A new sensitive non-isotopic method using sulfonated probes to detect picogram quantities of specific DNA sequences on blot hybridization.

The use of non-radioactive systems to detect target DNA or RNA displays many advantages such as safe manipulation, potential use in non-specialized scientific area and prolonged lifetime of the probes (one year or more). We here describe a method we have improved and optimized using sulfonated DNA probes for hybridization on dot and Southern blots. Sulfonation is an easy chemical modification procedure which does not require enzymatic coctail as does nick-translation. Sensitivity of this method has been particularly improved by using a new blocking solution, containing heparin, which allows easy and fast detection of picogram quantities of DNA. This method allows the use of nitrocellulose as well as nylon membranes with very low background. Equal resolution is obtained in comparative experiments involving both sulfonated and 32P-radiolabelled probes. Single copy gene sequences are readily detected in nuclear DNA. These results allow the use of this procedure for restriction fragment length polymorphism (RFLP) studies.