Detection of 27 molecules in a single injection volume by Hadamard transform capillary electrophoresis.

A concentration detection limit of 100 fM was achieved for the fluorescein ion by improving the experimental setup used for Hadamard transform capillary electrophoresis. Two argon-ion lasers, a gating laser for sample injection and a probe laser for the excitation of analyte molecules, were employed for the efficient photodegradation of analyte molecules in laser-induced fluorescence detection using an optically gated sample-injection method. In addition, a dichroic mirror, located in the pathway of the probe laser was used to exclude the other lines of the argon-ion laser. Using a Hadamard matrix on the order of 2046, the concentration limit of detection for fluorescein ion was determined to be 100 fM at S/N = 3, in which the average number of molecules in a single injection volume was calculated to be 27. The influences of the output power in both the gating and probe lasers on the sensitivity are also discussed.