A Compact UV-LED-Induced Fluorescence With Short Metal Capillary and Low Light Leakage: Application to Noninvasive Glucose Detection

Laser-induced fluorescence (LIF) is one of the most sensitive techniques for detection. As for the LIF with UV excitation, replacing UV laser with UV LED (i.e., UV LED-IF) has advantages of long life time and low cost. However, for LED-IF, the background signal (noise) would be much higher, due to the poor beam quality of LED. Here, an axial-excitation UV LED-IF with short metal capillary (MC) and black sealing (i.e., MC-LED-IF) was proposed for noninvasive detection of human saliva glucose (HSG). The SNR was improved 3.1-fold by employing the black sealing, due to the effective suppression of the background signal, which mainly results from light leakage. Moreover, the transmission loss of UV LED light in MC and saliva-filled MC was investigated, and an optimal MC length of only 4 cm was obtained. By using the MC-LED-IF, a detection limit of concentration (DLC) of $2.4 \mu \text{M}$ was realized for detecting HSG via conventional 3-(4-hydroxyphenyl)-propionic acid (HPPA) reagent with good selectivity and reliability. The MC-LED-IF features low cost and compact ( $11\times 4\times $ 4 cm), which is suitable for personal use.