Particle analysis and differentiation using a photovoltaic cell

A method is proposed for the sizing and counting of fluorescent and non-fluorescent particles of various sizes on a poly-dimethylsiloxane microchip. In the proposed approach, the detection region of the microchip is illuminated by a laser, which is then incident on a power-free photovoltaic cell. As the particles (both fluorescent and non-fluorescent) pass through the detection region, they block the laser beam, causing a reduction in the output voltage of the cell. The voltage signal is interfaced to a PC and is used to determine both the size and the number of the particles. Meanwhile, the fluorescence signal generated by the fluorescent particles within the sample is detected by an avalanche photodetector and is used to differentiate between the fluorescent and non-fluorescent particles in the sample. The effectiveness of the proposed approach is demonstrated using fluorescent-labeled beads with means diameters of 5, 8 and 10 µm, respectively, and unlabeled beads with a mean diameter of 7.2 µm. The experimental results confirm that the forward scattered light signal generated by the photovoltaic cell enables both the size and the number of the particles to be reliably determined. Moreover, it is shown that the number of non-fluorescent particles within the sample can be easily determined by comparing the signals received from the photovoltaic cell and avalanche photodetector, respectively. (paper)