On-chip detection

Warrington, B., Wong, S., The design of a continuous flow combinatorial screening micro-reactor system with on-chip detection, in van den Berg, A.,... 

Micro- and nano-beads have become a major tool in analytical chemistry sciences. On one hand, micrometer size beads were developed with a very large range of properties such as magnetic and/or fluorescent beads, having different surface functional groups for coupling chemistry or physicochemical properties. On the other hand, few nanometer size particles were shown to be potential powerful labels for on chip detection of DNA strands. 

On-chip detection firstly relied on optical techniques, such as ultraviolet (UV) absorbance, fluorescence or laser-induced fluorescence (LIF).1,2 The latter technique in particular has a sensitivity in the (sub)micromolar range which is suitable for microfluidic applications. Besides optical techniques, electrical-based techniques are also widely used for on-chip detection due to their sensitivity, e.g. detection based on conductivity,3 electrochemistry,4 electrochemiluminescence,5 etc. The main advantage of these techniques is that they... 

Coupling a microfluidic or microfabricated system to MS appears to be fruitful for both the detection on the chip (microchip point of view) and for the MS analysis (MS point of view). On the one hand, MS is a powerful technique for on-chip detection due to its sensitivity and the amount of information it provides on the sample on the other hand, by using microfluidics prior to the MS analysis, new opportunities for the field of MS are created as it provides better MS capabilities compared to conventional sample preparation techniques. 

On the other hand, spectroscopic detection methods, such as laser-induced fluorescence, UV/Vis absorption, chemiluminescence, and thermal lens microscopy, have been used for on-chip detection. Among these methods, the fluorescence detection method has been most widely used because of its high sensitivity and low detection limits for biologically relevant species. However, the fluorescence detection technique has some disadvantages. Many chemical... 

Camou et al. [6] used 2D-optical, PDMS lenses to improve the performance of fluorescent spectroscopy detection performed on a portable chip using optical fibers. The fibers are directly inserted into channels ending with PDMS optical lenses. Compared to conventionally use flat interface, these optical lenses increased the intensity of fluorescent response close to the fiber which leads to a higher sensitivity of the on-chip detection method for fluorescent spectroscopy. Chen et al. [7] implemented a simple, on-chip arrayed-waveguide excitation and detection scheme based on the scattering. Detected signals were processed, and not only sensitivity enhancement... 

In the early 2000s, researchers began to incorporate fiber optics with the LOG for doing on-chip detection. The number of publications involving on-chip detection using optical fibers has been growing exponentially each year [5],... 

The most common conhguration for performing on-chip detection has been the embedded hber type of device as listed in Table 1. A typical setup, shown in Fig. 1, includes a light source and fiber for delivery, exit fiber connected to a detection system, microfluidic channel, and liquid delivery components. The fibers are usually embedded in chip materials consisting of polydimethylsiloxane (PDMS), SU-8 epoxy, polymethyl methacrylate (PMMA), or glass [3]. 

The next most popular configuration for performing on-chip detection uses optical fibers in close proximity to the detection zone as summarized in Table 2 and shown in Fig. 2. The input fiber and the receiving fiber tips are usually within 1 mm of the chip surface. In some cases, lenses and filters are used to focus and/or collect the light. Other system components such as light... 

On-Chip Detection Using Optical Fibers, Table 1 Embedded fiber types of on- chip detectors ... 

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