Flow injection renewable drops technique for assay of micro-amounts of DNA

A flow injection renewable drops method is introduced for quantitative assay of micro amounts of DNA based on the fluorescence quenching of 3,3´,5,5´-tetramethylbenzidine dihydrochloride (TMB-d). The dynamically growing and falling drops formed at the end of a silanized silica capillary tube serve as reactors for a chromogenic reaction and windowless optical cells as well. The design and characteristics of the sensor system are described. An excitation beam directly illuminates the drops, the fluorescence emission is conducted to a photodiode (PD) to convert the photocurrent into voltage signal (mv). The optimum analytical conditions for DNA assay have been established. In NaOAc/HOAc buffer at pH 3.29, this assay has a wide linear range for calf thymus DNA from 0.03 to 8.4µg/ml with a detection limit of 10ng/ml. The use of renewable drops allowing fresh reaction surface for every sample is of particular value on solving the problems of irreversible reaction. Besides its high sensitivity, the sensor permits a simple, fast, and inexpensive measurement with only microquantities reagent consumption.