Distance readout of Al content with naked eyes on a cotton thread

We described a facile method for distance-based detection of aluminum on a thread based on the adsorption of formed complex onto thread. Chrome azurol S (CAS) containing Cetyltrimethylammonium Bromide (CTMAB) were used as chromogenic reagent, which reacts with aluminum to form AL-CAS-CTMAB complex on a thread. The complex was adsorbed onto thread to generate a colored band. Aluminum contents could be quantified by measuring the length of colored band on the thread using a ruler, thereby eliminating the need for electronic readout devices and trained personnel. This instrument-free method has features of low cost, easy to operation, fast analysis speed, disposability and low reagents/sample consumption. Moreover, considering that the thread fiber has adsorption capability to various molecules such as metal-ligand complexes and biomolecules, we believe that this technique holds the potentials to be widely adaptable to distance-based chemical and biochemical analysis.