fully automated, reliable, multiplex sample handling, and detect a broad range of explosives. The advent of microfluidic lab-on-a-chip technology might offer such a detection system. Microfluidic capillary electrophoresis chips have been utilized for the detection of nitroaromatics such as TNT, DNT, NT, and DNB [9-12]. Due to the good redox properties of nitroaromatics and the inherent suitability for miniaturization, most of the microfluidic methods so far used electrochemical methods for detection. The individual components of nitroaromatics can be detected in the capillary electrophoresis chips (analyte-specific) unlike the colorimetric methods (class-specific) where nitroaromatics are detected broadly. 

An important component of many bio- or chemical Lab-on-a-Chip devices is the microfluidic injection system, the precise control of the size and concentration of the dispensed sample in the microfluidic injection system determines the performance of these Lab-on-a-Chip devices. Two methods are commonly adopted in microfluidic injection systems electrokinetic injection and pressure injection. Pressure-driven... 

In the past two decades, the biological and medical fields have seen great advances in the development of biochips capable of characterizing and quantifying biomolecules. Biochips, also known as labs on a chip or pTAS (micro-total analysis systems), are microscale systems that interact with biological components on their characteristic length scale. Many biochips work with particles (cells, bacteria, DNA, etc.) suspended in fluids. 

Fig. 1 Illustration of a fully integrated Lab-on-a-Chip (LOC) system. Historically, the analysis component was first to be miniaturized and is indispensable to detect the analyte it often includes the indieated upstream separation process. Sample preparation is often required to make real-world samples amenable to analysis the core micro-/ nanofluidic chip thus consists of these three components, often connected by microchaimels. For systems to be manufactured inexpensively in large volumes, the micro-/nanofluidic chip might be fabricated on a consumable plastic card or other supporting substrate. Reagents may be needed for sample preparation or...

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