Multichannel fluorescence detection

CCD cameras have also been used for multichannel fluorescent detection. However, the use of the CCD detector suffers from the need to read out the entire image content information in order to determine the pixel intensity at the flow channel location. Accordingly, a CMOS imager was used. This method offers direct control over individual pixels, and can provide much faster response times and longer integration times for those desired pixels [252]. 

Huang, Z., Munro N., Huhmer, A.F.R., and Landers, J.P, Acousto-optical deflection-based laser beam scanning for fluorescence detection on multichannel electrophoretic microchips, Anal. Chem. 71, 5309, 1999. 

Huang Z, Jin L, Sanders JC, Zheng Y, Dunsmoor C, Tian H, et al. Laser-induced fluorescence detection on multichannel electrophoretic microchips using micro-porcessorembedded acousto-optic laser beam scanning. IEEE Trans Biomed Eng 2002 49 859-866. 

Photodiode Array Versus Photomultiplier Detection. The advantages of photodiode array detection, PDA, as compared to photomultiplier tube, pmt, detection for emission spectroscopy are well known (19). These advantages are especially important for the specific examples we discuss here, namely, upconverting emission spectroscopy. This is dramatically demonstrated in Figure 7 where we compare single channel pmt versus multichannel PDA detection of a small portion of the upconverted fluorescence spectrum of coumarin 520 in ethanol solvent at room temperature. 

A high-performance confocal fluorescence detection unit usable in either a single channel or multichannel mode. 

Lapainis, T., Scanlan, C., Rubakhin, S. S., and Sweedler, J. V., A multichannel native fluorescence detection system for capiUary electrophoretic analysis of neurotransmitters in single neurons. Anal. Bioanal. Chem., 387, 97-105, 2007. 

The overlap of different fluorophore spectra due to their wide emission range is an inherent problem of multichannel fluorescence imaging (Fig. IB). In the absence of additional signals, a fluorophore can be detected through a longpass filter that covers its whole emission spectrum. If additional fluorophores are present, a bandpass filter aroimd the emission peak is required to constrict the spectral detection range and to thus reduce the crosstalk. 

Some commercially available detectors have a number of detection modes built into a single unit. Fig. 2.4o is a diagram of the detector used in the Perkin Elmer 3D system, which combines uv absorption, fluorescence and conductivity detection. The uv function is a fixed wavelength (254 nm) detector, and the fluorescence function can monitor emission above 280 nm, based on excitation at 254 nm. The metal inlet and outlet tubes act as the electrodes in the conductance cell. The detection modes can be operated independently or simultaneously, using a multichannel recorder. In the conductivity mode, using NaCl, a linear range of 103 and a noise equivalent concentration of 5 x 10 8 g cm-3 have been obtained. 

A schematic diagram of the apparatus used in the energy transfer experiments is shown in Figure 8.22. The particles are produced and levitated in an electrodynamic levitator as described previously. Excitation is provided by the filtered output of either a Xe or Hg-Xe high-pressure arc. The intensity produced at the particle was found to be 10-50 mW/cm2. The fluorescence emitted from each of the levitated particles was monitored at 90° to the exciting beam using //3 optics, dispersed with a j-m monochromator, and detected with an optical multichannel analyzer. The levitator could be... 

With analytical methods such as x-ray fluorescence (XRF), proton-induced x-ray emission (PIXE), and instrumental neutron activation analysis (INAA), many metals can be simultaneously analyzed without destroying the sample matrix. Of these, XRF and PEXE have good sensitivity and are frequently used to analyze nickel in environmental samples containing low levels of nickel such as rain, snow, and air (Hansson et al. 1988 Landsberger et al. 1983 Schroeder et al. 1987 Wiersema et al. 1984). The Texas Air Control Board, which uses XRF in its network of air monitors, reported a mean minimum detectable value of 6 ng nickel/m (Wiersema et al. 1984). A detection limit of 30 ng/L was obtained using PIXE with a nonselective preconcentration step (Hansson et al. 1988). In these techniques, the sample (e.g., air particulates collected on a filter) is irradiated with a source of x-ray photons or protons. The excited atoms emit their own characteristic energy spectrum, which is detected with an x-ray detector and multichannel analyzer. INAA and neutron activation analysis (NAA) with prior nickel separation and concentration have poor sensitivity and are rarely used (Schroeder et al. 1987 Stoeppler 1984). 

A quantitative study of the RISC quantum yield was carried out with 55 [37]. This study involved UV irradiation of 55 in benzene or cyclohexane solution to produce the 7, state and subsequent photolysis by a second laser tuned to the T-T absorption band. The second pulse was accompanied by depletion (bleaching) of the T-T absorption and 5, — S0 fluorescence [the fluorescence was detected and quantified by an optical multichannel analyzer (OMA)]. The quantum yield of RISC, d>RISC, was calculated using Aberchrome 540, a reversible fulgide, as a two-laser actinometer. The values for benzene solvents, respectively. This compares with 0.19 found for 55 in ethanol solvent [36]. 

---