The maintenance of uric acid levels is crucial for the human body. In this study, the feasibility of using portable ultraviolet (UV) spectrophotometry to measure the uric acid of spot urine without the need to add reagents has been demonstrated for the first time. UV spectral analysis has been used to inspect the uric acid concentration in urine. It is found that the absorption spectrum of urine has a high correlation with the concentration of uric acid at a wavelength of around 290–300 nm. Uric acid levels measured with a spectral analyzer compared to uric acid concentrations measured with a traditional biochemical analysis showed good agreement. The portable prototype is label-free and capable of displaying the inspection result of each measurement within 10 s. In the long run, this device can assist people in checking uric acid levels of spot urine with higher frequency and can adjust diet or medication in real time for more efficient health management.

A Q-switched Nd:YAG laser with mode-locked modulations is utilized to explore the laser-induced air breakdown. The various modulation depths of the mode-locking within the Q-switched pulse can be utilized to investigate the threshold conditions. With the GHz high-speed detectors to accurately measure the temporal pulse shape pulse by pulse, it is verified that the air breakdown threshold is crucially determined by the peak-power density instead of the energy density from the statistic results, especially for mode-locked Q-switched lasers. The stability of the system for laser-induced breakdown can be evaluated by threshold width through fitting the statistical result. Otherwise, by measuring the temporal characteristics of the excitation pulse and the induced plasma, it is further found that the plasma radiation displays a few-nanoseconds time delay to the excitation pulse and shows a decaying tail to be 10 times longer than the plasma build-up time. Moreover, the incident laser pulse is observed to be self-scattered by the air breakdown, and a rapidly modulated scattering rate is found with a slight delay time to the excitation mode-locked subpulse modulations.

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