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A gold nanospheres (Au NSs)-enhanced photoacoustic (PA) system has been developed to detect parts per trillion (ppt)-level mercury ion (Hg2+) in aqueous environments, which combines the advantages of the high sensitivity of PA detection and high extinction coefficient of Au NSs. 4-mercaptophenylboronic acid (MPBA) is used as the aggregation agent to detect Hg2+ by a designed PA system. Experimental results demonstrate a linear relationship between the amplitude of PA signals and logarithmic concentration of Hg2+ in the range of 10 pM-1 μM (R=0.994). The detection limit of this Au NSs-enhanced PA system is 78 pM (16 ppt, S/N=3) with a quick response time of 1 min. This method has excellent selectivity for Hg2+ over other heavy metal ions, alkali, and alkaline earth metal ions. The system is cost-effective and shows a great potential for quick detection of Hg2+ trace in water with very high sensitivity.

Directional dithering of a laser beam potentially limits the detection accuracy of a laser triangulation displacement probe. A theoretical analysis indicates that the measurement accuracy will linearly decrease as the laser dithering angle increases. To suppress laser dithering, a scheme for reduction of the influence of laser beam directional dithering in a laser triangulation displacement probe, which consists of a collimated red laser, a laser beam pointing control setup, a receiver lens, and a charge-coupled device, is proposed in this paper. The laser beam pointing control setup is inserted into the source laser beam and the measured object and can separate the source laser beam into two symmetrical laser beams. Hence, at the angle at which the source laser beam dithers, the positional averages of the two laser spots are equal and opposite. Moreover, a virtual linear function method is used to maintain a stable average of the positions of the two spots on the imaging side. Experimental results indicate that with laser beam pointing control, the estimated standard deviation of the fitting error decreases from 0.3531 mm to 0.0100 mm , the repeatability accuracy can be lowered from ±7 mm to ±5 μ m , and the nonlinear error can be reduced from ±6 % FS (full scale) to ±0.16 % FS.

Diabetes mellitus (DM) is a chronic disease affecting nearly 400 million people worldwide. In order to manage the disease, patients need to monitor the blood glucose level by puncturing the finger several times a day, which is uncomfortable and inconvenient. We present here a potential non-invasive monitoring method based on the velocity of ultrasonic waves generated in glucose solution by the photoacoustic principal, which can recognize the glucose concentration down to 20mg/dL. In order to apply this method to warm bodies, we carefully designed the experiment and performed measurements from 30 °C to 50 °C to generate a set of calibration curves, which may be used by engineers to build devices. Most importantly, we have theoretically explained the relationship between the compressibility and the glucose concentration. Our results show that the compressibility of solution decreases with the glucose concentration, which clarified the controversy between theory and experiment results in the literature. The derived formula is generally validity, which can be used to nondestructively measure solution concentration for other types of solutions using photoacoustic principle.