# Chip-Based Cytometry Illuminated by a Blade-Shape Continuous Light for Multispectral Detection
## 1 Introduction  
Flow cytometry is a powerful technique for the measurement and analysis of various characteristics of cell samples, and is used in applications ranging from immunophenotyping [1; 2] to gene diagnosis [3; 4], bacterial analysis [5], clinical hematology diagnosis [6; 7; 8], and even food industry applications [9]. Accordingly, various discrete polychromatic detection systems [10] and spectral analysis systems [11; 12] have been developed in recent decades. In previous studies, this was generally achieved by using multiple light sources, filter sets, and photon detectors [13; 14; 15; 16]. Delicate and luxurious fluorescence illumination systems were adopted to produce multiple fluorescence detection signals with different colors [14]. The results showed that the developed optical systems permitted the analysis of up to 19 different parameters of quantum-dot-labeled samples. However, these approaches relied on large-scale optical components and automation processes to construct bench-top cytometry systems. Alternatively, some other researchers have proposed micro-scale cytometry chips incorporating buried optical fibers to couple and transmit the excitation light and to collect the fluorescence signals, respectively [5; 17; 18; 19; 20; 21]. However, whilst such devices provide an effective means of accomplishing multi-parametric analyses, the requirement for delicate optical components andmultiple optical filters and photo-detectors greatly increases their cost and complexity. Furthermore, the fabrication processes for these microfluidic chips are relatively delicate and time consuming. In spectral detection schemes, a multi-color detection capability was achieved using a single photo detector (e.g., a charge-coupled device (CCD), camera, or photomultiplier tube (PMT)) equipped with a grating [22], integrated micro-spectrometer [23], bio-photonic detector [24], or tunable filter [11; 25]. For example, [PERSON] et al. [26] utilized a diffraction grating to disperse the fluorescence signals emitted from the cells or microspheres passing through the interrogation region of the cytometer, and then used a CCD image sensor to analyze the spectral distribution of the collected signals. Individual fluorophores in multiple-tagged samples were successfully detected with high resolution. Typically, most spectral detection schemes use a single monochromatic light source, such as an argon laser with a UV wavelength (488 nm), to excite the fluorescent-labeled samples in order to broaden the fluorescence spectra and simplify the experimental setup. However, the use of a monochromatic excitation source limits the number of fluorescent probes which can be distinguished by the cytometry system. Several reports have indicated that this problem can be overcome by replacing the conventional organic fluorophores with quantum dot reagents due to their higher fluorescence emissions [27; 28; 29]. Similarly, [PERSON] et al. [30] achieved a multi-parameter analysis capability by replacing the CCD detector in the cytometer by a Raman spectral detection system. Raman flow cytometry makes the multi-parameter, multiplexed measurement of cells and particles using a single detector and light source possible. However, such systems involve a more complicated sample-labeling procedure than those required for conventional organic fluorescent probes. In this regards, the practical applications of this method are hindered. Dark-field illumination is generally used for the detection and tracking of small or transparent particles in a solution near the surface [31; 32]. The use of dark-field illumination in accomplishing multi-color fluorescence detection on a single microfluidic chip for capillary electrophoresis applications was also successfully demonstrated [33; 34]. A dark-field configuration was also used to quantify and characterize particles and cells in accordance with their light scattering properties [35].