The invention relates to a method for production of an activated biochip for covalent fixing of oligonucleotide probes to a solid support by means of a spacer compound of the NHS-PEG-VS type and biochips produced by the above method. The invention further relates to methods for detection of nucleic acids in a sample or methods for screening compounds which may be specifically bound to oligonucleotide probes in which said biochips are used.