Relative two-dimensional nanoparticle concentration measurement based on scanned laser pico-projection

The images projected by scanned laser pico-projectors (SLPPs) contain speckle noise caused by the reflection of the high coherent laser light source from the projection screen. The speckle contrast varies in accordance with the volume roughness of the screen and can be applied for relative two-dimensional (2-D) nanoparticle concentration measurement in both solid and liquid solutions. The great advantage in this study is that it can measure several samples simultaneously. The experimental results show that the green laser within the SLPP provides a better measurement sensitivity and resolution than the red or blue lasers. In solid solution measurement, different concentrations of nanoparticles embedded in a poly (methyl methacrylate) (PMMA) matrix are tested and the maximum sensitivity and resolution are found to be −8.59 ((speckle contrast %)/(wt%)) and 0.013 (wt%), respectively. In liquid solution measurement, different concentrations of nanoparticles dissolved in deionized water are also tested and the maximum sensitivity and resolution of green laser in SLPP are found to be −2050 ((speckle contrast %)/(molar concentration (M)) and 7.51 × 10−5 M, respectively. Finally, the system shows ability to measure the collagen concentrations from 0.125 to 0.025%. Accordingly, the proposed system provides a viable, low-cost solution for high-sensitivity in biomedical, chemical and environmental applications.