Sensitive and portable colorimetric detection of copper in water by cotton thread based pre-concentration

A sensitive and portable on-thread pre-concentration and colorimetric detection method of copper ions was proposed. Commercial cotton thread was proposed as a solid sorbent for effectively extracting copper ions (Cu 2+ ) from solution. The adsorbed Cu 2+ was converted to Cu + by ascorbic acid . The Cu + on the threads was visualized by horseradish-peroxidase-catalyzed color changes of a chromogenic oxidized tetramethylbenzidine substrate. The adsorption of Cu 2+ on the plasma- and Na 2 CO 3 -treated thread was verified by scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and zeta potential characterization. The Cu + -induced dysfunction of HRP on the thread was verified by X-ray photoelectron spectroscopy. With optimized reaction conditions, the concentration-dependent colorimetric response plot was characterized, where the linear detection range was 2–400 nM and the detection limit was about 0.15 nM. Measurements of a group of possible interfering ions and spiked real-water samples demonstrated the good selectivity of the proposed method. The proposed on-thread pre-concentration and colorimetric detection offers a low-cost and effective alternative for detecting of copper ions in real applications.