The development of a near-infrared optical fiber detector for the determination of metal ions was investigated. The optical fiber detector consists of a semiconductor laser diode, an optical fiber, an NIR dye and a photodiode detector. Two plastic fibers are connected together with poly(methyl methacrylate) (PMMA) with a reaction phase at the distal common end. The reaction phase had a diameter of about <2 mm. Excitation of the dye/analyte complex was induced with a semiconductor laser diode at 780 nm and the emission intensity signal was collected by two instrument systems. No photobleaching effect was observed during the investigations. The response time for 95% of the signal was less than 5 seconds. The use of plastic fibers has allowed easy immobilization of an NIR dye. The dye was entrapped in a polymer matrix that allows the diffusion of the analyte. Low background signal of the photodiode permitted the detection of dye in the picomolar level. Comparison of the optical fiber results between a PMT and a photodiode was made. The use of smaller components shown here will allow the manufacturing of portable optical fiber detectors for applications in industry, medicine and the environment.