Determination of trace amount of Cu2+ with a multi-responsive colorimetric and reversible chemosensor.

A multi-responsive sensor 1 was constructed by combining a ferrocene unit and a rhodamine block via a carbohydrazone bond. The sensor showed high selectivity toward Cu(2+) over other common metal ions in a wide pH range with excellent reversibility and rapid response. The obvious color change from colorless to pink upon the addition of Cu(2+) could make it a suitable 'naked-eye' indicator for Cu(2+).