A Disposable Optical Fiber-Based Capillary Probe for Sensing Lead Ions

A disposable capillary-based probe using optical fiber technology to create a compact and portable configuration has been designed for sensing lead ions. It is based around a glass capillary tube pretreated with a fluorophore with high sensitivity and selectivity towards lead ions. The capillary tube makes use of capillary action to uptake the same sample volume for each single-shot measurement. The probe response to lead has been shown to be in the 20–150 $\mu {\hbox {M}}$ concentration range with a dynamic range of 20–80 $\mu {\hbox {M}}$. A relative standard deviation of ${\sim {\hbox {6}}}\%$ was obtained from a series of results on different probes. This preliminary work is essentially a proof-of-principle for a probe design in which chemical indicators that cannot be immobilized onto a solid support can still be adapted for optical fiber sensing without any chemical modification. The disposable capillary probe provides a mechanical support and protection to the fluorophore without the use of membranes, thus avoiding problems with leaching. As far as the authors are aware, this is the first time that an optical fiber sensor using a fluorescent indicator for optical lead sensing in an organic solution has been produced.